Bai Giang Tieng Anh

Part 1: general Chemistry

Text 1

The pains and pleasures

of industrial analytical chemistry

One should keep in mind that industrial analysis is not necessarily a routine, boring occupation. It can be frustrating at times but it can also be fascinating, instructive, humorous, and even exciting. It is usually pleasant if one dedicates himself to learning about what goes on in chemical systems. The key to enjoying analytical work lies in knowing that the results will be useful and important.

Problem - solving in analytical chemistry

An analytical chemist should know enough about existing methodologies to choose the best one for application to a given sample, perhaps modifying it if necessary to fit the particular situation, and that there is also an analytical science which seeks the improvement of analytical methodologies with regard to scientific problems. Nowadays, with more and more instrumental methods in vogue, the analysts and determinators are coming closer together.

To be a good chemist one must first be a good analytical chemist. We can teach instrumental analysis in industry, but we should not teach basic chemistry.

Mercury? Questions and answers

Some of you may be interested in the question of mercury and its determination in the environment. This is a fascinating question with many aspects. It illustrates again the importance of analytical chemists looking at the whole picture.

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Swedish scientists had developed a gas chromatographic method for the determination of alkyl and aryl mercuric compounds extracted from fish with benzene and dilute hydrochloric acid. They were interested in those compounds because of their use as slimicides, but it turned out that regardless of what compound was used, the mercury found in fish was present as a monomethylmercuric ion.

A number of questions about the behavior of mercury remain to be answered. Several theories have been proposed as to how mercury might have gone from inorganic form in water or a bottom sediment, into a methylated form of a fish. One theory assumes anaerobic conversion in the mud to volatile dimethyl mercury which enters fish via the gills. Another assumes aerobic conversion to monomethyl mercury by bacteria, with subsequent transfer up to the food chain. Still another assumes that a fish itself can methylate mercury taken in either through the gills as elemental vapor, or via the stomach as inorganic ions, or in an adsorbed state in silt particles. Before all these questions can be answered, we need to develop highly sensitive methods for each individual form of mercury. At present the most sensitive methods can go down only to about 0.05-ppm inorganic mercury in water.

At the conference on environmental mercury contamination in 1970 in Ann Arbor, Michigan, USA a number of sources from which mercury may enter the environment was mentioned. Among them were the burning of fossil fuels, use of mercurial compounds for fungicides in agricultural seed treatments, use of elemental mercury in the electrical industry for manufacture of batteries and mercury vapor lamps, use of mercuric catalysts, and the disposal of domestic sewage sludge. It will be up to analytical chemists to evaluate all of the sources and to provide the data on which proper action can be based. This will be true not only for mercury, but also for all environmental contaminants.

It is interesting that both Finish and Swedish chemists have found fairly high content in fish from certain lakes in northern parts of their countries, remote from any known source of pollution.

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Another interesting fact is that mercury will be found in the hair of a person who has been exposed to it. The average person has about one or two ppm in his hair or even more.

Having analyzed sections of the hair of a long- haired person and having known its growth rate, one can approximate the time and intensity of exposure. Most of these analyses have been done by neutron activation, which is advantageous because very small samples can be employed. However, hair can be analyzed by the atomic absorbance method following the digestion procedure used for fish analysis. A 100-mg sample is sufficient for hair in the range of 1 to 10 ppm.

Exercises

I. Translate into Vietnamese paying attention to the finite and non- finite forms of the verb:

1. Having developed a gas chromatographic method for the determination of alkyl and aryl compounds the Swedish scientists got interested in those compounds.

2. Swedish scientists developed a gas chromatographic method for the determination of alkyl and aryl mercuric compounds extracted from fish.

3. The chemists extracted fairly high mercury contents from fish.4. The scientists found high mercury contents in fish from certain

lakes, remote from any known source of pollution.5. Mercury found in fish was present as a monomethylmercuric

ion.

II. Translate into Vietnamese paying attention to the pronoun ((one)):

1. One should keep in mind that industrial analysis is not necessarily a boring occupation.

2. It is pleasant if one dedicates himself to learning about what goes on in chemical systems.

3. An analytical chemist should know enough about existing methodologies to choose the best one for application.

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4. To be a good chemist one must first be first of all a good analytical chemist.

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III. Translate into Vietnamese paying attention to the Model Verbs + Perfect infinitive:

1. It was realized that drying may have caused some denaturation, but whatever the change it should not have affected the amino acid composition of the proteins.

2. It goes without saying that any of the acid derivatives (amide, ester, etc.) might have been prepared either from benzotrichloride or benzoic anhydride instead of from benzoic acid

3. The mercaptans obtained could have been oxidized in alkaline solutions to disulfides.

4. Zincate solutions could have been prepared by dissolving ZnO in aqueous KOH.

5. It accounts for the observation of Hauer that an X-ray fibre diagram could not be obtained when raw rubber was stretched very slowly, for in this case the region of maximum flow may never have been passed through and the molecular extension necessary for crystallization thus not achieved.

IV. Read the following model of a summary:

The article ((The pains and pleasures of industrial analytical chemistry)) discusses what an analytical chemist should know about existing methodologies and presents a gas chromatographic method for determination of alkyl and aryl mercuric compounds extracted from fish with benzene and dilute hydrochloric acid.

The paper provides examples of fairly high mercury content in fish from certain lakes of Sweden and Finland, which are remote from any known source of pollution and of finding mercury in the hair of a person exposed to it.

The article illustrates and describes the importance of an analytical chemist who should use the best methodology to a given sample modifying it to the fit the particular situation.

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TEXT 2

Chemical thermodynamics

The science of thermodynamics concerns the chemical and physical processes, which involve the interconversion of various forms of energy, and it is not confined to the relation between heat and mechanical energy. It is developed mathematically on the basis of a number of postulates, which have been supported by experiments.

Although its application to chemical processes quite general, thermodynamics is not at all concerned with either the rate of a process or the mechanism of it. Thermodynamics is based on two fundamental laws, called the first and second laws of thermodynamics. The two laws of thermodynamics constitute one of the most powerful tools of physical chemistry.

Of fundamental importance to thermodynamics is the concept of equilibrium state. Thermodynamic equilibrium in the true sense refers to a condition in which the properties of a system are absolutely unchanging with time so that, if the system is disturbed slightly in some way, it will return to essentially the same condition after the disturbing force is removed. This latter criterion may differentiate between a true state of equilibrium and a metastable one. If a metastable equilibrium is disturbed, as, for example, by introduction of a catalyst or by local heating, it may spontaneously undergo a drastic change to some new state.

Consider a container filled with chlorine gas. Provided that the container is sealed and thermally insulated from its surroundings a state of true thermodynamic equilibrium will be established in which the temperature and pressure are uniform. If we disturb the system by shining a light on it, some of the chlorine molecules will absorb radiation and dissociate into atoms. When we turn off the light, the chlorine atoms recombine and the system, except for the addition of small amount of energy from

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the light beam, returns to its original condition.

By way of contrast, a mixture of hydrogen and chlorine is metastable. Although chlorine and hydrogen react with one another at room temperature, the rate is so slow as to be virtually undetectable. Hence the system seems to behave in just the same way as the pure chlorine system, in which uniform temperature and pressure are established. However, if we direct a beam of light through this mixture, it explodes, forming hydrogen chloride and evolving a large amount of heat. After being disturbed in this way, the system can not revert spontaneously to its original condition. In fact, the change, which does occur (the explosion), is a state of true thermodynamic equilibrium.

Although thermodynamics can not deal with the rate at which reactions occur, it does establish the direction in which reaction can proceed. Metastable or unstable compounds can be treated by the methods of thermodynamics, provided that they have a lifetime sufficiently long for thermodynamic measurements to be made. This requirement may vary, depending on the type of experiment, from a minute fraction of a second to hours, or even days. In this regard, one can make the distinction between substances, which exits by virtue of its thermodynamic stability, or by reason only of its slow rate of reaction or decomposition.

There is a wide range in degree of inertness of unstable system. Diamond, on the one hand, is inert to the extent that there is no observable conversion (under ordinary condition) to the stable state of graphite. At the other extreme are such unstable substances as a supercooled liquid, or a sensitive explosive. In either of these cases only a slight perturbation is necessary to change these system drastically. Lewis and Ranall in their classic treatment of thermodynamic found that water and air, although inert, are thermodynamically unstable with respect to the formation of nitric acid.

Those substances, which are quite inert chemically, can generally be treated by the methods of thermodynamics.

As an example, both NO and NO2 are unstable with respect

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to decomposition into their elements, yet we can not only consider the reaction:

2NO2 =2NO + O2

but also study the equilibrium by a direct experiment.

Exercises

I. Answer the following question:

1. What does the science of thermodynamics deal with?

2. What are the main laws of thermodynamics?

3. What is meant under thermodynamic equilibrium?

4. Thermodynamics establishes the direction, in which a reaction proceeds, doesn't it?

5. What mixtures are considered to be metastable?

6. What conclusions did Lewis and Ranall draw?

II. Translate the following sentences

1. Water and air are thermodynamically unstable with respect to the formation of nitric acid.

2. The preparation of smokes has already been referred to in the scientific journal.

3. The inert dust presumably takes up in virtue of its heat capacity, which would otherwise be available for raising more coal dust to its ignition point.

4. The amino acids are amphoteric, i.e. can act either as acids by virtue of the carboxy, or as bases by virtue of the amino group.

5. With respect to catalytic activity, metals considerably exceed other catalytics for many reactions.

6. Oxide catalysts have provided interesting systems for the study of electronic factors in catalysis.

7. Provided the oxidation directly after chlorination is carried out at sufficiently high pH, little damage is done to the cellulose.

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8. Synthetic rubbers possess a marked advantage over natural ones by reason of the diversity of properties they affect.

III. Translate the following derivatives into Russian:

1. Catalysant, catalysate, catalysis, catalyst, catalytic, catalytical, catalysator, catalyzed, catalyzer.

2. Stability, stabilization, stabilizator, stabilize, stabilizer, stabilizing, stable.

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IV. Form nouns from the following verb:

behavecombineconvertdifferentiatedissociatedistinguishdisturbdirectequilibrate

establishexplodefilloccurperturbproviderequiresurround

IV. Translate the following sentences into Vietnamese paying attention to conditional sentences.

1. If a molecule with a lone pair of electrons is absorbed on a transition metal, it will donate a pair of electrons.

2. A stable of thermodynamic equilibrium will be established, provided that the container is sealed.

3. A mixture would explode, if one directed a beam of light through it.

4. Were gypsum heated to a much higher temperature than 1200

C, it would lose all its water of crystallization.5. Had we disturbed a system by shining a light on it, some of the

chlorine molecules would have absorbed radiation and dissociated into atoms.

6. If the fatty acid does not react chemically with the surface it is relatively ineffective as a lubricant.

7. It would be expected that the heat of adsorption would decrease with an increase of temperature if the thermodynamic state of the surface and adsorbed species remained the same.

V. Translate the following sentences into Vietnamese:

1. Lewis found water and air to be thermodynamically unstable with respect to the formation of nitric acid.

2. Metastable or unstable compounds can be treated by the methods of thermodynamics, provided that they have a lifetime sufficiently long for thermodynamic measurements to be made

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3. Scientists consider adsorption from solution to be physical or chemical.

4. It is noteworthy that in the case of phosphate buffers, the increase of pH is accompanied by a drop of interface tension between the two phases.

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VII. Translate into English:

1. §Þnh luËt thø nhÊt cña nhiÖt ®éng häc ®îc xem lµ ®Þnh luËt b¶o toµn n¨ng lîng.

2. C©n b»ng nhiÖt ®éng cã nghÜa lµ tr¹ng th¸i mµ ë ®ã tÝnh chÊt cña hÖ kh«ng bÞ thay ®æi theo thêi gian.

3. Nh ®· biÕt néi n¨ng cña mét chÊt phô thuéc vµo tr¹ng th¸i cña nã nghÜa lµ phô thuéc vµo nhiÖt ®é, ¸p suÊt, d¹ng tinh thÓ.

4. Theo ®Þnh luËt thø hai cña nhiÖt ®éng häc th× c©n b»ng kh«ng phô thuéc vµo çch thøc mµ nã ®¹t tíi.

Text 3

The PROPERTIES OF GELS

Structure. The structure of various xerogels and jellies has been thoroughly studied in the last decades by several methods, such as the X-ray method, observations in the ultramicroscope, studies with the electron microscope, and so on. From all these studies the important conclusion may be drawn that jellies which contain large amounts of liquid have a network structure in which the liquid is bound to the fibrous particles and is also mechanically immobilised between them. The less asymmetric are the colloidal particles, the higher must be their concentration to be able to form a jelly.

The shape of the colloidal particles however, is not the only factor, which determines the ability to form stable jellies. For instance, a 4% solution of nitrocellulose in a mixture of ether and alcohol does not set, although the molecules of the nitrocellulose are very long and thin. Another important factor, which determines the gelation, is the possibility of entanglement of the fibres or rods. The rods and fibres must be linked if a network is desired. Hence the structural elements of a jel need not have long fibrous macromolecules. The solid framework of a jelly may be composed also of plate or needleshaped crystals as micelles. In such

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instances the concentration of the solid is always relatively high, whereas with linear macromolecules the concentration may be lower. The framework of a jelly must be coherent. If the particles

do not stick together there is no gelation. For example, a concentrated graphite dispersion does not conduct electricity in the fluid state, although it becomes a conductor after it sets, because countless contact points are formed throughout the network. All gels can be classified into three structural groups: 1) gels with unstable frameworks; 2) jellies with metastable frameworks, and 3) systems with stable networks. A very labile framework is encountered in ferric hydroxide, alluminium hydroxide, bentonite, graphite and many other gels in which the structural elements are not very asymmetric. The crystallites or particles are joined in such cases by very weak cohesive forces (van der Waals attraction). Such gels are often thixotropic, i.e. the framework is so weak that it is destroyed by shaking. To this group belong also the entanglement gels of linear macromolecules, such as unvulcanized or rubber polystyrene. The corresponding solids, e.g. polystyrene, when placed in liquid in which they can dissolve, will swell first and then slowly go into solution. In the instances of weak frameworks of linear macromolecules the gels swell without limit; if the instance structural elements are not joined by sufficiently strong forces, the solvent may in time destroy the framework by gradually disconnecting the building units. Metastable frameworks are encountered in most of the protein jellies, for in those of gelatin. Finally, there are gels with stable frameworks, for example the gels of relatively concentrated silicic acid. Such gels can be obtained upon addition of acid to a solution of sodium silicate. The resulting gel is rigid and stable, and it cannot be reversibly transformed into a liquid system.

Exercises

I. Answer the following questions:

1. By what methods has the structure of various xerogels and jellies been studied?

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2. What conclusion may be drawn from all these studies?3. What factors determine the ability to form stable jellies?4. What must be linked if a network is desired?5. What may the solid framework of a jelly be composed of?6. In what cases may the concentration be high and low?7. Is there gelation when the particles do not stick together?8. Into what groups can all gels be classified?9. What are metastable frameworks encountered in?10. What examples of gels with stable frameworks can you give?11. How can gels with stable frameworks be obtained?

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II. Give antonyms to the following words:

ImmobilisedAsymmetricUnableShortThickUnimportantundesirable liquid

low fluidstabledestroyunvulcanizeddisconnectrigidstrong.

III. Translate the following derivatives into Vietnamese:

structure, structuralvary, variousconclude, conclusion, conclusiveliquid, liquidfyfibre, fibrousability, able, unablestable, unstable, stability

solution, solvent, soluble, dissolvepossible, impossibleline, linearcoherence, coherent, cohesivegelation, gelconduct, conductive, conductionferrous, ferric

IV. Translate the following sentences paying attention to the words in bold type:

1. The less asymmetric are the colloidal particles, the higher must be their concentration to be able to form a jelly.

2. The larger the viscosity, the larger will be the inefficient expenditure of energy.

3. The smaller the number of valence electrons, the more readily the atom yields them.

4. If the acid is nonvolatile, only the ammonia is driven off while the acid remains in the vessel.

5. The shape of the colloidal particles, is not the only factor, which determines the ability to form stable jellies.

6. Hence the structural elements of a jel need not have long fibrous macromolecules.

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V. Translate into Vietnamese paying attention to the Participles:

1. Some adsorbents may contain sufficient acid or alkali to after the pH of the water being treated.

2. Having been compressed the air is to be cooled.3. Having been composed of liquid particles emulsions disperse in

other liquids.4. Being used in different fields of chemistry, industry and

medicine colloid chemistry becomes increasingly important.5. When placed in a liquid, the corresponding solids will swell first

and then slowly go into solution

VI. Translate into English

1. H¹t keo cã tÝnh ®èi xøng cµng thÊp th× nång ®é cña chóng ph¶i cµng cao.

2. H×nh d¹ng cña h¹t keo kh«ng ph¶i lµ yÕu tè ®éc nhÊt quyÕt ®Þnh kh¶ n¨ng t¹o thµnh keo bÒn.

3. NÕu çc h¹t keo kh«ng dÝnh vµo nhau th× sù t¹o gel kh«ng s¶y ra.

4. Mét sè gel thu ®îc khi thªm axit vµo dung dÞch natri silicat. Gel t¹o thµnh nh vËy th× r¾n, bÒn v÷ng vµ kh«ng thÓ chuyÓn thµnh tr¹ng th¸i láng.

VII. Write an outline of the text and retell it

Text 4

Emulsions

An emulsion represents a disperse system in which the phases are immiscible or partly immiscible liquids.

In nearly all emulsions, one of the phases is aqueous and the other is an oil. If the oil is disperse phase, the emulsion is termed an oil in water (o/w) one. If the aqueous medium is the disperse phase, the emulsion is termed a water in oil (w/o)

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one.

If one shakes vigorously a vessel containing two immiscible liquids, both liquids are broken up into the droplets whose size depends upon the viscosity of the liquid, surface, interfacial tensions and the vigor of the shaking. As soon as the mechanical dispersive action ceases, the droplets begin to coalesce in order that the total surface free energy may be reduced. Most often, particularly in the case of two pure liquids, the coalescence process is rapid, and within a very few minutes the system consists only of two liquids layers. In the presence of the small amounts of additional components, termed emulsifiers the rate of coalescence of the droplets may be greatly reduced. Emulsions are intrinsically unstable, thus resembling lyophobic colloids. Three distinct kinds of instability are found to exist, each may be of great importance in industrial products.

Emulsions may “ cream” , i. e. separate into layers of aqueous phase with a concentrated layer of oil droplets floating on the top, the rate depending primarily on the viscosity of the aqueous phase, the size of the droplets, and the density difference between aqueous phase and the droplets. They may also flocculate as do other lyophobic colloids. The flocs, being larger than individual drops, have a higher creaming rate.

Finally, the drops may coalesce giving a separated bulk layer of the once emulsified liquid, in which case re-emulsification can be affected only by drastic mechanical action.

No satisfactory quantitative theory of the emulsion stability has yet been developed. It is nevertheless becoming apparent in the case of coalescence that it is the structure of the interfacial film, which is controlling the behaviour of the system. For flocculated o/w emulsions the rate of coalescence is linearly dependent on the concentration of the adsorbed emulsifier in the interfacial film, and appears to extrapolate to zero at complete coverage of the surface of droplets.

It might be thought that dilute emulsions would be ideal

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system on which to test theories of the flocculation of lyophobic colloids.

Many industrially important emulsions are “ stabilized “ (given long life) by the use of solids as emulsifiers.

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Exercises


1. What is an emulsion? 2. What emulsions are widely known? 3. What emulsions phases do you know? 4. What happen if one shakes vigorously a vessel containing two

immiscible liquids? 5. When is the coalescence process rapid?6. In what way can industrially important emulsions be “stabilized

“

II. Translate the following derivatives:

1. disperse, dispersed, disperser, dispersing, dispersion, dispersity, dispersive.

2. emulsification, emulsifier, emulsify, emulsifying, emulsion.3. miscibility, miscible, mix, mixer, mixed, mixing, mixture.4. polymer, polymeric, polymerism, polymerization, polymerize,

polymerized, polymerizing.

III. Translate the following sentences paying attention to the words in bold type:

1. Water dispersible dye is a good example of an emulsion in which the pigment helps to control the emulsion stability.

2. Polyformaldehyde is used for the manufacture of many consumer goods.

3. Latex foam from Government Rubber Styrene (GRS) of the proper type is good in colour, pore structure, and ageing but rather lacking in strength.

4. Even with a high alkali reserve, the storage life of neoprene latex is not as good as many other latices.

5. Neoprene is very desirable for dipped goods where special service conditions are required.

6. Gum arabic is a fairly goods dispersing agent and has one desirable feature - good ultraviolet resistance.

7. The extensive data obtained in emulsion polymerization of metyl methacrylate are in good agreement with the

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asumption that the rate of the reaction at high conversion is governed only by the diffusion rate of the monomer and the radical end of the polymeric chains.

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IV. Translate the following sentences paying attention to the negative pronoun "no":

1. No satisfactory quantitative theory of the emulsion stability has yet been developed.

2. The difference between suspension and emulsion polymerization points to a process of formation of particle in the latter, whereas no such process occurs in suspension reaction.

3. No equipment embodying brass or bronze should be allowed to come into contact with latex or its compounding ingredients at any stages of the manufacture.

4. No synthetic high polymers are chemically pure substances in the strict sense.

V. Translate the following sentences and states the function of the

1. In nearly all emulsions, one of the phases is aqueous and the other is an oil.

2. The colloidal state for a substance is one in which it exhibits colloidal properties.

3. If one shakes vigorously a vessel containing two immiscible liquids, both liquids are broken up into droplets.

4. If the oil is the disperse phase, the emulsion is termed an oil in water one, if the aqueous medium is the disperse phase, the emulsion is termed a water in oil one.

VI. Translate the following sentences into Vietnamese paying attention to the use of verb “to do” :

1. Emulsions may flocculate, as do other lyophobic colloids.2. When polymerization does take place, average molecular

weights in the thousands are not obtained.3. Reinforcing agents did not generally have the affect on latex

rubber that they did on milled rubber. 4. The experiments conducted show that adhesion does increase

for a time after curing, but that it comes to a stable value during the first 24 hours.

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VII. Translate into Vietnamese paying attention to the rule of Sequence of Tences.

1. Berzelius stated that rubber could be redispersed. 2. It was known that ultraviolet - light had a harmful influence on a

rubber surface and caused photochemical effects on antioxidants.

3. Dent assumed that in the alkali halides the positive and negative ions in the surface remained coplanar.

4. Willbourne assumed that the methyl absorptivity was constant regardless of the position of the methyl group in the molecule.

5. It might be thought that dilute emulsions would be ideal systems.

6. It was considered that stabilizers belonged to a class of substances, which had been known as “ surface active agents “.

7. In the early 1920’s it was reasoned in England that individual particles of latex would be vulcanized without breaking the emulsion.

VIII. Translate into English

1. Nh ®· biÕt, ®Æc tÝnh riªng biÖt cña nhò t¬ng ®iÓn h×nh lµ d¹ng h×nh cÇu cña h¹t keo.

2. Ngêi ta ®· biÕt r»ng, ®êng kÝnh cña h¹t nhò t¬ng phô thuéc vµo ®é nhít vµ søc c¨ng bÒ mÆt còng nh vµo cêng ®é l¾c.

3. Ngêi ta cho r»ng, khi thªm vµo mét lîng nhá chÊt nhò ho¸ th× cã thÓ t¨ng tÝnh æn ®Þnh cña nhò t¬ng.

4. Nh ®· biÕt , cho ®Õn nay cha cã mét lý thuyÕt ®Þnh lîng phï hîp nµo vÒ ®é bÒn cña nhò t¬ng ®îc ®a ra.

5. ý nghÜa thùc tiÔn cña nhò t¬ng trong thùc tÕ còng nh trong kü thuËt lµ rÊt lín.

6. Nh÷ng nhò t¬ng tæng hîp, ®îc ®iÒu chÕ tõ nh÷ng chÊt láng kh¸c nhau cã mÆt chÊt nhò ho¸ ®Æc biÖt, cã ý nghÜa lín.

IX. Write a short summary of the text.

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Text 5

Solvent properties of surfactant solutions

Emulsion polymerization

The term “emulsion polymerization” is applied to a variety of processes which have in common that the main chemical reaction is a polymerization and that the end product is a latex, i. e. a suspension of polymer particles of colloidal dimensions in an aqueous medium. Such a process is called emulsion polymerization as the initial mixture of reagents usually consists of an aqueous emulsion of monomer and small amounts of other chemicals. Polymerizations in which the monomer is initially dissolved in water producing a suspension of small particles of polymer are sometimes named emulsion polymerizations as well, though rather inappropriately.

If the product of a polymerization consists of a suspension of relatively large particles (dimensions ~ 1), the process is termed a suspension polymerization. The difference between suspension and emulsion polymerization points to a process of formation of particles in the latter, whereas no such process occurs in suspension polymerization. In fact, suspension polymerizations

were found to show the characteristics of a polymerization reaction in bulk monomer, the aqueous phase playing only a minor role.

In 1926 German scientists succeeded in producing synthetic rubber latices by polymerizing monomer emulsions stabilized by various surfactive agents. The addition of surfactants profoundly influences the course of polymerization. In 1938 Fikentscher was the first to express the view that in emulsion polymerization the monomer, dissolved in the aqueous phase polymerizes rather than the monomer present as emulsified droplets.

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A great deal of knowledge has been gained since emulsion polymers were first produced on a large scale. Smith and Ewart have developed a quantitative theory of particle formation and treated the growth of the particles during polymerization. One of the growth mechanisms considered has been found to hold true in many polymerizations with small particles.

The chemical reactions of emulsion polymerization take place in heterogenerous system in which polymer particles of colloidal dimensions are formed. Physical and chemical phenomena influence each other profoundly.

The extensive data obtained in emulsion polymerization of methyl methacrylate are in good agreement with the assumption that the rate of reaction at high conversion is governed only by the diffusion rate of the monomer and the radical end of the polymeric chains.

Exercises


1. What is meant under “ emulsion polymerization”?2. What is meant under “ suspension polymerization”?3. What is the difference between emulsion and suspension polymerization?4. Who treated the problem of the particle growth during polymerization?5. What are the dimensions of the particles formed during emulsion polymerization?

II. Give a summary of the text.

III. Give Vietnamese equivalent to:

bulk layerindividual dropsinitial mixture

once emulsified liquidradical end


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1. A great deal of knowledge has been gained since emulsion polymers were first produced on a large scale.

2. The term “emulsion polymerization” is applied to processes which have in common that the main chemical reaction is a polymerization and that the and product is a latex.

3. Most often, particularly in the case of two pure liquids, the coalescence process is rapid.

4. Polymerizations in which the monomer is initially dissolved in water producing a suspension of small particles of polymer are sometimes named emulsion polymerizations as well.

5. Ultra-violet light is known to have a harmful influence on a rubber surface, as well as causing photochemical effects on antioxidants.

6. The chemical reactions of emulsion polymerization take place in heterogeneous system in which polymer particles of colloidal dimensions are formed.

7. One of the growth mechanisms considered has found to hold true in many polymerizations with small particles.

8. In 1926 German scientists succeeded in producing synthetic rubber latices by polymerizing monomer emulsions stabilized by various surfactive agents.

9. In 1938 Fikentscher was the first to express the view that in emulsion polymerization the monomer, dissolved in the aqueous phase polymerizes rather than the monomer present as emulsified droplets.

V. Form adjective from the following words:

actionadditioncolloiddilutiondispersionheterogeneityindustrylineminoritymixture

phasepolymerquantityrelationsolutestabilitystructuresynthesisvarietyviscosity

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VI. Translate the following sentences paying attention to the Passive Voice:

1. The employment of latex is being aimed at reinforcing furs, particularly rabbit skins, which are very soft and weak.

2. When a solid is attacked by a liquid reagent the product might be either soluble or in soluble in the liquid.

3. Polyvinyl chloride was not thought of as a competitor of rubber until the war.

4. Branching may be referred to as changing mainly the shape of the molecule.

5. It was assumed that the rate of reaction at high conversion would be governed by the diffusion rate of the monomer.

6. Fundamental investigations concerning chemical catalysis were aimed at a quantitative expression of activity.

7. Polyethylene is not affected by aggressive mediums such as acids, alkalis and salt solutions.

8. Rubber is known to be unaffected by many neutral salts, organic acids, etc.

9. Soft vulcanized rubber in the presence of antioxidants was acted upon by the oxygen of the air.

10. If the substance being ground is a reactive one, the possibility of chemical alteration of the surface by chemisorption of oxygen or water vapour from the air must be reckoned with.

11. Since adhesion is greatly influenced by adsorption of gases and vapours, one would expect the bulk density to depend on the humidity of the air.

VII. Translate the following sentences paying attention to the Absolute Participle Construction:

1. The drops of rubber are suspended in water, when first obtained from the plant, the system resembling an emulsion.

2. Emulsion may “ cream “, i. e., separate into layers of aqueous phase with a concentrated layer of oil droplets floating on the

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top, the rate depending primarily on the viscosity of the aqueous phase, the size of the droplets, etc.

3. The emulsifier being a solubilizing agent for the monomer, the rate of polymerization varies with the emulsifier content.

4. Most of the accelerators used today are derivatives of carbon disulfide, the commonest one being mercaptobenzothiazole.

5. The rate of polymerization varies with the emulsifier content, the emulsifier being a solubilizing agent for the monomer.

VIII. Translate into English

1. Nh ®· biÕt mñ (latex) lµ s¶n phÈm cuèi cïng cña sù polime ho¸ nhò t¬ng.

2. Ph¶n øng ho¸ häc cña sù polime ho¸ nhò t¬ng x¶y ra trong hÖ dÞ thÓ vµ ®îc kÕt thóc bëi sù t¹o thµnh nh÷ng h¹t polime cã kÝch thíc h¹t keo.

3. Khi nghiªn cøu sù polime ho¸ metyl metacrylat, çc nhµ khoa häc ®· thu ®îc çc d÷ kiÖn ®¸ng chó ý.

4. Ngêi ta ®· x¸c nhËn r»ng poly metyl metacrylat thu ®îc b»ng çch polime ho¸ nhò t¬ng th× rÊt r¾n.

5. Latex tæng h¬p ®· ®îc sö dông lµ nhò t¬ng cña cao su tæng hîp vµ nhùa nh©n t¹o vµ chÝnh chóng ®îc diÒu chÕ b»ng çch polime ho¸ nh÷ng monome ban ®Çu trong cïng mét pha.

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text 6

the nature of rubber - like elasticity.

The characteristic property of rubber, its extensibility and complete recovery after even very large deformations, is shown also by many other substances. Of these we may mention supercooled molten sulphur and selenium, gelatin, muscle fibrils, substances built from long chain molecules such as polyvinyl ancohol, etc.. These substances are very different chemically, but their common feature is a long flexible molecule. There is a rubber- like state, which many substances made from long molecules, may assume under suitable conditions.

The two factors which are necessary if perfect rubber - like elasticity is to be obtained are, firstly, that whole molecules must not be able to slip past each other under the action of deforming forces, and, secondly, that these forces shall meet little resistance in straightening out the coiled molecular chains. In lightly vulcanized rubber, the long chains are connected across at certain points by the strong sulphur linkages. These presence of only a few such points of linkage is sufficient to prevent slipping of the whole molecules, which would result in plastic flow. The atoms of the molecule share in the general thermal motion at any temperature, so that the free molecules would be continually coiling, twisting, and changing its shape. There are many more ways in which such molecules can be arranged to give a crumpled chain.

The lengths of chain between sulphur crosslinks behave in essentially the same way as the free rubber molecule, so that the vast majority of them are in a contracted form, which changes momentarily with the thermal motion. This freedom comes from weakness of the Van der Waals forces between the chains, which are not strong enough to hold them permanently in position side by side.

When we apply a force to the rubber, the flexible chains are

32

slightly straightened, but are always attempting to return to their folded condition. It is evident that, the more violent the thermal motion, the greater the tendency of the chains to return to their normal positions. If a rubber band is stretched by means of a weight, it contracts on heating owing to the effect of the increased thermal motion. This is contrary to the behaviour of normal substances, which deform more easily at high temperatures.

The highly coiled and folded condition of the rubber chains permits their being extended up to seven times their original length. Long before this, however, some of the chains will have been pulled approximately parallel. When this occurs, the attractive forces between them become sufficiently strong to bind them together in a regular arrangement. Thus the rubber is crystallized by tension. This result was clearly demonstrated by Katz using X - ray diffraction to detect the crystallinity. He showed that ordinary, unstretched rubber has a disordered structure, resembling that of a liquid. Sufficient stretching gives an X - ray diffraction picture similar to that shown by fibrous materials. If the rubber is cooled, while under tension, to a low temperature, it does not contract when the tension is removed, and still gives a crystalline X - ray diffraction pattern. On reheating, “melting “ occurs and the rubber contracts. If the frozen stretched rubber is pulverized when cold, it splits up into fibrous pieces, owing to the parallel orientation of the chains.

If unstretched rubber is cooled, a slow crystallization takes place, giving a harder and less extensible material. On warming, ”melting” again occurs, but unlike that of ordinary crystalline substances, it takes place over a range of some 100C in temperature. These effects may be observed in crepe soles kept for some time exposed to very cold weather.

In an ideal rubber- like substance no energy is used in separating chains and in increasing their separation during the stretching. As a result there is no change in the total volume of the substance when extended. This condition is not fulfilled by most rubber - like substances, so that their properties only partially correspond to those of the ideal substances.

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Commercial rubbers are very complex systems, in which variation of the proportions of the constituents can give an immense range of products.

Exercises


1. What substances are known to display the characteristic properties of rubber?

2. What factors is perfect rubber-like elasticity due to?3. What happens if one applies a force to rubber?4. In what way did Katz succeed in detecting crystallinity?5. In what case does the process of slow crystallization take place?

II. Find (in the list given below) synonyms to the following words. Translate these words in to Vietnamese:

cancertaincompletecontractedto detectdifferentevidentlightlymotionobtainpropertyshapesubstancesufficienttotalviolent

to be able tobehaviourcompresseddefiniteenoughto find outformfullgetmattermovementobviousslightlystrongvariouswhole

III. What do you know about:

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a branched chaina coiled chaina crumpled chaina flexible chaina main chain

a molecular chainan oriented chaina side chaina straight chain


1. When parts of the long molecules of the natural rubber arrange themselves in an ordered state crystallizing they are assumed to exhibit a first - order transition.

2. There is a rubber like state, which many substances made from long molecules may assume under suitable conditions.

3. Mendeleyev’s theoretically assumed value of 240 for the atomic weight of uranium was confirmed by the scientists.

4. Synthetic rubber produced from isoprene was presumed to a long chain structure built up from isoprene units by 1-2, 1-4 linkages.

V. Fill in the blanks with prepositions:

1. The characteristic property ... rubber, its extensibility and complete recovery .... even large deformations, is shown ... many substances.

2. The lengths ... chain sulphur crosslinks behave ... essentially the same way as the free rubber molecule, which changes ... thermal motion.

3. The two factors which are necessary if perfect rubber- like elasticity is to be obtained are, firstly, that whole molecules must not be able to slip ... each other ... the action .... deforming forces, and, secondly, that these forces shall meet ... little resistance ... straightening ... the coiled molecular chains.

VI. Translate the following sentences paying attention to the -ing forms.

1. On reheating, “melting” occurs and rubber increases in volume.

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2. Reinforcing agents harden the rubber and make it more wear resistant.

3. Katz showed that ordinary, unstretched rubber has a disordered structure, resembling that of a liquid.

4. In an ideal rubber-like substance no energy is used in separating chains and in increasing their separation during stretching.

5. The highly coiled and folded condition of the rubber chains permits their being extended up to seven times their original length.

VII. Translate into English

1. GÇn 25 n¨m sau mét sè nhµ b¸c häc ®· ®a ra hµng lo¹t lý thuyÕt vÒ tÝnh ®µn håi cña cao su.

2. Sù ph¸t triÓn nh÷ng lý thuyÕt chung vÕ tÝnh ®µn håi lµ mét sù kiÖn quan träng trong khoa häc.

3. Çc nhµ khoa häc ®· x¸c ®Þnh lµ çc ph©n tö cao su bÞ biÕn d¹ng khi chuyÓn ®éng nhiÖt.

4. Ngêi ta còng ®· chøng minh ®îc r»ng cã sù phô thuéc trùc tiÕp gi÷a lùc co l¹i vµ nhiÖt ®é tuyÖt ®èi.

5. CÇn ph¶i nhí r»ng cao su cha lu ho¸ bao gåm mét sè lín çc ph©n tö.

6. Theo thuyÕt Brown th× bÊt kú mét m¹ch cao su nµo còng ë tr¹ng th¸i chuyÓn ®éng nhiÖt vÜnh cöu.

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text 7

Graft- copolymer formation in latex

The initiation of polymerization of vinyl monomer in rubber latex can be affected in various ways.

Initiation by polyamine- activated hydroperoxides

Early attempts to polymerize common vinyl monomers in natural rubber were vitiated by the presence of ammonia, and a search was therefore made for an initiating system which would work well with ammonia present and also without requiring de-aeration of the latex1. A successful method employs a hydroperoxide activated by a polyamine. Originally developed by Whitby, this system is utilized in rubber as follows. The hydroperoxide (e. g. t-butyl hydroperoxide) is dissolved in the monomer (typically, methyl methacrylate) and

then added with stirring to diluted latex containing, if need be, an added stabilizer. After dispersion is complete, the polyamine (usually tetraethylene pentamine) is added. Polymerization starts at room temperature and is complete in a few hours. Provided substantial proportions of stabilizing soaps are avoided, polymerization takes place entirely within the rubber particles and no separate polymer particles are formed. It is necessary to allow sometime for the monomer to diffuse into the rubber particles and, after polymerization is completed, the small particles contain a higher proportion of polymer than do the larger particles (in the case of methyl methacrylate). Graft copolymer latices of this type been referred to Heveaplus.

The products of polymerization can be separated into free rubber, graft copolymer and free vinyl polymer. In the case of methyl methacrylate it is found that the pattern of combination2 is almost precisely the same as that found when polymerization takes place in solution. Of the total poly (methyl methacrylate)

37

formed, only about half is grafted to the rubber (i. e. fv is about 0.5).

38

Initiation by aerated by aerated latex

Sekhar observed that if latex is aerated by rotating a half- filled container for a period of days the product is able to initiate polymerization of a range of monomers without the addition of a hydroperoxide. The procedure is simply to add monomer to aerated latex, followed by a small amount of ferrous and polyamine activator. Centrifuging experiment established that the activity was associated with the rubber component of the latex and not with the serum. Sekhar considers that reactive sites are formed on the rubber during aeration (or much more slowly on storage). These probably are being hydroperoxidic in nature.

Whilst there had been earlier observations that aerated latex can initiate polymerization of added monomers, the importance of Sekhar’s work is that he was able to establish that, in the case of methyl methacrylate, the grafting efficiency is very high. Little free polymer is formed, fv being 0,1 or less. This is contract with the conventional method of initiation and is presumably due to the fact that initiation proceeds directly from rubber or rubber peroxy- radicals. This must materially reduce the possibility of simultaneous formation of uncombined polymer.

Activated latex

Since the preparation of graft copolymer latices from aerated latices is a slow process, investigations were undertaken to find an alternative method, which would also give a product with efficiency of grafting. One such method involves pretreatment of latex with hydroperoxide and activator, followed by the addition of monomer after a time interval long enough to ensure that the original hydroperoxide will have decomposed. In a typical procedure, t- butyl hydroperoxide is added to 60% latex, followed by tetraethylene pentamine. This is allowed to react for 24 hours; separate tests (in the absence of latex) show that no hydroperoxide remains after this period. Methyl methacrylate, together with a small amount of stabilizer, is then added. Polymerization takes place quite rapidly at room temperature. To

39

obtain maximum conversion, it is advisable to add ~ 50 ppm of ferrous ion either before or after adding the redox catalyst.

With methyl methacrylate the efficiency of grafting is as high as found the aerated latex method, fv being typically as slow as 0,02.

Notes

1. de-aeration of the latex: sù lo¹i khÝ khái mñ2. pattern of combination: ®Æc trng cña ph¶n øng

Exercises


1.Were the early attempts to polymerize vinyl monomers in natural rubber successful?2. How can one effect the initiation of polymerization of vinyl monomer in latex?3. What kinds of initiating systems do you know?4. What phenomenon did Sekhar observe?5. What latices are referred to as Heveaplus?6. What fact was established due to the centrifuging experiments?

I. Group the following words into pairs of synonyms:

employeddiluted presumablyinvestigationifinitialutilizedentirelyprobably

providedwateredtotallyoriginalpreciselyprocedureexactlysearchprocess

III. Group the following words into pairs of antonyms:

original rapidly

conventional in particular

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start insoluble as high as final slowly complete

above as slow as soluble unusual below in general

41

IV. Give Vietnamese equivalents:

as slow as 0.02efficiency of graftingin contract with

long enough on storage refer to

V. State the function of the words after and before and translate the sentences:

1. The polyamine is added after the dispersion.2. After dispersion is complete, the polyamine is added.3. Before the discovery of vulcanization, the great drawbacks of

rubber were its thermoplastic nature and its sensibility to oxidation.

4. Neoprene was used for balloons, before natural rubber was available.

5. Polymerization starts at room temperature and is complete after a few hours.

6. After substantial proportions of stabilizing soaps are avoided, polymerization takes place.

VI. State the functions of the words in bold type:

1. Some scientists observed that aerated latex could initiate polymerization.2. A plasticizer is a material that increases the plasticity of a mass.3. Sekhar considers that reactive sites are formed on the rubber during aeration, these probably being hydroperoxidic.4. The vulcanization of plastic chloroprene polymer differs from that of all other rubbers in requiring the addition of no vulcanizing ingredient.5. The methods of producing modified latices depend on those of initiation.6. In the case of methyl methacrylate it is found that the pattern of combination in the same as that found when polymerization takes place in solution.

VII. Find in the text sentences with the absolute participle construction.

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VIII. Translate into English:

1. Sù kh¬i mµo cho qu¸ tr×nh polime ho¸ vinyl trong latex cã thÓ ®îc tiÕn hµnh b»ng nhiÒu ph¬ng ph¸p.

2. §Ó kh¬i mµo cho ph¶n øng trïng hîp ghÐp trong latex cã thÓ sö dông hÖ kh¬i mµo tan trong dÇu, trong ®ã mét cÊu tö ®îc hoµ tan trong níc, mét cÊu tö kh¸c ®îc hoµ tan trong dÇu.

3. Sau khi qu¸ tr×nh polime ho¸ kÕt thóc th× nh÷ng h¹t bÐ chøa nhiÒu polime h¬n nh÷ng h¹t lín.

4. §Ó tiÕn hµnh polime ho¸ ngêi ta sö dông réng r·i ph¬ng ph¸p dïng hydropeoxit ®îc ho¹t ho¸ bëi polyamin.

5. Xekhar nhËn thÊy r»ng møc ®é th«ng khÝ rÊt cao trong trêng hîp sö dông metyl metacrylat.

6. Sù ®iÒu chÕ copolime tõ latex b·o hoµ kh«ng khÝ s¶y ra chËm do ®ã ngêi ta cè g¾ng t×m mét ph¬ng ph¸p míi hiÖu qu¶ h¬n.

Text 8

Rubber latex

Latex, before the advent of synthetic rubber, was a term applied solely to the milk of tropical plants and rubber trees which are known to yield a rubber latex, a natural emulsion of rubber particles.

Today, latex is a term also used to refer to any rubber- like polymer in emulsified form.

The rubber molecules in the form of very long hydrocarbon chain.

It may have a molecular weight as high as 250.000. In natural rubber the molecules are intertwined and held together by van der Waals forces to give “drop” of rubber about 3 in diameter. These drops are suspended in water, when first obtained from the plant, the system resembling an emulsion. Proteins, fats,

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soaps, and other substances are present in the milky fluid, which is called “latex”.

The usual process applied to rubber latex is to add acid, usually formic, which renders the emulation unstable and coagulates the rubber. A spongy mass is produced which is passed through rolls to squeeze out excess latex and to form a sheet of rubber. The sheet is usually “smoked” with the fumes from burning green wood, which helps to preserve the rubber. This product is called “crepe rubber” and is the raw material for most rubber manufacture.

It is necessary, for certain purposes, to make use of the latex itself as a raw material. This necessitates two modifications to the natural latex. Firstly a preservative must be added to suppress bacterial action, which would eventually lead to coagulation. This is achieved by the addition of ammonia. This prevents the development of acidity, which is the means of causing coagulation. The natural product contains only 35 percent rubber suspended in about 60 percent of water. Concentration may be effected by using a centrifuge, in a manner similar to the centrifuging of milk to give cream. It has recently been shown that the addition of konnyakn meal, which is a complex carbonhyrate soluble in water, to latex is very effective in producing a rich cream of high rubber content. Rubber is lighter than water and hence form a cream and not sediment.

The creaming is done in a tank. The initial effect of the creaming agent is to cause a clustering of the rubber particles. The resulting large effective size of the units produces their Brownian motion and increases the speed with which they rise through the liquid. Clustering differ from coagulation in that it is reversible, suitable changes being able to redisperse the particles. This is of importance since coagulation would prevent the use of latex for special methods of manufacture. Soon after the addition of the creaming agent to the tank, a very deep cream layer is formed, which is built of clusters linked together, with water filling the spaces. Water then passes out of the cream layer, the lower boundary line gradually ascending. After about four days the liquid

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may be run off from valve A and the latex cream from valve B. Proteins and swollen meal particles may then centrifuged off, and the cream is stabilized with ammonia for shipment in drums.

The colloidal behavior of latex rubber is largely the result of the protective layer of protein with which the particles are surrounded. Clustering is influenced by the action of the creaming agent on this surface layer. Coagulation occurs when the acidity is such as to render the adsorbed protein molecules electrically neutral. These facts are closely related to the protective action of proteins on gold sols.

Exercises


1. What is latex?2. What components of latex do you know?3. What is meant by “crepe rubber”?4. What is difference between “a ream” and “a sediment”?5. Can you explain what is meant by the term “clustering”?6. What is coagulation?7. When is latex used as a raw material?

II. Describe the process of rubber latex production.

III. Translate the following sentences into Vietnamese paying attention to the words word combinations in bold type:

1. The colloidal behavior of latex rubber is largely the result of the protective layer of protein with which the particles are surrounded.

2. It is necessary, for certain purposes, to make use of the latex itself as a raw material.

3. Proteins, fats, soaps, and other substances are present in the milky fluid, which is called “latex”.

4. We shall not consider synthetic plastic materials, partly because of their similarity.

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5. The utility of rubber is ultimately related to the ease, with which it sustains very large distortions, returning to its original shape when released.

6. To coat positively charge electrodes with the particles, use can be made of the electric charge on the rubber particles,

7. The latex is mixed with sulphur, accelerators, zinc oxide, etc., in the form of powders dispersed in water with a protective colloid such as gelatin present.

8. Concentration may be effected by using a centrifuge, in a manner similar to the centrifuging of milk to give cream.

9. Numerous ingredients other than sulphur are normally included in the rubber mixing, the proportions depending on the grade of rubber required.

10. The rubber molecule may have a molecular weight as high as 250.000.

11. The sulphur, zinc oxide and accelerators are referred to collectively as the vulcanizing system.

12. Apart from its use in such specialized products as adhesive, the full potentialities of rubber latex are only realized on vulcanization.

IV. Give Vietnamese equivalents:

to break down to build from to centrifuge off to correspond to to rise through

to run offto split upto squeeze outto pass through

V. Translate into Vietnamese paying attention to the word with:

1. to coat positively charge electrodes with the particles;2. to combine with rubber molecules;3. to extract with acetone;4. to mix with sulphur;5. to smoke with fume;6. to stabilize with ammonia;7. when tested with iodine;

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8. some substances remain with impurities;9. with avoidance of agitation;

VI. Translate the following sentences into Vietnamese paying attention to the - ing forms:

1 Latex may be used for impregnating paper, leather, or cloth, the rubberized product being water proof.

2. The initial effect of the creaming agent is to cause a clustering of the rubber particles.

3. Clustering is influenced by the action of the creaming agent on this surface layer.

4. Soon after the addition of the creaming agent to the tank, a very deep cream layer is formed, which is built of clusters linked together, with water filling the space.

5. Articles are formed by dipping shapes in the latex, drying and vulcanizing in hot air.

6. The “drops” of rubber are suspended in water, when first obtained from the plant, the system resembling an emulsion.

VII. Translate the following sentences into Vietnamese and state the function of will and would:

a)

1. When stretched rubber flows, it will not return to its original shape.

2. If heating is carried on long enough in the presence of curatives, the latex will not form a continuous film on drying but will crack into a multitude of small pieces.

3. Styrene will polymerize to produce polymers other than rubber- like bodies.

4. Ethylene chloride will react with sodium polysulfide to form high molecular weight rubber- like substances.

b)5. Coagulation would prevent the use of latex for special methods

of manufacture.6. To suppress bacterial action, which would eventually lead to

coagulation, a preservative must be added to latex.

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7. Were unstretched rubber cooled, a slow crystallization would take place, giving a harder and less extensible material.

8. The atoms of the molecule share in the general thermal motion at any temperature, so that a free molecule would be continually coiling, twisting and, changing its shape.

9. Density considerations make it impossible to accept a theory, which would require substances to polymerize with the decease in density as, would be the case if the polymers spin.

VIII. Translate the following sentences into English:

1. Ngµy nay cao su tæng hîp ®îc sö dông réng r·i ®Ó thay thÕ cao su tù nhiªn còng nh ®Ó s¶n xuÊt çc vËt dông cã tÝnh chÊt ®Æc dông.

2. Chóng ta biÕt r»ng, latex, ®îc ®iÒu chÕ b»ng ph¬ng ph¸p Gevei, lµ hÖ phan t¸n cña çc h¹t cao su vµo níc.

3. T¸c dông cña çc chÊt t¸ch kem ë giai ®o¹n ®Çu lµ g©y ra sù ®«ng tô cña çc h¹t cao su.

4. Nh ®· biÕt, sù ®«ng tô lµ qu¸ tr×nh keo tô mµ cã thÓ lµ thuËn nghÞch tøc lµ trong mét sè ®iÒu kiÖn thÝch hîp th× ®¸m ®«ng tô Êy cã thÓ bÞ ph©n t¸n ra.

5. Ngêi ta ®· x¸c ®Þnh ®îc r»ng vÒ b¶n chÊt sù keo tô kh«ng ph¶i lµ qu¸ tr×nh ho¸ häc mµ lµ mét qu¸ tr×nh vËt lý.

6. Sù ®un nãng, sù lµm qu¸ l¹nh, sù khuÊy trén m¹nh,… lµ nh÷ng yÕu tè bªn ngoµi g©y ra sù keo tô.

Text 9

Storage hardening

The presence of microgel particles in natural rubber latex has a directly practical consequence in the phenomenon of storage hardening. Rubber, either in the form of latex or solid sheet, when stored for considerable periods develops an increased hardness (as measured by Mooney viscosity or Williams plasticity),

48

the change in the solid sheet being generally greater the lower the initial hardness.

The changes are greatly influenced by the relative humidity of storage. In dry air the rate at which hardening occurs increases with decreasing sample thickness or with increasing temperature. The removal of acetone soluble and nitrogenous components does not prevent the hardness increase.

One might expect that the increase in hardness, which occurs when ammoniated latex is stored, is a result of intra- particle crosslingking and microgel formation. With solid rubber the crosslinking process is no longer confined to within the original latex particles, but there is no reason to suppose that the mechanism of the crosslinking reaction differ in the two cases.

Although the nature of the spontaneous hardening reaction remains obscure considerable information about the functional groups involved and on methods of control has recently been forthcoming. Rubber hydrocarbon interacts with oxygen to form hydroperoxidic compounds and the decomposition of such compounds could result either in degradation or crosslinking of the rubber molecules, according to condition. However, crosslinking via hydroperoxide decomposition does not appear to be a major cause of storage hardening. Since hardening can be almost completely suppressed by the addition of the latex of monofunctional carbonyl reagents (especially demendone which is a specific reagent for aldehyde groups) it has been inferred that the crosslinking reaction involves carbonyl groups in the rubber. The number of such carbonyl groups per rubber molecule can be estimated by measuring the concentration of hydroxylamine required to inhibit completely storage hardening; value of 9-29 was found for a number of clonal rubber. Difunctional amnines, such as benzidine, in contract to their monofunctional analogues, promote crosslinking by coupling reaction.

If it is accepted that storage hardening results from the presence of carbonyl groups in very small proportion, it is then desirable to determine how these groups originate. It has been

49

suggested that they are incorporated at intervals along the “hydrocarbon chain”, but it has still to be shown that they are an integral feature of natural rubber molecules. Biologically induced oxidation could proceed in the vicinity of the tapping cut or in the latex vessels. The generation of oxygenated groups in secondary reactions is consistent with our present knowledge of polyisoprene biosynthesis.

50

Exercise


1. What is storage hardening?2. In what way can one measure rubber hardness?3. Does the removal of acetone- soluble components prevent

rubber harness?4. How can the hardening process be suppressed?5. The nature of spontaneous hardening reactions is obscure to

investigators, isn’t it?6. In what way is the number of carbonyl groups per rubber

molecule estimated?

II. Translate the following sentences into Vietnamese paying attention to the words in bold type:

1. Repeated washing of latex in a centrifuge, followed by drying, results in rubber suited for insulation purposes.

2. Homologs of aniline result from the reduction of their corresponding nitro compounds.

3. In the experiment conducted in the laboratory the resultant product is a vitreous solid that softens at 1000.

4. The fatty acids resulting from the hydrolysis are neutralized by the use of sodium or potassium hydroxide.

5. If chain molecules are dissolved in a low- molecular- weight solvent, the resulting solution is nonbifringent.

6. It is accepted that storage hardening results from the presence of carbonyl groups in very small proportion.

III. Translate the following sentences paying attention to the words in bold type:

1. Unvulcanized rubber is both plastic and elastic.2. Rubber either in the form of latex or solid sheet, when stored

for considerable periods develops increased hardness.3. The generation of oxygenated groups in secondary reactions is

consistent with our present knowledge of polyisoprene biosynthesis.

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4. It has been suggested that the carbonyl groups (in storage hardening) are incorporated at intervals along the “hydrocarbon chain”.

5. As a result of Goodyear’s work, along with improvements by Hancock, rubber goods of wide utility and durability could be made.

6. Modern industry could no longer function properly without reinforced rubber.

7. Polystyrene has been used commercially long before the high styrene resins.

IV. Put question to the words in bold type:

1. The Hardness of rubber is measured either by Mooney viscosity or Williams plasticity.

2. The generation of oxygenated groups in some secondary reaction is consistent with our present knowledge of polyisoprene biosynthesis.

3. The infra-red spectrum is closely similar to that of natural rubber.

4. The stress produced by shearing is very low compared with that of natural rubber.

V. Translate the following sentences paying attention to the function of the verb to do:

1. Monosaccharides do not hydrolize to simpler substances.2. An organic chemist has much to do with different reaction.3. It is known that most fibers when suspended in an alkaline

aqueous medium have s negative charge as do the particles in alkaline latex.

4. Upon what structural arrangement does the colour of an organic compound depend?

5. Some grades of synthetic material have a lower cis- content than does natural rubber.

6. The results of the experiment show that adhesion does increase for a time after curing, at least when measured at room temperature.

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7. On the basis of oxidizability, the zinc salt had the effect, as did mercaptobenzimidazole itself.

VI. Translate the following sentences paying attention to the “Complex Object”:

1. We consider the natural rubber to be isomerized.2. Investigators find the infra-red spectrum to be closely similar to

that of natural rubber.3. One might expect the increase in hardness to be a result of

intra- particle crosslinking.4. Researchers dealing with latex know biologically induced

oxidation to proceed in the vicinity of the tapping cut.

VII. Translate into English:

1. CÇn nhÊn m¹nh r»ng ®é cøng cña cao su trong latex chøa NH3

®îc t¨ng cêng trong qu¸ tr×nh b¶o qu¶n.2. Ngêi ta cho r»ng sù t¨ng ®é cøng cña cao su , mét mÆt ®îc

g©y ra bëi sù dÝnh kÕt néi h¹t, mÆt kh¸c bëi sù t¹o çc gel vi m«.

3. Còng nh ®· biÕt qu¸ tr×nh t¨ng ®é cøng cña cao su trong latex cã thÓ bÞ ngõng b»ng çch thªm vµo ®ã çc hîp chÊt cacbonyl.

4. Nh chóng ta ®· biÕt, çc amin lìng chøc kh¸c víi çc amin ®¬n chøc lµ chóng xóc tiÕn cho qu¸ tr×nh nèi kÕt trong ph¶n øng kÕt hîp.

5. Trong kh«ng khÝ kh«, tèc ®é t¨ng ®é cøng cña cao su t¨ng khi gi¶m ®é dµy cña mÉu còng nh khi t¨ng nhiÖt ®é.

Text 10

Thermoplastic elastomers

Physical properties and applications

The development of that part of the rubber industry concerned with the fabrication of rubber articles has been primarily concerned with two processes. First, in order that an

53

article of a given shape can be made by some kind of molding process, the viscous properties of raw material must be utilized and possibly enhanced by mastication and degradation. Once the article is shaped, however, viscous flow becomes undesirable, and intermolecular motion must be prevented while retaining sufficient chain segment mobility to provide elastomeric properties.

The thermoplastic industry was the first concerned with rigid polymers, which displaced traditional materials partly because of the economic advantages of high automatic production rates made possible by easy flowing melts and rapid set up on cooling. In recent years, the thermoplastic industry has introduced flexible material such as plasticized PVC and ethylene - vinyl acetate copolymer. Though these materials have some rubbery charater, they do not compare with conventional vulcanizates as regards rapid retraction with low set from high elongation, resilience, and other physical properties, or as regards versatility and aesthetic appeal in many applications.

There are many diverse materials which require chemical reaction (usually at elevated temperature) to make useful articles, and these are loosely classed as thermosetting materials. They range from hard rigid products, through flexible materials to soft high elastic rubber. Another loose classification can be termed thermoplastic. Representatives of theses materials occur only in the first categories, however, the rigid and the flexible.

Thermosetting ThermoplasticRigid Epoxies

Phenol- FormaldehydeUrea- FormaldehydesHard rubber

PolystyrenePoly- Vinyl ChloridePolypropylene

Flexible Highly Vulcanized Rubbers

PolyethyleneEthylene-Vinyl-Acetate Copolymer Plasticized PVC

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Rubbery

VulcanizedRubbers (NR, SBR, IR, etc,)

Thermoplastic Elstomers

Thermosetting and thermoplastic material

Description of new products

The materials are block copolymers of styrene and butadiene. Their low viscous component results from long chain entanglements and van der Waal’s forces between polymer chains. No covalent or chemical crosslinking, that is, no vulcanization or cure reaction is involved in their use. At lower temperature the interchain forces are sufficiently strong and the sites sufficiently immobile to permit typical snappy rubbery behavior, tensile strength up to 5.000 psi, high resilience, etc.; yet, at elevated temperatures, they are labile with the result that these materials have melt viscosities very similar to conventional thermoplastics at normal processing temperatures.

The thermoplastic elastomers are somewhat superior to conventional natural rubber or SBR vulcanizates in retaining their elastomeric properties down to low temperatures. The flexible thermoplastic, on the other hand, lose their flexibility at much higher temperatures, and in fact can become unusably stiff under fairly mild climatic conditions.

(to be continued)

Exercises


1. What processes are generally used in the fabrication of rubber articles?

2. What is influence of viscous flow on the shaping process?3. Is viscous flow desirable when the article is shaped?

55

4. Why do thermoplastic elastomers flow at elevated temperatures?

5. Why did thermoplastic polymers replace traditional materials?6. What flexible thermoplastics are widely known at present?7. Why are thermoplastic elastomers superior to conventional

natural rubber?8. What are the main characteristics of thermosetting material?

II. Translate the following sentences into Vietnamese, paying attention to the words in bold type:

1. A great number of experiment concerning the nature and extent of filler- rubber adhesion have been conducted?

2. The thermoplastic industry was first concerned with rigid polymers, which displaced traditional ones

3. Artificial ageing tests concerned are an extremely important part of rubber testing.

4. The development of that part of the rubber industry concerned with the fabrication of rubber articles has been primarily concerned with two processes.

III. Translate the following sentences into Vietnamese, paying attention to the words in bold type:

1. Though thermoplastic elastomers have some rubbery characters, they do not compare with conventional vulcanizates as regards rapid retraction with low set from high elongation, resilience, or as regards versatility and aesthetic appeal in many applications.

2. Petroleum and its distillates can not be regarded as a source of raw elemental sulphur.

3. The problems regarding the use of pigments in latex are similar to those in other types of coatings and finishes.

4. Gerlach developed an interesting table with regard to the boiling points of glycerol solutions.

IV. Form nouns from the following adjectives:

capableflexiblelabile

MobileVersatile

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V. Translate into Vietnamese, paying attention to the Prefixed:

covalentdegradationdisplaceinterchain intermolecular immobile

PremasticationRecycleUnaffectedUndesirableUndulyUnusable

VI. Translate into Vietnamese paying attention to the Gerund

1. Reheating rubber is always attention by increasing its volume.2. Merret identified the component responsible for producing the

sol with the graft copolymer.3. Many surface coatings shrink slowly on having been aged.4. Natural rubber vulcanized with zinc oxide in the absence of free

sulphur is known for being resistant to aeing.5. The highly coiled rubber chains permit their being extended up

to seven times their original length.

VII. Give a short summary of the text.

VIII. Translate the following sentences and state whether the ing- form is expressed by the gerund or by a participle:

1. The thermoplastic elastomers are somewhat superior to conventional natural rubber in retaining their elastomeric properties down to low temperatures.

2. The novel products permit the manufacture of elastomeric articles by the use of high speed thermoplastic processing techniques.

3. The new materials can be modified to impart desirable properties without affecting the strength of the polymer network or the capability of obtaining desirable melt flow characteristics.

4. The thermoplastic elastomers are capable of modification in many directions to give special properties while retaining their basic dual elastomeric nature.

57

5. Stress- strain properties are essentially unaffected by repeated melting and recovery of solid polymer.

6. The latex rubber, having had no mastication, produces a tough, strong film with superior ageing properties.

7. If the latex or latex compound is mixed with a certain thickening agent the amount of compound which clings to the surface of the forms after being immersed is increased.

IX. Translate the following sentences into English:

1. Çc ®å vËt nhùa ®îc ®Þnh h×nh cã thÓ ®iÒu chÕ ®îc tõ hçn hîp çc chÊt cã tÝnh nhít.

2. Ngêi ta cho r»ng, tÝnh ch¶y dÎo cña hçn hîp cÇn gi¶m ®i khi çc ®å vËt võa míi ®îc h×nh thµnh.

3. Nh ®· biÕt, gÇn ®©y nh÷ng vËt liÖu nhiÖt dÎo,r¾n vµ cøng ®· thay thÕ çc kim lo¹i trong hµng lo¹t çc lÜnh vùc kü thuËt.

4. Çc chÊt nhùa ®µn håi cã nh÷ng tÝnh chÊt gièng çc vËt liÖu nhiÖt dÎo, còng nh lµv çc tÝnh chÊt cña cao su.

5. Mét mÆt, ë nhiÖt ®é trung b×nh vµ thÊp nhùa ®µn håi gi÷ ®-îc çc tÝnh chÊt cña nhùa, nhng mÆt kh¸c ë nhiÖt ®é cao chóng cã kh¶ n¨ng ch¶y nhít.

6. Nh ®· biÕt, çc chÊt ®µn håi lµ copolyme cña styren vµ buta®ien.

7. Çc nhµ khoa häc cho r»ng, nhùa ®µn håi kh«ng chøa bÊt kú mét liªn kÕt ho¸ häc hoÆc mét liªn kÕt cÇu nµo.

8. Ngêi ta cho r»ng, ®Ó chÕ biÕn nhùa ®µn håi cã thÓ dïng çc thiÕt bÞ b×nh thêng cña nhµ m¸y s¶n xuÊt nhùa.

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Text 11

Thermoplastic elastomers

(continued)

Applications

The basic properties of the materials bring the advantages of both rubbers and the thermoplastics together in the same product and introduce the potential of manufacture rubber articles by the use of modern, high speed, automatic thermoplastics processing techniques from materials in the price range close to that of other general purpose rubbers . They are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided.

Like those of other polymers, their properties such as solution and bulk viscosities, hardness, tensile strength, et cetera, can be varied by suitable changes in molecular weight and monomer ratio. The materials can be modified to impart hardness and abrasion resistance, softness, flexibility, improve flow and other desirable properties without unduly affecting the strength of the polymer network, its thermal lability, or the capability of obtaining desirable melt flow characteristics.

These materials contain no gel. In crumb form, as Kraton 101 or Kraton 102, they readily dissolve in conventional rubber solvents; the premastication and cutting needed with baled rubbers is thus avoided. These materials give cast films with tensile strengths 4,500 - 5,000 psi, and can be formulated with conventional resins to produce excellent pressure sensitive, hot melt, and contact adhesives.

The products, which have so far been designed around these materials, range from soft, transparent rubbers to hard, highly abrasion resistant materials.

Summary

59

New styrene - butadiene copolymer without chemical vulcanization, exhibit true elastomeric properties, that is snappy return from high elongation, resilience, good tensile strength, and low set, together with rubbery frictional properties and melt flow characteristic similar to those of conventional thermoplastics. The unique properties of these polymers are derived from the complete reversibility of the interchain forces, which constitute crosslinks at ambient temperatures but are not operative in a melt or in a solution. Stress-train properties are essentially unaffected by repeated melting (or dissolution) and recovery of solid polymer.

These novel products permit the manufacture of elastomeric articles by the use of high -speed thermoplastics processing techniques. No curing step is used, hence, lengthy mixing processes are avoided. Scrap can be recycled.

Like conventional natural rubber or SBR vulcanizates, the thermoplastic elastomers retain elastomeric properties down to low temperatures (- 700F). In this, the behavior contrasts with conventional thermoplastics which lose flexibility at temperatures only slightly below ambient.

The polymers are soluble in conventional rubber solvents and are thus suitable for formulation of adhesives, sealants and coatings. The versatility of the materials is such that special properties, such as ozone resistance, can be introduced by the use of simple modifications.

Notes

1. general purpose rubbers: cao su ®a dông tæng hîp2. in nib form: d¹ng ban ®Çu, nguyªn thuû3. can be formulated: cã thÓ ®îc trén víi

Exercises


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1. What kinds of thermoplastic elastomers are known nowadays?

2. What is the nature of polymeric chains of thermoplastic elastomers?

3. How many monomers may be used to prepare thermoplastic elastomers?

4. What properties of thermoplastic elastomers are truly elastomeric?

5. What can you say about the behavior of thermoplastic elastomers at low temperatures?

6. What articles may one produce from thermoplastic elastomers?

7. Is it possible to recycle the scraps from the fabrication of elastomeric articles?

II . Translate the following sentences into Vietnamese, paying attention to the words in bold type:

1. Vulcanization is a vitally important part of all rubber processing.

2. To impart the materials hardness, softness and other desirable properties, the materials can be modified.

3. Rigid polymers displaced traditional materials partly because of the economic advantages.

4. A number of scientists took part in the research of new elastic materials to be applied in surgery.

5. The alkyl of R group parts company from the carbonyl carbon exists for a time as a free radical.

III. Translate the following sentences into Vietnamese paying attention to the words in bold type:

1. Thermoplastic elastomers are available in nib form, and since they need no vulcanization, the mastication and mixing steps required with conventional rubbers are avoided.

2. There are still some plastics, more or less rubbery, available in emulsion or dispersion form.

3. Vinyl chloride and vinyl copolymer latices are available both untreated and preplasticized.

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4. There are now available several modified Buna n latices having rather distinctive properties.

5. Butadiene, which can be made from readily available acetylene, is one of the raw materials of synthetic rubber.

IV. Give Vietnamese equivalents to the following words:

ArticleFormulationNovel

processingreadilyresin

V. State to what parts of speech the following words belong, paying attention to the suffixes:

a)

AmbientConventionalElasticElastomericFlexibleNaturalOperativePotential

rubbery soluble sufficient suitable superior thermoplastic transparent

b)

Abrasion Advantage Dissolution Elongation Entanglement Flexibility

lability resilience resistance reversibility softness vulcanizate

c)

Constitute Formulate

modifyvulcanize

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d)

Loosely Unduly

unusably.

VI. State the key words in the word combinations and translate them into Vietnamese:

1. Abrasion resistance2. Interchain force3. Inter molecular motion4. Melt viscosity5. Molding process6. Ozone resistance7. Processing technique

8. Processing temperature9. Abrasion resistance

materials 10. General purpose

rubbers11. Stress - train properties12. Styrene butadiene copolymers13. Ethylene - vinyl acetone

copolymer

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VII. Translate the following sentences paying attention to the pronoun no:

1. No covalent or chemical crosslinking, that is, no vulcanization or cure reaction is involved in the use of thermoplastic elastomers.

2. No new results have been presented for the stress relaxation of stocks containing black.

3. Thermoplastics contain no gel, and in crumb form, they readily dissolve in conventional rubber solvents.

4. No test can duplicate all the conditions that may occur during natural ageing.

VIII. Translate the following sentences into English:

1. Nh ®· biÕt, ngµy nay c«ng nghiÖp t¹o ra nhiÒu d¹ng nhùa ®µn håi.

2. TÝnh chÊt cña nhùa ®µn håi phô thuéc vµo c¶ ph©n tö lîng cña chÝng còng nh tØ lÖ monome trong m¹ch polime.

3. Ngêi ta ®· x¸c ®Þnh ®îc r»ng, ®é chÞu ozon cña nhùa ®µn håi lín h¬n nhiÒu so víi çc polime no b×nh thêng.

4. C«ng nghiÖp ho¸ häc sö dông nhiÒu cÆn th¶i kh¸c nhau ®Ó s¶n xuÊt çc ®å vËt cã phÈm chÊt cao tõ nhùa ®µn håi.

5. Tõ nhùa ®µn håi cã thÓ s¶n xuÊt çc ®å vËt kh¸c nhau nh: èng chÊt kÕt dÝnh, s¬n, chi tiÕt cña giµy. çc ch¸t lµm bÒn,...

6. Ngêi ta tiªn ®o¸n r»ng, nhùa ®µn håi cã thÓ sÏ ®îc øng dông réng r·i rong kü thuËt.

Text 12

ABS plastic

A unique family of plastics has evolved and developed during the last twenty years. These plastics are composed of three monomeric chemicals - acrylonitrile, butadiene and styrene. The name ABS, based on the first letters of each of the monomeric

64

components has been adopted for this family. ABS plastics are composed of styrene acrylonitrile copolymer as the continuous phase and a dispersed phase of butadiene - acrynitrile rubber or a butadiene containing rubber onto which styrene - acrynitrile monomers are grafted.

Various combinations of properties are possible, thus making these polymers most attractive for a larger number of current and newly developed applications.

ABS polymers are true thermoplastics similar to polystyrene, polyvinyl chloride, polyolefins, nylon, etc. On application of heat are softened, and when pressure is applied they attain viscous flow.

Upon cooling they harden, and on reheating are resoftened. Thus, they can be remelted and reformed into various shapes with essentially no loss2 in properties. As a result, ABS plastics are extemely useful and versatile, since ease of processing and forming allows them to be used for a great number of applications. In their natural form ABS plastics are opaque, similar in this respect to the impact polystyrenes.

General properties of ABS plastics

1. The excellent combination of properties which ABS plastics offer has spurred the growth of these plastics into many applications. No one single property, but rather the combination of properties of ABS plastics has made them outstanding. Some of the properties, which make these plastics extremely useful, are:

2. Moderate price.3. Ease of fabrication.4. Good combination of toughness, rigidity and mechanical

properties.5. Wide colorability.6. Good dimensional stability.7. Nontoxicity.8. Good water resistance.9. Excellent chemical resistance.

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The strength of a fabricated item produced from an ABS plastics is dependent on a number of variables, namely, the fabrication conditions used, the design and shape of the finished piece, the method of stress application, and the environmental conditions encountered. It should be stressed that the conditions under which the plastic part is formed play a very important role on the subsequent mechanical properties of ABS plastics. This is true to all thermoplastics. When ABS polymers are reheated and subjected to fabricating conditions, such as injection molding, sheet or profile or pipe extrusion, or thermoforming, many of the long chain polymer molecules change their position and shape and become more aligned: in other words, they become oriented or stretched out, pointing in the direction of flow. Thus, most properties of ABS plastics are not only time and temperature - dependent but are also frequently direction - dependent (anisotropic). Therefore, in describing the properties of ABS plastics, it is important, if at all possible, to specify the properties in relation to the flow direction and the degree of orientation.

Note

1. based on the first letters: (viÕt t¾t)tõ nh÷ng ch÷ çi ®Çu2. with essentially no loss: vÒ c¬ b¶n kh«ng mÊt

Exercises


1. What is a unique family of plastics composed of?2. What is the name ABS based on?3. How is significant improvement in toughness over polystyrene

attained?4. What other properties of plastics do you know?5. What are ABS polymers similar to?6. What happens to ABS polymer upon cooling and heating?7. Why are ABS plastics extremely useful?

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8. What plays a very important role on the mechanical properties of ABS plastics?

II. Translate into Vietnamese paying attention to the prefix re-:

heat - reheatsoften - resiftedform - reform

Melt - remeltConstruct - reconstruct

III. Translate the following derivative into Vietnamese:

develop, developmentcompose, compositionmonomer, monomericadopt, adoptationpolymer, copolymer, polymerization, polymerizenature, naturalimprove, improvement

Tough, toughnessIntroduce, introductionRigid, rigidityResist, resistant, resistanceApply, applicationViscous, viscosityUse, useful, uselessProcess, processing

IV. Translate into Vietnamese paying attention to the words in bold type:

1. The name ABS, based on the first letters of each of the monomeric components has been adopted for this family.

2. By introducing acrylonitrile monomer into a similar system, a significant improvement in all these properties is obtained, as well as outstanding toughness and resistance.

3. Various combinations of properties are possible, thus making these polymers most attractive for a larger number of current and newly developed applications.

4. ABS plastics are extremely useful and versatile, since ease of processing and forming allows them to be used for a great number of applications.

5. The strength of a fabricated item produced from ABS plastic is dependent on a number of variables.

V. Translate into English:

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1. Mét nhãm lín çc chÊt dÎo mµ thµnh phÇn cña chóng cã: acryloitrin, butadien, styren ®· ®îc t¹o ra trong 20 n¨m gÇn ®©y.

2. Çc polime thuéc nhãm ABS lµ chÊt nhiÖt dÎo vµ gièng çc poly styren, poly vinylclorua, poly olefin, nil«ng.

3. Khi gÆp nhiÖt th× chóng ch¶y mÒm ra, khi gÆp l¹nh th× chóng trë lªn r¾n l¹i.

4. Çc chÊt nhùa thuéc nhãm ABS ®îc sö dông réng r·i v× dÔ s¶n xu¸t çc vËt liÖu tõ chóng.

5. CÇn ph¶i nhÊn m¹nh r»ng, nh÷ng ®iÒu kiÖn ë ®ã ngêi ta s¶n suÊt çc ®å vËt b»ng nhùa cã ¶nh hëng nhiÒu ®Õn tÝnh chÊt c¬ häc cña ®å vËt.

6. §a sè çc tÝnh chÊt cña nhùa nhãm ABS phô thuéc vµo.....

Text 13

Plastics in the chemical age

The plastics industry is typical of the industries that have developed in recent years as a result of chemical research. The chemist is a key man in the plastics industry, and it is from chemical laboratories that new plastics are appearing almost day by day.

Little more than twenty years ago, plastic were still widely regarded as cheap substitutes for traditional materials such as wood and porcelain. Today, plastics have established themselves as wonderful new materials in their own right. They have ousted older materials because they can do a better job, often at lower cost.

We find new plastics encroaching in the fields where metals have reigned supreme. The development of new techniques, such as lamination, has shown how modern plastics may be used for many engineering and structural applications. We can make gears

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and bearings for heavy machinery from laminated plastics. We can build car bodies, and the hulls of boats, we can pump our water supplier through the plastic pipes, and support larger buildings on plastic beams.

In time we shall have seagoing ships with plastics used for almost everything from crockery on the tables to the hull itself. We shall fly at supersonic speeds in plastic aircraft, and motor in cars with plastic bodies. House and public buildings will be constructed from plastics panels supported by plastic beams. We shall find plastic spaceships carrying us to the moon.

As the demand for the plastics grows, the need for chemical raw materials will increase. Plastics are largely organic chemicals, in which the “ backbone “ of the molecule consists of carbon atoms. They are made from simpler organic chemical in which the molecules contain fewer carbon atoms, which are manipulated by the plastic chemist into thread - like structure.

Today, we draw our supplies of simple organic chemicals very largely from coal and petroleum. These are the chemical residues of plants and animals that lived millions of years ago, and they contain a variety of different organic substances. We obtain simple chemical raw materials from coal by heating it in retorts, and from petroleum by refining and processing techniques. Coal and petroleum are capital assets; the world has a limited supply, and we can not replace the materials we use. As the demand for organic chemicals increases, the stocks of coal and petroleum will diminish; and some day, they will be gone.

Before this happens, we shall have to seek new sources of organic chemical raw materials, and we shall find them in the carbon dioxide of the air. This is the gas from which the growing plant builds up the sugar and other substances as organic raw materials, without waiting for nature to turn them into coal and oil.

It seems likely that alcohol will become the most important chemical raw material of all as supplies of coal and petroleum dwindle. We can make alcohol by fermentation of the sugar produced by fast growing plants, and it will provide us with the raw

69

materials for plastics and other synthetic chemical industries. The tropical countries of the world will use their vast areas of land for the cultivation of sugar producing crops.

It is probable, too, that we shall in time discover the secrets of photosynthesis, by which the plant uses the sunshine to convert carbon dioxide into sugars and we shall use some synthetic process of this sort to turn carbon dioxide from the air into simple organic chemicals without depending entirely upon the growing plant to do it for us.

The twentieth century is the time when man began to understand how to make all the new synthetic materials from simple chemicals; materials, such as fibres and rubbers, synthetic drugs and dyes, insecticide and weed killers, hormones and vitamins - and, of course plastic.

Exercise


1. What have plastics ousted today?2. What can we made from laminated plastics? 3. What ships will carry us to the moon? 4. What does the backbone of the molecule in plastic consist of? 5. What do we draw our supplies of?( today)6. What do we obtain simple chemical raw materials from?7. Why do we have to seek for new sources of organic chemical

raw materials?8. Where shall we find them?9. What will become the most important chemical raw materials?

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II. Read and translate the following derivatives:

industry, industrialtype, typicalwood, woodenlaminate, laminatedapply, applicationmachine, machineryincrease, decrease

vary, varietyplace, replaceoxide, dioxidesynthetic, synthesis, synthesizediscover, discoveryfibre, fibrousrub, rubber, rubbery

III. Translate into Vietnamese paying attention to the words in bold type:

a)1. Plastics can do a better job, often at lower cost. 2. The development of lamination has shown how modern

plastics may be used for many engineering and structural applications.

3. We are able to build car bodies and the hulls of boats from plastics.

4. We shall have to seek new sources of organic chemical raw materials.

5. The twentieth century is the time when one has to understand how to make all the new synthetic materials from simple chemicals.

b)

1. In some time we shall have seagoing ships with plastics used for almost everything from the crockery on the table to the hull itself.

2. We used plastics as cheap substitutes for traditional materials such as wood and porcelain.

3. House constructed with the use of plastic parts are rather cheap.

4. House and public buildings will be constructed from plastic panels supported by plastic beams.

5. He supported himself by working at a chemical plant.

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6. We can make alcohol by fermentation of the sugar produced by fast - growing plants.

7. We produced a great variety of alcohol fast - growing plants.

IV. Translate into Vietnamese paying attention to the infinitives:

1. This is the gas from which the growing plant builds up sugar and other substances as organic raw materials, without waiting for nature to turn them into coal and oil.

2. In some time we shall discover the secrets of photosynthesis, by which the plant uses sunshine to convert carbon dioxide into sugars.

3. We shall use some synthetic process to turn carbon dioxide from the air into simple organic chemicals.

4. The twentieth century is the time when man began to understand how to make all the new synthetic materials from simple chemicals.

5. To make use of isotope instruments to supervise a number of chemical processes which formerly had been difficult to check properly is very important for chemical industry today.

6. Polymerization of monomer chloride proceeds more easily, than that of ethylene, an effect to be associated with the polar nature of the vinyl chloride molecule.

V. Write a summary of the text and retell the text.

VI. Translate into English:

1. ViÖc chÕ ho¸ çc chÊt dÎo d¹ng líp ®· chØ ra r»ng chóng cã thÓ ®îc sö dông trong nhiÒu ngµnh kü thuËt vµ trong x©y dùng.

2. Ngêi ta cho r»ng trong t¬ng lai kh«ng xa chóng ta cã thÓ lµm m¸y bay b»ng ch¸t dÎo.

3. Ngµy nay, nguyªn liÖu ®Ó s¶n xuÊt ch¸t dÎo lµ nh÷ng chÊt h÷u c¬ th«ng thêng lÊy tõ chÊt dÎo.

4. V× chóng ta cã tr÷ lîng than vµ dÇu má h÷u h¹n nªn chóng ta cÇn ph¶i t×m kiÕm nh÷ng nguån h÷u c¬ míi, .....

5. Cã thÓ lµ rîu sÏ trë thµnh mét trong nh÷ng nguån nguyªn liÖu ho¸ häc quan träng nhÊt.

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6. Cã thÓ lµ chóng ta sÏ ph¸t hiÖn ®îc nh÷n bÝ mËt cña sù quang hîp ®Ó biÕn CO2 thµnh ®êng nhê ¸nh s¸ng mÆt trêi.

Text 14

Enzymes

The study of enzymes is a subject, which has a special interest because it lies just on the borderline where the biological and the physical sciences meet. On the other hand, enzymes are of supreme importance in biology. Life depends on a complex network of chemical reactions brought by specific enzymes, and any modification of the enzyme pattern may have far- reaching consequences for the living organism. On the other hand, enzymes, as catalyst, are receiving increasing attention from physical chemists.

Enzymology has become a large and rapidly developing subject, which have close connections with many sciences, especially biochemistry, physical chemistry, bacteriology and microbiology, genetics, botany and agriculture, pharmacology and toxicology, pathology, physiology, medicine, and chemical engineering. It has in addition important practical applications to activities as diverse as brewing and industrial fermentation, pest control, and chemical warfare.

It is sometimes difficult to realize that enzymology is a subject of comparatively recent growth; the beginning of the subject can be traced back to the early nineteenth century, but the great developments have come during the last forty years.

Scientists found that an alcohol precipitate of malt extract contained a thermolabile substance, which converted starch into sugar. This substance is now called “amylase".

The great increase in the knowledge of the enzymes of the living matter has brought a greatly increased understanding of the

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mechanism of many of the most fundamental vital processes, especially of metabolic processes which lead to the production and utilization of energy, on which life depends.

The availability of enzymes in the pure state has made possible their quantitative study by physico - chemical methods.

The substance on which an enzyme acts is termed the “ substrate “ of the enzyme.

In many cases an additional substance besides the enzymes and substrate is required in order that the reaction may proceed. Such “ coenzymes “ are part of the catalytic mechanism, and are found unchanged at the end of the reaction. They are thus distinguished from substrates.

It is frequently found that the addition of substances, which do not take part in the reaction, diminishes its velocity. These substances are known as “ inhibitors “. Many of these inhibitors act as poisons of particular enzymes, and in some cases in very small concentrations.

Only comparatively recently has it been possible to develop the study of enzyme and enzyme systems in relation to the living cell.

Exercises


1. Why has the study of enzymes a special interest? 2. What does life depend on? 3. What has enzymology close connections with? 4. What substance is called “ amylase"?5. What is termed the “substrate"?6. What is a “coenzyme"?7. What is an inhibitor?

II. Give derivatives to:

SpecialEnzymeChemical

activityindustryprecipitate

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ModifyRapidlyPracticalPhysical

productionavailability pure


1. The study of the enzymes is a subject, which has special interest.

2. The treatments to which enzymes can be subjected are limited by their instability.

3. The path of energy migration is the subject of considerable controversy.

4. When subjected to a deforming force rigid structure will often fracture.

5. Only a comparatively recent has it been possible to systematically develop the enzyme studies in relation to the living cell.

6. In many cases an additional substance besides the enzyme and substrate is required.

7. Enzymology has in addition important practical applications in brewing and industrial fermentation, pest control and chemical warfare.

8. It is frequently found that the addition of substances, which do not take part in the reaction, diminishes its velocity.

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IV. Translate into English:

1. ViÖc nghiªn cøu çc ezim rÊt thó vÞ v× nã ë vµo giao ®iÓm cña hai ngµnh khoa häc: ho¸ häc vµ sinh häc.

2. Sù sèng phô thuéc vµo hµng lo¹t çc ph¶n øng ho¸ häc ®îc thc hiÖn nhê çc ezim ®Æc biÖt.

3. Enzim häc ®· trë thµnh mét ngµnh khoa häc ®ang ph¸t triÓn rÊt nhanh.

4. Sù më réng kiÕn thøc cña chóng ta vÒ ezim cña c¬ thÓ sèng ®· gióp chóng ta hiÓu râ h¬n vÒ c¬ chÕ cña nhiÕu qu¸ tr×nh c¬ b¶n.

5. ViÖc t¸ch ®îc çc ezim ë d¹ng tinh khiÕt lµm cho viÖc nghiªn cøu çc tÝnh chÊt cña ezim trë nªn cã thÓ thùc hiÖn ®îc.

V. Speak of the importance of enzyme.

Text 15

Gas chromatography

Gas chromatography is a method for separating components of mixtures of volatile compounds. In most applications the separations are made to identify and determine the quantity of each component of a sample of the mixture, and analytical gas chromatographic apparatus includes additional devices for this purpose. In some applications, separations are made for preparative purposes, but the scale is not generally greater than that required for quantities of the order of 100g.

The central item in the apparatus for gas chromatography is the chromatographic column, a long tube packed permeably with some adsorbent. In the commonest technique of gas chromatography, the elution technique, a stream of inert gas, the carrier gas, passes continuously through the column, and the mixture to be separated is introduced at the beginning of the column as a sample either of a gas or a volatile liquid. Let us suppose that the sample consists of one pure component. After introduction, it is swept by the carrier gas on to the column, first

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evaporating to form a vapour if it is introduced as a liquid. When it reach the column, it is largely adsorbed, but the equilibrium is set up between the column and the gas in the interstices of the column so that a proportion of the sample always remains in the gas phase. This portion moves a little further along the column in the carrier gas stream, where it again equilibrates with the column. At the same time, material already adsorbed in the column re - enters the gas phase so as to restore equilibrium with the clean carrier gas which follows up the zone of vapour.

The speed at which the zone moves depends on two factors, the rate of flow of the carrier gas and the extent to which the vapour is adsorbed. The faster the flow of carrier gas, the faster the zone moves; and the more strongly the vapour is adsorbed on the column, the more slowly the zone moves. When two or more components are present in the sample, each usually behaves, independently of the others so that for a given carrier gas flow rate, the speed of the zone of each component will depend on the extent to which it is adsorbed. Since different substances differ in their adsorption, they may therefore be separated by making use of their different speeds of progress through the column. If they are eluted to the far end of the column, they will appear one after the other in the gas stream, the fastest first and the lowest last.

Adsorbents such as carbon, alumina, or silicagel are used as the packing material for columns, but in more than 90% of applications, the column material is the liquid held in place on the column by being adsorbed on an inert solid support. Gas chromatography with this kind of column is called Gas Liquid Chromatography (G L G). This method is used for separating solutes from mixed solutions.

Exercises


1. What does gas chromatography mean?

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2. What is the central item in the apparatus for gas chromatography?

3. What gas passes through the column? 4. How does the process of chromatography pass? 5. What are adsorbents such as carbon, alumina, or silicagel used

for? 6. What method is used for separating solutes from mixed

solutions?

II. Read and translate the following derivative:

1. analytical, analysis, analyse; 2. scheme, schematic, schematically; 3. compress, compression; 4. identify, identification; 5. include, inclusion, inclusive; 6. prepare, preparation, preparative; 7. adsorb, adsorbent, adsorption; 8. technique, technical, technician; 9. evaporation, vapour; 10. equilibrium, equilibrate, equilibration; 11. behavior, behave; 12. solute, solution, solvent, soluble, dissolve;


1. The mixture is introduced as a sample either of a gas or a volatile liquid.

2. The material already adsorbed in the column re - enters the gas phase so as to restore equilibrium with the clean carrier gas.

3. The speed at which the zone moves depends on the rate of flow of the carrier gas and the extent to which the vapour is adsorbed.

4. The faster the flow of the carrier gas, the faster the zone moves.

5. The more strongly the vapour is adsorbed on the column, the more slowly the zone moves.

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6. The speed of the zone of each component will depend on the extent to which it is adsorbed.

IV. Translate into Vietnamese paying attention to the function of the infinitive:

1. The mixture to be separated is introduced at the beginning of the column.

2. The electrons have come to be known as valence electrons, because the valence of any given element depends on the number of these electrons.

3. Valence is the tendency of the atoms of any given element to donate or accept a strictly definite number of electrons.

4. Chlorine requires only one electron to form the stable electron layer of the following inert gas.

5. Hydrogen is a combustible gas, burning in air or oxygen to form water.

6. The organic compounds to be discussed are of great importance in the study of plastics.

7. Carbon has a tendency to combine with oxygen from the air to form gaseous carbon dioxide.

8. There is no problem to be associated with exuding, leaching or deterioration with polyethylene plastic.

9. The stability of polyethylene plastic in storage is to be associated with the lack of chemical active functional groups in the molecular structure.

10. To regard the polyethylene as a substitute for stainless steel is not proper design procedure.


1. S¾c kÝ khÝ lµ ph¬ng ph¸p t¸ch çc cÊu tö cña hçn hîp hoÆc t¸ch çc chÊt dÔ bay h¬i .

2. ViÖc t¸ch ®îc tiÕn hµnh ®Ó ®Þnh lîng mçi cÊu tö trong hçn hîp.

3. Bé phËn chÝnh cña thiÕt bÞ s¾c kÝ khÝ lµ cét s¾c kÝ( lµ mét èng dµi ®îc nhåi mét chÊt nµo ®ã cã kh¶ n¨ng hÊp phô ).

4. KhÝ mang liªn tôc ®i qua cét ®ã. Hçn hîp cÇn t¸ch ®îc cho vµo cét hoÆc ë d¹ng khÝ hé¨c ë d¹ng láng dÔ bay h¬i.

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VI. Write a short summary of the text.

Text 16

Basic apparatus of gas chromatography

The instrumentation of gas chromatography is remarkably simple compare to many other recent analytical techniques. The fingure shows a block schematic diagram of a typical gas- liquid chromatography apparatus, such as might be used for analysis.

Carrier gas from the tank of compressed gas first passes to a controller, the usual purpose of which is to maintain a constant flow of gas.. The gas then passes to the beginning of the column, at the inlet to which is a Sample Injector through which the sample to be analysed can be introduced. The carrier gas then elutes the components of the mixture through the column.

At the far end is a device, the Detector, the purpose of which is to detect the separate components of the mixture as they emerge one by one. The detector use some physical or chemical properties of the vapours by which they can be indicated and, if possible, measured. A further piece of apparatus not always incorporated is a Flowmeter to measure the rate of flow of gas.

1. Any gas, which is easily distinguishable in the detector from any components of the mixture, can be chosen as the carrier gas. In most cases a permanents gas such as helium, argon, nitrogen or hydrogen is used.

2. Flow controls can either be true flow controls, which allow a definite rate of flow of gas, or they can be pressure controls, which control the input pressure to the column. Pressure controls are simpler than flow controls and are used more commonly.

3. For analytical purposes, reasonable dimensions for a permeably packed column might be 6 feet long by 1/4 inch diameter. In G. L. C the actual dissolving agent is a liquid which

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must remain stationary in the column without draining. The supporting material is often called the Support. The liquid solvent is called the Stationary liquid. The two together are called the Stationary Phase. The stationary liquid must dissolve all the components of the mixture and they must have boiling points, which are high in comparison with the boiling points of the components of the mixture. Almost any high-boiling point may be used, for example, silicone oil, high-boiling esters such as phtalates, high-boiling point paraffines, and many others.

4. One of the most commonly used properties for detecting the vapour is the thermal conductivity of the gas, which changes when a vapour is present.

There are different types of detectors such as: 1) Differentiating detectors, which record concentrations or rate flow of mass of the vapour. (Differentiating detectors are used in the great majority of applications); 2) integrating detectors, in which the deflection is proportional to the total quantity rather than to the concentration. When no vapour is passing through, the reorder gives a straight line.

5. Sample injectors, aim to inject a sample of a mixture of interest and not an accurately known weight. The sample injector remains the least satisfactory item of gas chromatographic equipment. Sample injectors must satisfy the general conditions that their volume should be small and that the temperatures of the devices designed to handle liquids or solids be sufficiently high.

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The chromatogram

Analytical useful information obtainable from the chromatogram is of three kinds.

The simplest thing a chromatogram can show is whether or not a given sample is pure. If the chromatogram contains more than one peak, the sample contains more than one component. Very often this technique is used as a test of purity of substances.

The second use of chromatogram is to enable one to identify the individual components of a mixture qualitatively.

The third kind of information obtainable from the chromatogram is a quantitative analysis of the mixture, which is provided by the detector rather than column. With most detectors, the deflection of the meter is proportional to the concentration of vapour, and so, if the flow rate is constant, the area of peak will give the total amount of vapour. This may be made the basis for the exact quantitative analysis.

Gas chromatography is mainly used for quantitative analysis, for the method particularly suitable for the routine analysis of industrial sample, the interpretation of the data is simple, and the apparatus does not require skilled personnel.

Exercise


1. What is the technique of gas chromatography?2. Where does carrier gas from the tank of compressed gas first

pass to? 3. What is the usual purpose of controller? 4. What does the carrier gas elute?5. What is the purpose of Detector?6. What types of Detectors do you know?7. What can a chromatogram show? 8. What is gas chromatography used for?

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II. Read and translate the following derivative:

1. chromatography, chromatographic;2. separate, separation, separator; 3. volatile, volatility, volatilization, volatilize; 4. detector, detect, detection; 5. concentrate, concentration;6. solid, solidity, solidify; 7. quality, qualitative, qualitatively; 8. quantity, quantitative, quantitatively; 9. particular, particularly;

III. Read and translate the following sentences paying attention to the functions of the Infinitive:

1. Carrier gas from the tank of compressed gas first passes to a controller, the usual purpose of which is to maintain a constant flow of gas.

2. In the inlet to the column there is a simple injector through which the sample to be analysed can be introduced.

3. The purpose of the detector is to detect the separate components of the mixture as they emerge one by one.

4. A further piece of apparatus not always incorporated is a flowmeter to measure the rate of the flow of gas.

5. Almost any high boiling liquid may be used. 6. Sample injectors aim to inject a temperature control of the

column. 7. In the years to come many new synthetic products will appear. 8. It has taken centuries of scientific research and invention to

develop the civilization of the modern age. 9. The chemical industry of the Soviet Union began to develop in

the pre-war five year - periods. 10. Chemical processing method made it possible rationally to

utilize industrial wastes to speed up technological processes and to ensure automation.

11. The second use of the chromatogram is to enable one to identify the individual components of a mixture qualitatively.

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12. For the preparation of an aerosol the substance to be dispersed is first evaporated and the vapour is then quickly cooled.

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IV. Translate into Vietnamese paying attention to the words in bold type:

1. Not a single property, but rather the combination of the properties has made this substance outstanding.

2. In integrating detectors the deflection is proportional to the total quantity rather than to the concentration.

3. The supernatant fraction appeared to degrade lysolecithin rather than to utilize it for lecithin production.

4. When no vapour is passing through, the recorder gives a straight line.

5. No traces of water have been obtained during the test. 6. A quantitative analysis of the mixture is provided by the

detector rather than the column.7. Gas chromatography is mainly used for quantitative analysis,

for the method is suitable for the routine analysis of industrial samples, the interpretation of the data is simple, and the apparatus does not require skilled personnel.


1. ThiÕt bÞ ®îc sö dông trong s¾c kÝ khÝ rÊt ®¬n gi¶n.2. NhiÖm vô cña ®ªtect¬ lµ ®Ó ph¸t hiÖn çc cÊu tö riªng rÏ cña

hçn hîp khi chóng lÇn lît ®i ra khái cét .3. Dªtect¬ sö dông mét sè tÝnh chÊt ho¸ häc vµ vËt lý cña h¬i,

mµ nhê chóng çc cÊu tö ®îc ph¸t hiÖn vµ nÕu cã thÓ ®îc x¸c ®Þnh.

4. Trong s¾c kÝ khÝ- láng th× chÊt láng cè ®Þnh lµ çc chÊt cã kh¶ n¨ng hoµ tan çc cÊu tö cña mÉu.

5. ChÊt láng cè ®Þnh cÇn ph¶i hoµ tan tÊt c¶ çc cÊu tö trong hçn hîp.

VI. Make up an outline of the text and retell the text

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Text 17

Hafnium

Interest in hafnium has increased owing to improved methods for its separation from zirconium and the possible use of zirconium and hafnium in light- weight refractory materials for aircraft construction.

The chemistry of hafnium began about 75 years ago. Coster and Hevesy decided to look for element 72 in minerals containing quadrivalent zirconium. Accordingly, the residues remaining after Norwegian and Greenland zircons had been leached in boiling acid, were placed on a copper anticathode and an X ray spectroscopic analysis undertaken. Coster and Hevesy announced the discovery of element 72, proposing the name hafnium in honour of the city in which the discovery was made. This name is generally accepted in France.

Occurrence

Hafnium occurs in nature in small to moderate amount associated with zirconium in all types of zirconium - bearing mineral. The ratio of hafnium to zirconium has been estimated to be about 0.02. Zircons from granite rocks are reported to have higher Hf/Zr ratios than minerals from alkalic ones. Zircons, which may contain up to 7% hafnium, may have their hafnium content determined by radioactivity measurements. Inasmuch as hafnium is isomorphous with uranium and thorium, a constant ratio between hafnium and these radioactive elements is obtained. It is estimated that there are 4 parts per million of hafnium in the earth’s crust water-cooled nuclear reactors. In addition, hafnium is known to be used for making special glasses. It has been applied as a filament in incandescent lights, as a cathode in X - ray tubes, and as an electrode in high pressure discharge tubes. Hafnium - titanium alloys may be used as getters in evacuated or gas filled devices such as lamps, radio tubes, and television tubes.

86

87

Extraction

Hafnium and zirconium are always extracted together, and the separation of hafnium from zirconium is an important step in the production of reactor - grade zirconium. Thus any technique employed to separate the two elements necessarily must be fractional one.

Extraction of hafnium containing mineral is complicated by the fact that following the fusion of the mineral with ammonium hydrogen fluoride, the fused product may contain a considerable amount associated impurities and as a consequence is not easily dissolve. This necessitates repeated extractions, which result in the accumulation of a large volume in solution. The main problem in the production of hafnium is its separation from zirconium, inasmuch as no chemical reaction is known which is exhibited by one of these elements but not by the other. It is evident that any method used to open zirconium minerals will result in the inclusion of both zirconium and hafnium in the solution.

Physical, mechanical and chemical properties

The atomic number of hafnium is 72, the boiling point is known to be 54000C. Metallic hafnium has a brilliant luster. It is harder and less easily worked than zirconium. After melting in an arc furnace under argon1, hafnium is considered to be hot - rolled in air at 8400C. It can be cold - rolled into sheet, swaged or drawn into wire or rod. If the metal is cold reduced in thickness more than 30%, the sheet will fracture if bent. Cold - worked hafnium , if annealed in vacuum or in inert atmosphere, recrystalllizes between 7000 and 8000C.

Hafnium has excellent mechanical properties and is extremely corrosion resistant. The machineability of hafnium resembles that of stainless steel. Being a gas sensitive metal, traces of gases ruin its malleability, increase its electrical resistance, and decrease its temperature coefficient of resistance; its electrical conductivity being, at best, 6% that of copper.

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The chemical properties of hafnium resemble those exhibited by zirconium very closely.

Hafnium freshly prepared in vacuum is so reactive that no dioxidizers for it are known. The rate of penetration of oxygen into metallic hafnium is lower than that for zirconium.

Applications

Hafnium had few commercial uses because of its limited supply and high price, which were due to the difficulty in obtaining it free from its ores.

In recent years, however, this metal has become somewhat more readily available as by-product of reactor-grade zirconium 2, and considerable interest has been aroused in its potential usefulness as a control material in water -cooled nuclear reactors. In addition, hafnium is known to be used for making special glasses. It has been applied as a filament in incandescent lights, as a cathode in X - ray tubes, and as an electrode in high pressure discharge tubes.

Hafnium - titanium alloys may be used as getters in evacuated or gas -filled devices such as lamps, radio tubes, television tubes.

Notes

1. under argon: trong khÝ quyÓn argon2. reaction-grade zirconium: lß lµm s¹ch zirconi

Exercises


1. When did the chemistry of hafnium begin? 2. Who was the first to discover the hafnium? 3. What does the word “ hafnium “ mean? 4. What can you say about the physical properties of hafnium? 5. What are the chemical properties of hafnium? 6. Is hafnium widely used nowadays?

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II. Describe the process of hafnium extraction.

III. Translate the following sentences into Vietnamese paying attention to the words in bold type:

1. Inasmuch as hafnium is isomorphous with uranium and thorium, a constant ratio between hafnium and these elements is obtained.

2. The main problem in the production of hafnium is its separation from zirconium, inasmuch as no chemical reaction is known which is exhibited by one of these elements.

3. Inasmuch as the color of any oil product is practically always improve by acid, the color is to a certain extent taken as a criterion of the degree of refining.

4. Inasmuch as the rare earth metal are very difficult to prepare in pure form, these has been a lack of data on their physical properties.

IV. Select attributes(from the list given below) to the following words and translate them into Vietnamese:

AmountAnalysisAtmosphereConductivityCrustFilamentNumberTubeVacuumZirconium

atomicearth’sdeep electricalhighhot-rolledincandescentinertmoderatespectroscopicX-ray

V. Give Vietnamese equivalent to the following words:

1. extract, extraction, extractive, extractor;2. oxide, oxidize, oxidizer, deoxidizer, deoxidate, deoxidation,

deoxidization;3. nuclear, nucleate, nucleated, nucleation, nuclei, nucleonics,

nucleus;

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VI. State the key words in the following word combinations and translate them into Vietnamese:

arc furnacecold-rolled hafniumgas-filled devicegas-sensitive metal

hafnium-containing mineralsreactor-grade zirconiumzircon-bearing mineralswater-cooled nuclear reactor

VII. Translate the following sentences into Vietnamese paying attention to the words in bold type:

1. It is known that elementary hafnium was first prepared by Hevesy by the reduction of potassium hexafluohafnate with sodium.

2. The rate of penetration of oxygen into metallic hafnium is lower than that for zirconium.

3. The machineability of hafnium resembles that of stainless steel.

4. The chemical properties of hafnium resemble those exhibited by zirconium very closely.

VIII. Replace subordinate clauses by complex subject:

Model: a) It is known that hafnium is used for making special glasses. b) Hafnium is known to be used for making special glasses.

1. It was proved that the boiling point of hafnium was 54000C.

2. It is considered that hafnium is hot-roll in air at 8400C.

3. It is known that zircons from granite rocks have higher Hf/Zn ratios than minerals from alkalic rocks.

4. It has been estimated that the ratio of hafnium to zirconium is 0.02

5. It is reported that the main problem in the production of hafnium is its separation from zirconium.

IX. Translate into English:

1. Nh ®· biÕt, trong tù nhiªn hafni ®îc t×m thÊy hÇu nh trong tÊt c¶ çc kho¸ng vËt chøa zirconi.

2. VÒ mÆt tÝnh chÊt c¬ häc, hafni gièng nh thÐp kh«ng gØ.

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3. Ngêi ta ®· x¸c ®Þnh ®îc r»ng, hafni chÞu ®îc qu¸ tr×nh çn nãng còng nh çn l¹nh.

4. Nh s· biÕt hafni võa ®îc ®iÒu chÕ trong ch©n kh«ng cã kh¶ n¨ng ph¶n øng ho¸ häc h¬n bÊt cø mét chÊt khö ®· biÕt nµo.

5. Mét mÆt v× nh÷ng khã kh¨n trong viÖc ®iÒu chÕ hafni ë tr¹ng th¸i tù do, mÆt kh¸c v× gi¸ thµnh cao mµ ngµy nay viÖc sö dông hafni rÊt h¹n chÕ.

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Text 18

Rubidium and cesium

Rubidium and cesium are the fourth and fifth members of the alkali metal group. Rubidium and cesium were discovered by Bunsen and Kirchhoff in 1860 and 1861, respectively by the use of the spectroscope. Rubidium was named for the prominent red lines in its spectrum, and cesium for its prominent blue lines. Both elements are soft, ductile, low-density, silvery-white metals of low melting points.

In both physical and chemical properties, rubidium and cesium resemble the other alkali metals. They are monovalent in their compounds, which are very stable to oxidation and reduction. Rubidium and cesium are the second and the first most electropositive elements and the second and first most alkaline elements.

Physical properties

About 27.2% of ordinary rubidium is beta - emitting rubidium 87 with a half life of 6.3 * 107 years. It decomposes to strontium, and can be used to determine the age of rubidium- containing rocks.

The only natural isotope of cerium is cesium 133, but cerium 137 is one of the products of the atomic fission of uranium. It is also a beta emitter and has a half life of 33 years. Along with strontium 90, it is one of the most trouble some radioactive wastes to handle in the commercial applications of atomic fission.

Among the most interesting physical properties of rubidium and cesium are their large ionic radii, their low ionization

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potentials, their low densities and melting points, their high position in the electromotive series, and their low electron work functions. Both metals are photosensitive and are ionized readily and efficiently by visible light and by infra- red and ultraviolet radiations.

Occurrence

Rubidium is the sixteenth most prevalent element in the earth’s crust but is not found in any mineral as a principal constituent. Rather, it occurs widely dispersed in potassium minerals in very low concentrations.

This lack of concentration in any mineral deposits undoubtedly accounts for the scarcity of production and application of this rather prevalent element, however it is also found in lepidolites ores of South Africa, some of the lepidolites containing as much as 1 to 1.5 per cent rubidium and much smaller amounts of Cs. The extensive processing of these lithium ores has resulted in an increasing availability of rubidium and cesium by- product concentrates that are being used as sources of rubidium and cesium compounds.

Cesium is the fortieth most prevalent element in the earth’s crust and is found in minerals such as pollucite (2Cs2O.2Al2O3.9SiO2.H2O), a hydrated silicate of aluminium and cesium.

(to be continued)

Exercises


1. Who discovered rubidium and cesium?2. When were these elements discovered?3. What do the names “rubidium” and “cesium” mean?4. What do you know about the physical properties of rubidium

and cesium?5. What can you tell about rubidium 87?6. Which element is considered to be one of the products of

atomic fission of uranium?

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II. Translate the following derivatives:

1. Alkali, alkaline, alkalinity, alkalinous, alkalization, alkalize, alkalizing;

2. Concentrate, concentrated, concentrating, concentration, concentrator;

3. Decompose, decomposer, decomposing, decomposition;4. Disperse, dispersed, disperser, dispersing, dispersion,

dispersity, dispersive;5. Reduce, reduced, reducer, reducing, reduction;

III. Translate the following sentences paying the attention to the bold type:

1. Both rubidium and cesium are photosensitive and are ionized readily by visible light.

2. Both metals react very vigorously with water.3. In both physical and chemical properties, rubidium and cesium

resemble the other alkali metals.4. Both elements are soft, ductile, low-density metals.5. Both rubidium and cesium halides form double halide

complexes with such metals as antimony, bismuth, cobalt, etc.6. Both elements form a series of polyhalides wherein two of the

halide atoms must be of valence -1 and third of valence +1.

IV. Translate the following sentences paying the attention to the bold type:

1. Rubidium is not found in mineral as principal constituent. Rather, rubidium occurs widely dispersed in potassium minerals in very low concentrations.

2. Since rubidium and cesium are easily ionized at rather low temperature, they offer great potential.

3. Since ancient times, it has been known that silicous material were suitable for glass- making.

4. The fats and oils are esters of special class, (in) as much as all are derived from glycerol.

5. Some of the lepidolites containing as much as 1 to 1.5 per cent rubidium and much smaller amounts of cesium.

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6. The presence of as little as 0.01 mg of tellurium per cubic meter of air gives rise to the characteristic foul breath.

7. Many crystals break most readily along certain planes where the cohesive forces are weaker than in other directions.

8. Along with strontium 90, cesium 137 is one of the most radioactive wastes to handle.

9. In 1925 Ungerer observed a separation of small ions on account of their different sizes when he studied their adsorption on clay.

10. The lack of concentration in any mineral deposits accounts for the scarcity of production and application of such rather prevalent element as rubidium.

11. Cesium is found in minerals such as polucite, a hydrated silicate of aluminium and cesium.

12. Only oxygen is more abundant on the earth’s crust than silicon.

13. The only natural isotope of cesium is cesium 133.14. Most commercial rare earth salts contain the rare earths in

much the same ratio as they occur in the ore.

V. Translate the following sentences paying the attention to the singular and plural forms:

1. Alkali, alkalis, alkalies;2. Datum, data;3. Nucleus, nuclei;4. Phenomenon, phenomena;5. Radius, radii;6. Series, series;7. Spectrum, spectra;

VI. Translate the following sentences into English:

1. Rubidi vµ cesi thuéc nhãm 1 cña hÖ thèng tuÇn hoµn çc nguyªn tè ho¸ häc.

2. Khi lµm viÖc víi rubidi vµ cesi cÇn ph¶i nhí c¶ hai nguyªn tè nµy ®Òu kh«ng bÒn ®èi víi ph¶n øng oxi ho¸ vµ khö.

3. Nh ®· biÕt, rubidi vµ cesi ®¬n chÊt cã thÓ ®îc diÒu chÕ b»ng mét sè ph¬ng ph¸p.

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4. Ngêi ta cho r»ng ph¬ng ph¸p ®îc sö dông réng r·i nhÊt lµ ph-¬ng ph¸p nung cacbonat cña rubidi vµ cesi víi magie ë nhiÖt ®é 6750 C trong khÝ quuyÓn hydro.

5. CÇn ph¶i nhí r»ng, Cs137 lµ mét trong nh÷ng s¶n phÈm cña sù ph©n r· h¹t nh©n uran.

VII. Make an outline of the text.

VIII. Retell the text

Text 19

Rubidium and Cesium

(Continued)

Chemical properties

In their chemical reactions, rubidium and cesium are very similar to potassium. Both metals react very vigorously with air and water and must be protected from exposure to them.

Cesium hydroxide is the strongest base known and must be stored in silver or platinum out of contact with air because of its reactively with glass and CO2. Rubidium hydroxide is a powerful base as well.

Rubidium and cesium are known to form alloys with the alkali metals, mercury, antimony, bismuth, and gold. When alloyed with the last three metals, rubidium and cesium have the properties of the releasing electrons under the influence of light and can be employed in photoelectric tubes.

Applications

The present industrial applications of rubidium and cesium are limited and include use as getters in vacuum tubes, as photoelectric cell components and space missiles in ion propulsion

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engines, the latter being based upon the acceleration of ions and their discharge into space to provide the push for rockets. Since rubidium and cesium are easily ionized at rather low temperature, they offer great potential for this purpose.

The mass of cesium ions being greater than that of ions of lighter elements gives cesium an advantage. It is anticipated that the ion engine would be used to move vehicles through space once they are in orbit and that a nuclear power plant would provide the energy to run the engine.

One form which a thermoelectric generator using Rb or Cs can take utilizes the magnetohydrodynamic (MHD) principle. Cesium ions formed by heat are passed at a very high temperature through a magnetic field, and since they form an electrical conductor, they act like an armature of a conventional generator and cause electricity to be generated.

Cesium and rubidium are of importance because cesium , followed by rubidium is the most easily ionized element.

One believes, that production will rise to meet the demands1

at lower cost for rubidium and cesium.

Notes

1. To meet the demands: ®Ó lµm tho¶ m·n ®ßi hái

Exercises


1. What group of the periodic table do rubidium and cesium belong to?

2. What are the chemical properties of these elements?3. Do rubidium and cesium form complex salts?4. When do rubidium and cesium possess the property of releasing

electrons?5. Do you know any methods for preparing elemental rubidium

and cesium?6. Where are rubidium and cesium applied?

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II. Give a summary of the texts Nos. 18 and 19

III. Translate the following sentences paying the attention to the bold type:

1. Cesium and rubidium are of importance because cesium followed by rubidium is the most easily ionized element.

2. The oxidation of titanium follows the parabolic rate law with time* at any given temperature.

* the parabolic rate law with time: phô thuéc víi thêi gian theo ®-êng parabol3. Cesium hydroxide must be stored in silver or platinum out of

contact with air because of its reactively with glass and CO2.4. Since cesium ions form an electrical conductor, they act like

an armature of a conventional generator and cause electricity to be generated.

5. Cesium like lithium forms alkyl and aryl compounds of a wide variety

6. The needlelike crystals of potassium floutantalate X2 Ta E7, precipitate on cooling.

7. Zirconium nitride is such a stable compound that it is very unlikely that it can be used directly as a source of a metal.

8. It is anticipated that the ion engine would be used to move vehicles through space once they are in orbit.

IV. Translate the following sentences paying attention to complex Subject:

1. Rubidium and cesium are known to form alloys with the alkali metals.

2. In general, all tellurium deposits may be said to be gold bearing.

3. The action of flourine on thalium was found to be so vigorous that the metal became incandescent.

4. Klaproth was considered to have been the discoverer of the element uranium.

5. The stability of thorium metal with respect to oxidation in air appears to be a function of the oxide content of the metal.

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V. Translate the following sentences paying attention to complex Object:

1. We know transistors to be used as amplifiers and in place of conventional vacuum tubes.

2. Specialists connsider cast cobalt to have a tensile strength of 35.000 psi.

3. Exeriments showed gallium to have been recovered from sodium aluminate liquor by the Bayer process.

4. The iron- cobalt equilibrium diagram shows cobalt to be entirely miscible with gamma iron.

5. John demonstrated uranium to deform commonly by twinning.

VI. Translate the following sentences paying attention to the Participle:

1. Rubidium and cesium are used as getters in vacuum tubes and for space missiles in ion propulsion engines, the latter being based upon the acceleration of ions.

2. If alloyed with antimony, bismuth and gold, rubidium and cesium have the property of releasing electons under the influence of light.

3. When handling thallium a person must be protected against its poisonous effects.

4. Transistors are being produced on a pilot plant scale.5. Being one of the transition elements, titanium has a high

modulus of elasticity to density ratio and a high melting point.6. Selenites being formed by neutralizing selenous acid with

hydroxides and carbonates are poisonous.

VII. Translate the following sentences paying attention to the word in bold type:

1. It is known that the present industrial applications of rubidium and cesium are limited.

2. The mass of cesium ions being greater than that of ions of lighter elemets gives cesium an advantage.

3. The compounds of tellurium resemble those of selenium.4. One believes that production of rubidium and cesium will rise

to meet the demands at lower cost for these elements.

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5.Fluorine forms strong hydrogen bonds, oxygen weaker ones.

VIII. Translate into English:

1. Nh ®· biÕt, rubidi vµ cesi rÊt gièng kali trong çc ph¶n øng ho¸ häc.

2. Çc thÝ nghiÖm ®· chØ ra r»ng, ph¶n øng gi÷a cesi vµ níc kÌm theo tiÕng næ.

3. Cesi peoxit lµ mét baz¬ rÊt m¹nh nªn cÇn ph¶i b¶o qu¶n nã trong chai b¹c hoÆc chai platin vµ çch ly khái sù tiÕp xóc víi kh«ng khÝ.

4. Ngêi ta thÊy r»ng, rubidi vµ cesi t¹o thµnh çc hîp kim kh«ng nh÷ng víi kim lo¹i kiÒm mµ cßn víi mét sè kim lo¹i kiÒm thæ.

5. Sau nhiÒu nghiªn cøu ®Çy ®ñ cña çc nhµ khoa häc ngêi ta thÊy r»ng rubidi vµ cesi ®îc sö dông réng r·i trong tªn löa vµ vò trô.

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Part 2: Petrochemistry

Text 20

Composition of petroleum

Petroleum is a natural mixture of various hydrocarbons and their derivatives containing sulphur, nitrogen, oxygen, metals, etc.The main constituents of petroleum - hydrocarbons - may differ in the number of carbon and hydrogen atoms in the molecule and in the molecular structure. Petroleum hydrocarbons may relate to the following groups or series: paraffins [saturated, or stable hydrocarbons, alkanes], naphthenes [cycloankanes], and benzene hydrocarbons [arenes]. In most grades of petroleum, paraffins and naphthenes prevail. During processing of petroleum, unsaturated hydrocarbons [olefins and diolefins] may also form. The specific properties of petroleum products are decided by the predominance of some or other group of hydrocarbons in crude petroleum and by the presence of compounds containing sulphur, nitrogen or oxygen.

1. Paraffin hydrocarbons [alkanes] Their general formula is CnH2n+2, where n is the number of carbon atoms. Each next hydrocarbon can be obtained from the previous one by substituting a methyl group CH3 for the extreme hydrogen atom in the chain: CH4 C2H6 C3H8 C4H10

methane ethane propane butaneThe paraffin hydrocarbons are the most stable of the lot because all valence bonds are fully satisfied as indicated by the single linkage. Most reactions involve the replacement of by hydrogen atoms with other atoms, the carbon linkage remains stable.Under common conditions, the hydrocarbons from CH4 to C4H10 are gaseuos, those from C5H12 to C15H32 are liquids [they enter the composition of gasoline, kerosene and diesel- fuel fractions], and those from C16H34 are solid [paraffins].

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Beginning from the fourth term in the series [butane C4H10], hydrocarbons may exist in two or more forms differing in the structure. For instance, butane may exist in two forms: n- butane and isobutane. Compounds which have the same chemical formula but a different atomic structure are called isomers.The number of isomers increases for each next hydrocarbon in the series. Hydrocarbons of the formula C13H28 may have 802 isomers, those of the formula C14H30, 1858, and so on. Thus, the composition of petroleum is quite complicated. Isomers possess different physical and chemical properties. For instance, heptane of normal structure [n- C7H16] has an octane number of zero, whereas isooctane [iso- C7H16] has an octane number of 100.

2. Naphthenic Hydrocarbons [Cycloalkanes] Their general formula is CnH2n. They were discovered by V.V. Markovnikov, a prominent Russian chemist, when studying petroleum of Caucasian deposits.In their chemical properties; naphthenic hydrocarbons are similar to paraffins, but differ from the latter in having a cyclic structure.Cyclopentane and cyclohexane derivatives are especially important for the quality of petroleum and petroleum products.

3. Benzene Hydrocarbons [Arenes] Arenes of the benzene series have the general formula CnH2n-6. The cyclic structure of arenes differs from that of naphtenes by the presence of double bonds on the aromatic ring. If one or more atoms of hydrogen in the ring are replaced by a methyl [-CH3] or an ethyl [-C2H5] group, other arenes [toluene, xylenes and ethylbezene] are formed. Arenes are a valuable raw material for chemical technology and the manufacture of antinock gasoline.

4. Unsaturated Hydrocarbons [Olefins] Hydrocarbons of the ethylene series have general formula is CnH2n-2, are characterized by a double bond in the molecule [ethylene C2H4, propylene C3H6, butylenes C.4H8, amylenes C5H10, etc.] and may be of either normal or isomeric structure.They are not present in crude petroleum, but constitute an appreciable part of the products obtained in the thermal and some catalytic processes of petroleum processing. These hydrocarbons

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have a high reactivity and are used for the manufacture of some important products, such as polyethylene, polypropylene, ethylene and propylene oxides and their derivatives.Along with olefins, some less saturated hydrocarbons, with two double bonds in the structure, such as diolefins, can form in petroleum processing. These are extremely unstable and for that reason should not be present in final petroleum products. Some of them [ butadiene C4H6 and isoprene C.5H8] are obtained intentionally from petroleum and used for the manufacture of synthetic rubber and like products.

5. Oxygen- containing compounds These include naphthenic acids, phenols and tar- asphaltene compounds. Naphthenic acids are compounds containing a carboxyl group-COOH. Their density is from 0.96 to 1.05 g/cm3 and general formula, CnH2n-2O2. Naphthenic acids are strongly smelling oily liquids. They may be present in kerosene, diesel- fuel and light oil distillates of petroleum and are corrosion- aggressive; they are removed from petroleum fractions by leaching. Naphthenic acids and their salts are widely used in industry as components of greases, for impregnation of fabrics and footwear, etc.Phenols are contained only in some grades of petroleum and are liberated together with naphthenic acids during leaching of distillates.Tar- asphaltene compounds may be present in petroleum in considerable quantities [from traces to 25% and even more]. They are complex high- molecular compounds containing carbon[82-87.4%], hydrogen [10.3-12.5%], oxygen [up to 2.5%], sulphur [0.8-7%], and nitrogen [up to 1%]. Low molecular tar compounds can partially be distilled off together with petroleum distillates, while high molecular ones remain in fuel-oil fractions and especially in oil residue [goudron]. The presence of tar in these products makes them dark and promotes carbonization in cylinders of internal combustion engines. Tar- asphaltene products are harmful is white petroleum products and oils, but are desirable constituents in such products as bitumen, coke, insulating and impregnating materials.

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All tar-asphaltene products are usually classed into neutral resins soluble in light gasoline; asphaltenes [ the products of polymerization of neutral resins and oxyacids] which are insoluble in light gasoline, but soluble in benzene, chloroform and carbon bisulphide; asphaltogenous acids and their anhydrides of acid nature. which are insoluble in light gasoline, but soluble in alcohol.All the three types of tar-asphaltene compounds are high-molecular compounds of unsaturated nature containing oxygen and sulphur. At normal temperature they are very thick and viscous liquids or are solid and have a density above 1.0 g/cm3. The content of tar-asphaltene compounds is greater in petroleum grades of higher density and in those high in sulphur.

6. Sulphur compounds In Vietnam grades of petroleum, the content of sulphur is small. Sulphur is present in petroleum and petroleum products mostly in combined state, i.e. in the form of organic sulphur compounds. Sulphur compounds of the following types may be found in petroleum products: mercaptans RSH [where R is a hydrocarbon radical]; sulphides RS, disulphides RS-SR, thiophene C4H4S and its derivatives, and sometimes hydrogen sulphide and elemental sulphur. Hydrogen sulphide and mercaptans which have acid properties, and elemental sulphur form a group of active sulphur compounds which can cause strong corrosion of equipment and pipelines.Another group includes sulphides and disulphides which are neutral at low temperatures, but are thermally unstable; at 130-1600C they decompose [with breaking of C-S bonds] and form hydrocarbons, mercaptans and hydrogen sulphide. A third group includes thiophane and thiophene and their derivatives, such as benzothiophene.Like benzene hydrocarbons, they have a low reactivity and are relatively stable at elevated temperatures.High- molecular sulphur compounds are unstable and can be oxidized under relatively soft conditions; the products of oxidation increase the content of tar in petroleum products. In the atmosphere of hydrogen, they are reduced to corresponding hydrocarbons and hydrogen sulphide; this is the basis of the

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processes of hydrogen refining [hydrofining] of petroleum and petroleum products.In straight distillation of petroleum [without destruction] the content of sulphur increases from lighter fraction to heavier ones, with the residue having the highest concentration of sulphur. When higher temperatures and pressures are applied, however, organic sulphur compounds are destroyed together with high - molecular hydrocarbons to form hydrogen sulphide and mercaptans which are corrosive and toxic. Corrosion is enhanced in the presence of water vapours and hydrochloric acid which forms by decomposition of calcium and magnesium chlorides contained in undesalted petroleum.In order to diminish corrosion and improve labour conditions, petroleum before distillation might be desalted and dehydrated. The content of sulphurous compounds in petroleum products can be lowered by various methods of refining, mainly by hydrogen refining.

7. Nitrogen Compounds The content of nitrogen compounds is usually greater in heavier grades of petroleum. Nitrogen compounds are divided into basic, which contain nuclei of pyridine and quinoline, and neutral, which contain pyrrol and indol homologues. In petroleum processing, nitrogen compounds are distributed between fractions much like sulphur compounds, i. e. their concentration increases from lighter fractions to heavier ones, and the largest amount [65-75%] is concentrated in the residue.Among nitrogen compounds, porphyrins occupy a special place. They may be present in petroleum either in free state [four pyrrol rings] or as complexes containing organic nitrogen compounds and organic derivatives of vanadium and nickel. Notwithstanding the high thermal stability of nitrous compounds in the technological processes, they decompose partially, which is detected by the formation of ammonia. Certain refining processes [for instance, hydrogen refining] can remove an appreciable portion of sulphurous compounds [as hydrogen sulphide] and a part of nitrogen compounds [as ammonia] and oxygen compounds [as water vapours].

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8. Mineral SubstancesMineral substances are found in petroleum only in very small concentrations [provided that crude petroleum has been refined properly from mechanical impurities at the oil well]. As has been established by combustion of many samples of petroleum, the elements found in the ash form [in the decreasing order] the following row: S-O-N-V-P-K-Ni-I-Si-Ca-Fe-Mg-Na-Al-Mn-Pb-As-Cu-Ti-V-Sn-As. The total amount of ash in various grades of petroleum may vary from a few thousandths of a per cent to 0.8 per cent.

Exercises

Answer the following question1. What is the elemental composition of petroleum?2. What are the main constituents of petroleum ?3. Which series of hydrocarbon are present in petroleum ?4. Which series of hydrocarbon are formed during processing of petroleum ?5. What can you say about the chemical properties of paraffin hydrocarbons ?6. What are the physical properties of paraffin hydrocarbons ?7. Which compounds are called isomers?8. What can you say about the chemical and physical properties of isomers?9. What are the difference and the similarity in structure and properties between paraffinic and naphthenic hydrocarbons ?10. What are the difference and the similarity in structure and properties between naphthenic and benzene hydrocarbons ?11. What are the applications of benzene hydrocarbons ?12. What can you say about the properties of olefins and diolefins?13. What are the applications of olefins and diolefins?14. What are the applications of naphthenic acid?15. What is the elemental composision of tar-asphaltene compounds?16. How can you class tar-asphaltene products?

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17. Which types of sulphurous compounds are present in petroleum products?18. How can the content of sulphurous compounds in petroleum products be lowered?19. How are nitrogen compounds distributed?

Text 21

Basic Physico-chemical properties of petroleum and petroleum products

1. DensityThe density of petroleum and petroleum products can be expressed in either absolute or relative values. The relative density is the ratio of the density of a petroleum product at temperature t2 to the density of distilled water at temperature t1. The density of petroleum products is normally measured at 200 C and that of water, at 40 C. Since the latter is taken as unity, the numerical values of the relative and absolute density coincide.To find the absolute density [kg/m3 or g/cm3] the mass of a product is divided by its volume, i. e. =m/V.The density of petroleum and petroleum products depends on the

content and composition of light low-boiling [which have a low

density] and heavy high-boiling constituents [fractions]. Indeed,

among the components having roughly the same boiling point,

paraffin hydrocarbons have the lowest density and benzene

hydrocarbons have the highest value, with that of naphthalenes

being in the middle. This is why density is one of the principal

characteristics of petroleum and petroleum products.

The density of petroleum and petroleum products decreases with the increasing temperature and their volume respectively increases. The temperature relationship for density can be expressed by Mendeleev's formula: dt

4 = d204 - a[t-20]

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where dt4 is the relative density of a product at temperature t; d20

4

is the relative density of a product at 200C; a is a temperature correction factor.

2. Molecular MassThis is one of the basic physico-chemical characteristics of petroleum and petroleum products. The molecular mass of paraffin hydrocarbons can be found approximately by using the formula:

M = 60 + 0.3t + 0.001t2

where t is the average temperature of boiling of a petroleum fraction, 0C; it is calculated as the arithmetic mean of the temperatures at which equal volumes of the liquid, say, 10% fraction, are distilled off.

The relationship between the molecular mass and relative density of petroleum fractions is determined by the following empirical formula: M = 44.29d15

15/1.03- d1515

Using this formula, it is also possible to fine [with a certain approximation] the molecular mass of all classes of hydrocarbons.

3. Boiling Point. Fractional Composition The boiling point of a liquid is the temperature at which the pressure of vapours is equal to the external pressure; on reaching this point, vaporization, which up to that moment occurred from the surface only, begins in bulk of the liquid [at the bottom and walls of the vessel being heated], where vapour bubbles are formed; this is what is called the boiling proper. If vapours are not removed off the liquid surface during heating, an equilibrium is established between the liquid and vapour phase. Vapours in equilibrium with the liquid are called saturated. At a higher temperature of heating of a liquid, vaporization occurs more intensively, more vapours are formed above the liquid, and the pressure of saturated vapours is higher.

The boiling point of a liquid depends on the external pressure. For instance, water at a pressure of 0.1 MPa boils at 1000C. At a higher pressure, say 0.4 MPa, boiling begins only at

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1440C. Thus , the boiling point is higher at a higher external pressure and at a lower external pressure or in vacuum, water boils at a lower temperature. The same effect of pressure is found in other liquids. This phenomenon is utilized in vacuum distillation of fuel oil.

Petroleum and petroleum products can be separated into individual hydrocarbons only with certain difficulties. Usually separation is carried out by distillation which gives simpler mixtures of hydrocarbons than is the original mixture. These mixtures are called fractions. They boil not at a constant temperature, but in a temperature range between the point of the beginning of boiling and that of its end. Depending on the boiling points and contents of various hydrocarbons, a product may have different boiling ranges, i. e. may have a different fractional composition.

All petroleum products obtained from crude petroleum by distillation are essentially fractions that can boil off within particular temperature ranges. For instance, gasoline fractions boil off within 35-2050C, kerosene fraction within 150-315 0C, diesel-fuel fractions within 180-3500C, light oil distillates within 350-420 0C, heavy oil distillates within 420-490 0C, and oil residues at temperatures above 490 0C.

4. Thermal Properties of Petroleum and Petroleum products These properties are of high practical importance for calculating the heat balance of all processes associated with heating or cooling.Specific heat is the quality of heat needed to heat up 1 kg of substance by 10C. The approximate values of specific heat, kJ/kg K, are as follows: petroleum 2.1, petroleum vapours 2.1, water 4.19.With the specific heat of a petroleum product being known , it is possible to calculate the quantity of heat for heating. For this, the specific heat is multiplied by the mass of the product [kg] and by the difference between the final and initial temperature [0C]. The specific heat of petroleum products increases with increasing temperature and is higher for products of lower density.

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Specific latent heat of evaporation is the quantity of heat spent to vaporize 1 kg of a liquid at its boiling point [this characteristic is called latent, since the heat is spent for evaporation and the temperature of the product remains constant during heating]. The average values of the latent heat of evaporation at the atmospheric pressure, kJ/kg, are as follows: water 2257, gasoline 293.3-314.3, kerosene 230-251, diesel fuels 209-213, oils 167-209. Thus, the latent heat of evaporation decreases with increasing density and molecular mass of petroleum products, and also with increasing temperature and pressure.The heat of condensation is the quantity of heat liberated by vapours during their condensation and is numerically equal to the latent heat of evaporation.The latent heat of fusion is the quantity of heat absorbed during fusion of 1 kg of a solid at the melting point.The heat of combustion [calorific value] of fuel is the quantity of heat liberated by the fuel on full combustion. A distinction is made between the high and low heat of combustion: the former [Qh} takes into account the heat of condensation of the water present in the fuel and formed during combustion [it is taken conditionally that the combustion products contain liquid water rather than water vapours]. The low head of combustion, Ql, implies that the water of the fuel and the water formed by combustion is removed as vapours with combustion gases [i.e. it is lower than the high heat of combustion by the quantity of heat spent for evaporation of moisture of the fuel and of the water formed through combustion of hydrogen in the fuel].

5. Viscosity [internal friction] Viscosity is the ability of a liquid [or gas] to resist the motion of a layer relative to other layers. As regards petroleum products, a distinction is made between dynamic, kinematic and relative viscosity.Dynamic viscosity is measured in pascal-second [Pa s]. The dynamic viscosity of selected liquids is as follows:

Pa sEther [at 180C] 0.000026

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Gasoline [at 200C]Kerosene [at 200C]Alcohol [at 180C]Water [at 200C]Glycerine [at 180C]Spindle oil [at 200C]Cylinder oil [at 200C]Caster oil [at 180C]

0.00450.00170.001660.0010061.100.0420.351.20

An inverse value of dynamic viscosity is called fluidity. In process calculations and for testing the quality of many petroleum products, use is made of kinematic viscosity , which is the ratio of the dynamic viscosity to the relative density of a liquid, d, at the same temperature, i.e.

= /dKinematic viscosity is measured in square metre [square millimetre] per second[m2/s, mm2/s].In practical calculations, especially for quality control of petroleum products, use is often made of relative viscosity which is the time of efflux of 200 ml of a petroleum product at the testing temperature related to the time of efflux of the same volume of distilled water at 200C [the time of efflux of 200 ml of water at 200C is what is called the water number of a viscosimeter]. Viscosity- temperature relationships. Viscosity becomes lower with increasing temperature and vice versa. The pattern of variation of viscosity with temperature is an important characteristic of petroleum products, especially of lubricating oils. These variations can be determined by various methods, for instance, by the ratio of the viscosity at 50 0C to that at 1000C, which is now specified for many lubricating oils, or by the viscosity index; the latter is found from monograms for the known values of viscosity at 50 0C and 1000C. With a higher ratio of viscosities, the temperature curve of viscosity is steeper and on the contrary with a lower ratio, the curve is less steep and the quality of the oil is better.

6. The Setting and Fusion points When being cooled, petroleum and petroleum products gradually loss mobility and can set [solidify] notwithstanding the fact that

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they contain some substances that might be liquid at the temperature considered.The setting [solidification] point of a petroleum product is the temperature at which the product loses mobility under strictly specified testing conditions. The loss of mobility and freezing of petroleum and petroleum products depend mainly on the content of hydrocarbons which are solid [at the normal temperature]. The higher the content of such hydrocarbons [in dissolved or crystalline state], the more quickly the product loses its mobility during cooling, i.e. the products has a relatively high setting point. Tarry products and asphaltenes can retard somewhat the crystallization of solid hydrocarbons, that is why the setting point of detarred products is always higher than that of the distillates from which they have been obtained.During cooling to their setting point. white petroleum products pass through a number of intermediate stages- the stage of turbidity [blushing] and that of the beginning of crystallization. The highest temperature at which crystals [say, of benzene, etc.] can be detected in the cooled fuel by naked eye is called the temperature of the beginning of crystallization, or the chilling temperature [point]. The temperature at which crystals of hydrocarbons [mainly of paraffins] start to precipitate and make the product turbid is called the blushing temperature [point]. Along with the temperature of chilling of liquid petroleum products, the temperature of fusion of some products which are solid at normal temperature [paraffin and ceresin] is also practical importance.The fusion point is the temperature at which a solid product becomes liquid under strictly specified testing conditions.With these constants being known it is possible to select properly the method of petroleum processing and take the required measures to ensure pipeline transportation, especially in winter time, and also to choose the methods of storage and transportation of solid products having a high chilling point.

7. Flash and Ignition Points. Self- ignition temperature. Explosibility

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The fire hazard of petroleum products is judged upon by their flash, ignition and self- ignition temperatures [point]. At lower values of these characteristics, a product is more fire- hazardous.The flash point is the temperature at which a mixture of air and vapours of a product being heated under standard conditions ignites on contact with an ignition source, but the product proper is not ignited and the flame is damped. For light petroleum products [with the flash point not above 500C] the flash point is measured in a closed apparatus and that of heavier products [with the flash point above 70 0C] can be determined in an open vessel. The product to be tested is poured into the apparatus and a thermometer is put inside. With light products, the apparatus is covered by a lid with a window which can closed by a gate. During the test, the window is opened periodically and a burner is brought close to it. In an open apparatus, the burner is moved close to the liquid surface. Tests in an open apparatus give a higher value of a flash point, since the vapour formed are partially dissipated to the surroundings.In further heating, a petroleum product can ignite at a certain temperature. This temperature is called the ignition point.There is a certain relationship between the fractional composition of a product and its flash and ignition points: lighter hydrocarbons in its composition lower these points. For instance, gasoline has the flash point below - 500C, whereas the flash point of fuel oil is above 1100C.According to international recommendations, easily igniting liquids include those flash point is below 610C [in a closed vessel] or 660C [in an open vessel]. These liquids, which can be ignited by a short action or even a small ignition source [say, a spark] and without preliminary heating.The temperature of self- ignition of a petroleum product is lower at a higher content of heavy hydrocarbons. This is the temperature at which a product ignites spontaneously on contact with the air, i.e. in the absence of flame or spark. Some products, such as fuel oils, goudron, soot and coke, self- ignite quite easily at temperature slightly above 300 0C. Self- ignition usually occurs in untight pipelines and apparatus in which petroleum products are

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at temperature above their ignition point. It is therefore essential to check the equipment for tightness to prevent self- ignition and fires.Explosibility. In petroleum processing plants, mixtures of vapours of some products with air may be explosive. Such mixtures may form in open air, in closed premises and inside processing equipment. A mixture of vapours of a product with air become explosive when the concentration of the vapours in mixture exceeds a definite limit. At lower concentrations, the mixture is not explosion hazardous, since the greatest portion of the heat evolved in the ignition zone is spent to heat up the air. A mixture can not explode, too, if it contains little air and therefore there is not enough oxygen to sustain combustion.The lowest concentration of vapours of a petroleum product [or other substance] in the air at which explosion is probable is called the lower explosive limit and the highest concentration of vapours at which explosion is still possible is respectively the upper explosive limit. The concentration range between the two limit in which explosion can take place on contact with open fire [or spark] is called the explosibility range.The upper and lower explosive limits and the explosibility are different for various vapours and gases. The explosibility ranges for some vapours and gases obtained at petroleum processing plants [percent] are as follows: gasoline 0.8 to 5.1; kerosene 1.4 to 7.4; propane 2.1 to 9.5; methane 5 to 15; ammonia 15 to 28; ethylene 3 to 32; hydrogen sulphide 4.3 to 46; carbon monoxide 12.5 to 74; hydrogen 4 to 74; and acetylene 2.3 to 81.The highest permissible concentration of vapours of a product in working premises depends on the composition of that product. The selected products it is as follows [mg/m3]: 100 for gasoline fuels, 300 for gasoline solvents, 5 for benzene and methanol, 50 for toluene and xylene, 10 for pure hydrogen sulphide, 3 for mixture of hydrogen sulphide with C1- C5 hydrocarbons, and 5 for phenol.

Exercises

Answer the following question

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1. How can they express the density of petroleum and petroleum products?

2. What is the relative density of a petroleum product ?3. How can you calculate the absolute density?4. Is there any the relationship between the density of petroleum

products and their boiling point? What is it?5. What are the relationship between the density of petroleum

products and their temperature and volume?6. What is the boiling point of a liquid?7. What is the relationship between the boiling point and the

external pressure ?8. What are fractions?9. What is specific heat?10. How can you calculate the quantity of heat for heating?11. What is the specific latent heat of evaporation?12. How can you understand the term "latent"?13. How can you distinguish the high and low heat of

combustion?14. What is the viscosity of a liquid?15. How many types of viscosity of liquid do you know?16. What is the relationship between the viscosity index and the

quality of a oil?17. What is the setting point of a petroleum product?18. Why is the setting point of detared products higher than that

of the distillates from which they have been obtained?19. What is fusion point?20. What is flash point?21. How can you measure the flash point?22. What is ignition point?23. What is temperature of self-ignition?24. When does the explosibility happen?

Text 22

Petroleum products

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The products obtained from petroleum can be classed into four groups: I-fuels; II- lubricating oils, paraffins, etc.; III-miscellaneous petroleum products; and IV-chemical and petrochemical products.Group I includes liquefied hydrocarbon gases, fuels for carburettor engines [gasolines], fuels for jet (kerosene) and turbojet engines , Diesel fuels, boiler fuels; Group II-various lubricating oils, paraffins, ceresins and petrolatum; Group III- plastic greases, bitumenns, coke, etc.; and group IV- hydrocarbons of various classes which serve as starting materials for organic or petrochemical synthesis.I. Liquefied hydrocarbon gases and fuels

Liquefied hydrocarbon gases consist mainly of propane and butane and sometimes may contain small quantities of propylene and butylene. They have found the widest application as domestic fuel which may be commercial propane (at least 93 % of propane), commercial butane (at least 93 % of butane) or their mixture (in winter time, with a greater proportion of propane).Liquefied gases or their constituents of higher purity are used as starting materials for the manufacture of various chemical products and olefines [by pyrolysis].

1. Fuels for carburettor EnginesThis group of fuels includes aviation and motor gasolines and tractor kerosene. An important characteristic of these fuels is the pressure of saturated vapours, kPa, which should be 29.3 to 47.9 for aviation gasolines, 66.5 to 93.4 for motor gasolines (not more than 66.5 for summer grades).The fractional composition of fuels is also of large importance. For instance, the 10% boiling point of gasoline (the point at which 10% of the fuel boils off) can characterize the starting properties and reliability of an engine starting under various conditions, in particular, at a low temperature of the ambient air. The 50% boiling point of gasoline characterizes the speed of engine heating during starting, the smoothness of switching from one operating mode to another, and the stability of engine operation. The 90% and 97.5% boiling points of aviation gasoline and the temperature of the end of boiling of motor gasoline determine the homogeneity of the fuel mixture, i.e. the completeness of fuel combustion in the

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engine. This is extremely important, since with incomplete combustion of the fuel, liquid substances can penetrate into the crankcase and dilute the lubricating oil and thus cause a quick wear of the engine. Besides, incomplete combustion causes a stronger pollution of the air.Antiknock rating is another important characteristic of fuels which determines their proper combustion in carburettor engines. With detonation (knock-type) combustion, the rate of flame front propagation increases very quickly and causes explosion, or knock, in an engine; as a result, the engine may quickly be put out of operation. The antiknock rating of fuels is evaluated in terms of the octane number (ON).Aviation Gasolines (state Standard GOST 1012-72). They are used as fuel for carburettor-engine planes and helicopters. In the USSR, aviation gasoline is available in the following grades: B-70, B-100/130, and B-91/115. The grading includes a letter B and a number indicating the octane number or two numbers: The numerator indicating the octane number and the denominator, the rating. Aviation gasolines are prepared by mixing (compounding) of a base gasoline (obtained by catalytic cracking or catalytic reforming), high-octane components (isooctane, alkyl gasoline, isopentane, benzene hydrocarbons, etc.), tetraethyl lead (TEL) and other additives raising the octane number, and of inhibitors i.e. substances preventing fuel oxidation (with aviation gasoline, oxy- diphenylamine is used for the purpose). These components are taken in proportions required to make gasoline of the desired grade and quality.The boiling-off points of gasolines should not exceed the following temperatures: 90% boiling-off point 1450C; 50% 1050C; and 10% from 750 to 880C. The content of TEL (g/kg of gasoline) should be not more than 2.7 for grade B-100/130 and from 2.5 to 3.3 for other grades, except for B-70 which contains no TEL.Motor Gasolines. These grades of gasoline are employed in automobile carburettor engines. One of the most important indices of their quality is the anti-knock rating which is expressed in terms of the octane number.

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Octane number is numerically equal to the content of isooctane (% by volume) in a mixture with n- heptane, which is equivalent in its detonation intensity in a single cylinder engine to the fuel being tasted under standard conditions. The octane numbers of isooctane is taken conditionally to be 100 and that of n-heptane, zero. The octane numbers are determined by using mixture of these two hydrocarbons. The current control of fuels is done by using what is called secondary reference fuels having various values of the octane number.Octane numbers can be determined by various methods. The motor method uses apparatuses of the type IT9-2M and UIT-65 to measure the octane number of motor and aviation gasolines. Motor gasolines can also be tested by what is called the research method in apparatuses of the type IT9-6 and UIT-65 (State Standard GOST 8226-66). The temperature method(State Standard GOST 3337-52) with the use of IT9-5 apparatus is employed to determine the antiknock of high- octane aviation gasolines (ON 100 or higher). The pressurization method (State Standard GOST 3368-68) with the use of IT9-1 apparatus is used to determine the rating of aviation gasolines in rich mixtures.The octane number of gasoline increases on addition of benzene hydrocarbons and isomeric paraffin hydrocarbons and also on a decrease of the point of full boiling-off. If these measures fail to give gasoline with a desired octane number, an antiknock agent is added. Various metalorganic and organic substances can be used as antiknock agents. The most popular antiknock is tetraethyl lead Pb(C2H5)4 in the form of ethyl liquid.All hydrocarbons can be written in the following order of increasing effect of TEL on octane number: paraffin-naphenes-benzenes-olefins. With an increase in the content of TEL in gasoline, its effectiveness diminishes. The sensitivity of gasolines to TEL decreases sharply with an increasing concentration of sulphur which reacts with lead and petrifies the effect of TEL. For that reason, the starting materials of certain processes and some grades of gasoline are purified from sulphur compounds before adding TEL.

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The grades of motor gasoline produced in the USSR are as follows: A-66, A-72, A-76, AI-93 and AI-98 (the digits are octane numbers). All these grade can be ethylated, except for A-72. The content of TEL in them should not exceed 0.6 g/kg in A-66, 0.41 g/kg in A-76 and 0.82 g/kg in AI-93 and AI-98. The octane number of grade AI-93 and AI_98 is measured by the research method and that of the other grades, by the motor method. For easier operation of engines, motor gasolines are manufactured as summer and winter kinds, the latter, as has been given earlier, having a higher pressure of saturated vapours. Besides, they have (except for grade AI-980 different temperature of boiling-off of intermediate fractions and of the end of boiling. The fractional composition of motor gasolines is given below (numbers in numerators and denominators are boiling-off points respectively for summer and winter kinds of gasoline, 0C).

A-66 A-72, A-76AI-93

AI-98

Beginning of boiling, at leastBoiling-off points, lower limit:10%50%90%End of boiling

35/-

79/65125/125195/160205/185

35/-

70/55115/100180/160195/185

35/-

70/-115/-180/-195/-

New, more efficient makes of automobile engines have a high compression ratio and can be run only on high-octane gasoline. Motor gasolines are prepared by mixing (compounding) various components: high-octane gasolines of catalytic cracking and catalytic reforming, alkylates and isomerizates of light fractions of preliminary distillation. For preparation of gasoline with lower octane numbers (especially of grade A-66), use is also made of gasolines of thermal cracking and coking, gasolines obtained by straight-run distillation of petroleum, which have a higher temperature of boiling off, and dearomatized products (refined petroleum) obtained in the manufacture of benzene hydrocarbons by catalytic reforming of gasoline fractions.

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Since tars, if present in gasoline, can disturb the operation of engines, their content in gasolines is limited at 7 mg/100 ml in grade A-66 and 5 mg/100 ml in the other grades. The chemical stability of gasolines is checked by determining the induction period which should constitute at the manufacturer at least 450 min for grade A-66, 600 min for A-72, and 900 min for the other grades.

2. Fuels for diesel engines.In Diesel engines, air is compressed and its temperature rises and Diesel fuel injected into the engine is ignited by the hot air. The capability of diesel fuels for self- ignition is measured in term of cetane number.Cetane number is the index of ignitability of diesel fuel, which is equal numerically (in per cent) to the content of cetane (n-hexadecane C16H34) in a mixture with -methylnaphthalene C11H10, which possesses the same ignitability in a single-cylinder engine under standard testing conditions as the fuel being examined. The cetane number of cetane proper is taken equal to 100 and that of -methylnaphthalene, zero. The cetane number depends on fuel composition: the highest cetane number is shown by paraffin hydrocarbons, a lower, by naphthenes and the lowest, by benzene hydrocarbons which for that reason are undesirable in diesel fuels. The cetane number can be raised by mixing diesel fuel with certain components containing paraffin hydrocarbons of normal structure or by giving special additives.Diesel engines are divided into three classes: high-speed engines (above 1000 rpm) for agricultural machines, Diesel locomotives, cross-country vehicles, etc.; medium-speed engines (500-1000 rpm) for large locomotives and as auxiliary motors on ships; and low-speed engines (less than 500 rpm) employed as main marine engines and Diesel-generators. Depending on the content of sulphur in the original petroleum, diesel fuel fractions may be low-sulphurous (up to 0.2 % S) and sulphurous (0.7 to 1.8 % S). The content of sulphur can be reduced by hydrogen refining. Low-sulphur fuels are advantageous in being less corrosive and less liable to carbonization; besides, they form exhaust gases low in sulphurous and sulphuric

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anhydrides. The viscosity of diesel fuels also standardized to ensure proper atomization and reliable operation of the fuel-supply system. Heavy fractions in the fuel can cause in complete combustion and smokes in exhaust gases and carbonization in the engine.Medium-speed diesel engines can be run heavy distillate fuels and low-speed ones, on fuels obtained by dilution of fuel oils by distillates, including diesel fractions, to obtain the desired viscosity from 36 to 67 mm2/s at 500C]. The setting point of the mixture may be from -5 to 50C.

3. Boiler Oils (fuel oils)Fuel oils are used in many branches of national economy, in particular, at thermal power plants.According to the State Standard GOST 10585-75, fuel oil is graded as follows: marine grades F-5 and F-12 (light fuel), furnace fuel oil grade 40 (medium) and furnace fuel oil grade 100 (heavy fuel). The characteristics of fuel oils may vary appreciably in different grades. For instance, the relative viscosity of fuel oils should be respectively: not more than 5 and 12 mm2/s at 500C for marine grades and 8 and 16 mm2/s at 800C for furnace grades 40 and 100. Fuel oils of a higher viscosity have a higher flash point, which is specified at 80 and 90 for marine grades F-5 and F-12 (in a closed crucible) and at 900 and 1100C (in an open crucible) for furnace grades 40 and 100. The setting point of fuels is limited at -50 to 250C (or up to 42 for fuel oils obtained from high-paraffin petroleum). According to the sulphur content, fuel oils of each grade are divided into low-sulphurous (up to 0.5% S), medium-sulphurous (0.51 to 1.0 per cent), and high- sulphurous (1.01 to 3.5 %).The quality of fuel oils is decided by the following characteristics: viscosity, which determines the ease of transportation of the fuel and the probable degree of heating for effective atomization; setting point, which determines the conditions of storage and application of the fuel at various temperatures of the air; sulphur content, which determines the degree of corrosion of the engine and the exhaust of sulphurous compounds to the atmosphere. One of the decisive characteristics of fuel oils is the heat of combustion

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(calorific value) which depends on their composition. The low calorific value of low-sulphurous and medium-sulphurous fuel oils (recalculated to dry fuel) must be not less than 41454 kJ/kg for furnace grades, 40470 kJ/kg for furnace grade 40, 40530 kJ/kg for furnace grade 100.Fuel oil grades are chosen according to the conditions of operation of engines. Thicker (and cheaper) grades are commonly used at stationary plants where the fuel can be heated up and filtered. Marine grades of fuel oil (employed in marine power plants) differ from furnace grades in having a lower content of ash, water, sulphur and tars.Fuel oils are prepared by mixing residual products of preliminary distillation (residual fuel oil, semigoudron and goudron) with residual products of thermal and some catalytic processes (cracking residue, gasoil, reflux, polymers) and residual products of oil manufacture.

4. Fuels for Jet and Gas-turbine EnginesFuels for aviation jet engines are divided into two main groups: for subsonic and supersonic speeds. The latter must have an elevated density and a sufficiently high calorific value to ensure the required power of the engine and the desired flight range. At higher speeds of flight, fuel is heated much more. Jet-engine fuels (aviation kerosene] are kerosene fractions of preliminary distillation of petroleum having the temperature of the beginning of boiling from 1500 to 1950C and the boiling-off point from 2500 to 3150C. Fuels for jet engines must easily be vaporizable, have a high calorific value (the lowest calorific value being not less than 42950-44 160 kJ/kg], high thermal stability, a low temperature of the beginning of crystallization (not higher than -600C) and cause no corrosion of engine elements. Jet-engine fuels of the highest thermal stability are obtained by catalytic refining in hydrogen under pressure. Gas-turbine fuels for terrestrial machines differ from aviation kerosene by a wider fractional composition and higher content or sulphur (up to 3 %). Their relative viscosity at 500C must be not more than 2.

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Exercises

Answer the following question1. How many group can petroleum products be classed into?

What are they?2. Which group do the liquefied hydrocarbon gases belong to?3. What are the main compositions of liquefied hydrocarbon

gases?4. How many important characteristic have fuels for carburettor

engines got? What are they?5. What can happen if there is a incomplete combustion?6. What is the antiknock rating evaluated?7. What is the octane number of a petroleum product?8. Which kind of hydrocarbons have the higher octane number?9. What do they do to increase the octane number of gasoline?10. What are the limit content of TEL in the grades of motor

gasoline in USSR?11. The winter kind of motor gasoline has a higher pressure of

saturated vapour than the summer, hasn't it?12. In what is the chemical stability of gasoline checked?13. For which fuels is the term cetane number used for?14. What is the cetane number of petroleum products?15. What does cetane number depend on?16. What is the order of increasing the cetane number of

hydrocarbon?17. Which methods are used to raise the cetane number?18. How are fuel oils classified?19. By what is the quality of fuel oils decided?20. What is the decisive characteristic of fuel oils?21. Fuel oil grades are chosen according to the conditions of

operation of engines, aren't they?22. What are the thicker grades commonly used for?23. How do they prepare fuel oils?24. How do they classify fuels for aviation jet engines?25. What are the characteristics of fuel for jet engines?

II. Lubricants, Products of Oil-paraffin Processing and Other Petroleum Products

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In addition to high-quality fuels, lubricating materials are also essential for normal operation of various engines and mechanisms. All lubricants can be divided into four types: gaseous, solid, liquid, and semisolid (thickened), or greases.Some gases can react with metals to form a lubricating film which lowers friction and wear. Solid lubricants, such as graphite or molybdenum disulphide, are employed at very high temperatures and under heavy loads where ordinary lubricants, including oils and greases, are ineffective. In this section, we shall discuss only lubricating oils and greases.

1. Lubricating and other OilsPetroleum processing industry manufactures mineral oils of many kinds: motor oils (aviation, diesel and automobile grades), industrial oils, turbine oils, electroinsulating oils, compressor oils, etc.Viscosity is the most important characteristic of all kinds of oil. On the one hand, it should be sufficiently low to ensure lubrication and easy start of engines at low temperatures and, on the other, sufficiently high to lubricate properly even the hottest parts of an engine. This requirement is met by oils having a high viscosity index. Other important characteristics of oils are their oxidation stability at the elevated temperature, a low setting point (especially for winter grades), good anticorrosive properties, and others.All grades of lubricating oils for modern mechanisms and engines, especially for diesel engines and the like, contain additives which improve their performance. Diesel and automobile oils are made by mixing purified residual and distillate oils.Aviation Oils. These are employed for lubricating of aviation piston engines. They are prepared from goudron residue after distillation of specially selected petroleum grades by deep refining with selective solvents and sometimes by mixing with distillate oils. Aviation engines operate under heavy loads and at high temperatures, so that the oils for them will have a high chemical stability and great lubricating power.

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Industrial Oils. These are intended for lubrication of machines and mechanism of industrial equipment which operate at relatively low temperatures and of pairs of machines and engines not subjected to the effect of steam, hot air or gases. There is no strict scientific classification of industrial oils. They are commonly classified by their viscosity and by the conditions and fields of application. Depending on viscosity, industrial oils are divided into light (3.5-10 mm2/s at 500C), medium (10-58 mm2/s at 500C), and heavy (11-96 mm2/s at 500C). Depending on the conditions of application, they are classed into oils for light and moderate speeds and loads and heavy-duty oils, and by the fields of application, into oils for gear transmissions, slip guides, spindles, instrument oils, break-in oils, and special oils. These grades of oil are prepared by using base oils of selective purification produced from eastern grades of petroleum.Industrial oils should be pressure-and corrosion-resisting, retain their fluidity at the working temperatures, and be stable against foaming and oxidation.Turbine oils. These are used for lubrication of bearings and auxiliary mechanisms of turbomachines (steam and gas turbines, turbocompressors, hydraulic turbines, marine turbines, etc.); they are also used as pressure fluids. Turbine oils without additives are produced by contact acid refining, those with additives are manufactured by selective refining from low-sulphurous and sulphurous grades of petroleum. Additives improve their antioxidizing, deemulsifying, anticorrosive and antifoaming properties. Some grades oils contain antiwear additives. Turbine oils must have a high chemical stability and separate easily from water which enters occasionally the lubrication system.Insulating oils. Oils are liquid dielectrics and therefore can be used for insulation of current-conducting elements of electric equipment (transformers, capacitors, cables, etc.). Insulating oils also serve for removing heat and favour quick are extinction between electric contacts. This group of oils includes transformer, capacitor and cable oils.Transformer oils have found the widest application in the group. They are intended for long operation at 70-80 0C in the

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atmosphere of air and for that reason should possess a very high chemical stability and should not form low- molecular acids on oxidation. Besides, transformer oils should naturally have dielectric characteristics. Most grades of transformer oils have a viscosity of not more than 9 mm2/s at 50 0C, exceptions being grade ATM-65, arctic transformer oil, with a viscosity of not more than 3.5 mm2/s at 50 0C and grade T-1500 (for equipment of transmission lines for 1500kV) whose viscosity is limited at 8 mm2/s at 50 0C. Transformer oils cannot be replaced by other kinds of oil.Compressor oils. These oils serve for lubrication of cylinders, valves and piston rods of compressor operating at temperatures of 200-2500C and pressures of 20-25 Mpa. The main requirement to compressor oils is that they should have an appropriate oxidation stability. Compressor oil grade 12 M, of a kinematic viscosity of 11-14 mm2/s at 100C, is intended for single-stage horizontal and vertical compressors for a pressures 0.7-0.8 MPa and for two-stage compressor for an average pressure up to 5 Mpa. Compressor oil grade 19T, of a kinematic viscosity of 17-21 mm2/s at 1000C, is employed in multi-stage high-pressure compressors (for 20-30 MPa). The oxidation stability of these oils is ensured by deep refining.Oils for steam engines. They are divided into two main groups: for saturated-steam and for superheated-steam machines. These oils are distinguished by a low evaporability and a high viscosity (the kinematic viscosity at 1000C is 9-13 mm2/s for cylinder oil grade 2 and 44-64 mm2/s for grade 52 vapour oil). Cylinder oils of the first group are prepared from distillates and those of the second group, from residues by deasphalting with propane or by distillation of goudron in high vacuum.Synthetic oils. These oils are essentially organic or elementoorganic compounds [containing silicon, iron, etc.] and are intended for heavy-duty applications.

2. Paraffine, ceresins and petroleum

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Paraffins. These are soft [liquid] or solid petroleum products of crystalline structure obtained from distillates of paraffinic and high- paraffinic grades of petroleum.Solid petroleum paraffins are crystalline products of white to bright- brown colour, depending on the amount of oil. The oil content in paraffins may vary within 0.8-0.5 per cent for high- purified grades and up to 2.2-2.3 and even 5 per cent for other grades. Special grades of paraffine are manufactured in the USSR for application in food industry. They are obtained by deep refining of raw paraffins and employed mainly for impregnation of packing materials either contacting loose fry foodstuffs [grade P-2 with the oil content up to 0.9 per cent by mass] or non-contacting [grade P-3, oil content up to 2.3 per cent by mass]. Paraffin grade P-1 [oil content up to 0.5 per cent by mass] is used for the same purposes as grade P-2, and also in candy industry.The fusion point of paraffin grades P-1, P-2, P-3 is respectively 54, 52 and 500C.Ceresins. Ceresin is mixture of solid hydrocarbons obtained in processing and refining of ozokerite, unpurified petroleum ceresin or their mixtures. Ceresins are used for making greases, wax alloys, insulating material, etc.The most important characteristic of cerecins is the dropping point, 0C. According to the state standard GOST 2488-73, the dropping point is the basis of grading of ceresins [the grade of ceresin manufactured in the USSR are disignated respectively 80, 75, 67 and 57]. The volume resistivity at 1000C is specified only for grade 80 ceresin: it should be not less than 1*1012 ohm cm.Synthetic high-fusion ceresin has the highest dropping point. It is a mixture of solid hydrocarbons of the methane series, mostly of normal structure, which are obtained by synthesis of carbon monoxide and hydrogen [Fisher-tropsch process ]. According to the state GOST 7658-74, the dropping point of this of ceresin must be not less than 1000C and the volume resistivity at 1000C, not less than 1014 ohm cm.

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Medical [liquefied] Petrolatum. This product is obtained by fusion of ceresin, paraffin, purified petrolatum or their mixtures with petroleum oil. Its dropping point is 37-500C.Capacitor Petrolatum. It is employed for filling in and imprenating of capacitors. Its kinematic viscosity at 600C must be at least 28 mm2/s. An important specified characteristic of this product is the volume resistivity, which must be at least 1*1012 ohm cm at 1000C.

Exercises

Answer the following question1. How many type can lubricants be divided? What are they?2. What are the effects of lubricants?3. Viscosity is the most important characteristic of all kinds of

lubricant, isn't it?4. Which properties must the viscosity of lubricating oils must be

have?5. What are the characteristics of lubricating oils?6. What are the purposes of aviation oils?7. What are the characteristics of aviation oils?8. How can industrial oils be classified?9. How can additive type for industrial oils be prepared?10. What are the properties of industrial oils?11. What are turbine oils used for?12. What are insulating oils include?13. Which grade of insulation oil have the widest application?14. What are the applications of compressor oils?15. How can they prepare the cylinder oils for steam engines?16. What are the applications of the solid petroleum paraffins?17. What is ceresin?18. What is ceresin used for?19. The most important characteristic of ceresin is the dropping

point, isn't it?20. How can they prepare medical petrolatum?21. What is capacitor petrolatum?

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II Miscellaneous Petroleum ProductsGreases. Grease is a thick salvelike product consisting of oil and a thickener. Various soaps [calcium- sodium, aluminium, lithium, barium, etc.] are commonly used as thickeners. Greases thickened by hydrocarbon components [ceresin, paraffin or petrolatum] are mainly employed for protective coatings. They are physically and chemically stable, but their operating range is limited to temperatures of 50-600C. Special greases are also produced, in which various compounds are used instead of oil as a liquid base.Greases are employed in cases where mineral oils cannot ensure proper lubrication of machines and mechanism, and also for tightening gaps. Greases are often used as slushing compounds; they protect mechanisms against corrosion during storage and then can serve as lubricants in operation.Petroleum Bitumens. Bitumens are usually obtained by oxidation of goudrons from heavy tarry grades of petroleum, and also by mixing with asphalt, extracts of oil manufacture and asphaltile. The main characteristics of bitumens are; [needle] penetration, ductility, and softening temperature which characterizes the thermal stability of bitumen. The penetration and ductility at low temperature determine, in combination, the capacity of bitumen to retain its elasticity.Petroleum bitumens are mainly used in road construction. Dirt and gravel roads are sometimes impregnated by liquid bitumen obtained by dilution of bitumen with a less viscous petroleum product, such as fuel oil. Some special grades of bitumen are made for application in civil engineering and for manufacture of paints and varnishes, electroinsulating materials, etc.Petroleum acids and their sails. Petroleum acids, mainly naphtenic, are present in some grades of petroleum. They are separated during alkali refining of fuel and oil distillates as sodium salts [soaps] and employed for manufacture of naphtenate soap, acidol and acidol- naphtenate soap. Naphtenate soap [contain 43 per cent of petroleum acids] is a mixture of sodium soaps of petroleum acids, mineral oil and water. Acidol [contains 42- 50 per cent of petroleum acids] consists of petroleum acids with an admixture of mineral oil. Acidol - naphtalenate soap [67-70 per

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cent of petroleum acids] is a mixture of free naphtenic acids and their sodium soaps. All these products are employed as substitutes of fats in manufacture of industrial soaps, since they possess high emulsifying and foaming properties. They are also used in the textile industry for dyeing, for wood impregnation, as drying agents in paints and for some other purposes. A general requirement to these products is that the content of mineral oil be not above a specified limit.Solvents. The paint- and- varnish industry uses most widely gasoline [fraction 45-1700C], while spirit [fraction 165-2000C], and solvent naphtha [mixture of xylenes] as solvents. In the food industry, the commonest solvents are extraction gasoline [fraction 70-950C] and petroleum ether [fractions 40-700C and 70-1000C]. In other industries, these and some other solvents [including benzene] can be employed. All solvents are specified for the content of benzene and unsaturated hydrocarbons and sulphur compounds.Solvents are usually obtained from accompanying petroleum gases and low- sulphurous petroleum and in gas fractionation, preliminary distillation of petroleum and in catalytic reforming [from refining products]. The desired fraction in sometimes separated in deep- distillation plants. In many cases, the fractions obtained are specially purified [mostly to minimize the content of benzene hydrocarbons and sulphur compounds].Domestic [illumination] kerosene. Domestic kerosene is obtained by straight- run distillation of petroleum. It should have a specified composition to ensure normal burning [mostly paraffin hydrocarbons], burn without forming fly ash [the height of non- smoky flame should be not less than 20 mm], and have an appropriate brightness of flame.Coke. This is a product of petroleum coking, used for making electrodes, abrasives and some other materials and as a solid fuel. Electrode coke has the highest industrial significance for electrolytic manufacture of aluminium and making of artificial graphites which are used as antifriction materials in mechanical engineering.

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Commercial carbon [carbon black]. This is an amorphous substance usually in the form of a powder with black spherical particles 30-40 m in diameter. Commercial carbon may be named channel black or furnace black depending on the method of manufacture. It is employed as a filler in the rubber and paint and varnish industry and as a dyer in the manufacture of printing ink, ebonite, electrodes, etc. The principal standardized characteristics of carbon black are as follows; adsorption, dispersion, colouring power, absence of foreign inclusions, uniform distribution [in rubber mixtures], and fractional composition.At petroleum-processing plants, carbon black can be made from gases, green oil [obtained in pyrolysis of kerosene -solar oil fractions], coke residue [from coking plants], gas oil of catalytic cracking, and extracts of oil processing [more often after thermal treatment in cracking plants], coal tar pitch, and aromatized extracts from gas oil of secondary processes.Softeners. Residual products of straight run distillation of petroleum ['softener' fuel oil], shale oil, and some products of oil processing can be used as softeners. They are employed in the rubber industry and as softeners of rubber mixtures in rubber regeneration.

Exercises

Answer the following question1. What is the composition of grease?2. What are the characteristics of grease?3. What are grease employed?4. How is bitumen prepared?5. What are the main characteristic of bituments?6. What is the main application of petroleum bituments?7. What are other applications of petroleum bituments?8. What is the main application of product of petroleum acids?9. What are other applications of product of petroleum acids?10. Which products of petroleum are used as solvents ?11. In which industries are solvents used?12. How are solvents obtained?13. How is domestic kerosene obtained?

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14. Which properties that flame of domestic kerosene should have?

15. What is coke used for?16. How many is the dimension of particles of commercial

carbon?17. What is commercial carbon used for?18. What are the principal standardized characteristic of

commercial carbon?19. What are softeners used for?

IV. Products of petrochemical and basic organic synthesis.The industry of basic organic and petrochemical synthesis is a link between petroleum processing and chemical- recovery coke industries and all other branches of organic synthesis. It provides the latter with the required starting materials - organic products and, besides, supplies national economy with many valuable final products. Very many products of basic organic and petrochemical synthesis are intermediate, rather than end products. These include, in particular, many organic compounds of chlorine in which chlorine atoms can be substituted by other or groups of atoms.Starting substances for polymer materials. Their manufacture plays an important part in basic organic synthesis and petrochemical synthesis. It provides starting materials for the manufacture of plastics, synthetic rubber, synthetic lacquers, glues, film materials, fibres, etc. Polymer materials are now made in hundreds of kinds having various properties and diverse applications. The most important among them are polyethylene, polystyrene, polyvinyl chloride, polypropylene, and synthetic

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rubbers. Many of them are used as starting materials for manufacture of commercial goods. For instance, various rubber articles, including tyres, are made from synthetic rubbers; many articles made from polyethylene and polypropylene can successfully replace non - ferrous metals, etc.Plastifiers and other auxiliary substances for polymer materials. Along with the basic materials for manufacture of synthetic polymers, plastifiers and various auxiliary materials are also of large importance: they either facilitate the process of synthesis or improve the properties of final products. For instance, plastifiers [softeners] are added [in an amount of up to 30-40 per cent] to certain polymers [especially to synthetic rubbers and polyvinyl chloride] to improve the plastic and elastic characteristics of these materials.Among various types of plastifiers, one of the most important groups includes high - boiling esters [dibutyl phthalate, dioctyl phthalate, tricresyl phthalate] and some esters of higher alcohols and dicarboxylic acids and of higher carboxylic acids and diatomic alcohols. Softeners obtained at petroleum processing plants are used in the manufacture of synthetic rubbers. Other auxiliary substances used in polymer technology [and in other processes] include initiators, catalysts, inhibitors, regulators, etc.Synthetic surfactants and detergents. Surfactants and detergents are used very widely in domestic life as powders and liquids for washing and cleaning. These substances are distinguished by a combination of hydrophobic and hydrophilic groups in the molecule. During washing, this facilitates wetting of the fabric and passage of dirt to the washing water. All surfactants and detergents are divided into ionogetic and non- ionogenic, depending on the presence or absence of groups capable of dissociating in aqueous solutions. Ionogenic substances, in turn, may be either anion- or cation- active, with their surface- active properties being determined respectively by anions or cations.Most of anion- active surfactants are sodium salts of sulfonic acids and acid esters of sulphuric acid, in particular, [1] alkylarylsulfonates with a C10- C15 alkyl group; [2] alkylsulfonates

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with 12-18 carbon atoms; and alkylsulphates with an alkyl group roughly of the same length:p-RC6H4SO2ONa R SO2ONa ROSO2ONaIn recent time, non- ionogenic substances have found a wide use. They are synthesized from ethylene oxide and various organic compounds- carboxylic acids, alcohols, amines, etc. having active hydrogen atoms. Their hydrophilic properties are due to a [CH2CH

2O]n chain obtained by successive attachment of molecules of ethylene oxide: RO-[CH2CH 2O]n-H. In order to improve their washing ability and lower the consumption, detergent substances might be mixed with various additives and these compositions are called washing means [in contrast to washing substances, or detergents, proper]. Such compositions [for instance, washing powders] contain sodium phosphate, pyrophosphate and hexamethaphosphate, sodium silicate, sulphate, carbonate, etc.Synthetic fuels, lubricants and additives. This group includes synthetic motor and let fuels, lubricating oils, additives, antifreezing agents, braking and pressure fluids.Solvent and extractive agents. Synthetic solvents and extractive agents may belong to various groups of organic compound: chlorine derivatives, ancohols, cellosolves, ethers, ketones, esters, etc.Miscellaneous products. These include insecticides, medicaments and explosives.

Exercises

Answer the following question1. What are the products of petrochemical and basic organic

synthesis?2. Most of products of petrochemical and basic organic synthesis

are intermediate, aren't they?3. Why does the manufacture of polymer materials play an

important part in basic organic and petroleum synthesis?4. What are the most important polymer materials?5. What are polymer materials used for?6. What are the effects of plastifiers and other auxiliary

substances in manufacture of synthetic polymers?

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7. For what are auxiliary substances used?8. What is the structure of the molecules of surfactants and

detergents?9. What is the difference between ionogenic and non- ionogenic

substances?10. How are the hydrophilic properties of non- ionogenisc

substances obtained?11. What should we do to improve the washing ability and to

lower the consumption?

Text 22

Distillation

The property that differentiates most petroleum products from each other is "volatility", or tendency to vaporize. More volatile products are called "lighter", less volatile products, "heavier". The volatility of a product is determined, of course, by the boiling points of its components. Inasmuch as distillation separates liquid by boiling points, distillation is the principal separation process.

Theory of DistillationThe basic principle of distillation is simple. When a solution is boiled, the lighter components vaporize preferentially and the solution is separated into a lighter overhead product and a heavier residue. For most petroleum applications, this simple operation does not suffice, and multistage units must be employed. Such units consist of cylindrical columns, or "towers", through which vapour and liquid streams pass countercurrently. Depending upon circumstances, feed may be charged at any point in the column. Products are withdrawn from the top and bottom and sometimes from intermediate points as well. Liquid withdrawn from the bottom is usually reboiled to supply vapours to the column; vapours from the top are condensed and a portion is returned as

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'"reflux". It seem paradoxical to build complex and expensive equipment to separate out an overhead product and then to return part of it to the separation zone. Indeed, many of technologists of the time considered refluxing foolish when it was first introduced. We may conclude from this that the function of reflux is somewhat obscure. Why it is used in multistage unit can best be illustrated by analogy with singlestage operations.Staging. Consider a singlestage distillation system in which a solution is heated until half of it vaporizes, the vapour being separated from the liquid and condensed. Suppose that a two-component solution is processed in this system to concentrate the lighter component in the overhead fraction. Suppose further that the desired concentration is not attained. A more concentrated product could be obtained by charging the overhead to a second unit, and this procedure could be repeated until the desired concentration was obtained. Similarly, the heavier component could be concentrated in the bottoms cut by reprocessing successive residues. In either case, the yield of the desired product would be low. and large amounts of intermediate materials would be made. Yields could be improved by returning each intermediate material with the next charge to the preceding stage. By this means, all the original charge would be recovered ultimately in one or the other of the desired products. Such an operation is diagrammed in Fig. 1a; each stage in this diagram includes equipment to vaporize a portion of the charge and to condense the vapours. Although the indicated operation is possible, equipment would be complex and expensive, and labour and energy requirements would be high. The equipment could be simplified somewhat by converting each batch stage to continuous operation as shown in Fig. 1b, but the equipment would still be complex and the operation expensive. The next step is to eliminate vaporization and condensation equipment from the intermediate steps by permitting the vapour from each stage to pass directly into the stage above, where it mixes with the liquid from the next higher stage; the contained heat in the vapour substitutes for indirect heating of the liquid. Now all that remains

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is to house all the intermediate steps in a single column, and we have the modern distillation unit shown in Fig. 1c.

Column Sections. The part of the column above the feed inlet is called the "rectifying section", and the part below it is called the "stripping section". The two sections have different purposes. One serves to increase the purity of a product; the other increases its recovery. In Fig. 1a, for example, stages 2, 4, and 6, which correspond to the rectifying section, increase the purity of the light product taken overhead. The liquid leaving stage 1 contains a considerable amount of the light component, and steps 3, 5, and 7, which correspond to the stripping section, strip the light component out and thereby improve its recovery in the overhead. For the heavy product, the functions of the two sections are reversed; the rectifying section improves recovery, the stripping section, purity. In some applications only one or the other of these two sections is required, depending upon the particular purity and recovery requirements of the operation.

Extractive and Azeotropic DistillationBecause distillation separates by virtue of differences in volatility, distillation can not normally be used to separate close- boiling materials. However, when the materials to be separated are chemically dissimilar, modified distillation procedures can be used. Examples are the separation of butenes from butanes and of toluene from isooctane. In such cases; an extraneous liquid can be

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added which has an affinity for one of the components in the charge; as a result the relative volatilities of the original components change, and separation becomes possible. If the added material is less volatile than the original components, it is added at the top of the column and withdrawn from the bottom, and the operation is called extractive distillation. If the added material is more volatile than the original components, it is added at the top of the column or with the feed and is withdrawn in the overhead product; the operation is then called azeotropic distillation.Solvents and Entrainers. In extractive distillation, the extraneous liquid is called a solvent; in azeotropic distillation, it is called entrainer. In either case, its effectiveness is determined by its concentration in the liquid phase. Consequently, the boiling point of an entrainer is limited; it must be about as volatile as the lighter feed components so that it will pass overhead, but it must not be so volatile that it will disappear from the downflowing liquid stream much above the bottom of the tower. An entrainer must be separable, of course, from the overhead product- by distillation or by some other technique. Similarly, a solvent in extractive distillation must be separable from the bottoms product. How the entrainer or the solvent is separated from the overhead or bottoms product is an important consideration, because large volumes must be used. To be effective in changing the relative volatilities of the original components, an entrainer or a solvent must constitute at least 40% of the liquid phase [60], and its concentration is usually much higher.Effects of Reflux. In extractive distillation, reflux has two opposing effects. By increasing the counterflow of liquid and vapor, increasing the reflux promotes the separation. However, increasing the reflux lowers the concentration of the solvent in the liquid streams; this lessens its effect in spreading the volatilities of the original feed components and thus retards their separation. Because of these conflicting effects, there is apt to be sharp optimum in the reflux rate for an extractive distillation operation.Feed Preparation. Only narrow-boiling materials are charged to extractive or azeotropic distillation. The reason may be seen most

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readily from an example. Consider extractive distillation for the separation of toluene from a mixture with isooctane, which normally boil very closely to toluene. Lower- boiling materials [like hexane and benzene] and higher - boiling materials [like isononanes] are first separated by ordinary distillation. The sharpness of removing the light ends affects only the amount of material charged to extractive distillation. On the other hand, the purity of the toluene product will depend upon the sharpness of prefactionating the heavy ends out of the feed.How poor removal of heavy ends affects product purity may be seen by considering the normal volatilities of the feed components and how they are affected by the presence of a solvent. Toluene and isooctane boil together, and isononanes are about half as volatile. In the concentration usually employed, a solvent approximately doubles the volatilities of the paraffins relative to toluene. In the presence of the solvent, then, the isononanes have about the same volatility as toluene, and their separation is very difficult, and sometimes impossible.Even when heavy materials can be taken overhead in extractive distillation, they may be very undesirable in the feed. When phenol is used as the solvent, for example, volatility relationships are such that heavy paraffins in the overhead tend to carry some phenol with them. Phenol is expensive, and only small losses can be tolerated.

Exercises

Answer the following question1. What is the principle of distillation?2. What are the distilling towers?3. Where can they withdraw product of distillation?4. What is reflux?5. What do they do to increase the pure of products?6. What are the rectifying section and stripping section?7. What are the purposes of them?8. When must they add the extraneous liquid in distillation?9. What is the extractive distillation?10. What is the azeotropic distillation?

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11. What are a solvent and an entrainer?12. What is the boiling point of entrainer like?13. What are the important characteristics of solvent and

entrainer?14. Which materials are used in extractive or azeotropic

distillation?

Text 23

Thermal processes. Thermal cracking

Thermal processes At high temperatures, the bonds between atoms in molecules of hydrocarbons are weakened and can break to form new compounds. In any homologous series, lighter [low-boiling] hydrocarbons split less easily than high-boiling ones. Along with splitting into lighter hydrocarbons, other transformations can take place, in particular, packing of molecules in which heavier fractions from preliminary petroleum processing are decomposed at elevated temperatures are call thermal processes. In petroleum processing industry, the most common processes of this type are thermal cracking, coking, and pyrolysis.

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Thermal cracking, usually carried out at pressures up to 5 MPa and temperatures of 420-550 0C, is a process in which the starting material is changed qualitatively with the formation of new compounds having different physicochemical properties. Depending on the composition of the starting material and the process conditions, the yield of gasoline cracking is 7-30 % of the mass of the starting material; the process also gives some other products: gaseous, liquid and solid [coke].Coking of residue is done at temperatures of 445-5600C [still coking] or 485-5400C. Depending on the quality of the starting material and the type and conditions of the process, it may yield 15-18 % of commercial coke, 49-77.5 % of liquid products [including 7-17 % of gasoline fractions] and 5-12 % of gases [up to C4].Pylolysis of distillates and light hydrocarbons [from ethane to butane] is usually effected at 650-8500C. The main object of pyrolysis is to produce ethylene and propylene; earlier, it was aimed at producing aromatic [benzene] hydrocarbons.In 1930-1950's, pyrolysis played an important part as a method for increasing the manufacture of gasolines for carburettor engines. At a later time, the quality of gasolines produced in thermal cracking plants could no more satisfy the rising requirements of consumers. Upon development of catalytic processes, thermal cracking still retains its role mainly for the manufacture of low-viscous fuel oils from residue products of preliminary petroleum processing , and also of gas oils intermediate products for making carbon black. The processes of coking are being developed further, mainly to satisfy the demands for coke, especially electrode coke. Liquid products of coking are utilized for increasing production of white petroleum products. Pyrolysis is being developed rapidly in association with increasing demands for olefin materials for the chemical and petrochemical industries.

Thermal Cracking In 1890, V.G. Shukhov, a famous Russian scientist, designed the first cracking plant for producing light petroleum products from fuel oil. Later, as the need for automobile gasoline increased, a

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system with reaction chambers was developed, in which the starting material, preheated to the reaction temperature in the furnace coil, was retained and subjected to cracking up to the formation of coke. The time of filling of the reactor with coke determined the length of the whole working cycle of the plant. At a later time, the reaction chamber was replaced by the reaction volume formed in radiant pipes of a furnace. To prevent the clogging of the apparatus with coke, the reaction products were chilled at the exit from the furnace by the cold starting material [quench] which stopped the cracking process [in particular, Winker-Koch plants operated by this principle]. In later years, further improvements have been made in thermal cracking in foreign countries and in the USSA where the process was implemented in 1927-28.As has been given earlier, the principal reaction of thermal cracking is the decomposition [or cracking ] reaction. Among various hydrocarbons, paraffins can be cracked most easily. Then follow naphthenic hydrocarbons. Benzene hydrocarbons are most stable against cracking. In any homologous series, hydrocarbons of a higher molecular mass are cracked more readily. Thus heavier fraction of petroleum products are less stable and can be cracked more easily than lighter ones. Brief data on the chemistry and mechanisms of cracking of the principal classes of hydrocarbons will be given below.Paraffin hydrocarbons. Cracking of commercial paraffins which consist mainly of C24H50, C25H52 and C26H54 hydrocarbons forms paraffin hydrocarbons and olefins composed of 12, 13, or 14 carbon atoms, i.e. roughly one-half of the carbon atoms in the original paraffin. This is an indication of that the breakdown of C-C bonds in cracking of paraffins of high molecular mass occurs in the middle of a molecule. The new paraffin hydrocarbons formed by cracking can in turn break down into simpler molecules say a molecule of a paraffin hydrocarbon and that of an olefin, for instance: 4250C C12H26 C6H14 + C6H12 dodecan hexane hexene

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[paraffinic] [paraffinic] [olefinic]At higher temperatures of cracking of paraffinic hydrocarbons, reactions in which the breakdown of molecules occurs at the end portion of the chain begin to prevail over those in which molecules break in the middle. The larger fragment of a broken molecule is an olefin and the smaller one is the paraffinic hydrocarbon [gaseous] or hydrogen. Isoparaffinic hydrocarbons are thermally less stable than those of the normal structure. The rate of the reaction at a given temperature increases almost linearly with the molecular mass. This is true of all groups of hydrocarbons.Olefinic Hydrocarbons. These are the principal ones among all unsaturated hydrocarbons produced by cracking. They prevail as gaseous compounds [from ethylene C2H4 to butylene C4H8] and liquid ones [from amylenes C5H10 to pentadecenes C15H30]. Cyclic olefins and diolefins form in relatively small quantities. In contrast to paraffinic hydrocarbons, olefins undergo appreciably more diverse primary reactions during cracking, the most important among them being polymerization reactions [i.e. combination of a few molecules into a single molecule] and depolymerization reactions, especially at an early stage of the process . Polymerization is the main reaction at moderately high and high pressures; it can occur not only between like molecules, but also between unlike molecules of olefins, for instance: C2H4 + C3H6 C5H10

At later stages of the process, olefins are dehydrogenated partially and form diolefins, which typically have two double bonds, and hydrogen or split into diolefins and paraffinic hydrocarbons: CH3- CH2- CH= CH2 CH2= CH- CH= CH2 + H2 butylene divinyl [olefin] [diolefin]Secondary reactions between olefins and diolefins may give cycloolefins which are present in cracking products in very small quantities. Olefins can transform into cyclic hydrocarbons [naththenes]:

n-hexene -1 cyclohexaneNaphthenic hydrocarbons. The main reaction in cracking of these hydrocarbons are dealkylation [splitting of paraffinic side

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chains] and dehydrogenation of hexacyclic naphthenic hydrocarbons into benzene hydrocarbons; the two reaction can occur simultaneously.Dehydrogenation of hexacyclic naphthenes in thermal cracking with the formation of benzene hydrocarbons is of minor importance. Owing to the dealkylation reaction taking place in thermal cracking, naphthenic and benzene hydrocarbons loss most of their long side chains. Paraffinic side chains in turn break to form gaseous and low-boiling paraffinic hydrocarbons and olefins. In high-temperature processes, naphthenic rings can break; the result is that hydrocarbons lose their cyclic structure and that polycyclic structures are partially decycled [if they had several rings]. In that case, paraffinic, olefinic and naphthenic hydrocarbons form.Benzene Hydrocarbons. These are obtained by dehydrogenation of the cycloolefins or naphthenes which were formed at earlier stages of the process. Benzene hydrocarbons are quite stable at high temperatures, especially benzene, toluene and xylenes. The main reaction in cracking of benzene hydrocarbons with alkyl chains are dealkylation and condensation. Condensation may occur between the molecules of benzene hydrocarbons [or some other unsaturated hydrocarbons]. This gives polycyclic benzene hydrocarbons which can condense further to asphaltenes and coke.Sulphur compounds. They are decomposed in cracking and form hydrogen sulphide. Cyclic sulphur-organic compounds, such as thiophene and thiophane, have the greatest stability against decomposition. Hydrogen sulphide and elemental sulphur [as the product of oxidation of hydrogen sulphide] which form in cracking of sulphurous petroleum grades can cause strong corrosion of process equipment.Inert tars and asphaltenes. These may contain various heterocyclic compounds [usually including oxygen, sulphur, nitrogen and some metals]. In cracking they form gases, liquid products and large amount of coke. The yield of coke in cracking of asphaltenes may reach 60% and that in cracking of tars 7-20% [depending on the molecular mass of tars].

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Since the starting materials for industrial thermal cracking are usually mixtures of many hydrocarbons of complicated structure, many reaction can occur simultaneously and the mechanism of thermal cracking can not be explained in detail. It is assumed however, that most reaction of thermal cracking can be described by the theory of formation of free radicals.

Exercises

Answer the following question1. What are thermal processes ?2. What are the most common processes of thermal processes ?3. What are the products of thermal cracking ?4. What are the products of coking?5. What are the products of pyrolysis?6. Who designed the first cracking plant?7. Which type of hydrocarbon can be cracked most easily?8. Which C-C bonds are broken down in cracking of high paraffins

at lower temperature ?9. Which C-C bonds are broken down in cracking of high paraffins

at higher temperature ?10. What are the products of cracking of high molecular mass

paraffins at higher temperature ?11. Which relationship is there between the rate of a reaction

and its temperature?12. What are the primary reaction of olefins in thermal cracking

condition?13. What are the secondary reaction of olefins in thermal

cracking condition?14. Which reactions happen with naphthenic hydrocarbons in

thermal cracking condition?15. Why are gaseous, low-boiling parafinic hydrocarbons and

olefins formed in thermal cracking of naphthenic hydrocarbons ?

16. What are the main reactions of benzene hydrocarbons ?17. Which compounds can be obtained in cracking of benzene

hydrocarbons ?18. Which sulphurous compounds are formed in cracking ?

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19. What is the main product in cracking of tars and asphaltenes?

20. What is the main mechanism of thermal cracking ?

Text 24

Catalytic processes

A typical feature of catalytic processes is the use of catalysts, i.e. substances which can accelerate [or decelerate] the reactions and cause the formation of new hydrocarbons and other substances not present in the starting material. Catalytic processes occur under softer conditions [at lower temperatures and pressures] than thermal ones, but may involve the reactions which are impossible in purely thermal processes.A catalyst usually consists of an active substance [which determines the course of desirable reactions] applied onto a carrier substance [mostly alumina] having a largely extended surface. In some cases, some other substances [promptors] are added to improve characteristics of catalytic process. The particles [granules] of catalytic process an enormous porosity and therefore a very large internal surface area. The activity of a catalyst is due mainly to the surface of pores rather than to their external surface. The name of a catalyst depends on the process where it is to be used, for instance, reforming catalysts, cracking catalysts, etc.The technico-economical characteristics of a catalytic process are determined by the quality of the starting material and the process conditions, as well as by the properties of the catalyst used. The capability of a catalyst to accelerate the rate of desirable reactions and retain the rate of unwanted ones at a constant low level is called selectivity. Activity is another important characteristic of

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catalysts; it is estimated in terms of the yield of the end product relative to the use of the starting material. In particular, the catalyst activity in catalytic cracking is determined as the yield of gasoline [end product].Catalysts can participate in process reactions in a stationary [fixed-bed] or moving [circulating] state. In both cases, they gradually lose their activity and selectivity owing to ageing. This may be call normal ageing, it is unavoidable and can only be accelerated under more rigid process conditions. Along with normal ageing of a catalyst may also take place. This occurs often when the process is run under abnormal conditions, say, at an excessively high temperature. Many catalysts can be affected by certain substances containing sulphur, nitrogen and heavy metals [V, Ni, and other] and by water in the starting material.Catalysts can be regenerated to restore their activity and partially, the selectivity, which is usually done by removal [burning-off] of the coke deposits settled on catalyst particles during operation. By another method, the properties of catalysts [especially of fixed-bed type] are restored by gradually raising the temperature in the reactor. With circulating catalysts, a fresh catalyst is added in portions to compensate for the loss of the catalyst in the system.Catalyst processes make it possible to remove unwanted impurities, for instance, sulphurous compounds, and to convert certain hydrocarbons into the products which cannot be obtained by preliminary distillation of petroleum or in thermal processes.

Brief Description of Catalyst processesCatalytic cracking is the process of conversion of high-boiling petroleum fractions into high-octane base components of aviation and automobile gasolines and middle distillates.Industrial processes of catalytic cracking are based on contacting the starting material with an active catalyst under appropriate conditions to convert a considerable portion of the material into gasoline and other light products. In cracking reactions, carbon deposits form on the particles of the catalyst and thus reduce sharply the activity, in particular, the cracking ability. The activity of the catalyst is restored by burning off the carbon precipitates [usually called coke] in air.

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There exist many types and systems of catalyst cracking plants, those with circulating flow of the catalyst, especially in a fluidized bed, being most popular.Catalytic reforming is employed widely to obtain high-octane gasolines from low-octane gasoline fractions. Reforming of gasoline or gasoline fractions in combination with various methods of separation of benzene hydrocarbons, for instance, with solvent extraction, make it possible to produce benzene hydrocarbons [benzene, toluene, xylenes and higher aromatics] for the petrochemical and chemical industries.Catalytic reforming processes are based on contacting the starting material with an active catalyst usually containing platinum. The yield of reformate may vary within 63 to 85 % of the mass of the starting material. The catalyst is regenerated periodically to restore its activity. A feature of importance is that the catalytic reforming occurs in a medium of hydrogen-containing gas at high temperatures and pressures. The hydrogen formed in various reactions of reforming is removed from the system as an excess of hydrogen-containing gas. The high content of hydrogen is the gas mixture [up to 80% by volume] makes it possible to utilize it in hydrogenation processes, in particular, for hydrofining of diesel fuels.Hydrogenation processes occur in the medium of hydrogen at elevated temperatures and pressures. They can be used for preparing high-quality products from sulphurous and high-sulphurous petroleum grades, the yields and quality of these products being varied depending on the degree of destruction and the prevailing reactions. Among the processes of this kind, hydrofining of various fractions and products is most important.Hydrofining of petroleum distillates and products is one of the most popular catalytic processes, especially for treating sulphurous and high-sulphurous petroleum grades. The process is carried out in a hydrogen medium at a pressure of 3-5 MPa. The main object of hidrofining of petroleum distillates and products is to reduce the content of sulphur and other harmful compounds in them. These substances are destructed in the process, and the

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destruction products [hydrogen sulphide and ammonia] are removed from the system with gases.Hydrofining processes are based on contacting petroleum distillates and products with a fixed-bed or circulating catalyst , usually alumina-cobalt-molybdena or alumina-nikel-molybdena. The process takes place in the medium of hydrogen at elevated temperatures and pressures so as to convert 95-99% of the starting material into the refined product or distillate [hydrogenate]. Minor quantities of gasoline, hydrogen sulphide and ammonia also form in the process.Alkylation is a process by which isoparaffinic hydrocarbons are combined with olefins to form higher-boiling isoparaffinic hydrocarbons which can be used as high-octane components in aviation and automobile gasolines. Other kind of alkylation are also in use, in particular, alkylation of benzene hydrocarbons by olefins [for instance, alkylation of benzene by ethylene to make ethylbenzene or alkylation of benzene by propylene to make iospropylbenzene].Up to quite recently, catalyst alkylation of isobutane was carried out by butylenes in the presence of sulphuric or hydrofluoric acid as a catalyst. In modern plants, alkylation of isobutane is done by using the materials containing ethylene, propylene and even amylenes, as well as butylenes.Alkylation processes may differ in the starting material, catalysts, productivity, and especially in the design of catalyst plants. With the use of sulphuric acid as a catalyst, the alkylation process is characterized by a low temperature of the reaction and the necessity to maintain a high concentration of isobutane and olefins in the reaction zone. The total yield of alkylate from olefinic starting materials is 1.5-1.8 units per unit volume of the starting material, depending on the quality of the material and the process conditions. The significance and scope of alkylation increase with the rising production of high- octane automobile gasolines having a low content of TEL.Isomerization is the process of conversion of relatively low-octane paraffinic hydrocarbons [mostly C5-C6 and their mixtures] into corresponding isoparaffinic hydrocarbons having a high

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octane number. In industrial isomerization plants using various catalysts, including alumo-platinum ones, the yield of isomerizates attains 97%. The process of isomerization takes place in a hydrogen atmosphere. As in other processes, the catalyst is regenerated peridically.Isomerizates are used together with alkylates for preparation of high-quality gasolines, by compounding them with high-aromatic gasolines of catalytic cracking and reforming.Novel catalyst processes, in particular disproportionation. are being paid much attention now. The process is based on converting two molecules of a hydrocarbon into two unlike molecules, one having by one carbon atom more and the other, by one atom less than the original molecules, for instance:

2C3H6 C2H4 + C4H8 The process is carried out at 66-2600C and a pressure of 1.4-4.1 MPa, with the starting material being supplied at a high rate [10 to 100 h -1]. Disproportional takes place with a high selectivity: the total yield of ethylene and butylenes attains 97% of the propylene converted and the degree of conversion of the latter, up to 45%. Disproportionation can be employed for making benzene from toluene [2C7H8 C6H6 + C8H8 ] to replace the less efficient process of toluene alkylation.In industrial practice, a number of processes are often combined in a single plant [for instance, hydrogen cracking and catalytic reforming]. This make it possible to process low-octane starting materials into high- octane gasoline with a high concentration of benzene hydrocarbons [obtained by reforming] and isoparaffinic ones [obtained by hydrogen cracking]. In this combined technique, the process of hydrogen cracking occurs without hydrogen supply from the outside.

ExercisesAnswer the following question1. What is the typical feature of catalytic processes?2. What can you say about the conditions of catalytic processes?3. What is the composition of a catalyst?4. What is the main characteristic of a catalyst?5. What is the selectivity of a catalyst?

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6. How can catalysts participate in process reaction?7. When does the quick ageing happen?8. What can affect the activity and selectivity of catalysts?9. How can you regenerate catalysts?10. Do you know what the main catalytic processes are?11. Can you show the basis of catalytic cracking?12. What is the purpose of catalytic reforming?13. In which condition do catalytic reforming happen?14. What is the purpose of hydrogenation processes?15. Which process is the most important in hydrogenation

processes?16. What is the basis of hydrofining process?17. Can you define the alkylation reaction?18. Which alkylation processes are used in petroleum

processing?19. How can they carry out the catalytic alkylation of isobutane?20. What do the alkylation processes depend on?21. By what is the akylation processes with the use of sulphuric

acid as a catalyst characterized?22. What is the purpose of isomerization?23. What is disproportionation?24. How can you say about the characteristic of gasoline

obtained by catalytic processes?

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Text 25

Catalytic cracking

There are two main types of catalyst cracking: one is carried out in the presence of a catalyst -porous solid particles of a definite composition and structure; the other is also carried out with a catalyst, but in a hydrogen atmosphere at a high pressure [up to 30 MPa] and a slightly reduced temperature [hydrocracking].As compared to thermal cracking, catalytic cracking gives lower yields of methane, ethane and olefins, but higher yields of C3 and C4 hydrocarbons and of gasolines high in benzene and isoparaffinic hydrocarbons. This is the principal advantage of catalytic cracking over thermal cracking. Aluminosilicates are used most often as cracking catalysts now. In recent time, zeolite-containing [crystlline aluminosilicate] catalysts with rare-earth additives have come into wide use.The main object of catalytic cracking is to produce high-octane components for automobile or, less frequently, for aviation gasolines. The process gives the highest yield of white products with any kind of petroleum. The by-products obtained in catalytic cracking plants include gases, catalytic gas oils [light grades boiling off up to 3500C and heavier ones, which begin to boil above 3500C] and coke which precipitates on the catalyst and is burned off in regeneration.The operation of catalytic cracking plants can be characterized by what is called cracking ratio, i.e. the relative quantity of the starting material converted into gasoline, gas and coke. Thus, the

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depth of conversion is 100 ninus the yield of gas oil [in per cent]. In single cracking, the cracking ratio does not exceed 55%, whereas in deeper kinds of cracking [recycle cracking] it may reach 80% by mass. In some cases use is made of the cracking efficiency, which is the ratio of the total yield of debutanized gasoline and C4 fraction to the cracking ratio. The cracking efficiency is usually 0.75 to 0.80.

Principal reactions of catalytic cracking In the cracking process, the contact of crude petroleum with a catalyst results in the formation of gas, gasoline, coke and some liquid products with the boiling temperature above the boiling -off temperature of gasoline. These products from by the following principal reactions.Cracking of hydrocarbons with the formation of lighter molecules: for instance, an n-butyl radical splits from a molecule of n-butylbenzene to form benzene and butylene. The molecules of cetane C16H34 give on splitting C8H18, C8H16 and some other hydrocarbons. The rate of hydrocarbon splitting increases substantially with increasing temperature, which makes it possible to control the process, i.e. to increase or diminish the yields of certain products by changing the temperature.Dehydrogenation. In this reaction, only hydrogen molecules split from hydrocarbon molecules. A typical example is the catalytic reaction of dehydrocylization of methylcyclohexane C7H14 [naphthenic hydrocarbon], which give up three hydrogen molecules and converts into toluene. Part of the hydrogen liberated in dehydrogenation is attached in catalyst cracking to olefinic hydrocarbons, thus reducing the content of unsaturated hydrocarbons in catalytic cracking gasolines.Isomerization is characterized by that the atoms in a molecule change their positions, but their number remains the same. Isomerization of normal paraffinic hydrocarbons gives hydrocarbons of a branched structure, for instance, isopentane form from n-pentane.Hydrogenation. In this reaction, the molecules of the starting material attach hydrogen and thus form new compounds more

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saturated in hydrogen. for instance, octylene [an olefinic hydrocarbon] is converted into octane by the reaction:

C8H16 + H2 C8H18

The hydrogenation reaction is quite common and can take place not only with olefins, but with other classes of hydrocarbons as well. For instance, cyclohexane can be obtained by hydrogenation of benzene.Polymerization. In this reaction, two or more molecules combine into a single large molecule. For example, two molecules of ethylene are polymerized into a higher boiling hydrocarbon, butylene. Using polymerization, gaseous olefinic hydrocarbons [ethylene, propylene, butylenes] can be converted into liquid or even solid hydrocarbons of a higher molecular mass.In catalytic cracking, the rate of breakdown of paraffinic hydrocarbons is higher at a higher molecular mass. At the ordinary temperatures of catalytic cracking, i.e. 450-5200C, catalysts have almost no effect on light paraffinic hydrocarbons: propane and butane, white high-boiling paraffins undergo deep changes. For instance, the cracking rate of cetane, whose boiling temperature is 2870C is roughly 13 times that heptane which boils at 980C. The oleffins formed on breakdown of normal paraffinic hydrocarbons are isomerized, partially saturated by hydrogen and convert into paraffinic hydrocarbons of a branched structure and a lower molecular mass. Olefins can be subjected to catalytic cracking much more easily than paraffinic hydrocarbons. The reactions of splitting, isomerization, polymerization and hydrogen attachment are very typical of them. Some other reactions are also possible, by which olefins are converted into benzene hydrocarbons and high boiling compounds.Catalytic cracking of naphthenic hydrocarbons occurs at higher rates than that of paraffinic ones and gives more light liquid products and less gases. Besides, naphthenic hydrocarbons give many benzene hydrocarbons on splitting of hydrogen atoms. Distillates high in naphthenic hydrocarbons are a valuable starting material for catalytic cracking. They give more gasoline and of higher quality than do distillates of a similar fractional composition obtained from paraffinic grades of petroleum.

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The nuclei of benzene hydrocarbons are thermally stable and split insignificantly even at 450-500 oC. On the contrary, the molecules of benzene hydrocarbons with side paraffinic chains are cracked easily: their bonds break mainly in sites of attachment of a side chain to the benzene nucleus. Benzene hydrocarbons with no side chains in the molecule and paraffinic hydrocarbons of normal structure turn to be most stable against catalytic cracking. Hydrocarbons of other homologous series [with the same number of carbon atoms in the molecule], such as olefinic, naphthenic, aromatic with long side chains, are less stable and can be cracked more easily.

Starting materials and products of the processStarting materials. The starting materials for catalytic cracking are various distillate fractions obtained by atmospheric or vacuum distillation of crude petroleum. In catalytic cracking plants for obtaining the components of base aviation gasoline, lighter types of the starting material are used, in particular, distillates with the boiling-off range of 220-3600C and relative density of 0.83-0.87. The plants for making the components of automobile gasoline use heavier distillates with the boiling-off range of 300-5500C and relative density of 0.87-0.93. In some cases, starting materials of an intermediate composition can be used, such as mixtures of various distillates obtained in preliminary processing of petroleum [atmospheric or vacuum distillation] and in secondary processes of preparation of fuels and oils; these mixtures can be used only for making automobile gasolines. In recent time, attempts have been made to process low-ash fuel oils and deasphatizates by catalytic cracking.The starting material must contain no fractions boiling below 1900C, since they remain practically unchanged upon catalytic cracking and lower the octane number of the final gasoline.The processing of starting materials containing harmful impurities involves certain difficulties, in particular, stronger corrosion of equipment and heavier coking of the catalyst, which may result in a lower yield of gasoline and lower productivity of the plant. Metal compounds can be present in vacuum distillates owing to carry-

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over of goudron droplets into the top portion of the column. Some compounds are volatile at high temperatures. For that reason, the operation of a vacuum column should be carefully checked and sometimes it is advisable to lower the boiling-off temperature of a vacuum distillate to be used for catalytic cracking.The coking ability of the starting material should usually be not less than 0.25%. The materials with the coking ability of up to 0.7% can be processed of the regenerator has an extra capacity for coke burn-off. Moist material should not be used for processing, since moisture can disturb the process conditions, in particular, raise the pressure in the reactor, disturb the normal circulation of the catalyst, increase the flow rate of vapours in the rectification column, and impair the quality of the end products. In some cases, this may form emergency situations. The composition of the starting material can also influence the yield and quality of the products of catalytic cracking.Products of catalytic cracking. Catalytic cracking plants produce up to 20% [by mass] of gases [containing hydrogen and light hydrocarbons up to C4], up to 60% of high- octane components of automobile gasolines, and up to 2.5-8% of coke, the balance [except for losses] being light and heavy gas oils. Some plants make unstable gasolines which are further delivered to gas separation. Besides, catalytic cracking for production of the base aviation component may give ligroin and polymers as by-products, and also motor gasoline- an intermediate product which is subjected to catalytic refining at the second stage.Wet gas. Its composition is characterized by a high concentration of isomeric hydrocarbons, in particular of isobutane, which increases the value of the gas as of an intermediate product for further processing. These data disregard steam, hydrogen sulphide and inert gases which may be present in various minor amounts in gases of catalytic cracking.Wet gas and unstable gasoline from catalytic cracking plants are fed into an absorption- gas fractionation plant for separation of light gases. Apart from stable gasoline, the products obtained in such a plant include propane-propylene, butane-butylene and

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pentane-amilene fraction. Propane-propylene and butane-butylene fractions are further polymerized and alkylated to prepare gasoline components or are used in petrochemical processes [propane and butane can also be used as domestic fuel].Unstable gasoline. It is stabilized to obtain a stable component for preparing high-octane automobile and aviation gasolines.Light catalytic gas oil. As compared to the products of similar fractional composition obtained by preliminary distillation of petroleum, light catalytic gas oil [a distillate with the beginning of boiling at 175-2000C and the end of boiling at 320-3500C] has a lower cetane number [up to 25], higher contents of sulphur [roughly the same as in crude petroleum] and benzene hydrocarbons [up to 55 %], and a certain concentration of unsaturated hydrocarbons. The setting temperature of these gas oils is however substantially lower than that of the starting material for catalytic cracking. Under more rigid conditions of the process, and without increase in recirculation light gas oil is produced in smaller amounts and with a lower cetane number, but with a higher concentration of benzene hydrocarbons.Light catalytic gas oil is utilized as the starting material for manufacture of commercial carbon [carbon black], as a component in commercial grades of fuel oil, and for some other purposes. In rare cases, it can be used as a component of diesel fuel, provided that other components of the fuel produced by preliminary distillation have a higher cetane number and a reduced content of sulphur [compared to the standard value]. In some cases, light catalytic gas oil is extracted; the refined layer with a reduced content of benzene hydrocarbons and a higher cetane number is used as a component of diesel fuels and the extracted layer, which is high in benzene hydrocarbons, is a valuable by- product for preparing carbon black.Heavy catalytic gas oil is the liquid residue of catalytic cracking. Its quality depend mainly on the process conditions and the boiling -off temperature of the light gas oil produced. Heavy gas oil often contains many mechanical impurities [rests of the catalyst]. Its sulphur content is usually higher than that of the starting material

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used for cracking. Heavy catalytic gas oil is used for making fuel oils and carbon black.

Exercises

Answer the following question1. How many main types of catalytic cracking are there? What are

they?2. Is there the difference between the products of thermal

cracking and catalytic cracking?3. What is the principal advantage of catalytic cracking over

thermal cracking?4. Which compounds are used as cracking catalysts?5. What is the main object of catalytic cracking?6. What are the by-products of catalytic cracking?7. By what can the operation of catalytic cracking plants be

characterized?8. What is cracking efficiency?9. How many principal reactions happen in catalytic cracking?10. Which molecules are formed in cracking of hydrocarbons?11. How does the rate of hydrocarbon splitting depend on

temperature ?12. Which compounds are formed in the dehydrocyclization of

methylcyclohexane C7H14?13. Why is the content of unsaturated hydrocarbons in catalytic

cracking of gasolines reduced?14. By what is the isomerization characterized?15. What is polymerization?16. On what is the rate of breakdown of paraffins depend?17. How can the molecular mass of hydrocarbons affect on the

rate of cracking?18. Olefins can be subjected to catalytic cracking more easily

than paraffinic hydrocarbons, can't they?19. Which reaction happen with olefin in catalytic cracking?20. What can you say about the content of naphthenic

hydrocarbons in starting material for catalytic cracking?21. What can you say about the reaction ability of benzene

hydrocarbons?

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22. Which hydrocarbons are more stable in catalytic cracking?23. Which materials are used as starting materials for catalytic

cracking?24. Which starting materials are used in catalytic cracking plants

for obtaining the components of base aviation gasoline?25. The same question for making the components of automobile

gasoline?26. Why aren't fractions boiling below 1900C used in catalytic

cracking ?27. Why is it advisable to lower the boiling -off temperature of a

vacuum distillate to be used for catalytic cracking?28. Why shouldn't moist material be used for catalytic cracking ?29. What are the products of catalytic cracking?30. What are the by-products of catalytic cracking?31. What is the composition of wet gas?32. How can they separate the light gasses from wet gas?33. What can you say about the composition of light gas oil?34. What is the light catalytic gas oil used for?35. What do the quality of heavy catalytic gas oil depend on?36. What can you say about the composition of heavy gas oil?37. What can heavy catalytic gas oil be used for?

Text 26

Catalytic Reforming

Because higher- octane gasoline permit the building of engines that extract more power from gasoline, there has been a constant push toward higher octanes since differences is octane quality were first recognized. A major factor in this development has been the large - scale use of catalytic reforming to raise octane ratings

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of gasoline stocks. The first commercial unit, Hydroformer, went on stream just before World War II, and the process proved to be a major source of aromatics and aviation gasoline for military uses. However, catalytic reforming did not "catch on" until about 1950, when Haensel and others at the Universal Oil Products Co. demonstrated that platinum catalysts could be used commercially despite their high cost. By 1955, catalytic reforming processes had almost completely supplanted thermal reforming. Catalytic processes not only give higher quality products, they give a higher yields as well.

ReactionsIn catalytic reforming, the principal object is to convert other hydrocarbon to aromatics. The reason may be seen by comparing the octane numbers of some corresponding hydrocarbons [Table 1]. Thus, high conversions to aromatics result in high octane products. There is a loss in volume, because aromatics are denser than other hydrocarbons; however, the loss is small in comparison with the loss [to gas and tar] suffered in thermal reforming. Other reactions of some importance in catalytic reforming are cracking and isomerization.

Table 1Research rating Motor rating

n-Heptane2- MethylhexaneHeptene-2Methylcyclohexane2,3-Dimethylpentane2,2,3-Trimethylbutane[triptane]Toluen

042737591113120

045577189101104

Production of Aromatics. Because aromatics contain less hydrogen than do other hydrocarbons, dehydrogenation is the primary reaction. Of the nonaromatics, cyclohexane derivatives are dehydrogenated most readily: C6H11CH3 C6H5CH3 + 3H2

Methylcyclohexan Toluene

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Cyclopentane derivatives react similarly, but they require a preliminary isomerization to cyclohexan derivatives: C5H9CH2CH3 C6H11CH3 C6H5CH3 + 3H2

Ethylcyclopentane Methylcyclohexane TolueneConversion of paraffins to aromatics involves a cyclization step. For normal heptane, the reaction may be written:n-C7H16 C6H11CH3 + H2

C6H11CH3 C6H5CH3 + 3H2

To undergo these reactions, a paraffin must have at least six carbon atoms in a chain or be isomerizable to such a compound.

Aliphatic olefins can also be converted to aromatics directly, but this fact is of little practical significance because such olefins are readily hydrogenated to paraffins under the conditions used in catalytic reforming. Thus , aliphatic olefins behave as paraffins, with the exception that they deactivate the catalyst more rapidly. Similarly, cyclic olefins behave as naphtenes.

Hydrocracking. Under the conditions employed in catalytic reforming, cracking completes with dehydrogenation reactions. Because high hydrogen pressure are used, any olefins that form are saturated immediately, and the reaction usually called "hydrocracking". Whether hydrocracking occurs in one step or in two is of little consequence. In either case, a typical over-all reaction is:n-C8H18 + H2 C3H8 + n-C5H12

Octane Propane PentaneBecause lower-boiling paraffins have higher octane numbers,

hydrocracking improves octane ratings; however, the improvement is less than if the paraffins were converted to aromatics. Also, there is considerable loss of gasoline to butanes and lighter materials, and the vapour pressure of the debutanized product is raised. Increasing the vapour pressure reduces the amount of butane that can be blended into the product to make a finished gasoline; thus, the effective yield of gasoline is reduced still further.Hydrocracking of naphthenes also occurs to some extent. Cyclopentane derivatives are more susceptible than cyclohexane derivatives, especially over catalysts with little isomerization

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activity. The first step in the hydrocracking of naphthenes is probably scission of the ring:

C5H9CH2CH3 + H2 n-C7H16

The paraffins are formed may react further to produce aromatics, or it may be hydrocracking.Isomerization. With some catalysts, paraffins are isomerized under reforming conditions. Usually, isomerization of paraffins does not have a large effect on octane quality because the production of highly branched paraffins are small. If the paraffins in a given charge were chiefly normal, their isomerization would have a large effect on octane. In most instances, however, paraffins in the charge are mixtures of isomers; therefore the isomerizing activity of a catalyst is important chiefly for the isomerization of cyclopentane derivatives.

CatalystsAlthough aromatics can be produced from either

hydrocarbons without catalysts, severe conditions are required, and yields are low. To obtain acceptable yields, dehydrogenation catalysts must be employed. Those of commercial interest include platinum on alumina, platinum on sillica-alumina, chromia on alumina, molybdena on alumina, and cobalt molybdate on alumina. The ideal catalyst would convert all other hydrocarbons selectiely to aromatics rapidly, with only a small catalyst inventory. Such a catalyst would not promote hydrocracking, and it would have to operate under conditions thermodynamically favourable to production of aromatics. To the extent that a catalyst deviates from this conditions it is a poorer catalyst. Derivations may be either in the selectivity of the catalyst toward the production of aromatics or in the activity of the catalyst for the several reactions that actually occur. Selectivity is determined by the relative rates of the competing reactions- dehydrogenation to aromatics and hydrocracking, and isomerization in so far as it affects the other two. Activity is determined by the magnitude of the rate constants. Platinum catalysts appear to be the most selective and the most active, as well as the most expensive.

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Dehydrogenation of Naphthenes. Selectivities of catalysts depend to some extent on the make-up of the feed stock. Alkylcyclohexanes are readily converted to aromatics by all dehydrogenation catalysts, provided that the reaction conditions are favourable thermodynamically. For the conversion of alkylcyclopentanes, on the other hand, there are large differences. Because alkylcyclopentanes require an isomerization step, their conversion to aromatics depends upon the isomerization activity of the catalyst. Published data on platinum, molybdena, and chromia catalysts show that platinum has the highest isomerization activity, chromia the lowest. Even with platinum catalysts, the isomerization reaction is the rate-controlling step. Thus the conversion of alkylcyclopentanes to aromatics is lower than the conversion of alkylcyclopentanes to aromatics is lower than the conversion of cyclohexane derivatives; consequently there is more opportunity for hydrocracking, and yields of aromatics are poorer.

Dehydrocyclization of Paraffins. Data on platinum, molibdena, and chromia catalysts have also been published for the conversion of paraffins to aromatics. When operating in the pressure range normally use in catalytic reforming, platinum is the most effective catalyst, chromia the least. The poor results obtained with chromia catalyst are surprising, inasmuch as high conversions of n-heptane to toluene are obtained at low pressures. Apparently, the chromia catalyst has the unusual property of adsorbing hydrogen so strongly at higher pressure that paraffins can not readily reach its surface.

Reaction MechanismExtensive studies have been made to elucidate the

mechanism of reforming over platinum catalysts. Such catalysts are duel-functional; they contain platinum as a dehydrogenating agent and an acidic material, such as chlorine, fluorine, or alumina-promoted silica, as an isomerization agent. In commercial catalysts, enough platinum is used to ensure that the dehydrogenation activity is large in comparison with the isomerization activity.

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Although only traces of olefins can exist under reforming conditions, they apparently are intermediates in the reactions. Both naphthenes and paraffins are dehydrogenated to olefins [in trace amounts] on dehydrogenation sites in the catalyst. Cyclohexenes continue to dehydrogenate rapidly to aromatics. Alkylcyclopentanes transfer to acid sites, where they are isomerized to cyclohexanes; the cyclohexanes then pass back to dehydrogenation sites, where they are converted to aromatics. Alkyl olefins also transfer to acid sites where they may either isomerize to other alkyl structures or cyclize to naphthenes. The isomerized olefins pass back to dehydrogenation sites, where alkyl olefins are hydrogenated to paraffins and cyclohexenes are dehydrogenated to aromatics.In view of the low isomerization activity of chromia catalysts, the excellent results obtained with them at low pressure suggest that n-heptane is easier to aromatize than are its isomers. This idea is also suggested by data on the conversion of n-heptane over a platinum catalyst; the ratio of aromatics production to hydrocracking was higher at low conversions [where n-heptane predominates in the reactants] than at higher conversion [where isoheptanes predominate]. It has also been shown that paraffins with more than seven carbon atoms are converted more readily to aromatics than are heptanes. All these observations fit the hypothesis that naphthene intermediates are not formed from paraffins over platinum catalysts by linking of two end [primary] carbon atoms. It has been suggested that platinum catalysts form derivatives of cyclopentane by the linkage of second and sixth carbon atoms; the alkylcyclopentanes so formed isomerize to alkylcyclohexanes, which are dehydrogenated to aromatics. This mechanism could not apply for cgromia catalysts, which have little isomerization activity. When n-heptane is processed over a chromia catalyst, the second and seventh carbon atoms appear to link up to form methylcyclohexane directly.

Exercises

Answer the following question1. What is the purpose of catalytic reforming ?

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2. Why had catalytic reforming supplanted thermal reforming ?3. Do you know why conversion other hydrocarbons to aromatics

is principle of catalytic reforming ?4. What are the main reactions in catalytic reforming ?5. Would isomerization have a large effect on octane number?6. By what is the activity of catalysts determined?7. What is the characteristic of platinum catalysts?8. Why is the conversion of alkylcyclopentanes to aromatics lower

than that of cyclohexane derivatives?9. What does the selectivity of catalysts depend on?10. Which catalyst has the highest isomerization activity?11. Why is the activity of the dehydrocyclization of paraffins low

at pressure range normally used in catalytic reforming?12. What are dual-functional catalysts?13. Which reaction is performed in dehydrogenation sites?14. Which reaction is performed in acid sites?15. Why are the paraffins with more than seven carbon atoms

converted to aromatics easier than heptanes?16. Can you show the mechanism of conversion of paraffins to

aromatics?

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Petroleum products

The products obtained from petroleum can be classed into four groups: I-fuels; II- lubricating oils, paraffins, etc.; III-miscellaneous petroleum products; and IV-chemical and petrochemical products.Group I includes liquefied hydrocarbon gases, fuels for carburettor engines [gasolines], fuels for jet (kerosene) and turbojet engines , Diesel fuels, boiler fuels; Group II-various lubricating oils, paraffins, ceresins and petrolatum; Group III- plastic greases, bitumenns, coke, etc; and group IV- hydrocarbons of various classes which serve as starting materials for organic or petrochemical synthesis.I. Liquefied hydrocarbon gases and fuelsLiquefied hydrocarbon gases consist mainly of propane and butane and sometimes may contain small quantities of propylene and butylene. They have found the widest application as domestic fuel which may be commercial propane (at least 93 % of propane), commercial butane (at least 93 % of butane) or their mixture (in winter time, with a greater proportion of propane).Liquefied gases or their constituents of higher purity are used as starting materials for the manufacture of various chemical products and olefines [by pyrolysis].

a) Fuels for carburettor Engines

This group of fuels includes aviation and motor gasolines and tractor kerosene. An important characteristic of these fuels is the pressure of sasturated vapours, kPa, which should be 29.3 to 47.9 for aviation gasolines, 66.5 to 93.4 for motor gasolines (not more than 66.5 for summer grades).The fractional composition of fuels is also of large importance. For instance, the 10% boiling point of gasoline (the p[oint at which 10% of the fuel boils off) can characterize the starting properties and reliability of an engine starting under various conditions, in particular, at a low temperature of the ambient air. The 50% boiling point of gasoline characterizes the speed of engine heating during starting, the smoothness of switching from one operating mode to another, and the stability of engine operation. The 90% and 97.5% boiling points of aviation gasoline and the temperature of the end of boiling of motor gasoline determine the homogeneity of the fuel mixture, i.e. the completeness of fuel combustion in the engine. This is extremly important, since with incomplete combustion of the fuel, liquid substances can penetrate into the crankcase and dilute the lubricating oil and thus cause a quick wear of the engine. Besides, incomplete combustion causes a stronger pollution of the air.

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Antiknock rating is another important characteristic of fuels which determines their proper combustion ic carburettor engines. With detonation (knock-type) combustion, the rate of flame front propagation increases very quickly and causes explosion, or knock, in an engine; as a result, the engine may quickly be put out of operation. The antiknock rating of fuels is evaluated in terms of the octane number (ON).Aviation Gasolines (state Standard GOST 1012-72). They are used as fuel for carburettor-engine planes and helicopters. In the USSR, aviation gasoline is avalable in the following grades: B-70, B-100/130, and B-91/115. The grading includes a letter B and a number indicating the octane number or two numbers: The numerator indicating the octane number and the denominator, the rating. Aviation gasolines are prepared by mixing (compounding) of a base gasoline (obtained by catalytic cracking or catalytic reforming), high-octane components (isooctane, alkyl gasoline, isopentane, benzene hydrocarbons, etc.), tetraethyl lead (TEL) and other additives raising the octane number, and of inhibitors i.e. substances preventing fuel oxidation (with aviation gasoline, oxy- diphenylamine is used for the purpose). These components are taken in proportions required to make gasoline of the desired grade and quality.The boiling-off points of gasolines should not exceed the following temperatures: 90% boiling-off point 1450C; 50% 1050C; and 10% from 750 to 880C. The content of TEL (g/kg of gasoline) should be not more than 2.7 for grade B-100/130 and from 2.5 to 3.3 for other grades, except for B-70 which contains no TEL.Motor Gasolines. These grades of gasoline are employed in automobile carbuurettor engines. One of the most important indices of their quality is the anti-knock rating which is expressed in terms of the octane number.Otane number is numerically equal to the content of isooctane (% by volume) in a mixture with n- heptane, which is equivelent in its detonation intensity in a single cylinder engine to the fuel being tasted under standard conditions. The octane numbers of isooctane is taken conditionally to be 100 and that of n-haptane, zero. The octane numbers are determined by using mixture of these two hydrocarbons. The current control of fuels is done by using what is called secondary reference fuels having various values of the octane number.Octane numbers can be determined by various methods. The motor method uses apparatuses of the type IT9-2M and UIT-65 to measure the octane number of motor and aviation gasolines. Motor gasolines can also be tested by what is called the research

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method in apparatuses of the type IT9-6 and UIT-65 (State Standard GOST 8226-66). The temperature method(State Standard GOST 3337-52) with the use of IT9-5 apparatus is employed to determine the antiknock of high- octane aviation gasolines (ON 100 or higher). The pressurization method (State Standard GOST 3368-68) with the use of IT9-1 apparatus is used to determine the rating of aviation gasolines in rich mixtures.The octane number of gasoline increases on addition of benzene hydrocarbons and isomeric paraffin hydrocarbons and also on a decrease of the point of full boiling-off. If these measures fail to give gasoline with a desired octane number, an antiknock agent is added. Various metalorganic and organic substances can be used as antiknock agents.The most popular antiknock is tetraethyl lead Pb(C2H5)4 in the form of ethyl liquid.All hydrocarbons can be written in the following order of increasing effect of TEL on octane number: paraffin-naphenes-benzenes-olefins. With an increase in the content of TEL in gasoline, its effectiveness diminishes.The sensitivity of gasolines to TEL decreases sharply with an increasing concentration of sulphur which reacts with lead and petrifies the effect of TEL. For that reason, the starting materials of certain processes and some grades of gasoline are purified from sulphur compuonds before adding TEL.The grades of motor gasoline produced in the USSR are as follows: A-66, A-72, A-76, AI-93 and AI-98 (the digits are octane numbers). All these grade can be ethylated, except for A-72. The content of TEL in them should not exceed 0.6 g/kg in A-66, 0.41 g/kg in A-76 and 0.82 g/kg in AI-93 and AI-98. The octane number of grade AI-93 and AI_98 is measured by the research method and that of the other grades, by the motor method. For easier operation of engines, motor gasolines are manufactured as summer and winter kinds, the latter, as has been given earlier, having a higher pressure of saturaed vapours. Besides, they have (except for grade AI-980 different temperature of boiling-off of intermediate fractions and of the end of boiling. The fractional composition of motor gasolines is given below (numbers in numerators and denominators are boiling-off points respectively for summer and winter kinds of gasoline, 0C).

A-66 A-72, A-76AI-93

AI-98

Beginning of boiling, at leastBoiling-off points,lower

35/-

79/65

35/-

70/55

35/-

70/-

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limit:10%50%90%End of boiling

125/125195/160205/185

115/100180/160195/185

115/-180/-195/-

New, more efficient makes of automobile engines have a high compression ratio and can be run only on high-octane gasoline. Motor gasolines are prepared by mixing (compounding) various components: high-octane gasolines of catalytic cracking and catalytic reforming, alkylates and isomerizates of light fractions of preliminary distillation. For preparation of gasoline with lower octane numbers (especially of grade A-66), use is also made of gasolines of thermal cracking and coking, gasolines obtained by straight-run distillation of petroleum, which have a higher temperature of boiling off, and dearomatized products (refined petroleum) obtained in the manufacture of benzene hydrocarbons by catalytic reforming of gasoline fractions.Since tars, if present in gasoline, can disturb the operation of engines, their content in gasolines is limited at 7mg/100ml in grade A-66 and 5 mg/100ml in the other grades. The chemical stability of gasolines is checked by determining the induction period which should constitute at the manufacturer at least 450 min for grade A-66, 600 min for A-72, and 900 min for the other grades.

b) Fuels for diesel engines.

In Diesel engines, air is compressed and its temperature rises and Diesel fuel injected into the engine is ignited by the hot air. The capability of diesel fuels for self- ignition is measured in term of cetane number.Cetane number is the index of ignitability of diesel fuel, which is equal numerically (in per cent) to the content of cetane (n-hexadecane C16H34) in a mixture with -methylnaphthalene C11H10, which possesses the same ignitability in a single-cylinder engine under standard testing conditions as the fuel being examined. The cetane number of cetane proper is taken equal to 100 and that of -methylnaphthalene, zero. The cetane number depends on fuel composition: the highest cetane number is shown by paraffin hydrocarbons, a lower, by naphthenes and the lowest, by bezene hydrocarbons which for that reason are undesirable in Diezel fuels. The cetane number can be raised by mixing Diezel fuel with certain components containing paraffin hydrocarbons of normal structure or by giving special additives.

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Diesel engines are divided into three classes: high-speed engines (above 1000 rpm) for agricultural machines, Diesel locomotives, cross-country vehicles, etc.; medium-speed engines (500-1000 rpm) for large locomotives and as auxiliary motors on ships; and low-speed engines (less than 500 rpm) employed as main marine engines and Diesel-generators. Depending on the content of sulphur in the original petroleum, diezel fuel fractions may be low-sulphurous (up to 0.2 % S) and sulphurous (0.7 to 1.8 % S). The content of sulphur can be reduced by hydrogen refining. Low-sulphur fuels are advantageous in being less corrosive and less liable to carbonization; besides, they form exhaust gases low in sulphurous and sulphuric anhydrides. The viscosity of diezel fuels also standardized to ensure proper atomization and reliable operation of the fuel-supply system. Heavy fractions in the fuel can cause in complete combustion and smokes in exhaust gases and carbonization in the engine.Medium-speed diezel engines can be run heavy distillate fuels and low-speed ones, on fuels obtained by dilution of fuel oils by distillates, including diesel fractions, to obtain the desired viscosity from 36 to 67 mm2/s at 500C]. The setting point of the mixture may be from -5 to 50C.

c) Boiler Oils (fuel oils)

Fuel oils are used in many branches of national economy, in particular, at thermal power plants.According to the State Standard GOST 10585-75, fuel oil is graded as folows: marine grades F-5 and F-12 (light fuel), furnace fuel oil grade 40 (medium) and furnace fuel oil grade 100 (heavy fuel). The characteristics of fuel oils may vary appreciably in different grades. For instance, the relative viscosity of fuel oils should be respectively: not more than 5 and 12 mm2/s at 500C for marine grades and 8 and 16 mm2/s at 800C for furnace grades 40 and 100. Fuel oils of a higher viscosity have a higher flash point, which is specified at 80 and 90 for marine grades F-5 and F-12 (in a closed cruible) and at 900 and 1100C (in an open crucible) for furnace grades 40 and 100. The setting point of fuels is limited at -50 to 250C (or up to 42 for fuel oils obtained from high-paraffin petroleum). According to the sulphur content, fuel oils of each grade are divided into low-sulphurous (up to 0.5% S), medium-sulphurous (0.51 to 1.0 per cent), and high- sulphurous (1.01 to 3.5 %).The quality of fuel oils is decided by the following characteristics: viscosity, which determines the ease of transportation of the fuel

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and the propable degree of heating for effective atomization; setting point, which determines the conditions of storage and application of the fuel at various temperatures of the air; sulphur content, which determines the degree of corrosion of the engine and the exhaust of sulphurous compounds to the atmosphere. One of the decisive charateristics of fuel oils is the heat of combustion (calorific value) which depends on their composition. The low calorific value of low-sulphurous and medium-sulphurous fuel oils (recanculated to dry fuel) must be not less than 41454 kJ/kg for furnace grades, 40470 kJ/kg for furnace grade 40, 40530 kJ/kg for furnace grade 100.Fuel oil grades are chosen according to the conditions of operation of engines. Thicker (and cheaper) grades are commonly used at stationary plants where the fuel can be heated up and filtered. Magine grades of fuel oil (employed in marine power plants) differ from furnace grades in having a lower content of ash, water, sulphur and tars.Fuel oils are prepared by mixing residual products of preliminary distillation (residual fuel oil, semigoudron and goudron) with residual products of thermal and some catalytic processes (cracking residue, gasoil, reflux, polymers) and residual products of oil manufacture.

d) fuels for Jet and Gas-turbine Engines

Fuels for aviation jet engines are divided into two main groups: for subsonic and supersonic speeds. The latter must have an elevated density and a sufficienly high calorific value to ensure the required power of the engine and the desired flight range. At higher speeds of flight, fuel is heated much more. Jet-engine fuels (aviation kerosene] are kerosene fractions of preliminary distillation of petroleum having the temperature of the begining of boiling from 1500 to 1950C and the boiling-off point from 2500 to 3150C. Fuels for jet engines must easily be vaporizable, have a hight calorific value (the lowest calorific value being not less than 42950-44 160 kJ/kg], high thermal stability, a low temperature of the begining of crystallization (not higher than -600C) and cause no corrosion of engine elements. Jet-engine fuels of the highest thermal stability are obtained by catalytic refining in hydrogen under pressure. Gas-turbine fuels for terrestrial machines differ from aviation kerosene by a wider fractional composition and higher content or sulphur (up to 3 %). Their relative viscosity at 500C must be not more than 2.

Exercises

172

Answer the following question

1. How many group can petroleum products be classed into? What are they?

2. Which group do liquefied hydrocarbon gases belong to?

3. What are the main compositions of liquefied hydrocarbon gases?

4. How many important characteristic have fuels for caburettor engines got? What are they?

5. What happen if there is incomplet combustion?

6. What does the antiknok rating determine?

7. What is the octane number?

8. Which kind of hydrocarbons have the higher octane number?

9. What do they do to increase the octane number of gasoline?

10. What are the limit content of TEL in the grades of motor gasoline in USSR?

11. The winter kind of motor gasoline has a hihger pressure of saturated vapors than the summer, hasn't it?

12. What is the chemical stability of gasoline checked?

13. Which fuels is the term cetane number used for?

14. What is cetane number?

15. What does cetane number depend on?

16. What is order of increasing the cetane number of hydrocarbon?

17. Which method are used to raise cetane number?

18. How are fuel oils classified?

19. What is the quality of fuel oils decided by?

20. What is decisive characteristic of fuel oils?

21. Fuel oil grades are chosen according to the conditions of operation of engines, aren't they?

22. Where are thicker grades commonly uesed?

23. How do they prepare fuel oils?

24. How do they classify fuels for aviation jet engines?

25. What are the characteristics of fuel for let engines?

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II. Lubricants, Products of Oil-paraffin Processing and Other Petroleum ProductsIn addition to high-quality fuels, lubricating materials are also essential for normal operation of various engines and mechanisms. All lubricants can be divided into four types: gaseous, solid, liquid, and semisolid (thickened), or greases.Some gases can react with metals to form a lubricating film which lowers friction and wear. Solid lubriants, such as graphite or molybdenum disulphide, are employed at very high temperatures and under heavy loads where ordinary lubricants, including oils and greases, are ineffective. In this section, we shall discuss only lubricating oils and greases.

a) Lubricating and other Oil

Petroleum processing industry manufactures minaral oils of many kinds: motor oils (aviation, diesel and automobile grades), industrial oils, turbine oils, electroinsulating oils, compressor oils, ectc.Viscosity is the most important characteristic of all kinds of oil. On the one hand, it should be sufficiently low to ensure lubrication and easy start of engines at low temperatures and, on the other, sufficiently high to lubricate properly even the hottest parts of an engine. This requirement is met by oils having a high viscosity index. Other important chaaracteristics of oils are their oxidation stability at the elevated temperature, a low setting point (especially for winter grades), godd anticorrosive properties, and others.All grades of lubricating oils for modern machenisms and engines, especially for diesel engines and the like, contain additives which improve their performance. Diesel and automobile oils are made by mixing purified residual and distillate oils.Aviation Oils. These are employed for lubricating of aviation piston engines. They are prepared from goudron residue after distillation of specially selected petroleum grades by deep refining with selective solvents and sometimes by mixing with distillate oils. Aviation engines operate under heavy loads and at high temperatures, so that the oils for them will have a high chemical stability and great lubricating power.Industrial Oils. These are intended for lubrication of machines and mechanism of industrial equipment which operate at relatively low temperatures and of pairs of machines and engines not

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subjected to the effect of steam, hot air or gases. There is no strict scientific classification of industrial oils. They are commonly classified by their viscosity and by the conditions and fiels of application. Depending on viscosity, industial oils are divided into light (3.5-10 mm2/s at 500C), medium (10-58 mm2/s at 500C), and heavy (11-96 mm2/s at 500C). Depending on the conditions of application, they are classed into oils for light and moderate speeds and loads and heavy-duty oils, and by the fields of application, into oils for gear transmissions, slip guides, spindles, instrument oils, break-in oils, and special oils. These grades of oil are prepared using base oils of selective purification produced from eastern grades of petroleum.Industrial oils should be pressure-and corrosion-resisting, retain their fluidity at the working temperatures, and be stable against foaming and oxidation.Turbine oils. These are used for lubrication of bearings and auxiliary machanisms of turbomachines (steam and gas turbines, turbocompressors, hydraulic turbines, marine turbines, etc.); they are also used as pressure fluids. Turbine oils without additives are produced by contact acid refining, those with additives are manufactured by selective refining from low-sulphuruos and sulphuruos grades of petroleum. Additives improve their antioxidizing, deemulsifying, anticorrosive and antifoaming properties. Some grades oils contain antiwear additives. Turbine oils must have a high chemical stability and separate easily from water which enters occasionally the lubrication system.Insulating oils. Oils are liquid dielectrics and therefore can be used for insulation of current-conducting elements of electric equipment (transformers, capacitors, cables, etc.). Insulating oils also serve for removing heat and favour quick are extinction between electric contacts. This group of oils includes transformer, capacitor and cable oils.Transformer oils have found the widest application in the group. They are intended for long operation at 70-80 0C in the atmosphere of air and for that reason should possess a very high chemical stability and should not form low- molecular acids on oxidation. Besides, transformer oils should naturally have dielectric characteristics. Most grades of transformer oils have a viscosity of not more than 9 mm2/s at 50 0C, exceptions being grade ATM-65, arctic transformer oil, with a viscosity of not more than 3.5 mm2/s at 50 0C amd grade T-1500 (for equipment of transmission lines for 1500kV) whose viscosity is limited at 8 mm2/s at 50 0C. Transformer oils cannot be replaced by other kinds of oil.

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Compressor oils. These oils serve for lubrication of cyliders, valves and piston rods of compressor operating at temperatures of 200-2500C and pressures of 20-25 Mpa. The main requirement to compressor oils is that they should have an appropriate oxidation stability. Compressor oil grade 12 M, of a kinematic viscosity of 11-14 mm2/s at 100C, is intended for single-stage horizontal and vertical compressors for a pressures 0.7-0.8 MPa and for two-stage compressor for an average pressure up to 5 Mpa. Compressor oil grade 19T, of a kinematic viscosity of 17-21 mm2/s at 1000C, is employed in multi-stage high-pressure compressors (for 20-30 MPa). The oxidation stability of these oils is ensured by deep refining.Oils for steam engines. They are divided into two main groups: for saturated-steam and for superheated-steam machines. These oils are distinguished by a low evaporability and a high viscosity (the kinematic viscosity at 1000C is 9-13 mm2/s for cylinder oil grade 2 and 44-64 mm2/s for grade 52 Vapor oil). Cylinder oils of the first group are prepared from distillates and those of the second group, from residues by deasphalting with propane or by distillation of goudron in high vacuum.Synthetic oils. These oils are essentially organic or elementoorganic compounds [containing silicon, iron, etc.] and are intended for heavy-duty applications.b. Pareffine, ceresins and petroleumPareffines. These are soft [liquid] or solid petroleum products of crystalline structure obtained from distillates of paraffinic and high- paraffinic grades of petroleum.Solid petroleum paraffins are crystalline products of white to bright- brown colour, depending on the amount of oil. The oil content in paraffines may vary within 0.8-0.5 per cent for high- purified grades and up to 2.2-2.3 and even 5 per cent for other grades. Special grades of paraffine are manufactured in the USSR for application in food industry. They are obtained by deep refining of raw paraffins and employed mainly for impregnation of packing materials either contacting loose fry foodstuffs [grade P-2 with the oil content up to 0.9 per cent by mass] or non-contacting [grade P-3, oil content up to 2.3 per cent by mass]. Paraffin grade P-1 [oil cotent up to 0.5 per cent by mass] is used for the same purposes as grade P-2, and also in candy industry.The fusion point of paraffin grades P-1, P-2, P-3 is respectively 54, 52 and 500C.Ceresins. Ceresin is mixture of solid hydrocarbons obtained in processing and refining of ozokerite, unpurified petroleum ceresin

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or their mixtures. Ceresins are used for making greases, wax alloys, insulating material, etc.The most important characteristic of cerecins is the dropping point, 0C. According to the state standard GOST 2488-73, the dropping point is the basis of grading of ceresins [the grade of ceresin manufactured in the USSR are disignated respectively 80, 75, 67 and 57]. The volume resistivity at 1000C is specified only for grade 80 ceresin: it should be not less than 1*1012 ohm cm.Synthetic high-fusion ceresin has the highest dropping point. It is a mixture of solid hydrocarbons of the methane series, mostly of normal structure, which are obtained by synthesis of carbon monoxide and hydrogen [Fisher-tropsch process ]. According to the state GOST 7658-74, the dropping point of this of ceresin must be not less than 1000C and the volume resistivity at 1000C, not less than 1014 ohm cm.Medical [liquefied] Petrolatum. This product is obtained by fusion of ceresin, paraffin, purified petrolatum or their mixtures with petroleum oil. Its dropping point is 37-500C.Capacitor Petrolatum. It is employed for filling in and imprenating of capacitors. Its kinamatic viscosity at 600C must be at least 28 mm2/s. An important specified characteristic of this product is the volume resistivity, which must be at least 1*1012 ohm cm at 1000C.

ExercisesAnswer the following question1. How many type can lubricants be divided? What are they?2. What are effects of lubricants?3. Viscoity is the most important characteristic of all kinds of

lubricant, isn't it?4. How does the viscosity of lubricating oils must be like?5. What are characteristics of lubricating oils?6. What are purposes of aviation oils?7. What are characteristics of aviation oils?8. How can industrial oils be classified?9. How can additive type for industrial oils be prepared?10. What are properties of industrial oils?11. What are turbine used for?12. What are insulating oils include?13. Which grade have the widest application?14. What are applications of compressor oils?15. How can they prepare cylinder oils for steam engines?16. What are applications of solid petroleum paraffins?17. What is ceresin?18. What is ceresin used for?

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19. The most important characteristic of ceresins is the dropping point, isn't it?

20. How can they prepare medical petrolatum?21. What is capacitor petrolatum?

III. Miscellaneous Petroleum ProductsGreases. Grease is a thick salvelike product consisting of oil and a thickener. Various soaps [calcium- sodium, aluminium, lithium, barium, etc.] are commonly used as thickeners. Greases thickened by hydrocarbon components [ceresin, paraffin or petrolatum] are mainly employed for protective coastings. They are physically and chemically stable, but their operating range is limited to temperatures of 50-600C. Special greases are also produced, in which various compounds are used instead of oil as a liquid base.Greases are employed in cases where mineral oils cannot ensure proper lubrication of machines and mechanism, and also for tightening gaps. Greases are often used as slushing compounds; they protect mechanisms against corrosion during storage and then can serve as lubricants in operation.Petroleum Bitumens. Bitumens are usually obtained by oxidation of goudrons from heavy tarry grades of petroleum, and also by mixing with asphalt, extracts of oil manufacture and asphaltile. The main characteristics of bitumens are; [needle] penetration, ductility, and softening temperature which characterizes the thermal stability of bitumen. The penetration and ductility at low temperature determine, in combination, the capacity of bitumen to retain its alasticity.Petroleum bitumens are mainly used in road construction. Dirt and gravel roads are sometimes imprenated by liquid bitumen obtained by dilution of bitumen with a less viscous petroleum product, such as fuel oil. Some special grades of bitumen are made for application in civil engineering and for manufacture of paints and varnishes, electroinsulating materials, etc.Petroleum acids and their sails. Petroleum acids, mainly naphtenic, are present in some grades of petroleum. They are separated during alkali refining of fuel and oil distillates as sodium salts [soaps] and employed for manufacture of naphtenate soap, acidol and acidol- naphtenate soap. Naphtenate soap [contain 43 per cent of petroleum acids] is a mixture of sodium soaps of petroleum acids, minaral oil and water. Acidol [contains 42- 50 per cent of petroleum acids] consists of petroleum acids with an admixture of minaral oil. Acidol - naphtalenate soap [67-70 per cent of petroleum acids] is a mixture os free naphtenic acids and their dodium soaps. All these products are employed as subtitutes

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of fats in manufacture of industrial soaps, since they possess high emulsifying and foaming properties. They are also used in the textile industry for dyeing, for wood imprenation, as drying agents in paints and for some other purposes. A general requirement to these products is that the content of mineral oil be not above a specified limit.Solvents. The paint- and- varnish industry uses most widely gasoline [fraction 45-1700C], while spirit [fraction 165-2000C], and solvent naphta [mixture of xylenes] as solvents. In the food industry, the commonest solvents are extraction gasoline [fraction 70-950C] and petroleum ether [fractions 40-700C and 70-1000C]. In other industries, these and some other solvents [including benzene] can be employed. All solvents are specified for the content of benzene and unsaturated hydrocarbons and sulphur compounds.Solvents are usually obtained from accompanying petroleum gases and low- sulphurous petroleum and in gas fractionation, preliminary distillation of petroleum and in catalytic reforming [from refining products]. The disired fraction in sometimes separated in deep- distillation plants. In many casess, the fractions obtained are specially puriffied [mostly to minimize the content of benzene hydrocarbons and sulhpur compounds].Domestic [illumination] kerosene. Domestic kerosene is obtained by straigt- run distillation of petroleum. It should have a specified composition to ensure normal burning [mostly paraffine hydrocarbons], burn without forming fly ash [the height of non- smoky flame should be not less than 20 mm], and have an approriate brightness of flame.Coke. This is a product of petroleum coking, used for making electrodes, abrasives and some other materials and as a solid fuel. Electrode coke has the highest industrial significane for electrolytic manufacture of aluminum and making of artificial graphites which are used as antifriction materials in mechanical engineering.Commercial carbon [carbon black]. This is an amorphous substance usually in the form of a powder with black spherical particles 30-40 m in diameter. Commercial carbon may be named channel black or furnace black depending on the method of manufacture. It is employed as a filler in the rubber and paint and varnish industry and as a dyer in the manufacture of printing ink, ebonite, electrodes, etc. The principal standardized characteristics of carbon black are as follows; adsorption, dispersion, colouring power, absence of foreign inclusions, uniform distribution [in rubber mixtures], and fractional composition.

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At petroleum-processing plants, carbon black can be made from gases, green oil [obtained in pyrolysis of kerosene -solar oil fractions], coke residue [from coking plants], gas oil of catalytic cracking, and extracts of oil processing [more often after thermal treatment in cracking plants], coal tar pitch, and aromatized extracts from gas oil of secondary processes.Softners. Residual products of straight run distillation of petroleum ['softener' fuel oil], shale oil, and some products of oil processing can be used as softeners. They are employed in the rubber industry and as softeners of ruber mixtures in rubber regeneration.

ExercisesAnswer the following question1. What is the composition of grease?2. What are characteristics of grease?3. What are grease employed?4. How are bitumens prepared?5. What are the main characterictic of bituments?6. What is the main application of petroleum bituments?7. What are other applications of petroleum bituments?8. What is the main application of product of petroleum acids?9. What are other applications of product of petroleum acids?10. Which products of petroleum are used as solvents ?11. Which industries are solvents used in?12. How are solvents obtained?13. How is domestic kerosene obtained?14. Which properties that flame of domestic kerosene should

have?15. What is coke used for?16. How many is the dimension of particles of commercial

carbon?17. What is commercal carbon used for?18. What are the principal standardized characteristic of

commercial carbon?19. What are softeners used for?

IV. Products of petrochemical and basic organic synthesis.The industry of basic organic and petrochemical synthesis is a link between petroleum processing and chemical- recovery coke industries and all other branches of organic synthesis. It provides the latter with the required starting materials - organic products

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and, besides, supplies national economy with many valuable final products. Very many products of basic organic and petrochemical synthesis are intermediate, rather than end products. These include, in particular, many organic compounds of chlorine in which chlorine atoms can be substituted by other or groups of atoms.Starting substanes for polymer materials. Their manufacture plays an important part in basic organic synthesis and petrochemical synthesis. It provides starting materials for the manufacture of plastics, synthetic rubber, synthetic lacquers, glues, film materials, fibres, etc. Polymer materials are now made in hundreds of kinds having various properties and diverse applications. The most important among them are polyethylene, polystyrene, polyvinyl choride, polypropylene, and synthetic rubbers. Many of them are used as starting materials for manufacture of commercial goods. For instance, various rubber articles, including tyres, are made from synthetic rubbers; many articles made from polyethylene and polypropylene can successfully replace non - ferrous metals, etc.Plastifiers and other auxiliary subbstances for polymer materials. Along with the basic materials for manufacture of synthetic polymers, plastifiers and various auxiliary materials are also of large importance: they either facilitate the process of synthesis or impvove the properties of final products. For instance, plastifiers [softeners] are added [in an amount of up to 30-40 per cent] to certain polymers [especially to synthetic rubbers and polyvinyl chloride] to improve the plastic and elastic characteristics of these materials.Among various types of plastifiers, one of the most important groups includes high - boiling esters [dibutyl phthalate, dioctyl phthalate, tricresyl phthalate] and some esters of higher alcohols and dicarboxylic acids and of higher carboxylic acids and diatomic alcohols. Softeners obtained at petroleum processing plants are used in the manufacture of synthetic rubbers. Other auxiliary substances used in polymer technology [and in other processes] include initiators, catalysts, inhibitors, regulators, etc.Synthetic surfactants and detergents. Surfactants and detergents are used very widely in domestic life as powders and liquids for washing and cleaning. These substances are distinguished by a combination of hydrophobic and hydrophilic groups in the molecule. During washing, this facilitates wetting of the fabric and passage of dirt to the washing water. All surfactants and detergents are divided into ionogetic and non- ionogenic, depending on the presence or absence of groups capable of

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dissociating in aqueous solutions. Ionogenic substances, in turn, may be either anion- or cation- active, with their surface- active properties being determined respectively by anions or cations.Most of anion- active surfactants are sodium salts of sulfonic acids and acid esters of sulphuric acid, in particular, [1] alkylarylsulfonates with a C10- C15 alkyl group; [2] alkylsulfonates with 12-18 carbon atoms; and alkylsulphates with an alkyl group roughly of the same length:p-RC6H4SO2ONa R SO2ONa ROSO2ONaIn recent time, non- ionogenic substances have fuond a wide use. They are synthesized from ethylene oxide and various organic compounds- carboxylic acids, alcolhols, amines, etc. having active hydrogen atoms. Their hydrophilic propeties are due to a [CH2CH

2O]n chain obtained by successive attachment of molecules of ethylene oxide: RO-[CH2CH 2O]n-H. In order to improve their washing ability and lower the consumption, detergent substances might be mixed with various additives and these compositions are called washing means [in contrast to washing substances, or detergents, proper]. Such compositions [for instance, washing powders] contain sodium phosphate, pyrophosphate and hexamethaphosphate, sodium silicate, sulphate, carbonate, etc.Sythetic fuels, lubricants and additives. This group includes synthetic motor and let fuels, lubricating oils, addditives, antifreezing agents, braking and pressure fluids.Solvent and extractive agents. Synthetic solvents and extractive agents may belong to various groups of organic compound: chlorine derivatives, ancohols, cellosolves, ethers, ketones, esters, etc.Miscellaneous products. These include insecticides, medicaments and explosives.

ExercisesAnswer the following question1. What are products of petrochemical and basic organic

synthesis?2. Most of products of petrochemical and basic organic synthesis

are intermediate, aren't they?3. Why does manufacture of polymer materials play an important

part in basic organic and petroleum synthesis?4. What are the most important polymer materials?5. What are polymer materials used for?6. What are effects of plasitifiers and other auxiliary substances?7. What are auxiliary substances used for?8. What is structure of molecules of surfactants and detergents?

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9. What is difference between ionogenic and non- ionogenic substances?

10. How are hydrophilic properties of non- ionogenisc substances obtained?

11. What should we do to improve washing ability and to low the consumption?

Composition of petroleumPetroleum is a natural mixture of various hydrocarbons and their derivatives containing sulphur, nitrogen, oxygen, metals, etc.The main constituents of petroleum - hydrocarbons - may differ in the number of carbon and hydrogen atoms in the molecule and in the molecular structure. Petroleum hydrocarbons may relate to the following groups or series: paraffins [saturated, or stable hydrocarbons, alkanes], naphthenes [cycloankanes], and benzene hydrocarbons [arenes]. In most grades of petroleum, paraffins and naphthenes prevail. During processing of petroleum, unsaturated hydrocarbons [olefins and diolefins] may also form. The specific properties of petroleum products are dicided by the predominace of some or other group of hydrocarbons in crude petroleum and by the presence of compounds containing sulphur, nitrogen or oxygen.Paraffin hydrocarbons [alkanes]. Their general formula is CnH2n+2, where n is the number of carbon atoms. Each next hydrocarbon can be obtained from the previous one by substituting a methyl group CH3 for the extreme hydrogen atom in the chain: CH4 C2H6 C3H8 C4H10

methane ethane propane butaneThe paraffin hydrocarbons are the most stable of the lot because all valence bonds are fully satisfied as indicated by the single linkage. Most reactions involve the replacement of by hydrogen atoms with other atoms, the carbon linkage remains stable.Under common conditions, the hydrocarbons from CH4 to C4H10 are gaseuos, those from C5H12 to C15H32 are liquids [they enter the

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composition of gasoline, kerosene and diesei- fuel fractions], and those from C16H34 are solid [paraffins].Beginning from the fourth term in the series [butane C4H10], hydrocarbons may exist in two or more forms differing in the structure. For instance, butane may exist in two forms: n- butane and isobutane. Compounds which have the same chemical formula but a different atomic structure are called isomers.The number of isomers increases for each next hydrocarbon in the series. Hydrocarbons of the formula C13H28 may have 802 isomers, those of the formula C14H30, 1858, and so on. Thus, the composition of petroleum is quite complicated. Isomers possess different physical and chemical properties. For instance, heptane of normal structure [n- C7H16] has an octane number of zero, whereas isooctane [iso- C7H16] has an octane number of 100.Naphthenic Hydrocarbons [Cycloalkanes]. Their general formula is CnH2n. They were discovered by V.V. Markovnikov, a prominent Russian chemist, when studying petroleums of Caucasian deposits.In their chemical properties; naphthenic hydrocarbons are similar to paraffines, but differ from the latter in having a cyclic structure.Cyclopentane and cyclohexane derivatives are especially important for the quality of petroleum and petroleum products.Benzene Hydrocarbons [Arenes]. Arenes of the benzene series have the general formula is CnH2n-6. The cyclic structure of arenes differs from that of naphtenes by the presence of double bonds on the aromatic ring. If one or more atoms of hydrogen in the ring are replaced by a methyl [-CH3] or an ethyl [-C2H5] group, other arenes [toluene, xylenes and ethylbezene] are formed. Arenes are a valuable raw material for chemical technology and the manufacture of antinock gasoline.Unsaturated Hydrocarbons [Olefines]. Hydrocarbons of the ethylene series have general formula is CnH2n-2, are characterized by a double bond in the molecule [ethylene C2H4, propylene C3H6, butylenes C.4H8, amylenes C5H10, etc.] and may be of either normal or isomeric structure.They are not present in crude petroleum, but constitute an appreciable part of the products obtained in the thermal and some catalytic processes of petroleum processing. These hydrocarbons have a high reactivity and are used for the manufacture of some important products, such as polyethylene, polypropylene, ethylene and propylene oxides and their derivatives.Along with olefines, some less saturated hydrocarbons, with two double bonds in the structure, such as diolefines, can form in petroleum processing. These are extremely unstable and for that

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reason should not be present in final petroleum products. Some of them [ butadien C4H6 and isoprene C.5H8] are obtained intentionally from petroleum and used for the manufacture of synthetic rubber and like products.Oxygen- containing compounds. These include naphthenic acids, phenols and tar- asphaltene compounds.

Naphthenic acids are compounds containing a carboxyl group-COOH. Their density is from 0.96 to 1.05 g/cm3 and general formula, CnH2n-2O2. Naphthenic acids are strongly smelling oily liquids. They may be present in kerosene, diezel- fuel and light oil distillates of petroleum and are corrosion- aggressive; they are removed from petroleum fractions by leaching. Naphthenic and their salts are widely used in industry as components of greases, for imprenation of fabrics and footwear, etc.Phenols are contained only in some grades of petroleum and are liberated together with naphthenic acids during leaching of distillates.Tar- asphaltene compounds may be present in petroleum in considerable quantities [from traces to 25% and even more]. They are complex high- molecular compounds containing carbon[82-87.4%], hydrogen [10.3-12.5%], oxygen [up yo 2.5%], sulphur [0.8-7%], and nitrogen [up to 1%]. Low molecular tar compounds can partially be distilled of together with petroleum distillates, while high molecular ones remain in fuel-oil fractions and especially in oil residue [goudron]. The presence of tar in these products makes them dark and promotes carbonization in cylinders of internal combustion engines. Tar- asphaltene products are harmful is white petroleum products and oils, but are desirable constituents in such produsts as bitumen, coke, isulating and imprenating materials.All tar-asphaltene products are usually classed into neutral resins soluble in light gasoline; asphaltenes [ the products of polymerization of neutral resins and oxyacits] which are insoluble in light gasoline, but soluble in benzene, chloroform and carbon bisulphide; asphaltogenous acids and their anhydrides of acid nature. which are insoluble in light gasoline, but soluble in alcohol. As has been shown experimentally by N. I. Chernozhukov and S. E. Krein, petroleum hydrocarbons are oxidized simultaneously in two directions:All the three types of tar-asphaltene compounds are high-molecular compounds of unsaturated nature containing oxygen and sulphur. At normal temperature they are very thick and viscous liquids or are solid and have a density above 1.0 g/cm3.

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The content of tar-asphaltene compounds is greater in petroleum grades of higher density and in those high in sulphur.Sulphur compounds. In Vietnam grades of petroleum, the content of sulphur is small. Sulphur is present in petroleum and petroleum products mostly in combined state, i.e. in the form of organic sulphur compounds. Sulphur compounds of the following types may be found in petroleum products: mercaptans RSH [where R is a hydrocarbon radical]; sulphides RS, disulphides RS-SR, thiophene C4H4S and its derivatives, and sometimes hydrogen sulphide and elemental sulphur. Hydrogen sulphide and mercaptans which have acid properties, and elemental sulphur form a group of active sulphur compounds which can cause strong corrossion of equipment and pipelines.Another group includes sulphides and disulphides which are neutral at low temperatures, but are thermally unstable; at 130-1600C they decompose [with breaking of C-S bonds] and form hydrocarbons, mercaptans and hydrogen sulphide. A third group includes thiophane and thiophene and their derivatives, such as benzothiophene.Like benzene hydrocarbons they have a low reactivity and are relatively stable at elevated temteratures.High- molecular sulphur compounds are unstable and can be oxidized under relatively soft conditions; the products of oxidation increase the content of tar in petroleum products. In the atmosphere of hydrogen, they are reduced to corresponding hydrocarbons and hydrogen sulphide; this is the basis of the processes of hidrogen refining [hydrofining] of petroleum and petroleum products.In straight distillation of petroleum [without destruction] the content of sulphur increases from lighter fraction to heavier ones, with the residue having the highest concentration of sulphur. When higher temperature and pressure are applied, however, organic sulphur compounds are destroyed together with high - molecular hydrocarbon to form hydrogen sulphide and mercaptans which are corrosive and toxic. Corrosion is enhanced in the presence of water vapours and hydrochloric acid which forms by decomposition of calcium and magnesium chlorides contained in undesalted petroleum.In order to diminish corrosion and improve labour conditions, petroleum before dictillation might be desalted and dehydrated. The content of sulphurous compounds in petroleum products can be lowerd by various methods of refining, mainly by hydrogen refining.

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Nitrogen Compounds. The content of nitrogen is usually greater in heavier grades of petroleum. Nitrogen compounds are divided into basic, which contain nuclei of pyridine and quinoline, and neutral, which contain pyrrol and indol homologues. In petroleum processing, nitrogen compounds are distributed between fractions much like sulphur compounds, i. e. their concentration increases from lighter fractions to heavier ones, and the largest amount [65-75%] is concentrated in the residue.Among nitrogen compounds, porphyrins occupy a special place. They may be present in petroleum either in free state [four pyrrol rings] or as complexes containing organic nitrogen compounds and organic derivatives of vanadium and nickel. Notwithstanding the high thermal stability of nitrogen compounds in the technological processes, they decompose partially, which is detected by the formation of ammonia. Certain refining processes [for instance, hydrogen refining] can remove an appreciable portion of sulphurous compounds [as hydrogen sulphide] and a part of nitrogen compounds [as ammonia] and oxygen compounds [as water vapour].Mineral Substances. Mineral substances are found in petroleum only in very small concentrations [provided that crude petroleum has been refined properly from mechanical impurities at the oil well]. As has been established by combustion of many samples of petroleum, the elements found in the ash form [in the decreasing order] the following row: S-O-N-V-P-K-Ni-I-Si-Ca-Fe-Mg-Na-Al-Mn-Pb-As-Cu-Ti-V-Sn. The total amount of ash in various grades of petroleum may vary from a few thousandths of a per cent to 0.8 per cent.

ExercisesAnswer the following questionWhat is the elemental composision of petroleum?What is the main constituents of petroleum ?Which series of hydrocarbon are present in petroleum ?Which series of hydrocarbon are formed during processing of petroleum ?What are the chemical properties of paraffin hydrocarbons ?What are the physical properties of paraffin hydrocarbons ?Which compounds are called isomers?What can you say about the chemical and physical properties of isomers?What is the difference and similarity in structure and properties between paraffinic and naphthenic hydrocarbons ?What is the difference and similarity in structure and properties between naphthenic and benzene hydrocarbons ?

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What are applications of benzene hydrocarbons ?What can you say about properties of olefins and diolefins?What are applications of olefins and diolefins?What are applications of naphthenic acid?What is the elemental composision oftat-asphaltene compounds? How can you class tar-asphaltene products?Which types of sulphurous compounds are present in petroleum products?How can the content of of sulphurous compounds in petroleum products be lowered?How are nitrogen compounds distributed?

Basic Physico-chemical properties of petroleum and petroleum products

Density. The density of petroleum and petroleum products can be expressed in either absolute or relative values. The relative density is the ratio of the density of a petroleum product at temperature t2 to the density of distilled water at temperature t1. The density of petroleum products is normally measured at 200 C and that of water, at 40 C. Since the latter is taken as unity, the numerical values of the relative and absolute density coincide.To find the absolute density [kg/m3 or g/cm3] the mass of a product is divided by its volume, i. e. =m/V.The density of petroleum and petroleum products depends on the content and the composition of light low-boiling [which have a low density] and heavy high-boiling constituents [fractions]. Indeed, among the components having roughly the same boiling point, paraffin hydrocarbons have the lowest density and benzene hydrocarbons have the highest value, with that of naphthalenes being in the middle. This is why density is one of the principal characteristics of petroleum and petroleum products.The density of petroleum and petroleum products decreases with the increasing temperature and their volume recpectively increases. The temperature relationship for density can be expressed by Mendeleev's formula: dt

4 = d204 - a[t-20]

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where dt4 is the relative density of a product at temperature t; d20

4

is the relative density of a product at 200CMolecular Mass. This is one of the basic physico-chemical

characteristics of petroleum and petroleum products. The molecular mass of paraffin hydrocarbons can be found approximately by using the formula:

M = 60+0.3t+0.001t2

where t is the average temperature of boiling of a petroleum fraction, 0C; it is calculated as the arithmetic mean of the temperatures at which equal volumes of the liquid, say, 10% fraction, are distilled off.

The relationship between the molecular mass and relative dendity of petroleum fractions is determinded by the following empirical formula: M = 44.29d15

15/1.03- d1515. Using this formula, it is also possible to fine [with a certain

approximation] the molecular mass of all classes of hyfrocarbons.Boiling Point. Fractional Composition. The boiling point

of a liquid os the temperature at which the pressure of vapours is equal to the external pressure; on reaching this point, vaporization, which up to that moment occured from the surface only, begins in bulk of the liquid [at the bottom and walls of the vessel being heated], where vapour bubbles are formed; this is what is called the boiling proper. If vapours are not removed off the liquid surface during heating, an equilibrium is established between the liquid and vapour phase. Vapours in equilibrium with the liquid are called saturated. At a higher temperature of heating of a liquid, vaporization occurs more intensively, more vapours are formed above the liquid, and the pressure of saturated vapours is higher.

The boiling point of a liquid depends on the external pressure. For instance, water at a pressure of 0.1 MPa boils at 1000C. At a higher pressure, say 0.4 MPa, boiling begins only at 1440C. Thus , the boiling point is higher at a higher external pressure and at a lower external pressure os in vacuum, water boils at a lower temperature. The same effect of pressure is found in other liquids. This phenomenon is utilized in vacuum distillation of fuel oil.

Petroleum and petroleum products can be separated into individual hydrocarbons only with certain difficulties. Usually separation is carried out by distillation which gives simpler mixtures are called fractions. They boil not at a constant temperature, but in a temperature range betwwen the point of the begining of boiling and that of its end. Depending on the boiling

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points and contents of various hydrocarbons, a product may have different boiling ranges, i. e. may have a different fractional composition.

All petroleum products obtained from crude petroleum by distillation are essentially fractions that can boil off within particular temperature ranges. For instance, gasiline fractions boil off within 35-2050C, kerosene fraction within 150-315 0C, diezel-fuel fractions within 350-4200C, light oil distillates within 350-420 0C, heavy oil distillates within 420-490 0C, and oil residues at temperatures above 490 0C.Thermal Properties of Petroleum and Petroleum products. These properties are of high pratical importance for calculating the heat balance of all processes associated with heating or cooling.Specific heat is the quality of heat needed to heat up 1 kg of substance by 10C. The approximate value of specific heat, kJ/kg.K, are as follows: petroleum 2.1, petroleum vapours 2.1, water 4.19.With the specific heat of a petroleum product being known , it is possible to calculate the quantity of heat for heating. For this, the specific heat is multiplied by the mass of the product [kg] and by the difference between the final and initial temperature [0C]. The specific heat of petroleum products increases with increasing temperature and is higher for products of lower density.Specific latent heat of evaporation is the quantity of heat spent to vaporize 1 kg of a liquid at its boiling point [this characteristic is called latent, since the heat is spent for evaporation and the temperature of the product remains constant during heating]. The average values of the latent heat of evaporation at the atmospheric pressure, kJ/kg, are as follows: water 2257, gasoline 293.3-314.3, kerosene 230-251, diesel fuels 209-213, oils 167-209. Thus the latent heat of evaporation decreases with increasing density and malecular mass of petroleum products, and also with increasing temperature and pressure.The heat of condensation is the quantity of heat liberated by vapours during their condensation and is numerically equal to the latent heat of evaporation.The latent heat of fusion is the quantity of heat absorbed during fusion of 1 kg of a solid at the melting point.The heat of combustion [calorific value] of fuel is the quantity of heat liberated by the fuel on full combustion. A distinction is made between the high and low heat of combustion: the former [Qh} takes into account the heat of condensation of the water present in the fuel and formed during combustion [it is taken conditionally that the combustion prodducts contain liquid water rather than

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water vapours]. The low head of combustion, Ql, implies that the water of the fuel and the water formed by combustion gases [i.e. it is lower than the high heat of combustion by the quantity of heat spent for evaporation of moisture of the fuel and of the water formed through combustion of hydrogen in the fuel].Viscosity [internal friction]. Viscosity is the ability of a liquid [or gas] to resist the motion of a layer relative to other layers. As regards petroleum products, a distinction is made between dynamic, kinematic and relative viscosity.Dynamic viscosity is measured in pascal-second [Pa s]. The dynamic viscosity of selected liquids is as follows:

Pa sEther[at 180C]Gasoline[at 200C]Kerosene[at 200C]Alcohol[at 180C]Water[at 200C]Glycerine[at 180C]Spindle oil[at 200C]Cylinder oil[at 200C]Caster oil[at 180C]

0.0000260.00450.00170.001660.0010061.100.0420.351.20

An inverse value of dynamic viscosity is called fluidity. In process calculations and for testing the quality of many petroleum products, use is made of kinematic viscossity , which is the ratio of the dynamic viscosity to the relative density of a liquid, d, at the same temperature, i.e.

= /dKinematic viscosity is measured in square metre [square millimetre] per second[m2/s, mm2/s].In practical calculations, especially for quality control of petroleum products, use is often made of relative viscosity which is the time of efflux of 200 ml of a petroleum product at the testing temperature related to the time of refflux of the same volume of distilled water at 200C [the time of refflux of 200 ml of water at 200C is what is called the water number of a viscosimeter]. Viscosity- temperature relationships. Viscosity becomes lower with encreasing temperature and vice versa. The patern of variation of viscosity with temperature is an important characteristic of petroleum products, especially of lubricating oils. These variations can be determined by various methodes, for instance, by the ratio of the viscosity at 50 0C to that at 1000C, which is now specified for many lubricating oils, or by the viscosity index; the latter is found from monograms for the known values of

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viscosity at 50 0C and 1000C. With a higher ratio of viscosities, the temperature curve of viscosity is steeper and on the contrary with a lower ratio, the curve is less steep and the quality of the oil is better.The Setting and Fusion points. When being cooled, petroleum and petroleum products gradually loss mobility and can set [solidify] notwithstanding the fact that they contain some substances that might be liquid at the temperature considered.The setting [sodification] point of a petroleum product is the temperature at which the product loses mobility under strictly specified testing conditions. The loss of mobility and freezing of petroleum and petroleum products depend mainly on the content of hydrocarbons which are solid [at the nomal temperature]. The higher the content of such hydrocarbons [in dissolved or crystalline state], the more quikly the product loses its mobility during cooling, i.e. the products has a relatively high setting point. Tarry products and asphaltenes can retard somewhat the crystallization of solid hydrocarbons, that is why the setting point of detarred products is always higher than that of the distillates from which they have been obtained.During cooling to their setting point. white petroleum products pass through a number of intermediate stages- the stage of turbidity [blushing] and that of the beginning of crystallization. The highest temperature at which crystals [say, of benzene, etc.] can be detected in the cooled fuel by nakes eye is called the temperature of the beginning of crystallization, or the chilling temperature [point]. The temperature at which crystals of hydrocarbons [mainly of paraffins] start to precipitate and make the product turbid is called the blushing temperature [point]. Along with the temperature of chilling of liquid petroleum products, the temperature of fusion of some products which are solid at nomal temperature [paraffin and ceresin] is also practical importance.The fusion point is the temperature at which a solid produst becomes liquid under strictly specified testing conditions.With these constants being known it is possible to select properly the method of petroleum processing and take the required measures to ensure pipeline transportation, especially in winter time, and also to choose the methods of storage and transportation of solid products having a high chilling point.Flash and Ignition Points. Self- ignition temperature.Explosibility. The fire hazard of petroleum products is judged upon by their flash, ignition and self- ignition

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temperatures [point]. At lower values of these characteristics, a product is more fire- hazardous.The flash point is the temperature at which a mixture of air and vapours of a product being heated under standard conditions ignites on contact with an ignition source, but the product proper is not ignited and the flame is damped. For light petroleum products [with the flash point not above 500C] the flash point is measured in a closed apparatus and that of heavier products [with the flash point above 70 0C] can be determined in an open vessel. The product to be tested is poured into the apparatus and a thermometer is put inside. With light products, the apparatus is covered by a lid with a window which can closed by a gate. During the test, the window is opened periodically and a burner is brought close to it. In an open appararus, the burner is moved close to the liquid surface. Tests in an open apparatus give a higher value of a flash point, since the vapour formed are partially dissipated to the surroundings.In further heating, a petroleum product can ignite at a certain temperature. This temperature is called the ignition point.There is a certain relationship between the fracrtional coposition of a product and its flash and ignition points: lighter hydrocarbons in its composition lower these points. For instance, gasoline has the flash point below - 500C, whereas the flash point of fuel oil is above 1100C.According to international recommendations, easily igniting liquids include those flash point is below 610C [in a closed vessel] or 660C [in an open vessel]. These liquids, which can be ignited by a short action or even a small ignition source [say, a spark] and without preliminary heating.The temperature of self- ignition of a petroleum product is lower at a higher content of heavy hydrocarbons. This is the temperature at which a product ignites spontaneuosly on contact with the air, i.e. in the absence of flame or spark. Some products, such as fuel oils, goudron, soot and coke, self- ignite quite easily at temperature slightly above 300 0C. Self- ignition usually occurs in untight pipelines and apparatus in which petroleum products are at temperature above their ignition point. It is therefore essential to check the equipment for tightness to prevent self- ignition and fires.Explosibility. In petroleum processing plants, mixtures of vapours of some products with air may be explosive. Such mixtures may form in open air, in closed premises and inside processing equipment. A mixture of vapours of a product with air become explosive when the concentration of the vapours in mixture

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exceeds a definite limit. At lower concentrations, the mixture is not explosion hazardous, since the greatest portion of the heat evolved in the ignition zone is spent to heat up the air. A mixture can not explode, too, if it contains little air and therefore there is not enough oxygen to sustain combustion.The lowest concentration of vapours of a petroleum product [or other substance] in the air at which explosion is probable is called the lower explosive limit and the highest concentration of vapours at which explosion is still possible is respectively the upper explosive limit. The concentration range between the two limit in which explosion can take place on contact with open fire [or spark] is called the explosibility range.The upper and lower explosive limits and the explosibility are different for various vapours and gases. The explosibility ranges for some vapours and gases obtained at petroleum processing plants [percent] are as follows: gasoline 0.8 to 5.1; kerosene 1.4 to 7.4; propane 2.1 to 9.5; methane 5 to 15; ammonia 15 to 28; ethylene 3 to 32; hydrogen sulphide 4.3 to 46; carbon monoxide 12.5 to 74; hydrogen 4 to 74; and acetylene 2.3 to 81.The highest permissible concentration of vapours of a product in working premises depends on the composition of that product. The selected products it is as follows [mg/m3]: 100 for gasoline fuels, 300 for gasoline solvents, 5 for benzene ans methanol, 50 for toluene and xylene, 10 for pure hydrogene sulphide, 3 for mixture of hydrogen sulphide with C1- C5 hydrocarbons, and 5 for phenol.

ExercisesAnswer the following question1. How can they express the density of petroleum ans petroleum

products?2. what is the relative density of petroleum product ?3. How can you calculate the absolute density?4. Is there the relationship between the density of petroleum

products and the poiling point of them? What is it?5. Is there the relationship between the density of petroleum

products and their temperature and their volume?6. What is the boiling point of a liquid?7. What is the relationship between the bpoiling point and the

external pressure ?8. What is the fractions?9. What is the specific heat?10. How can you calculate the quantity of heat for heating?11. What is the specific latnet heat of e Is there the relationship

between the density of petroleum products and the evaporation?

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12. How can you understand the term"latent"?13. How can you distinguish the high and low heat of

combustion?14. What is the viscosity of liquid?15. How many type of viscosity of liquid do you know?16. What is the relationship between the viscosity index and the

quality of the oil?17. What is the setting point?18. Why is the setting point of detared products higher than that

of the distillates from which they have been obtained?19. What is the fusion point?20. What is the flash point?21. How can you measure the flash point?22. What is the ignition point?23. What is the temperature of self-ignition?24. When does the explosipility happen?

DistillationThe property that differentiates most petroleum products from each other is "volatility", or tendency to vaporize. More volatile products are called "lighter", less volatile products, "heavier". The volatility of a product is determined, of course, by the boiling points of its components. Inusmuch as distillation separates liquid by boiling points, distillation is the principal separation process.

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Theory of DistillationThe basic principle of distillation is simple. When a solution is boiled, the lighter components vaporize preferentially and the solution is separated into a lighter overhead product and a heavier residue. For most petroleum applications, this simple operation does not suffice, and multistage units must be emloyed. Such units consist of dylindrical columns, or "towers", through whish vapor and liquid streams pass countercurrently. Depending upon circumstances, feed may be charged at any point in the column. Products are withdrawn from the top and bottom and sometimes from intermediate points as well. Liquid withdrawn from the bottom is usually reboiled to supply vapors to the column; vapors from the top are condensed and a portion is returned as '"reflux". It seem paradoxical to build complex and expensive equipment to separate out an overhaed product and then to return part of it to the separarion zone. Indeed, many of technologists of the time considered refluxing foolish when it was first introduced. We may conclude from this that the function of reflux is somswhat obscure. Why it is used in multistage unit can best be illustrated by analogy with singlestage operations.Staging. Consider a singlestage distillation system in which a solution is heated until half of it vaporizes, the vapor being separated from the liquid and condensed. Suppose that a two-component solution is processed in this system to concentrate the lighter component in the overhead fraction. Suppose further that the desired concentration is not attained. A more concentrated product could be obtained dy charging the overhead to a second unit, and this procedure could be repeated until the desired concentration was obtained. Similarly, the heavier component could be concentrated in the bottoms cut by reprocessing succesive residues. In either case, the yield of the desired product would be low. and large amounts of intermediate materials would be made. Yields could be improved by returning each intermediate material with the next charge to the preceding stage. By this means, all the original charge wouldd be recovered ultimately in one or the other of the desired products. Such an operation is diagramed in Fig.1a; each stage in thid diagram includes equipment to vaporize a portion of the charge and to condense the vapors. Although the indicated operation is possible, equipment would be complex and expensive, and labor and energy requirements would be high. The equipment could be simplified somewhat by converting each batch stage to continuous operation as shown in Fig.1b, but the equipment would still be complex and the operation expensive. The next step is to eliminate vaporization

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and condensation equipment from the intermediate steps by permitting the vapor from each stage to pass directly into the stage above, where it mixes with the liquid from the next higher stage; the contained heat in the vapor substitutes for indirect heating of the liquid. Now all that remains is to house all the intermediate steps in a single column, and we have the modern distillation unit shown in Fig. 1c.Column Sections. The part of the column above the feed inlet is called the "rectifying section", and the part below it is called the "stripping section". The two sections have different purposes. One serves to increase the purity of a product; the other increases its recovery. In Fig. 1a, for example, stages 2, 4, and 6, which correspond to the rectifying section, increase the purity of the light product taken overhead. The liquid leaving stage 1 contains a considerable amount of the light component, and steps 3, 5, and 7, which correspond to the stripping section, strip the light component out and thereby improve its recovery in the overhead. For the heavy product, the functions of the two sections are reversed; the rectifying section improves recovery, the stripping section, purity. In some applications only one or the other of these two sections is required, depending upon the particular purity and recovery requirements of the operation.Extractive ans Azeotropic DistillationBecause distillation separates by virtue of differences in volatility, disstillation can not normally be used to separate close- boiling materials. However, when the materials to be separated are chemically dissimilar, modified distillation procedures can be used. Examples are the separation of butenes from butanes and of toluene from isooctanes. In such cases; an extraneous liquid can be added which has an affinity for one of the components in the charge; as a result the relative volatilities of the original components change, and separation becomes possible. If the added material is less volatile than the original components, it is added at the top of the column and withdrawn from the bottom, and the operation is called extractive distillation. If the added material is more volatile than the original components, it is added at the top of the column or with the feed and is withdrawn in the overhead product; the operation is then called azeotropic distillation.Solvents and Entrainers. In extractive distillation, the extraneous liquid is called a solvent; in azeotropic distillation, it is called entrainer. In either case, its effectiveness is determined by its concentration in the liquid phase. Consequently, the boiling point of an entrainer is limited; it must be about as volatile as the

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lighter feed components so that it will pass overhead, but it must not be so volatile that it will disappear from the downflowing liquid stream much above the bottom of the tower. An entrainer must be separable, of course, from the overhead product- by distillation or by some other technique. Similarly, a solvent in extractive distillation must be separable from the bottoms product. How the entrainer or the solvent is separated from the overhead or bottoms product is an important consideration, because large volumes must be used. To be effective in changing the relative volatilities of the original components, an entrainer or a solvent must constitute at least 40% of the liquid phase [60], and its concentration is usually much higher.Effects of Reflux. In extractive distillation, reflux has two opposing effects. By increasing the counterflow of liquid and vapor, increasing the reflux promotes the separation. However, increasing the reflux lowers the concentration of the solvent in the liquid streams; this lessens its effect in spreading the volatilities of the original feed components and thus retards their separation. Because of these conflicting effects, there is apt to be sharp optimum in the reflux rate for an extractive distillation operation.Feed Preparation. Only narrow-boiling materials are charged to extractive or azeotropic distillation. The reason may be seen most readily from an example. Consider extractive distillationfor the separation of toluene from a mixture with isooctane, which nomally boil very closely to toluene. Lower- boiling materials [like hexane and benzene] and higher - boiling materials [like isononanes] are first separaated by ordinary distillation.The sharpness of removing the light ends affects only the amount of material charged to extractive distillation. On the other hand, the purity of the toluene product will depend upon the sharpness of prefactionating the heavy ends out of the feed.How poor removal of heavy ends affects product purity may be seen by considering the nomal volatilities of the feed components and how they are affected by the presence of a solvent. Toluene and isooctane boil together, and isononanes are about half as volatile. In the concentration isually employed, a solvent approximately doubles the volatilities of the paraffins relative to toluene. In the presence of the solvent, then, the isononanes have about the same volatility as toluene, and their separation is very difficult, and sometimes impossible.Even when heavy materials can be taken overhead in extractive distillation, they may be very undesirable in the feed. When phenol is used as the solvent, for example, volatility relationships are such that heavy paraffins in the overhead tend to carry some

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phenol with them. Phenol is expensive, and only small losses can be tolerated.

ExercisesAnswer the following question1. What is the principle of distillation?2. What are the distilling towers?3. Where can they withdraw product of distillation?4. What is the reflux?5. What do they do to increase the pure of products?6. What are the rectifying section and stripping section?7. What are the purposes of them?8. When must they add the extraneous liquid in distillation?9. What is the extractive distillation?10. What is the azeotropic distillation?11. What are a solvent andanentrainer?12. What is the boiling point of entrainer like?13. What is the important characteristic of solvent and entrainer?14. Which materials are used in extractive or azeotropic

distillation?

Catalytic ReformingBecause higher- octane gasoline permit the building of engines that extract more power from gasoline, there has been a constant push toward higher octanes since differences is octane quality were first recognized. A major factor in this development has been the large - scale use of catalytic reforming to raise octane ratings of gasoline stocks. The first commercial unit, Hydroformer, went on stream just before World War II, and the process proved to be a major source of aromatics and aviation gasoline for minitary uses. However, catalytic reforming did not "catch on" until about 1950, when Haensel and others at the Universal Oil Products Co. demonstrated that platinum catalysts could be used commercially despite their high cost. By 1955, catalytic reforming processes had almost completely supplanted thermal reforming. Catalytic processes not only give higher quality products, they give a higher yields as well.ReactionsIn catalytic reforming, the principal object is to convert other hydrocarbon to aromatics. The reason may be seen by comparing the octane numbers of some corresponding hydrocarbons [Table 1]. Thus, high conversions to aromatics result in high octane products. There is a loss in volume, because aromatics are denser than other hydrocarbons; however, the loss is small in comparison with the loss [to gas and tar] suffered in thermal reforming. Other

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reactions of some importance in catalytic reforming are cracking and isomerization.Table 1

Research rating Motor ratingn-Heptane2- MethylhexaneHeptene-2Methylcyclohexane2,3-Dimethylpentane2,2,3-Trimethylbutane[triptane]Toluen

042737591113120

045577189101104

Production of Aromatics. Because aromatics contain less hydrogen than do other hydrocarbons, dehydrogenation is the primary reaction. Of the nonaromatics, cyclohexane derivatives are dehydrogenated most readily: C6H11CH3 C6H5CH3 + 3H2

Methylcyclohexan TolueneCyclopentane derivatives react similarly, but they require a preliminary isomerization to cyclohexan derivatives: C5H9CH2CH3 C6H11CH3 C6H5CH3 + 3H2

Ethylcyclopentane Methylcyclohexane TolueneCoversion of paraffins to aromatics involves a cyclization step. For normal heptane, the reaction may be written:n-C7H16 C6H11CH3 + H2

C6H11CH3 C6H5CH3 + 3H2

To undergo these reactions, a paraffin must have at least six carbon atoms in a chain or be isomerizable to such a compound.

Aliphatic olefins can also be converted to aromatics directly, but this fact is of little practical significance because such olefins are readily hydrogenated to paraffins under the conditions used in catalytic reforming. Thus , aliphatic olefins behave as paraffins, with the exception that they deactivate the catalyst more rapidly. Similarly, cyclic olefins behave as naphtenes.

Hydrocracking. Under the conditions employed in catalytic reforming, cracking completes with dehydrogenation reactions. Because high hydrogen pressure are used, any olefins that form are saturated immediately, and the reaction usually called "hydrocracking". Whether hydrocracking occurs in one step or in two is of little consequence. In either case, a typical over-all reaction is:n-C8H18 + H2 C3H8 + n-C5H12

Octane Propane Pentane

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Because lower-boiling paraffins have higher octane numbers, hydrocracking improves ontane ratings; however, the improvement is less than if the paraffins were converted to aromatics. Also, there is considerable loss of gasoline to butanes and lighter materials, and the vapor pressure of the debutanized product is raised. Increasing the vapor pressure reduces the amount of butane that can be blended into the product to make a finished gasoline; thus, the effective yield of gasoline is reduced still further.Hydrocracking of naphthenes also occurs to some extent.

Cyclopentane derivatives are more susceptible than cyclohexane derivatives, especially over catalysts with little isomerization activity. The first step in the hydrocracking of naphthenes is probably scission of the ring:

C5H9CH2CH3 + H2 n-C7H16

The paraffins are formed may react further to produce aromatics, or it may be hydrocracking.Isomerization. With some catalysts, paraffins are isomerized

under refarming conditions. Usually, isomerization of paraffins does not have a large effect on octane quality because the production of highly branched paraffins are small. If the paraffins in a given charge were chiefly normal, their isomerization would have a large effect on octane. In most instances, however, paraffins in the charge are mixtures of isomers; therefore the isomerizing activity of a catalyst is important chiefly for the isomerization of cyclopentane derivatives.

CatalystsAlthough aromatics can be produced from either

hydrocarbons without catalysts, severe condotions are required, and yields are low. To obtain acceptable yields, dehydrogenation catalysts must be employed. Those of commercial interest include platinum on alumina, platinum on sillica-alumina, chromia on alumina, molybdena on alumina, and cobalt molybdate on alumina.The ideal catalyst would convert all other hydrocarbons selectiely to aromatics rapidly, with only a small catalyst inventory. Such a catalyst would not promote hydrocracking, and it would have to operate under conditions thermodynamically favorable to production of aromatics. To the extent that a catalyst deviates from this conditions it is a poorer catalyst. Derivations may be either in the selectivity of the catalyst toward the production of aromatics or in the activity of the catalyst for the several reactions that actually occur. Selectivity is determined by the relative rates of the competing reactions- dehydrogenation to aromatics and hydrocracking, and isomerization in so far as it

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affects the other two. Activity is determined by the magnitude of the rate constants. Platinum catalysts appear to be the most selective and the most active, as well as the most expensive.Dehydrogenation of Naphthenes. Selectivities of catalysts

depend to some extent on the make-up of the feed stock. Alkylcyclohexanes are readily converted to aromatics by all dehydrogenation catalysts, provided that the reaction conditions are favorable thermodynamically. For the conversion of alkylcyclopentanes, on the other hand, there are large differences. Because alkylcyclopentanes require an isomerization step, their conversion to aromatics depends upon the isomerization activity of the catalyst. Published data on platinum, molybdena, and chromia catalysts show that platinum has the highest isomerization activity, chromia the lowest. Even with platinum catalysts, the isomerization reaction is the rate-controlling step. Thus the conversion of alkylcyclopentanes to aromatics is lower than the conversion of alkylcyclopentanes to aromatics is lower than the conversion of cyclohexane derivatives; consequently there is more opportunity for hydrocracking, and yields of aromatics are poorer.Dehydrocyclization of Paraffins. Data on platinum, molibdena,

and chromia catalysts have also been published for the conversion of paraffins to aromatics. When operating in the pressure range normally use in catalytic reforming, platinum is the most effective catalyst, chromia the least. The poor results obtained with chromia catalyst are surprising, inusmuch as high conversions of n-heptane to toluene are obtained at low pressures. Apparently, the chromia catalyst has the unusual property of adsorbing hydrogen so strongly at higher pressure that paraffins can not readily reach its surface.

Reaction MechanismExtensive studies have been made to elucidate the

mechanism of reforming over platinum catalysts. Such catalysts are duel-functional; they cotain platinum as a dehydrogenating agent and an acidic material, such as chlorine, fluorine, or alumina-promoted silica, as an isomerization agent. In commercial catalysts, enough platinum is used to ensure that the dehydrogenation activity is large in comparision with the isomerization activity.Although only traces of olefins can exist under reforming conditions, they apparently are intermediates in the reactions. Both naphthenes and paraffins are dehydrogenated to olefins [in trace amounts] on dehydrogenation sites in the catalyst. Cyclohexenes continue to dehydrogenate rapidly to aromatics.

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Alkylcyclopentanes transfer to acid sites, where they are isomerized to cyclohexanes; the cyclohexanes then pass back to dehydrogenation sites, where they are converted to aromatics. Alkyl olefins also transfer to acid sites where they may either isomerize to other alkyl structures or cyclize to naphthenes. The isomerized olefins pass back to dehydrogenation sites, where alkyl olefins are hydrogenated to paraffins and cyclohexenes are dehydrogenated to aromatics.In view of the low isomerization activity of chromia catalysts, the exellent results obtained with them at low pressure suggest that n-heptane is easier to aromatize than are its isomers. This idea is also suggeted by data on the conversion of n-heptane over a platinum catalyst; the ratio of aromatics production to hydrocracking was higher at low conversions [where n-heptane predominates in the reactants] than at higher conversion [where isoheptanes predominats]. It has also been shown that paraffins with more than seven carbon atoms are converted more raedily to aromatics than are heptanes. All these observations fit the hypothesis that naphthene intermediates are not formed from paraffins over platinum catalysts by linking of two end [primary] carbon atoms. It has been suggected that platinum catalysts form derivatives of cyclopentane by the linkage of second and sixth carbon atoms; the alkylcyclopentanes so formed isomerize to alkylcyclohexanes, which are dehydrogenated to aromatics. This mechanism could not apply for cgromia catalysts, which have little isomerization activity. When n-heptane is processed over a chromia catalyst, the second and seventh carbon atoms appear to link up to form methylcyclohexane directly.

ExercisesAnswer the following question1. What is the purpose of catalytic reforming ?2. Why had catalytic reforming supplanted thermal reforming ?3. Do you know why conversion other hydrocarbons to aromatics

is principle of catalytic reforming ?4. What are the main reactions in catalytic reforming ?5. Would isomerization have a large effect on octane?6. What is the activity of catalysts determined by?7. What is the characteristic of platinum catalysts?8. Why is the conversion of alkylcuclopentanes to aromatics lower

than that of cyclohexane derivatives?9. What does selectivity of catalysts depend on?10. Which catalyst has the highest isomerization activity?11. Why is activity of dehydrocyclization of paraffins low at

pressure range normally used in catalytic reforming?

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12. What are dual-functional catalysts?13. Which reaction is performed in dehydrogenation sites?14. Which reaction is performed in acid sites?15. Why are paraffins with more than seven carbon atoms

converted to aromatics than heptanes?16. Can you show the mechanism of conversion of paraffins to

aromatics?

Thermal processesAt high temperatures, the bonds between atoms in molecules of hydrocarbons are weakened and can break to form new compounds. In any homologous series, lighter [low-boiling] hydrocarbons split less easily than high-boiling ones. Along with splitting into lighter hydrocarbons, other transformations can take place, in particular, packing of molecules in which heavier fractions from preliminary petroleum processing are decomposed at elevated temperatures are call thermal processes. In petroleum processing industry, the most common processes of this type are thermal cracking, coking, and pyrolysis.Thermal cracking, usually carried out at pressures up to 5 MPa and temperatures of 420-550 0C, is a process in which the starting material is changed qualitatively with the formation of new compounds having different physicochemical properties. Depending on the composition of the starting material and the process conditions, the yield of gasoline cracking is 7-30 % of the mass of the starting material; the process also gives some other products: gaseous, liquid and solid [coke].Coking of residue is done at temperatures of 445-5600C [still coking] or 485-5400C. Depending on the quality of the starting material and the type and conditions of the process, it may yield 15-18 % of commercial coke, 49-77.5 % of liquid products [including 7-17 % of gasoline fractions] and 5-12 % of gases [up to C4].Pylolysis of distillates and light hydrocarbons [from ethane to butane] is usually effected at 650-8500C. The main object of pyrolysis is to produce ethylene and propylene; earlier, it was aimed at producing aromatic [benzene] hydrocarbons.In 1930-1950's, pyrolysis played an important part as a method for increasing the manufacture of gasolines for carburettor engines. At a later time, the quality of gasolines produced in thermal cracking plants could no more satisfy the rising requirements of consumers. Upon development of catalytic processes, thermal cracking still retains its role mainly for the manufacture of low-

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viscous fuel oils from residue products of preliminary petroleum processing , and also of gas oils intermediate products for making carbon black. The processes of coking are being developed further, mainly to satisfy the demands for coke, especially electrode coke. Liquid products of coking are utilized for increasing production of white petroleum products. Pyrolysis is being developed rapidly in association with increasing demands for olefin materials for the chemical and petrochemical industries.

Thermal Cracking In 1890, V.G. Shukhov, a famous Russian scientist, designed the first cracking plant for producing light petroleum products from fuel oil. Later, as the need for automobile gasoline increased, a system with reaction chambers was developed, in which the starting material, preheated to the reaction temperature in the furnace coil, was retained and subjected to cracking up to the formation of coke. The time of filling of the reactor with coke determined the length of the whole working cycle of the plant. At a later time, the reaction chamber was replaced by the reaction volume formed in radiant pipes of a furnace. To prevent the clogging of the apparatus with coke, the reaction products were

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chilled at the exit from the furnace by the cold starting material [quench] which stopped the cracking process [in particular, Winker-Koch plants operated by this principle]. In later years, further improvements have been made in thermal cracking in foreign countries and in the USSA where the process was implemented in 1927-28.As has been given earlier, the principal reaction of thermal cracking is the decomposition [or cracking ] reaction. Among various hydrocarbons, paraffins can be cracked most easily. Then follow naphthenic hydrocarbons. Benzene hydrocarbons are most stable against cracking. In any homologous series, hydrocarbons of a higher molecular mass are cracked more readily. Thus heavier fraction of petroleum products are less stable and can be cracked more easily than lighter ones. Brief data on the chemistry and mechanisms of cracking of the principal classes of hydrocarbons will be given below.Paraffin hydrocarbons. Cracking of commercial paraffins which consist mainly of C24H50, C25H52 and C26H54 hydrocarbons forms paraffin hydrocarbons and olefins composed of 12, 13, or 14 carbon atoms, i.e. roughly one-half of the carbon atoms in the original paraffin. This is an indication of that the breakdown of C-C bonds in cracking of paraffins of high molecular mass occurs in the middle of a molecule. The new paraffin hydrocarbons formed by cracking can in turn break down into simpler molecules say a molecule of a paraffin hydrocarbon and that of an olefin, for instance: 4250C C12H26 C6H14 + C6H12 dodecan hexane hexene[paraffinic] [paraffinic] [olefinic]At higher temperatures of cracking of paraffinic hydrocarbons, reactions in which the breakdown of molecules occurs at the end portion of the chain begin to prevail over those in which molecules break in the middle. The larger fragment of a broken molecule is an olefin and the smaller one is the paraffinic hydrocarbon [gaseous] or hydrogen. Isoparaffinic hydrocarbons are thermally less stable than those of the normal structure. The rate of the reaction at a given temperature increases almost linearly with the molecular mass. This is true of all groups of hydrocarbons.Olefinic Hydrocarbons. These are the principal ones among all unsaturated hydrocarbons produced by cracking. They prevail as gaseous compounds [from ethylene C2H4 to butylene C4H8] and liquid ones [from amylenes C5H10 to pentadecenes C15H30]. Cyclic olefins and diolefins form in relatively small quantities. In contrast

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to paraffinic hydrocarbons, olefins undergo appreciably more diverse primary reactions during cracking, the most important among them being polymerization reactions [i.e. combination of a few molecules into a single molecule] and depolymerization reactions, especially at an early stage of the process . Polymerization is the main reaction at moderately high and high pressures; it can occur not only between like molecules, but also between unlike molecules of olefins, for instance: C2H4 + C3H6 C5H10

At later stages of the process, olefins are dehydrogenated partially and form diolefins, which typically have two double bonds, and hydrogen or split into diolefins and paraffinic hydrocarbons: CH3- CH2- CH= CH2 CH2= CH- CH= CH2 + H2 butylene divinyl [olefin] [diolefin]Secondary reaction between olefins and diolefins may give cycloolefins which are present in cracking products in very small quantities. Olefins can transform into cyclic hydrocarbons [naththenes];n-hexene -1 cyclohexaneNaphthenic hydrocarbons. The main reaction in cracking of these hydrocarbons are dealkylation [splitting of paraffinec side chains ] and dehydrogenation of hexacyclic naphthenic naphthenic hydrocarbons into benzene hydrocarbons; the two reaction can occur simultaneously.Dehydrogenation of hexacyclic naphthenes in thermal cracking with the formation of benzene hydrocarbons is of minor importance. Owing to the dealkylation reaction taking place in thermal cracking, naphthenic and benzene hydrocarbons loss most of their long side chains. Paraffinic side chains in turn break to form gaseous and low-boiling paraffinic hydrocarbons and olefins. In high-temperature processes, naphthenic rings can break; the result is that hydrocarbons lose their cyclic structure and that polycyclic structure are partially decycled [if they had several rings]. In that case, paraffinic, olefinic and naphthenic hydrocarbons form.Benzene Hydrocarbons.These are obtained by dehydrogenation of the cycloolefins or naphthenes which were formed at earlier stages of the process. Benzen hydrocarbons are quite stable at high temperatures, especially benzene, toluene and xylenes. The main reaction in cracking of benzene hydrocarbons with alkyl chains are dealkylation and condensation. Condensation may occur between the molecules of benzene hydrocarbons [or some

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other unsaturated hydrocarbons]. This gives polycyclic benzene hydrocarbons which cancondense further to asphaltenes and coke.Sulphur compounds. They are decomposed in cracking and form hydrogen sulpide. Cyclic sulphur-organic compounds, such as thiophene and thiophane, have the greatest stability against decomposition. Hydrogen sulphide and elemental sulphur [as the product of oxidation of hydrogen sulphide] which form in cracking of sulphurous petroleum gredes can cause strong corrosion of process equipment.Innert tars and asphaltenes. These may contain various heterocyclic compounds [usually including oxygen, sulphur, nitrogen and some metals]. In cracking they form gases, liquid products and large amount of coke. The yield of coke in cracking of asphaltenes may reach 60% and that in cracking of tars 7-20% [depending on the molecular mass of tars].Since the starting materials for industrial thermal cracking are usually mixtures of many hydrocarbons of complicated structure, many reaction can occur simultaneously and the mechanism of thermal cracking can not be explained in detail. It is assumed however, that most reaction of thermal cracking can be described by the theory of formation of free radicals.

ExercisesAnswer the following question1. What are called thermal processes ?2. What are the most common processes of thermal processes ?3. What are products of thermal cracking ?4. What are products of coking?5. What are products of pyrolysis?6. Who designed the first cracking plant?7. Which type of hydrocarbon can be cracked most easily?8. Which C-C bonds are broken down in cracking high paraffins at

lower temperature ?9. Which C-C bonds are broken down in cracking high paraffins at

higher temperature ?10. What are the products of cracking high molecular mass

paraffins at higher temperature ?11. What relationship is there between the rate and temperature

of the reaction?12. What are the primary reaction of olefins in thermal cracking

condition?13. What are the second reaction of olefins in thermal cracking

condition?

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14. Which reactions happen with naphthenic hydrocarbons in thermal cracking condition?

15. Why are gaseous and low-boiling parafinic hydrocarbons and olefins formed in thermal cracking of naphthenic hydrocarbons ?

16. What are the main reactions of benzene hydrocarbons ?17. Which compounds can be obtained in cracking of benzene

hydrocarbons ?18. Which sulphurous compounds are formed in cracking ?19. What is the main product in cracking tars and asphaltenes?20. What is the main mechanism of thermal cracking ?

Catalytic processesA typical feature of catalytis processes is the ues of catalysts, i.e. substances wgich can accelerate [or decelerate] the reactions and cause the formation of new hydrocarbons ans other substances not present in the starting material. Catalytic processes occur under softer conditions [at lower temperatures and pressures] than thermal ones, but may involve the reactions which are impossible in purely thermal processes.A catalyst usually consists of an active substance [which determines the course of desirable reactions] applied onto a carrier substance [mostly alumina] having a largely extended asurface. In some cases, some other substances [promotors] are added to improve characteristics of catalytic process. The particles [granules] of catalytic process an enormous porosity and therefore a very large internal surface area. The activity of a catalyst is due mainly to the surface of pores rather than to their wxternal surface. The name of a catalyst depends on the process where it is to be used, for instance, reforming catalysts, cracking catalysts, ect.The technico-economical characteristics of a catalytic process are determined by the quality of the starting material and the process conditions, as well as by the properties of the catalyst used. The capability of a catalyst to accelerate the rate of desirable reactions and retain the rate of unwanted ones at aconstant low level is called selectivity. Activity is another important characteristic of catalysts; it is estimated in term of the yield of the end product relative to the use of the starting material. In particular, the catalyst activity in catalytic cracking is determined as the yield of gasoline [end process].Catalysts can participate in process reactions in a stationary [fixed-bed] or moving [circulating] state. In both cases, they

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gradually lose their activity and selectivity owing to ageing. This may be accelerated under more rigid process conditions. Along with normal ageing of catalyst may also take place. This occurs often when the process is run under abnormal conditions,say at an excessively high temperature. Many catalysts can be affected by certain substances containing sulphur, nitrogen and heavy metals [V, Ni, and other] and by water in the starting material.Catalysts can be regenerated to rectore their activity and partially, the selectivity, which is usually done by removal [burning-off] of the coke deposits setted on catalyst particles during operation. By another method, the properties of catalysts [especially of fixed-bed type] are restored by gradually raising the temperature in the reactor. With circulating catalysts, a fresh catalyst is added in portions to compensate for the loss of the catalyst in the system.Catalyst processes make it possible to remove unwanted impurities, for instance, sulphurous compounds, and to convert certain hydrocarbons into the products which cannot be obtained by preliminary distillation of petroleum or in thermal processes.Brief Description of Catalyst processesCatalytic cracking is the process of conversion of high-boiling petroleum fraction into high-octane base components of aviation and automobile gasolinesand middle distillates.Industrial processes of catalytic cracking are based on contacting the starting material with an active catalyst under approriate conditions to convert a considerable portion of the material into gasoline and other light on the particles of the catalyst and thus reduce sharply the activity, in particular, the cracking ability. The activity of the catalyst is restored by burning off the carbon prcipitates [usually called coke] in air.There exist many types and systems of catalyst cracking plants, those with circulating flow of the catalyst, especially in a fluidized bed, being most popular.Catalytic reforming is employ widely to obtain high-octane gasoline fraction. Reforming of gasoline or gasoline fractions in combination with various methods of separation of benzene hydrocarbons, for instance, with solvent extraction, make it possible to produce benzene hydrocarbons [benzene, toluene, xylenes and higher aromatics] for the petrochemical and chemical industries.Catalytic reforming processes are based on contacting the starting material with an active catalyst usually containing platinum. The yield of reformate may vary within 63 to 85 % of the mass of the starting material. The catalyst is regenerated periodically to restore its activity. A feature of importance is that the catalytic

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reforming occurs in a medium of hydrogen-containing gas at high temperatures and pressures. The hydrogen formed in various reactions of reforming is removed from the system as an excess of hydrogen-containing gas. The tigh content of hydrogen is the gas mixture [up to 80% by volume] makes it possible to utilize it in hydrigenation processes, in particular, for hydrofining of diesel fuels.Hydrogenation processes occur in the medium of hydrogen at eleated temperatures and pressures. They can be used for preparing high-quality products from sulphurous and high-sulphurous petroleum grades, the yield and quality of these product being varied depending on the degree ofdestruction and the prevailing reactions. Among the processes of this kind, hydrofining of various fractions and products is most important.Hydrofining of petroleum distillates ans products is one of the most popular catalytic processes, especially for streating sulphurous and high-sulphrous petroleum grades. The process is carried out in a hydrogen medium at a pressure of 3-5 MPa. The main object of hidrofining of petroleum distillate and products is to reduce the content of sulphur and other harmful compounds in them. These substances are destructed in the process, and the destruction products [hydrogen sulphide and ammonia] are removed fromthe system with gases.Hydrofining processes are based on contacting petroleum distillates and products with a fixed-bed or circulating catalyst , usually alumina-cobalt-molybdena or alumina-nikel-molybdena. The process takes place in the medium of hydrogen at elevated temperatures and pressures so as to convert 95-99% of the starting material into the refined product or distillate [hydrogenate]. Minpr quantities of gasoline, hydrogen sulphide and ammonia also form in the process.Alkylation is a process by which isoparaffinic hydrocarbons are combined with olefins to form higher-boiling isoparaffinic hydrocarbons which can use as high-octane components in aviation and automobile gasolines. Other kind of alkylation are also in use, in particular, alkylation of benzene y by olefins [for instance, alkylation of benzene by propylene to make iospropylbenzene].Up to quite recently, catalyst alkylation of isobutane was carried uot by butylenes in the presence of sulphuric or hydrofluoric acid as a catalyst. In modern plants, alkylation of isobutane is done by using the materials containing ethylene, propylene and even amylenes, as well as butylenes.

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Alkylation processes may differ in the starting material, catalysts, productivity, and especially in the design of catalyst plants. With the use of sulphuric acid as a catalyst, the alkylation process is characterized by a low temperature of the reaction and the necessity to maintain a high concentration of isobutane and olefins in the reaction zone. The total yield of alkylate from olefinic starting materials is 1.5-1.8 units perunit volume of the starting material, depending on the quality of the material and the process conditions. The significance and scope of alkylation increase with the rising production of high- octane automobile gasolines having a low content of TEL.Isomerization is the process of conversion of relatively loe-octane paraffinic hydrocarbons [mostly C5-C6 and their mixtures]into corresponding isoparaffinic hydrocarbons having a high octane number. In industrial isomerization plants using various catalysts, including alumo-platinum ones, the yield of isomerizates attains 97%. The process of isomerization takes place in hydrogen atmosphere. As in other processes, the catalyst is regenerated peridically.Izomerizates are used together with alkylates for preparationof high-quality gasolines, by compounding them with high-aromatic gasolines of catalytic cracking and reforming.Novel catalyst processes, in paricula disproportionation. are being paid much attention now. The process is based on converting two molecules of a hydrocarbon into two unlike molecules, one having by on carbon atom more and the other, by one atom less than the original molecules, for instance:

2C3H6 C2H4 + C4H8 The process is carried out at 66-2600C and a pressure of 1.4-4.1 MPa, with the starting material being supplied at a high rate [10 to 100 h -1]. Disproportional takes place with a high selectivity: the total yield of ethylene and butylene attains 97% of the propylene converted and the degree of conversion of the latter, up to 45%. Disproportional can be employed for making benzene from toluene [2C7H8 C6H6 + C8H8 ] to replace the less efficient process of toluene alkylation.In industial practice, a number of processes are often combined in a single plant [for instance, hydrogen cracking and catalytic reforming]. This make it possible to process low-octane starting materials into high- octane gasoline with a hihg concentration of benzene hydrocarbons [obtained by reforming] and isoparaffinic ones [obtained by hydrogen cracking]. In this combined technique, the process of hydrogen cracking occurs without hydrogen supply from the outside.

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1. What is the typical feature of catalytic processes?

2. What can you say about the conditions of catalytic processes?

3. What is the composition os a catalyst of catalytiv processes?

4. What is the main characteristic of a catalyst?

5. What is the selectivity of a catalyst?

6. How can catalysts participate in process reaction?

7. When does the quick ageing happen?

8. What can affect the activity and selectivity of catalysts?

9. How can you regenenate catalysts?

10. Do you know what the main catalytic characteristics are?

11. Can you show the basis of catalytic cracking?

12. What is the purpose of catalytic reforming?

13. Which codition do catalytic reforming happen in?

14. What is the purpose of hydrogenation processes?

15. Which process is most important in hydrogenation processes?

16. What is basis of hydrofining process?

17. Can you define the alkylation reaction?

18. Which alkylation processes are used in petroleum processing?

19. What was catalytic alkylation of isobutane carried out by?

20. What do alkylation processes depend on?

21. What is akylation processes characterixed by with the use of sulphuric acid as a catalyst?

22. What is purpose of isomerization?

23. What is disproportionation?

24. How can you say about the characteristic of gasoline obtained by catalytic processes?

Catalytic cracking There are two main types of catalyst cracking: one is carried out in the presence of a catalyst -porous solid particles of a definite composition and structure; the other is also carried out with a catalyst, but in a hydrogen atmosphere at a high pressure [up to 30 MPa] and a slightly reduced temperature [hydrocracking].

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As compared to thermal cracking, catalytic cracking gives lower yields of methane, ethane and olefins, but higher yields of C3 and C4 hydrocarbons and of gasolines high in benzene and isoparaffinic hydrocarbons. This is the principal advantage of catalytic cracking over themal cracking. Aluminosilicates are used most often as cracking catalysts now. In recent time, zeolite-containing [crystlline aluminosilicate] catalysts with rare-earth additives have come into wide use.The main object of catalytic cracking is to produce high-octane components for automobile or, less frequently, for aviation gasolines. The process gives the hihgest yield of white products with any kind of . The by-products obtained in catalytic cracking plants include gases, catalytic gas oils [light grades boiling off up to 3500C and heavier ones, which begin to boil above 3500C] and coke which precipitates on the catalyst and is burned off in regeneration.The operation of catalytic cracking plants can be characterized by what is called cracking ratio, i.e. the relative quantity of the starting material converted into gasoline, gas and coke. Thus, the depth of conversion is 100 ninus the yield of gas oil [in per cent]. In singke cracking, the cracking ratio does not esceed 55%, whereas in deeper kinds of cracking [recycle cracking] it may reach 80% by mass. In some cases use is made of the cracking efficiency, which is the ratio of the total yield of debutanized gasoline and C4 fraction to the cracking ratio. The cracking efficiency is usually 0.75 to 0.80.a. Principal reactions of catalytic cracking In the cracking process, the contact of crude petroleum with a catalyst results in the formation of gas, gasoline, coke and some liquid products with the boiling temperature above the boiling -off temperature of gasoline. These products from by the following principal reactions.Cracking of hydrocarbons with the formation of lighter molecules: for instance, an n-butyl radical splits from a molecule of n-butylbenzene to form benzene and butylene. The molevules of cetane C16H34 give on splitting C8H18, C8H16 and some other hydrocarbons. The rate of hydrocarbon splitting increases substantially with increasing temperature, which make it possible to control the process, i.e. to increase or diminish the yields of certain products by changing the temperature.Dehydrogenation. In this reaction, only hydrogen molecules split from hydrocarbon molecules. A typical example is the catalytic reaction of dehydrocylization of methylcyclohexane C7H14 [naphthenic hydrocarbon], which give up three hydrogen

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molecules and converts into toluene. Part of the hydrogen liberated in dehydrogenation is attached in catalyst cracking to olefinic hydrocarbons, thus reducing the content of unsaturated hydrocarbons in catalytic cracking gasolines.Isomerization is characterized by that the atoms in a molecule change their positions, but their number remains the same. Isomerization of normal paraffinic hydrocarbons gives hydrocarbons of a branched structure, for instance, isopentane form from n-pentane.Hydrogenation. In this reaction, the molecules of the starting material attach hydrogen and thus form new compounds more saturated in hydrogen. for instance, octylene [an olefinic hydrocarbon] is converted into octane by the reaction:

C8H16 + H2 C8H18

The hydrogenation reaction is quite common and can take place not with olefins, but with other classes of hydrocarbons as well. For instance, cyclohexane can be obtained by hydrogenation of benzene.Polymerization. In this reaction two or more molecules combine into a single large molecule. For example, two molecules of ethylene are polymerization into a higher boiling hydrocarbon, butylene. Using polymerization, gaseous olefinic hydrocarbons [ethylene, propylene, butylenes] can be converted into liquid or even solid hydrocarbons of a higher molecular mass.In catalytic cracking, the rate of breakdown of paraffinic hydrocarbons is higher at a higher molecular mass. At the ordinary temperatures of catalytic cracking,i.e. 450-5200C, catalysts have almost no effecton light paraffinic hydrocarbons: propane and butane, white high-boiling paraffins undergo deep changes. For instance, the cracking rate of cetane, whose boiling temperature is 2870C is roughly 13 times that heptane which boils at 980C. The oleffins formed on breakdown of normal paraffinic hydrocarbons are isomerized, partially saturated by hydrogen and convert into paraffinic hydrocarbons of a branched structure and a lower molecular mass. Olefins can be subjected to catalytic cracking much more easily than paraffinic hydrocarbons. The reactions of splitting, isomerization, polymerization and hydrogen attachment are vey typical of them. Some other reactions are also possible, by which olefins are converted into benzene hydrocarbons and high boiling compounds.Catalytic cracking of naphthenic hydrocarbons occurs at higher rates than that of paraffinic ones and gives more light liquid products and less gas. Besides, naphthenic hydrocarbons give many benzene hydrocarbons on splitting of hydrogen atoms.

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Distillates high in naphthenic hydrocarbons are a valuable starting material for catalytic cracking. They give more gasoline and of higher quality than do distillates of a similar fractional composition obtained from paraffinic grades petroleum.The nuclei of bnzene hydrocarbons are thermally stable ans split insignificantly even at 450-500oC. On the contrary, the molecules of benzene hydrocarbons with side paraffinic chains are cracked easily: their bonds break mainly in sites of attachment of a side chain to the benzene nucleus. Benzene hydrocarbons with no side chains in the molecule and paraffinic hydrocarbons of nomal structure turn tobe most stable againt catalytic cracking. Hydrocarbons of other homologous series [with the same number of carbon atoms in the molecule], such as olefinic, naphthenic, aromatic with long side chains, are less stable and can be cracked morw easily.b. Starting materials and products of the process.Starting materials. The starting materials for catalytic cracking are various distillate fractions obtained by atmospheric or vacuum distillation of crude petroleum. In catalytic cracking plats for obtaining the starting material are used, in particular, distillates with the boiling-off range of 220-3600C and relative density of 0.83-0.87. The plants for making the compounds of automobile gasoline use heavier disstilates with the boiling-off range of 300-5500C and relative density of 0.87-0.93. In some cases, starting materials of an intermediate composition can be used, such as mixtures of various distillates obtained in preliminary processing of petroleum [atmospheric or vacuum distillation] and in secondary processes of preparation of fuels and oils; these mixtures can be used only for making automobile gasolines. In recent time, attempts have been made to process low-ash fuel oils and deasphatizates by catalytic cracking.The starting material must contain no fractions boiling below 1900C, since they remain practically unchanged upon catalytic cracking and lower the octane numbr of the final gasoline.The processing of starting materials containing harful impurities involves certain difficulties, in particular, stronger corrosion of equipment and heavier coking of the catalyst, which may result in a lower yield of gasoline and lower productivity of the plant. Metal compounds can be present in distillates owing to carry-over of goudron droplets into the top portion of the column. Some compounds are volatile at high temperatures. For that reason, the operation of a vacuum column should be careefully checked and sometimes itis advisable to lower the boiling-off temperature of a vacuum distillate to be used for catalytic cracking.

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The coking ability of the starting mashould usually be not less than 0.25%. The materials with the coking ability of up to 0.7% can be processed of the regenerator has an extra capacity for coke burn-off. Moist material should not be used for processing, since moisture can disturb the process conditions, in particular, raise the pressure in the reactor, disturb the normal circulation of the catalyst, increase the quality of the end products. In some cases, this mayform emergency situations. The composition of the starting material can also influence the yield and quality of the products of catalytic cracking.Products of catalytic cracking. Catalytic cracking plants produce up to 20% [by mass] of gases [containing hydrogen and light hydrocarbons up to 60% of high- octane components of automobile gasolines, and up to 2.5-8% of coke, the balance [except for losses] being light and heavy gas oils. Some plants make unstable gasolines which are further delivered to gas separation. Besides, catalytic cracking for production of the base aviation component may give ligroin and polymers as by-products, and also motor gasoline- an intermediate product which is subjected to catalytic reforming at the second stage.Wet gas. Its composition is characterized by a high concentration of isomeric hydrocarbons, in particular of isobutane, which increases the value of the gas as of an intermediate product for further processing. The wet gas obtained by catalytic cracking of light and heavy distillates has roughly the following composition [in % by mass]These data disregard steam, hydrogen suphide and inert gases which may be present in various minor amounts in gases of catalytic cracking.Wet gas and unstable gasoline from catalytic cracking plants are fed into an absortion- gas frctionation plant for separarion of light gases. Apart from stable gasoline, the products obtained in such a plant include propane-propylene, butane-butylene and pentane-amilene fraction. Propane-propylene and butane-butylene fractions are further polymerized and alkylated to prerare gasoline components or are used in petrochemical processes [propane and butane can also be used as domestic fuel].Unstable gasoline. It is stabilized to obtain a stable component for preparing high-octane automobile and aviation gasolines.Light catalytic gas oil. As compared to the products of similar fractional composition obtained by preliminary distillation of petroleum, light catalytic gas oil [a distillate with the beginning of boiling at 175-2000C and the and of boiling at 320-3500C] has a lower cetane number [up to 25], higher content of sulphur

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[roughly the same as in crude petroleum] and benzene hydrocarbons [up to 55 %], and a certain concentration of unsaturatd hydrocarbons. The setting temperature of these gas oils is however substantially lower than that of the starting material for catalytic cracking. Under more rigid conditions of the process, and without increase in recurculation light gas oil is produced in smaller amoints and with a lower cetane number, but with a higher concentration of benzene hydrocarbons.Light catalytic gas oil is utilized as the starting material for manufacture of commercial carbon [carbon black], as a component in commercial grades of fuel oil, and for some other purposes. In rare cases, it can be used as a component of diesel fuel, provided that other components of the fuel produced by preliminary distillation have a higher cetane nimber and a reduced content of sulphur [compared to the standard value]. In some cases, lihgt catalytic gas oil is extracted; the refined layer with a reduced content of benzene ys and a higher cetane nimber used as a component of diesel fuels and the extracted layer, which is high inbenzene hydrocarbons, is a valuable by- product for preparing carbon black.Heavy catalytic gas oil is the liquid residue of catalytic cracking. Its quality depend mainly on the process conditions and the boiling -off temperature of the light gas oil produced. Heavy gas oil often contains many mechanical impurities [rests of the catalyst]. Its sulphur content is usually higher than that of the starting material used for cracking. Heavy catalytic gas oil is usedf for making fuel oils and carbon black.Catalytic cracking

1. How many main types of catalytic cracking are there? What are they?

2. Is there difference between products of thermal cracking and catalytic cracking?

3. What is the principal advantage of catalytic cracking over themal cracking?

4. Which compound are used as cracking catalysts?

5. What is main object of catalytic cracking?

6. Do you know what by-products are?

7. What can the operation of catalytic cracking plants be characterized?

8. What is cracking efficiency?

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9. How many principal reactions happen in catalytic cracking?

10. Which molecules are formed in cracking of hydrocarbons?

11. How are the rate of hydrocarbon splitting depend on temperature ?

12. Which compounds are formed in dehydrocyclization of methylcyclohexane C7H14?

13. Why is the content of unsaturated hydrocarbons in catalytic cracking gasolines reduced?

14. What is isomerization characterized by?

15. What is polymerization?

16. What is the rate of breakdown of paraffins depend on?

17. How can the molecular mass of hydrocarbons effect on rate of cracking?

18. Can olefins be subjected to catalytic cracking more easily than paraffinic hydrocarbons, can't they?

19. Which reaction happen with olefin in catalytic cracking?

20. How can you say about content of naphthenic hydrocarbons in starting material for catalytic cracking?

21. What can you say about reaction ability of benzene hydrocarbons?

22. Which hydrocarbons are more stable in catalytic cracking?

23. Which materials are used as starting materials for catalytic cracking?

24. Which starting material are used in catalytic cracking plants for obtaining the components of base aviation gaspline?

25. The same question for making the components of automobile gasoline?

26. Why aren't fraction boiling below 1900C used in catalytic cracking ?

27. Why is it advisable to lower the boiling -off temperature of a vacuum distillate to be used for catalytic cracking?

28. Why shouldn't moist material be used for catalytic cracking ?

29. What are products of catalytic cracking?

30. What are by-products of catalytic cracking?

31. What is the composition of wet gas?

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32. How can they separate light gasses from wet gas?

33. What can you say about composition of light gas oil?

34. What is light catalytic gas oil used?

35. What do quality of heavy catalytic gas oil depend on?

36. What can you say about composition of heavy gas oil?

37. What can heavy catalytic gas oil be used for?

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