Handbook of Chemical Technology and Pollution

19PETROCHEMICALS

Take Carbon for example thenWhat shapely towers it constructsTo house the hopes of men!

—A.M. Sullivan (1896–1980)

19.1. BACKGROUND

Organic chemicals, such as dyestuffs and derivatives of benzene and hetero-cyclic compounds, were first produced from coal-based raw materials. Sincethe mid-nineteenth century these products were obtained by the further pro-cessing of discrete volatile fractions recovered during the coking of coal. Alarge fraction of the coke product was destined for the reduction of iron ore toproduce pig iron (Chap. 14). Although volatile fractions from the coking ofcoal, such as benzene, toluene, and the xylenes are still items of commerce,petroleum-based sources for these materials have now become much moreimportant [1]. The attractiveness of petroleum-based feedstocks grew as boththe reliability and scale of petroleum production increased. These aspects,plus the gradually increased sophistication of refining methods of the oilindustry of the early twentieth century contributed to the increased appealof petroleum as a resource for chemicals production.

As a consequence of its recent development the petrochemical industry isrelatively much younger than the major inorganic chemicals industry. How-ever, one can easily be misled by the classification of products that are termed‘‘petrochemical’’. Basically a petrochemical is derived directly or indirectlyfrom a petroleum or natural gas fraction. It may be organic, such as ethylene,benzene, or formaldehyde, or it may be inorganic, such as ammonia, nitricacid, and ammonium nitrate (Chap. 11). So a ‘‘petrochemical’’ is not syn-onymous with an organic chemical, although most petrochemicals are alsoorganic chemicals.

What is the incentive to produce petrochemicals? It is producer accessi-bility to profit from the additional value-added stages that are obtained from

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637

conversion of a refined petroleum or gas fraction into a petrochemical,compared to the value of crude petroleum. Depending on the complexityand number of stages involved, a petrochemical product may command aprice that is five or six times the price of the oil or gas used to produce it. Ifmore value-added stages are used to convert a petrochemical commodity intoa consumer product, this may fetch a price as high as 20 times that of the oilfrom which it is derived. In short, oil (or natural gas) is worth far more whenconverted to chemicals than as fuel.

In considering the scale of production of the top 30 industrial chemicalswithout regard to source, one may gain an impression of the relative impor-tance of the petrochemical sector to the chemical industry as a whole. Fully 21of the top 30 chemicals are classified as petrochemicals with a gross annualproduction in the United States in 1995 of 140 million metric tonnes (Table19.1) [2]. Only nine are nonpetrochemical inorganic compounds. Neverthe-less, the gross volume of production of these nine compounds of 166 millionmetric tonnes annually is still larger than the annual mass of petrochemicals.The product distribution pattern for Canada and other developed nations issimilar. Sulfuric acid is the largest scale inorganic commodity chemical pro-duced in developed nations. In Canada, where the sulfur for sulfuric acidproduction is derived largely from the sweetening of sour natural gas (Chap.9), it could be argued that in this case even sulfuric acid should be classified asa petrochemical.

Not only are petrochemicals produced on a vast scale but the diversity ofmaterials represented is substantial. More than 3,000 petrochemicals are incurrent commercial production. Despite this large scale, however, only 5–6%of current oil and gas production is consumed to produce organic petrochem-icals and another 4–5% for inorganic petrochemicals. It seems to be anextravagant use of a key chemical raw material to apply only 10% of it forhigh value-added products, many of them in recoverable or durable applica-tions, and simply burn the remaining 90% for energy production.

19.2. FIRST PETROCHEMICAL PRODUCTS

Carbon black was the first simple product to be commercially produced fromhydrocarbons, and has continues without interruption since 1872. Isopropylalcohol was the first commercial petrochemical requiring more than one stepand continues to be manufactured by virtually the same process as its initi-ation by Standard Oil in 1920. Details of these early processes follow.

19.2.1. Carbon Black

Carbon black is the largely carbon-containing product of complex structurederived from the low temperature combustion of a hydrocarbon with adeficiency of air. This was initially produced from natural gas (mostly methane).Normal combustion of natural gas with adequate air produces carbon dioxideand water together with a flame temperature of 1,000–1,2008C. However, ifthe combustion is carried out in a deficiency of air with strong cooling of


638 19 PETROCHEMICALS

the flame, a large proportion of the ‘‘combustion’’ proceeds to yield finelydivided carbon (carbon black) and water vapor (Eq. 19.1).

CH4 þ O2 ��!ca: 5008CC þ 2 H2O 19:1

The flame was cooled by cold iron bars (channels) placed into the flame andonto which the carbon deposited. The product, called channel black, wasperiodically scraped from the iron channels for further processing and sale.Yield of carbon from this process was about 1 tonne per 50,000 m3 (at 1 atm,

TABLE 19.1 The 30 Largest Volume Chemicals and Their Scale ofProduction in the U.S.A. and Canada in 1995a

Production (million tonnes)

U.S.A. rank 1995 Petrochemical Product U.S.A. Canadab

1 Sulfuric acid 43.25 4.22

2 Nitrogen 30.86 –

3 Oxygen 24.26 –4

pEthylene 21.30 3.13

5 Lime 18.70 –

6p

Ammonia 16.15 4.66

7 Phosphoric acid 11.88 –8 Sodium hydroxide 11.88 1.18

9p

Propylene 11.65 0.72

10 Chlorine 11.38 1.13

11 Sodium carbonate 10.11 –

12p

Methyl-t-butyl ether 7.99 –

13p

Ethylene dichloride 7.83 –14

pNitric acid 7.82 0.99

15p

Ammonium nitrate 7.25 1.03

16p

Benzene 7.24 0.7817

pUrea 7.07 3.33

18p

Vinyl chloride 6.79 –

19p

Ethylbenzene 6.20 –

20p

Styrene 5.17 –

21p

Methanol 5.12 –

22p

Carbon dioxide 4.94 –

23p

Xylene 4.25 –24

pFormaldehyde 3.68 –

25p

Terephthalic acid 3.61 –

26p

Ethylene oxide 3.46 –27 Hydrochloric acid 3.32 0.14

28p

Toluene 3.05 0.28

29p

p-Xylene 2.88 0.43

30p

Cumene 2.55 –

Total inorganic chemicals (9) 165.64

Total petrochemicals (21) 140.00

aCalculated from data of Chem. Eng. News [2].bSome data unavailable because of Statistics Canada confidentiality regulations.


19.2. FIRST PETROCHEMICAL PRODUCTS 639

15.68C) of natural gas, or about 5% [3]. The low yields from this process andthe increasing concerns about the traces of particulate lost in combustiongases from channel black plants have contributed to their obsolescence.

Better yields of carbon black are obtained by improved separation of thecombustion function from the carbon-forming function, as is accomplished inthe newer furnace black processes. This approach enables ‘‘gas oil’’ (highboiling point liquid petroleum fractions) or natural gas to be used to producecarbon black. The cooling function from 1,4008C to about 2008C is accom-plished by direct water sprays. The product is removed from the gas streamvia a combination of cyclone collectors and glass or Teflon fiber bag filters.One tonne of furnace black is obtained from 5,300 to 7; 000 m3 (1 atm;15.68C) of natural gas, or 1,400–2,800 L of gas oil corresponding to 50–70% yields. Oil-based furnace black now supplies about 90% of the currentcarbon black market, although the special features of the product from small-scale processors still contribute some product [4].

‘‘Thermal black’’ is produced by another variant in which natural gas iscracked to carbon and hydrogen by the direct application of heat via firebrickchecker work in a cyclical process (Eq. 19.2) [5].

CH4 ��!>8708CC þ 2 H2 19:2

Elemental analysis of carbon blacks gives a carbon content of 90þ%, and insome grades as high as 97%. Although the chemical composition is simple,the structures of carbon black products are complex and vary widely with thefeedstock used [6], the process and conditions employed, and minor amountsof feedstock additives that may be used [7]. Since the discovery of the rubberreinforcement properties of carbon blacks in about 1912, this industry hasgrown to about 400,000 and 1.5 million tonnes/year in Canada and theUnited States, respectively. It ranks about 35th in volume among large-scalecommodity chemicals. About 90% of the oil-based furnace blacks are used inrubber reinforcement, mostly for automobile tires. Printing inks and plasticsare much smaller but important pigment uses for carbon blacks.

Other forms of carbon are also of significant industrial interest, among themthe various types of activated carbon that are used in many air and water emissioncontrol applications. These porous forms of carbon are made from raw materials,such as lignite, coal, wood if it is to be used for liquid phase adsorption, andpetroleum residues, coal, or coconut shells if for gas adsorption. Carbon fiberused for reinforcement of composite materials in aerospace and sporting goodsapplications can sell from $22 to more than $220 per kilogram, a very attractivevalue added product [8, 9]. Industrial diamonds are used for the cutting andgrinding of very hard materials, for optical devices, such as lasers, for heatdissipation, and for diamond coatings to produce enhanced wear resistance.This also represents a small-scale, high-technology carbon product [10].

19.2.2. Isopropanol (Isopropyl Alcohol)

This petrochemical was first produced commercially via basically a scaled-uplaboratory procedure. By 1925 its scale of production reached about 68



tonnes/year. By 1995 volumes of about a million tonnes per year were pro-duced in the United States.

The initial step is the absorption of propylene-rich gases into 85% sulfuricacid at temperatures of 20–258C to form isopropyl hydrogen sulfate viaaddition of the acid across the double bond (Eq. 19.3). Control of acidtemperature and concentration is important to provide selectivity and avoid

CH3---CH¼¼CH2 þ H2SO4�H2O ! CH3C(H)(SO3H)CH3 19:3

absorption of olefins, which require higher concentrations or temperatures toreact. Hydrolysis of the intermediate monoester with water in a lead-linedvessel then gives isopropanol and diluted sulfuric acid (Eq. 19.4).

CH3C(H)O(SO3H)CH3 þ H2O (excess)! CH3CHOHCH3 þ 19:4

H2SO4 (dil:)

The heat of reaction, plus additional heat from added steam, drives off thecrude isopropanol from the spent sulfuric acid, now about 20% acid. The acidis reconcentrated to 85% by boiling off the excess water, after which it isready for reuse. Since it plays an active part in the process, the sulfuric acid isa recycled reactant rather than a true catalyst in this instance.

The condensed, crude isopropanol-water solution is concentrated andpurified by distillation to the 91% isopropanol–water azeotrope (boilingpoint 80.48C, Fig. 19.1).

Any higher alcohols that may have formed in the process from traces ofhigher olefins present in the propylene feed are absorbed from the azeotropeinto mineral oil, in which isopropanol is insoluble. Pure isopropanol isobtained by ternary distillation of the cleaned water azeotrope with theappropriate proportion of added di-isopropyl ether. The ternary azeotrope(Table 19.2) is the top product from the column, and pure isopropanol isremoved from the bottom (see Section 16.4 for related information).

About two-thirds of the isopropanol produced is used as an intermediateto form other chemicals, mostly for acetone production. The remainder isused as a solvent in paints and coatings and other chemical processes.

Sulfuric acid (85%)

Propylene

Vent gases(recycled)

Water

DilutionVessel

Acidrecovery

Abs

orbe

r Preheat

Rec

over

yC

olum

n

To waste

CondenserMineral

oil

Mineral oilwasher

Isopropylether

Mineral oilextract for recovery

of butyl andamyl alcohols

Col

umn

Ternaryazeotrope

Isopropylalcohol 99%

Isopropyl alcohol91% (binary azeotrope)

Steam

W

W

FIGURE 19.1 Simplified flowsheet for isopropanol production from propylene. (Adaptedfrom Lowenheim and Moran [5].)


19.2. FIRST PETROCHEMICAL PRODUCTS 641

From the chemically simple process of methane or gas oil to carbon blackto the first more complex petrochemical process to isopropanol the scope ofthis industry has expanded to the production of a truly vast range of large-scale chemicals. Here we will cover outlines of representative samples of themore important of these chemicals. For more detailed information consult theitems listed in the Further Reading section at the end of this chapter.

19.3. ALKENE AND AROMATIC PRODUCTS

The majority of the chemical processes of the modern petrochemical industryrely on just three refinery streams, methane (or natural gas), olefins, andaromatics comprising just seven hydrocarbons—methane, ethylene, propyl-ene, the butylenes, benzene, toluene, and the xylenes (dimethyl benzenes).Details of the processes used to isolate naturally occurring methane from rawoil or gas streams have been discussed (Chap. 18). A few of the otherhydrocarbons listed also occur to a varying extent in crude oil streams butin concentrations that are inadequate to meet the demand. Thus molecularchanges are necessary to convert these hydrocarbon streams. Some of theprocedures used to do this, such as polymerization, cyclo-alkylation, andaromatization, produce components of gasoline as has already been described(Section 18.3). Others differ in important respects but still employ similarprinciples to obtain the desired product, namely sufficiently high temperaturesto cause carbon–carbon and/or carbon–hydrogen bond homolytic cleavage,plus suitable conditions (contact time, catalyst, concentration, etc.) to achievethe optimum product yield. Since many refinery operations lead to several ofthese products simultaneously, computer programs are used to aid in processoptimization to produce the currently required ratio of products. The ten-dency to get several simultaneous products from a single process will beevident from the following discussion of related product groups.

19.3.1. Ethylene (Ethene)

Ethylene, the largest scale petrochemical, is probably also the oldest to havehad confirmed preparation in the laboratory. The initial method used, cata-lytic dehydration of ethanol, was reported as early as 1797 (Eq. 19.5).

TABLE 19.2 Parameters for the Drying of 91% Isopropanol via the TernaryAzeotrope

Percent composition

Boiling point (8C) Condensate layer

Component Pure Azeotrope Azeotrope Upper Lower

Isopropyl ether 67.5 91.0 94.7 1.0

Isopropanol 82.3 61.8 4.0 4.0 5.0

Water 100.0 5.0 1.3 94.0



CH3CH2OH ��!300�400�C

catalystCH2¼¼CH2 þ H2O 19:5

Although this method is capable of well over 90% yields of ethylene, and maybe used when the local availability and price of ethanol (e.g., occasionallyfermentation sources, Brazil) are attractive, other methods are usually moreimportant.

Refinery ethylene is usually made by the catalytic cracking of ethane,propane, or a mixed hydrocarbon stream, such as recovered natural gasliquids, naphthas, or gas oil [11]. Cracking conditions are quite severe: 750–9008C and 0.1–0.6 second residence time for a low partial pressure hydrocar-bon stream. A number of metal oxide catalysts have recently been evaluatedfor this purpose [12]. The usual diluent is steam, used at a weight ratio ofsteam to hydrocarbon of 0.2:1 for ethane feed, to progressively higher ratioswith the higher molecular weight hydrocarbons of up to 2.0:1 for gas oil.

With an ethane feed the dominant cracking reaction is to ethylene andhydrogen, together with traces of methane and higher hydrocarbons. Theinitiation step involves the homolysis of the carbon–carbon bond (Eq. 19.6).

CH3CH3 ! 2 H3C� 19:6

Carbon hydrogen bonds, which are stronger, are much less affected. Themethyl radicals formed can then abstract hydrogen atoms from ethane inthe first of a series of rapid propagation reactions (Eqs. 19.7–19.9).

H3C� þ CH3CH3 ! CH4 þ �CH2CH3 19:7

�CH2CH3 ! CH2¼¼CH2 þ H� 19:8

H� þ CH3CH3 ! H2 þ �CH2CH3 19:9

Termination reactions are one of the ways in which the higher hydrocarbonsare formed in the cracking of ethane (Eqs. 19.10 and 19.11).

2 �CH2CH3 ! CH3CH2CH2CH3 19:10

H� þ �CH2CH3 ! CH3CH3 19:11

Propane cracks to both ethylene and methane, and to propylene and hydrogen(Eqs. 19.12 and 19.13) with product proportions, which change with thecracking temperature (Fig. 19.2).

CH3---CH2---CH3 ! CH2¼¼CH2 þ CH4 19:12

CH3---CH2---CH3 ! CH2¼¼CH-CH3 þ H2 19:13

The initial step in the process with propane is still predominantly carbon–carbon bond cleavage, with methyl and ethyl radicals and to lesser extenthydrogen atoms serving in the propagation steps, which lead to the products.

Naphtha, or gas oil, may also be efficiently cracked to ethylene andpropylene, although the proportion of ethylene in the product stream isgenerally lower for these feedstocks than from ethane or propane. However,this flexibility of possible feedstocks to ethylene enables a refinery to processthose streams in current excess in order to produce the olefins that it maycurrently need.


19.3. ALKENE AND AROMATIC PRODUCTS 643

Recovery of ethylene (b.p. �103.78C) from the mixed hydrocarbon prod-uct vapors is accomplished by compression, condensation, and then fraction-ation at progressively lower temperatures. Ethane (b.p. �88.68C) is the mostdifficult constituent to separate from ethylene, but even this is technicallyfeasible.

The single largest use of ethylene is for the production of all types ofpolyethylene, which consumes about half of the total. Other major uses arefor the production of ethylene oxide, ethylene dichloride (1,2-dichloroethane),and ethylbenzene enroute to styrene. The remaining 10–15% of production isdistributed among a multiplicity of smaller scale products, including vinylacetate, ethanol, and acetaldehyde.

19.3.2. Propylene (Propene)

Propylene, or propene by IUPAC (International Union of Pure and AppliedChemistry) nomenclature, is probably the oldest petrochemical feedstock,employed as it was in the early processes to isopropanol. It is produced bythe cracking of propane or higher hydrocarbons in the presence of steam

HydrogenHydrogen

Ethylene

PropylenePropylene

700 800 900 1,000

Temperature �C

Exit gas compostion, vol %30

25

20

15

10

5

0

FIGURE 19.2 Changes in the product distribution with temperature on the thermalcracking of propane. (Drawn from the data of Frolich and Wiezevich [13].)



under conditions very like those outlined for ethylene. Propane is the feed-stock of choice for a product stream to contain the maximum concentrationof propylene. The yield of propylene rises as the cracking severity of thepropane is increased, but reaches a maximum before the maximum conver-sion of ethylene is achieved (Fig. 19.2). Thus, even with use of propane as thefeedstock for propylene production, it is common to have more moles ofethylene than propylene product in the exit stream for optimum crackingeconomics.

Propylene is also recovered as a by-product of other refinery operations,principally from the fluid catalytic cracking (FCC) of gas oils and to a lesserextent from the volatile products of coking, when coking is used. All refinerystreams containing recoverable fractions of propylene will be combined into amixed C3 stream for propylene separation. Distillation of this combinedstream then gives propylene (b.p. �47.78C) as the overhead product andpropane (b.p. �42.18C) plus traces of other higher boiling point products asthe bottom fraction.

About 45% of the propylene produced is used for the production ofisotactic polypropylene. About 10% fractions of the total are consumed foreach of acrylonitrile production, the preparation of the ‘‘oxo-alcohols,’’ forpropylene oxide, and for cumene (isopropylbenzene) production.

19.3.3. The Butylenes (Butenes)

There are four C4H8 mono-olefins because of the various possible geometricisomers. These are 1-butene, cis-, and trans-2-butene, and isobutylene(2-methylpropene). All occur in many catalytically processed refinery streams,and predominantly in the C4 fraction separated from the products of thermalor fluid catalytic cracking. Some may also be produced in the refinery pro-cesses designed to raise the octane rating of gasolines. Including the butanes,which are also present in this stream, we get a total of six compounds presentin this C4’s fraction, all boiling in the range �11.7 to þ3.78C. This presentsa formidable separation task (Table 19.3). Fractional distillation is capableof separating the isobutane, isobutylene, and 1-butene fraction from then-butane and the 2-butenes. Extractive distillation, using acetonitrile or aque-ous acetone, is used to separate the 1-alkenes from isobutane. Extractivedistillation with furfural separates the components of the bottom fraction ofthe distillation. The production of methyl t-butyl ether (MTBE), used as anoctane improver in gasolines, has been is the single largest consumer of theisobutylene fraction of the butylenes. The next largest market for the buty-lenes (both 1-butene and the 2-butenes) is for the production of 1,3-butadiene,destined for the production of various types of synthetic rubber.

19.3.4. Benzene, Toluene, and the Xylenes (BTX)

This BTX monoaromatic product stream is usually produced in several dif-ferent refinery operations. Each of these rank in the top 30 chemicals pro-duced in the United States by volume. They have reached this significancebecause of their large demand as feedstocks for many of the important


19.3. ALKENE AND AROMATIC PRODUCTS 645

plastics. Preparation of these materials is discussed together because severalare produced at the same time from many of the processes from which theyarise. The chief sources of these aromatics may be conveniently divided intothree groups.

In the first group, the production of aromatics is a complementary ob-jective to the refinery processing of gasoline fractions to raise the aromaticcontent, which evidently links these refining functions. Catalytic reformingprocesses are used to convert paraffins to naphthenes (cycloparaffins) to befollowed by dehydrogenation of naphthenes to aromatics (Chap. 18). Sincearomatization of naphthenes is an easier process to accomplish than cyclo-alkylation, the emphasis in refinery operations is on maximization of thesecond step in this sequence, when there is an adequate supply of naphthenes.The demand for the aromatics component of gasoline will compete with thefeedstock aromatic need from this source.

The second group includes some of the processes used for ethylene pro-duction, particularly those using naphtha or gas oil as feedstocks, which mayalso produce large amounts of BTX. The conditions used (temperature, pres-sure, feedstock ratios, etc.) to operate these processes provide some flexibilityto alter the product distribution slightly in response to the distribution of thedemand.

The third group of processes to benzene, toluene, and xylenes, or p-xyleneis discretionary and depends on the proportion of these products that areavailable from the first two classes of processes in comparison to the currentdemand. Benzene consumption is more than twice that of toluene. It may beconveniently produced in almost 90% yields by the catalytic hydrodealkyla-tion of toluene (Eq. 19.14) [14]. Or if both benzene and xylenes are in shortsupply, toluene may be catalytically transalkylated to mainly benzene andxylenes [15].

C6H5CH3 þ H2 ��!540�800�C

H2, catalystC6H6 þ CH4 19:14

Ethylbenzene, too, may be isomerized to xylenes. Xylenes are normally recov-ered from a mixed aromatics stream by extraction with sulfolane or a glycol.

TABLE 19.3 Boiling Points of theButanes and Butylenes (the ‘‘BBFraction’’) of the C4 Refinery Streama

Hydrocarbon B.p. (8C)

2-Methylpropane (isobutane) �11.7

2-Methylpropene (isobutylene) �6.91-Butene �6.3

n-Butane �0.5

trans-2-Butene þ0.88

cis-2-Butene þ3.7

a1,3-Butadiene, which may occasionally be

present in this fraction, boils at �4.48C.



If the market for one xylene isomer is greater than that available by separationof the mixture, the low demand isomers may be isomerized to raise theproportion of the desired isomer(s).

About half of the benzene produced as a chemical feedstock is for styreneproduction, followed by large fractions for phenol and cyclohexane-basedproducts. As much as half of the toluene produced is converted to benzene,depending on the price and demand differential. The largest use of tolueneitself is as a component of gasoline. Much smaller amounts are used as asolvent, or in the manufacture of dinitrotoluene and trinitrotoluene for mili-tary applications. Xylenes are also used in gasoline formulations and functionas octane improvers like toluene. para-Xylene and o-xylene are the dominantisomers of value as chemical feedstocks, for the production of terephthalicacid (and dimethyl terephthalate) and phthalic anhydride, respectively.Polyester and the synthetic resin markets, in turn, are major consumersof these products. meta-Xylene is oxidized on a much smaller scale to pro-duce isophthalic acid, of value in the polyurethane and Nomex aramid(poly(m-phenylene isophthalamide)) technologies.

19.4. PRODUCTS FROM METHANE

Ammonia is by far the largest scale chemical product derived from methane.Production of ammonia and its downstream products nitric acid, urea, andammonium nitrate, which currently rank 6th, 14th, 15th, and 17th in Ameri-can volume of production, are discussed in Chapter 11. Two other petrochem-icals derived from methane, methanol and formaldehyde, currently rank 21stand 24th in volume in the United States at about 4 million tonnes per yeareach. Details of their production will be outlined here.

Most of the methane recovered, primarily from gas wells, is not used forchemicals, but is simply burned for heat and/or electricity production.

19.4.1. Methanol (Methyl Alcohol)

Methanol is made from a mixture of carbon monoxide and hydrogen. Thefeed gases required are produced by the reforming of natural gas (Section 9.1).At about 8008C in the presence of a promoted nickel catalyst a gas mixture ofclose to the correct proportions of carbon monoxide and hydrogen is obtained(Eq. 19.15).

3 CH4 þ CO2 þ 2 H2O(as steam)

�! 4 CO þ 8 H2 19:15

Similar gas mixtures may also be made by the old water-gas reaction usingcoal, which gives an approximately 1:1 ratio of carbon monoxide to hydro-gen. The hydrogen may be supplemented to the correct proportions fromrefinery sources or from hydrogen obtained by the electrolysis of water orbrine.

The methanol synthesis reaction requires compression of the gas mixtureto 200–330 atm, temperatures in the region of 3008C, and a catalyst, such as


19.4. PRODUCTS FROM METHANE 647

a chromium oxide-promoted zinc oxide, to result in an approximately 60%conversion to methanol (Eq. 19.16).

CO þ 2 H2 ! CH3OH DH ¼ �103 kJ (�24:6 kcal) 19:16

Methanol is condensed from the exit gases, still at converter pressures, and theunreacted gases are recycled after a partial purge and recompression. As withammonia production, the purge is required to avoid accumulation of inertgases in the recycle stream. The product under these conditions is about 99%pure methanol plus 1–2% of dimethyl ether and traces of higher alcohols.

The process just described may also be operated at somewhat lowerpressures and temperatures than outlined by using some of the more recentcopper-based catalysts. Energy saved by doing this achieves some productioneconomies. It is also possible, with an extra mole of hydrogen, to producemethanol from carbon dioxide (Eq. 19.17).

CO2 þ 3 H2 ! CH3OH þ H2O 19:17

In this instance distillation in a series of columns is necessary for methanolrecovery [5].

Major end uses for methanol are for the production of formaldehyde,about 30%, which is used for the preparation of phenol-formaldehyde resins.About 20% is used for the production of methyl t-butyl ether, which is used asan additive alone, and in blends with methanol as a fuel component. Furtheruses are for the esterification of terephthalic, and acrylic acids, and for aceticacid preparation, about 10% each.

19.4.2. Acetic Acid

The Monsanto process to acetic acid uses a rhodium-iodine-containing cata-lyst to convert a mixture of methanol and carbon monoxide under mildconditions and ambient pressure to very high (99þ% based on methanol)yields of the product (Eq. 19.18) [16]. Several stages of distillation arerequired to recover the acetic acid (b.p. 1188C) in purities of 99.8% or

CH3OH þ CO ��!catal:

CH3COOH 19:18

better. A substantial fraction of acetic acid is also made commercially via theliquid or gas phase oxidation of acetaldehyde or the liquid phase oxidation ofbutane, in each case using air plus a catalyst.

The largest single use for acetic acid, about half the total, is for themanufacture of vinyl acetate for use in the production of poly(vinyl acetate)(Section 19.10.4). Cellulose acetate destined for fiber spinning consumes afurther quarter.

19.4.3. Formaldehyde

Catalytic oxidation of methanol in the presence of a catalyst based ontransition metal oxides produces good yields of formaldehyde [17]. Both



oxidation and dehydration reactions participate in this process (Eqs. 19.19and 19.20).

CH3OH þ 1/2 O2 (from air) ! CH2O þ H2O 19:19

CH3OH ! CH2O þ H2 19:20

Evidence for the contribution of the second reaction is obtained by thedetection of hydrogen in the reactor exit gases. Formaldehyde (b.p. �218C)is recovered from these by fractionation.

Most of the formaldehyde produced is consumed in the production ofurea-formaldehyde resins and phenol-formaldehyde resins. These cross-linkedpolymer products are in turn used in adhesive and laminate applications.

19.5. PRODUCTS FROM ETHYLENE

The various types of polyethylene together consume close to half of the totalethylene produced. Most of the remainder is used to produce the followinghigh volume chemicals.

19.5.1. Ethylene Oxide (EO)

Production of ethylene oxide is the next largest single use of ethylene. It usedto be produced via the chlorohydrin process, as propylene oxide still is.However, now it is made by the direct oxidation of ethylene with air in thepresence of a catalyst of silver supported on a-alumina (Eq. 19.21).

19:21

Temperatures in the 270–2908C range, a pressure of about ambient, and a1-second contact time give conversions to ethylene oxide of about 60%. Theethylene oxide is absorbed in water from the reactor exit gases, and theaqueous solution is then fractionated for ethylene oxide (b.p. 13.58C) recov-ery. The nonabsorbed ethylene and the absorption water recovered from thebottom of the ethylene oxide fractionator are both recycled. Recently use of aCu/Ag alloy catalyst has shown greater selectivity for ethylene oxide in thisprocess [18].

Close to half of the ethylene oxide produced is directly converted toethylene glycol (1,2-ethanediol) by acid-catalyzed or pressure hydration.Roughly half the ethylene glycol is as an automotive coolant antifreeze andhalf in polyester (poly(ethylene terephthalate)) fiber production (Chap. 21).Smaller amounts are consumed for alkyd resins production and for the for-mulation of latex paints.

19.5.2. Ethylene Dichloride (1,2-Dichloroethane) and Vinyl Chloride

Direct reaction of ethylene and chlorine in the presence of a catalyst, in eithervapor phase or liquid phase reactors under mild conditions produces a 96þ%yield of ethylene dichloride (Eq. 19.22) [19].


19.5. PRODUCTS FROM ETHYLENE 649

CH2¼¼CH2 þ Cl2 ! ClCH2CH2Cl 19:22

Some producers with a good supply of hydrogen chloride available as a by-product from the production of chlorinated solvents may prefer to use theoxychlorination route to ethylene dichloride (Eqs. 19.23 and 19.24).

CH4 þ Cl2 ! CCl4 þ 4 HCl 19:23

Oxychlorination:

CH2¼¼CH2 þ 2 HCl þ 1/2 O2(from air) ��!CuCl2 cat:19:24

ClCH2CH2Cl þ H2O

Small amounts of ethylene dichloride (b.p. 83.58C) are also recovered as aby-product from the direct chlorination of ethane to ethyl chloride (chlor-oethane).

Whatever the source, 80% or more of the ethylene dichloride produced isdirectly converted into vinyl chloride [20]. Target conversions are 50% underthe usual operating conditions of about 3–4 atm pressure and 5008C to givebetter than 94% yields of vinyl chloride (Eq. 19.25).

ClCH2CH2Cl ! CH2¼¼CHCl þ HCl 19:25

Gas exposure times to furnace temperatures are kept short by a direct spray ofethylene dichloride at ambient temperatures onto the exit gases and by anindirect heat exchanger. Hydrogen chloride may be recovered by scrubbingwith water, or by some form of fractionation if it is to be fed in anhydrousform to an oxychlorination unit. Many vinyl chloride producers operate anoxychlorination unit solely to convert the by-product hydrogen chloride fromthe ethylene dichloride cracker to produce additional ethylene dichloridefeedstock. Vinyl chloride (b.p. �13.48C) is almost entirely consumed for theproduction of poly(vinyl chloride) (PVC).

19.5.3. Ethylbenzene and Styrene (Vinylbenzene)

Ethylbenzene production has a smaller demand for the ethylene stream thanthe products already described and currently stands 19th in volume of pro-duction. It is made by both liquid phase processes under moderate conditionsemploying aluminum chloride catalysis and by vapor phase processes at 150–2508C and 30–50 atm in the presence of a supported boron trifluoride catalyst(Eq. 19.26).

C6H6 þ CH2¼¼CH2 ��!catalystC6H5CH2CH3 19:26

Ethylbenzene (b.p. 1368C) is recovered from the excess unreacted benzene andthe more heavily alkylated material by fractionation. The polyalkylated res-idues may be partly recycled to take advantage of transalkylation reactions toproduce more ethylbenzene, or may be burned as fuel to help drive theprocess.

Virtually all of the ethylbenzene produced is destined for styrene produc-tion, ultimately leading to polystyrene and other polymers. A preheatedmixture of ethylbenzene vapor and superheated steam passed over one of



several possible dehydrogenation catalysts preheated to 620–6408C crack30–40% of the ethylbenzene in one pass (Eq. 19.27).

C6H5CH2CH3 ��!catalystC6H5CH¼¼CH2 þ H2 19:27

The exit stream is condensed and, after addition of a polymerization inhibitor(usually sulfur), is successively distilled under reduced pressure to a styrenepurity of better than 99.7%. A few ppm of 4-t-butylcatechol inhibitor isadded to the purified product after which it is ready to be shipped. Industrialyield (selectively) of styrene from ethylbenzene is about 90%.

19.5.4. Vinyl Acetate

Currently ranked 41st in American volume of production, vinyl acetate ismade by the vapor phase reaction of ethylene with acetic acid at 170–2008C.Pressures of 5–8 atm and a palladium catalyst supported on carbon arerequired to give conversions of 10–15% on ethylene and 15–30% on aceticacid. Equation 19.28 is an overall representation of the stoichiometry of thecomplex process.

CH2¼¼CH2 þ CH3COOH þ 1/2 O2 ! CH3COOCH¼¼CH2 þ H2O

19:28

The reactor exit gases are cleaned up by various washes and the vinyl acetate(b.p. 72.28C) separated from unreacted starting materials, water, and a smallamount of polymeric material by distillation. Industrial yields based on ethyl-ene are 92–95%. The product purity is 99%, to which traces of inhibitor, suchas hydroquinone will be added to stabilize it during storage and shipment.

All of the product vinyl acetate is consumed in the production of homo-polymer (one monomer) and copolymer products, among them poly(vinylacetate) latices and resins, poly(vinyl alcohol) by postpolymerization hydro-lytic removal of the acetate, and copolymers with vinyl chloride and ethylene.

19.5.5. Ethanol (Ethyl Alcohol)

Production of ethanol by fermentation processes probably represents amongthe earliest processes operated by humankind. Certainly until the late 1940s itwas the dominant process used to produce industrial alcohol (Fig. 19.3). Theworld market for industrial ethanol in 1991 was about 19� 109 L. Most ofthis was for fuel use, Brazil alone consuming about 12� 109 L, more than halfof the total, and the United States a further 3:5� 109 L. Most of the Brazilianmarket was supplied by the domestic fermentation of sugar solutions plusdistillation, although the proportion produced in this way varies inverselywith world sugar prices (Chap. 16). Any Brazilian supply shortfall that mayresult is supplied from imports of industrial alcohol. In the United Statesfermentation supplied almost all of the industrial ethanol in 1930. Fermenta-tion sources provided only about a tenth of the total in 1960 but with thestimulus of subsidies had grown to about one-third of a larger total by 1990.The balance of the American industrial ethanol market was supplied from


19.5. PRODUCTS FROM ETHYLENE 651

petrochemical sources. Today fermentation of sugarcane juice provides mostof the world’s ethanol, thanks to the massive contribution to this source fromBrazil.

The earliest petrochemical process to convert ethylene to ethanol was firstpracticed in about 1930, and was indirect. In this process ethylene, underpressure, is absorbed by countercurrent passage against sulfuric acid (90–98%) at about 808C in an absorber to form a mixture of the monoesters,and diesters (Eqs. 19.29 and 19.30).

CH2¼¼CH2 þ H2SO4 ! CH3CH2OSO3H 19:29

2 CH2¼¼CH2 þ H2SO4 ! (CH3CH2O)2SO2 19:30

Both the acid concentration and the temperature have to be higher for esterformation from ethylene than for ester formation from propylene because of theless reactive carbon–carbon double bond in ethylene. The monoester is pre-ferred for its easier hydrolysis and its lower tendency to form diethyl ether. Afterreaction, the mixed esters are hydrolyzed with just sufficient excess water tocomplete the hydrolysis, which takes about 2 hr at 60–708C (Eq. 19.31).

CH3CH2OSO3H þ (CH3CH2O)2SO2 þ 3 H2O ! 19:31

3 CH3CH2OH þ H2SO4 (dil:)

The ethanol product (b.p. 78.38C) is recovered by distillation and the dilutedacid is recovered as the bottom stream of the column. Yields (selectivities) on

TOTALTOTAL

TotalSyntheticTotalSynthetic

FermentationFermentationEsterificationEsterification

DirecthydrationDirecthydration

1930 1940 1950 1960 1970 1980 1990

Year

Ethanol, 106 L

1,200

1,000

800

600

400

200

0

FIGURE 19.3 Volume of production of industrial ethanol in the United States, by process.



ethylene are 90–95%. Diluted acid is reconcentrated in several stages, the laststages under reduced pressure, for recycling to the absorption stage. Thevolume of ethyl alcohol produced in the United States by this process peakedin about 1960. Since the late 1940s it has gradually been supplemented andthen largely replaced by the process, which uses direct hydration of ethylene(Fig. 19.3).

The direct hydration process began to be important for American indus-trial alcohol production in the late 1940s. It has grown from this beginningto produce roughly 70% of the total industrial alcohol in 1975 and certainlyhas provided most of the supply since then. Like many catalytic petrochemicalprocesses, high pressures (ca. 70 atm) and temperatures of around 3008C arerequired to convert a 0.6:1 mole ratio of steam:ethylene, to ethanol. In thepresence of a supported phosphoric acid catalyst using a space velocity of1800 hr�1 gives conversions of 4.0–4.2% and yields on ethylene of 95þ%(Eq. 19.32).

CH2¼¼CH2 þ H2O Ð CH3CH2OH DH ¼ �40:2 kJ (�9:6 kcal) 19:32

The exit stream is cooled and the condensate separated in a high-pressureseparator. After scavenging any remaining product from this stream, theunreacted ethylene is recycled.

Ethanol is recovered from the condensate of the direct hydration processby distillation. Traces of acetaldehyde, which probably arise from the hydra-tion of a small amount of acetylene present in the feed ethylene, are cataly-tically reduced to ethanol with hydrogen (Eqs. 19.33 and 19.34).

HC � CH þ H2O ! CH3CHO 19:33

CH3CHO þ H2 ��!Ni cat:

CH3CH2OH 19:34

Traces of diethyl ether impurity are hydrated back to ethanol using conditionssimilar to those used for the ethylene hydration reaction.

Ethanol is used in a variety of fuel, solvent, and chemical applications inindustry. Chemical applications have dropped sharply in the last 20 years asmore direct routes to products, such as acetaldehyde, acetic acid, ethyl acet-ate, and ethyl chloride, which were formerly made from ethanol, came onstream. The automotive fuel component, as a component to improve octanerating, is anticipated to have the highest potential for growth.

19.6. PRODUCTS FROM PROPYLENE (PROPENE)

Almost half of the propylene produced is used to prepare polypropylene(Chap. 23). Most of the remainder is consumed for production of the follow-ing products.

19.6.1. Acrylonitrile (Vinyl Cyanide)

This versatile monomer is produced by the catalytic ammonoxidation ofpropylene. A mixture of propylene, ammonia, and air in the volume ratio


19.6. PRODUCTS FROM PROPYLENE (PROPENE) 653

1:1:10 provides roughly two volumes (moles) of oxygen per volume (mole) ofthe other reactants, or a 30% excess to that required by the process. The gasmixture at near ambient pressures is given a 10–20 second contact time over amolybdenum-based catalyst on a silica support kept at about 4008C. Betterthan 70% conversion to acrylonitrile is obtained, together with traces of by-product acetonitrile and hydrogen cyanide (Eq. 19.35).

CH3---CH¼¼CH2 þ NH3 þ 3/2 O2 ! CH2¼¼CHCN þ 3 H2O 19:35

Reactor exit gases are cooled and washed with water, from which the acrylo-nitrile is recovered and purified by distillation.

A recently developed one-step ammonoxidation process to acrylonitriledeveloped by BP Chemicals uses propane instead of propylene feed [21]. Keyto the feasibility of this lower cost option was the development of the newcatalyst system, which is now at the commercial demonstration stage. Almostall the acrylonitrile production goes into synthetic polymers and copolymersmostly for applications as fibers, some for plastics applications, and a smallpercentage to elastomer markets (the nitrile rubbers).

19.6.2. Isopropyl Alcohol (Isopropanol)

The indirect, sulfate ester-based process, used to introduce this chapter, wasone of the first petrochemical processes (Section 19.3). This method still has aplace since its capability of selective absorption of propylene enables it to beused with refinery gas streams to capture low concentrations of propylene,unlike the conditions for alternative processes. The direct hydration of pro-pylene to isopropanol is also possible, but this requires a refinery streamcontaining a much higher concentration of propylene to be competitive. Forthis reason both petrochemical processes are still viable in their respectivefeedstock niches.

With the direct hydration process to ethanol, the Le Chatelier principlewould suggest that high pressures and low temperatures would tend to favorproduct formation. This is also true with propylene. Pressures of 100–250 atm and temperatures of 150–2708C are used because, unfortunately,all known catalysts (supported sulfonic acids, or phosphoric acid) for thisprocess require high temperatures to be effective (Eq. 19.36).

CH3CH¼¼CH2 þ H2O Ð (CH3)2CHOH 19:36

DH ¼ �210 kJ (�50 kcal)

Isopropanol formation is thought to proceed via an intermediate isopropylcarbocation generated by interaction with water and the acid catalyst, whichis then hydrated with water. Recovery is by distillation, to the 91% azeotrope,or by ternary distillation of the azeotrope to 100% isopropanol.

19.6.3. The Oxo Alcohols: n-Butanol and Isobutanol (2-Methylpropanol-1)

The oxo reaction is used to produce aldehydes or alcohols containing oneadditional carbon atom, from the corresponding a-olefin. Propylene, in thepresence of a 1:1 mixture of carbon monoxide and hydrogen (synthesis gas)



and raised to 100–250 atm and about 1708C, gives 70–80% yields of theinitial products butyraldehyde and isobutyraldehyde (Eq. 19.37).

CH3CH¼¼CH2 þ CO þ H2 ! CH3CH2CH2CHO60�40%

þ (CH3)2CHCHO40�60%

19:37

An organocobalt derivative, such as cobalt naphthenate, is used as a catalyst.In a second step, the mixed aldehydes are reduced with hydrogen in thepresence of a nickel-based catalyst to give n-butanol (b.p. 1188C) and iso-butanol (b.p. 108.18C) (Eq. 19.38).

CH3CH2CH2CHO þ H2 ! CH3(CH2)2CH2OH þ 19:38

CH3CH(CH3)CH2CH2OH

The products are recovered and purified by distillation. It should be men-tioned that this process is not limited to the oxygenation of propylene, butmay be applied to a-olefins generally.

19.6.4. Propylene Oxide (PO)

Two process routes to propylene oxide are commercially practiced; hydroper-oxide formation and then use of this to oxidize propylene, and formation ofpropylene chlorohydrin followed by treatment with a base to form propyleneoxide [22, 23]. It has not been possible to produce adequate yields of propyl-ene oxide via the direct oxidation of propylene with air in the manner inwhich ethylene oxide is now produced, although attempts to come close tothis continue [24].

Epoxidation of propylene by a hydroperoxide is commercially viable forthose hydroperoxides which, when spent, can easily give another commercialproduct. One option is to produce t-butyl hydroperoxide (plus some t-buta-nol) by the air oxidation of isobutane at 908C and ca. 30 atm in the presenceof molybdenum naphthenate (Arco and Texaco). The separated hydroperox-ide is then used to oxidize propylene to propylene oxide with yields onhydroperoxide of over 90% (Eqs. 19.39 and 9.40).

(CH3)2CHCH3 þ O2 ! (CH3)3COOH 19:39

19:40

Coproduct t-butanol is produced at the rate of about 2.2 kg per kilogram ofpropylene, and is converted to methyl t-butyl ether for sale as an automotivefuel additive.

Ethylbenzene hydroperoxide from ethylbenzene provides the other viableoption to oxidize propylene (Arco, Eq. 19.41 and 19.42).

PhCH2CH3 þ O2 ! PhCH(OOH)CH3 19:41



19:42

In this case the spent oxidant is a-methylbenzyl alcohol, which is produced atalmost twice the mass per unit of propylene oxide as t-butanol. However, easydehydration of a-methylbenzyl alcohol converts the coproduct to styrene, forwhich a large market exists (Eq. 19.43).

PhCHOHCH3 ! PhCH¼¼CH2 þ H2O 19:43

The chlorohydrin process practiced by Dow Chemical in the United States,weds the chlorine component of chloralkali technology to propylene oxideproduction. Chlorine added to water produces hypochlorous acid and hydro-chloric acid (Eq. 19.44).

Cl2 þ H2O Ð HOCl þ HCl 19:44

Contacting this solution countercurrently with propylene converts some of thepropylene to propylene chlorohydrin, which dissolves in the aqueous phaseleaving the bottom of the contacting tower. Both possible isomers are formed(Eq. 19.45).

CH3---CH¼¼CH2 þ HOCl ! CH3---CH(OH)CH2Cl90%

þ 19:45

CH3---CH(Cl)CH2OH10%

The rate of reaction of chlorine with propylene is much slower, though 7–8%by weight propylene chloride (1,2-dichloropropane) is also formed. In asecond stage the propylene chlorohydrin is contacted with lime slurry inwater, which cyclizes the chlorohydrin to the epoxide (Eq. 19.46).

19:46

To minimize hydrolysis of the propylene oxide (b.p. 34.28C) as it is formed, itis flashed (rapidly removed) from the reactive lime slurry. Yields of propyleneoxide are 75% or better based on propylene. The advantage of the chlorohy-drin route to propylene oxide over the two hydroperoxidation processes isthat it yields essentially a single product to market. The disadvantage is thelarge quantities of coproduced aqueous calcium chloride that has to bediscarded safely. The small amount of by-product 1,2-dichloropropane maybe pyrolyzed to allyl chloride, useful for the preparation of allyl monomers,allyl alcohol, and allylamines. Or it may be blended with 1,3-dichloropropeneto produce an effective soil fumigant.

Close to two-thirds of the propylene oxide produced goes to polypropyl-ene glycol and polyester glycols production destined for use in polyurethanes.The polyol diols are made by the base-catalyzed reaction of propylene glycol



with propylene oxide (Eq. 19.47). Replacing propylene glycol by glycerol inthis process produces polyol triols.

19:47

Most of the rest of the propylene oxide is hydrolyzed in water using a trace ofmineral acid to give propylene glycol (1,2-propanediol, b.p. 1878C) used forthe manufacture of polyester resins.

19.6.5. Cumene (Isopropylbenzene) and Phenol

About 10% of the propylene produced is consumed for the alkylation ofbenzene to produce cumene. Use of a supported phosphoric acid catalystand a high-purity stream of propylene in the presence of a large excess ofbenzene (to minimize dialkylation and oligomer formation) gives cumene witha 90þ% yield based on ethylene, 96þ% yield on benzene (Eq. 19.48).

C6H6 þ CH3---CH¼¼CH2 ! C6H5CH(CH3)2 19:48

Reaction conditions are about 2008C at 20–30 atm pressure. Product cumene(b.p. 1528C) is recovered and purified by distillation.

Almost all of the cumene produced is consumed by the cumene peroxida-tion process to phenol and acetone. Aspects of this process resemble theperoxidation processes to propylene oxide already described, except that inthis case the final products are formed by an intramolecular rearrangement ofthe same molecule that is peroxidized rather than by a reaction of a perox-idized molecule with a second component, propylene. In the first stage of thecumene to phenol process a suspension of purified cumene in a dilute solutionof sodium carbonate in water is heated to about 1108C under slight pressure.Air is blown through this suspension until about 25% of the cumene hasformed the hydroperoxide (Eq. 19.49).

PhCH(CH3)2 þ O2 (from air) ! PhC(CH3)2OOH 19:49

The dissolved sodium carbonate helps to maintain the system to near neutralpH to avoid premature rearrangement of the hydroperoxide. The partiallyconverted cumene from the first stage is carefully concentrated to about 80%cumene hydroperoxide before proceeding to the rearrangement step.

Dilute sulfuric acid at 70–808C is used to rearrange the cumene hydro-peroxide to phenol and acetone, for which the stoichiometry is represented byEq. 19.50.

PhC(CH3)2OOH ! PhOH þ (CH3)2CO 19:50

The details of the complicated mechanism of this rearrangement were onlydiscovered some time after the startup of commercial facilities (Fig. 19.4).Distillation is used to recover the 90þ% yield of the rearrangement products.Unreacted cumene is recycled after careful purification to remove any tracesof phenol, which would be a powerful inhibitor of hydroperoxide formation,



and a-methylstyrene (a by-product), which would reduce the yield of theperoxidation stage.

Any separated a-methylstyrene may be sold as such or may be catalyti-cally reduced with hydrogen back to cumene again.

Early petrochemical routes to phenol involved sulfonation followedby hydrolysis, or catalytic chlorination in the presence of iron followed bydrastic hydrolysis (Eqs. 19.51–19.53).

C6H6 þ H2SO4 ! C6H5SO3H, C6H5SO3H ��!H2OC6H5OH þ H2SO4

19:51

C6H6 þ Cl2 ! HCl þ C6H5Cl 19:52

C6H5Cl þ H2O þ NaOH ! C6H5OH þ NaCl 19:53

Improved yields under less drastic conditions and the decreased waste streamproblems of the cumene process to phenol have led to the phasing out of theseolder processes.

A large fraction of the phenol product, currently ranked 34th in Americanvolume of production, is directed toward the production of several types ofphenol-formaldehyde resins of utility as plywood adhesives and as compon-ents of laminates (e.g., Arborite). Some is routed to the preparation of bis-phenol A enroute to epoxy resin production.

19.7. PRODUCTS FROM ISOBUTYLENE (2-METHYLPROPENE)

Isobutylene itself ranks 38th in volume in the American chemical industry.Its two major uses are for the production of methyl t-butyl ether and1,3-butadiene, which stood 12th and 36th in volume of production in 1995.

19.7.1. Methyl t-butyl Ether (MTBE)

Commercial production of methyl t-butyl ether began in 1979, shortly afterthe discovery of its octane-improving capability for motor fuels. Although ahigher proportion of this additive was required for equivalent octane enhance-ment, it was less costly and eliminated the lead particulate discharges associ-ated with the tetraethyl lead previously used (Chap. 18). By 1984 it ranked49th in American volume of production and jumped to 12th by 1995, an

FIGURE 19.4 Mechanistic details of the acid catalyzed rearrangement of cumene hydro-peroxide to phenol and acetone.



average compound growth of almost 50% per year. It had been predicted thatby the year 2000 MTBE production would rank second in volume afterethylene among American organic chemicals, but problems from its contam-ination of water supplies have reversed its fortunes.

Methyl t-butyl ether production is the single largest consumer of butylenes.Liquid phase reaction of methanol with isobutylene in the presence of an acidicion-exchange resin catalyst at temperatures of below 1008C and moderatepressures give excellent yields of this oxygenated gasoline additive (Eq. 19.54).

CH3OH þ CH2¼¼C(CH3)2 ! CH3OC(CH3)3 19:54

Purification of MTBE (b.p. 558C) for general solvent use is by distillation. Itsuse in general solvent applications is still small. However, since MTBE has nosecondary or tertiary hydrogens it is very resistant to oxidation and peroxideformation. This makes it an attractive replacement for the more traditionaldiethyl, and diisopropyl ethers.

19.7.2. 1,3-Butadiene

The other major use for the n-butene fraction (both 1-butene and the2-butenes) of the butylenes is as a feedstock for 1,3-butadiene manufacture,ultimately destined for the production of synthetic rubber. Careful thermalcatalytic dehydrogenation in the presence of steam gives a 75–86% yield of1,3-butadiene from a 25–30% butene conversion per pass (Eq. 19.55).

n C4H8 ��!ca: 6508CCH2¼¼CH---CH¼¼CH2 þ H2 19:55

In 1997 1.7 million metric tonnes of n-butenes were consumed in the UnitedStates for this purpose, about one-third of that consumed to produce MTBE.

Butane may also be used as the raw material for butadiene productionin a different, though related, process. The need to remove four hydrogensrequires process operation at lower conversions of 10–11% per pass tomaintain reasonable yields, and results in ultimate yields of 1,3-butadienefrom this process of about 60%.

19.8. PRODUCTS FROM BENZENE, TOLUENE, AND THE XYLENES (BTX)

The number of derivatives commercially produced from this group of aro-matic substrates is extensive, many targeted as monomers for polymerizationto the large-volume fibers and plastics. Some of these, the ethylbenzene tostyrene sequence and cumene to phenol, have already been discussed inconnection with ethylene and propylene derivatives. Details of some furtherrepresentative examples of major products are outlined here.

19.8.1. Benzene to Cyclohexane

Benzene is the aromatic petrochemical used as such to ultimately producestyrene and phenol, both very large-scale products in their own right. Othermajor products from benzene use it in hydrogenated form, as cyclohexane.


19.8. PRODUCTS FROM BENZENE, TOLUENE, AND THE XYLENES (BTX) 659

Adipic acid (48th in volume), for example, is almost entirely derived fromcyclohexane (47th) as is much of the production of caprolactam and hexam-ethylenediamine (1,6-diaminohexane). The production sequences to all ofthese products will be outlined.

Cyclohexane is made by the catalytic reduction of benzene with hydro-gen, usually in a train of several reactors with partial conversion conducted ineach. This process uses a nickel or platinum catalyst and requires tempera-tures of about 2008C, 25–40 atm pressure, and the presence of a cyclohexanerecycle diluent to help absorb the exotherm of the hydrogenation (Eq. 19.56).

C6H6(g) þ 3 H2(g) ! C6H12(g) DH ¼ �151 kJ (�36 kcal) 19:56

Cyclohexane recovery (99þ% yields) is by distillation.

19.8.2. Cyclohexane to Adipic Acid (1,6-Hexanedioic Acid)

Oxidation of cyclohexane, usually in two stages, gives adipic acid. In the firststage cyclohexane is oxidized with air in the presence of a cobalt naphthenatecatalyst under moderate conditions to give a mixture of cyclohexanol andcyclohexanone (Eq. 19.57, stoichiometry only).

19:57

On completion, water is added to the mixture after which it is fractionated.Cyclohexane (b.p. 818C) containing some benzene is collected from the top ofthe column, and after hydrogenation of the benzene, is recycled. The cyclo-hexanol–cyclohexanone mixture consists of approximately equal volumes ofcyclohexanol (b.p. 1618C), cyclohexanone (b.p. 1568C), plus a mixture ofseveral esters and ethers. It is collected from the bottom with 80þ% yields oncyclohexane. An alternative route to cyclohexanol used by some plants is tocatalytically hydrogenate phenol.

The cyclohexanol–cyclohexanone mixture isolated from air oxidation,without separation, is oxidized with 5 volumes of 50% nitric acid plus catalystat 50–908C, and pressures only slightly above ambient for 10–30 min, depend-ing on the temperature used (Eq. 19.58).

2 HO2C(CH2)2CO2H þ 2 H2O þ 2 N2O "(approximate stoichiometry)

19:58

Adipic acid (m.p. 1528C) is crystallized from the reaction mixture by coolingthis to ca. 58C.

Over 90% of the adipic acid is consumed for the production of nylon forfiber and engineering resin applications. A large fraction of this consumptionis direct, as the adipic acid used in the production of nylon 6,6, but asubstantial fraction of the adipic acid is further processed to give hexamethy-lene diamine, the other monomer required. A further small fraction of the



adipic acid is converted into di-octyl (di-2-ethylhexyl) or di-hexyl esters foruse as plasticizers in flexible grades of PVC, etc., or as a very stable highboiling point component of synthetic motor oils.

19.8.3. Hexamethylenediamine (Hexane-1,6-diamine)

Vapor phase reaction of adipic acid with ammonia at about 4008C and 270–410 atm in the presence of boron phosphate catalyst gives good yields ofadiponitrile (Eq. 19.59).

HO2C(CH2)4CO2H þ 2 NH3 ! NC(CH2)4CN þ 4 H2O 19:59

Alternatively, adiponitrile may also be made from 1,3-butadiene via chlorin-ation, followed by treatment with sodium cyanide. Catalytic reduction ofadiponitrile with hydrogen then produces hexamethylenediamine (b.p. 2058C,Eq. 19.60).

NC(CH2)4CN þ 4 H2 ! H2N(CH2)6NH2 19:60

Product recovery is by distillation.Production of this petrochemical is dedicated to a single end use, the

preparation of nylon 6,6.

19.8.4. «-Caprolactam (2-Oxohexamethyleneimine)

This cyclic amide is of major importance as the single monomer used toproduce nylon 6, which rivals nylon 6,6 in utility and in volume of produc-tion (Chap. 21). Cyclohexanone is required as the starting material fore-caprolactam production. The mixture of cyclohexanol and cyclohexanoneobtained initially from the air oxidation of cyclohexane for the second stageen route to adipic acid may be used. Subjecting the mixture to dehydroge-nation converts the cyclohexanol component to cyclohexanone producingsuitable starting material for this process (Eq. 19.61).

C6H11OH ! C5H10C¼O þ H2 19:61

Alternatively, pure cyclohexanone may be made by the catalytic hydroge-nation of phenol in the presence of palladium on charcoal.

Cyclohexanone oxime, an intermediate, is made by reacting aqueoushydroxylamine sulfate with cyclohexanone (Eq. 19.62).

19:62

A Beckmann rearrangement of the oxime in hot concentrated sulfuric acidthen gives the desired seven-membered cyclic amide, e-caprolactam. Thecrude product forms a separate oily phase which is separated fromthe reaction mixture and purified by distillation under reduced pressure(b.p. 136–1388C at 10 mm; m.p. 728C). There are also several alternativeroutes to produce caprolactam [25].

Caprolactam production, like that of hexamethylenediamine, is dedicatedto the production of a single product, in this case the various forms of nylon 6,6.



19.8.5. Toluene to Toluenediisocyanate (TDI)

Toluene output at one time used to be almost entirely directed to trinitrotoluene(TNT) production for industrial and military uses. Cheaper industrial explo-sives, such as various ammonium nitrate formulations have now become avail-able making TNTa less important product. Uses of TNTare now almost entirelyconfined to military applications. However, the first stage in the preparation oftoluenediisocyanate still involves the mono-, and di-nitration of toluene using amixture of nitric and sulfuric acids, as in the first stages of TNT production.Depending on the nitration strategies employed, one of two isomer mixtures of2,4-dinitrotoluene and 2,6-dinitrotoluene, an 80:20 ratio and a 65:35 ratio, orthe pure 2,4-dinitrotoluene may be obtained (Eq. 19.63) [26].

C6H5CH3 þ HNO3/H2SO4 ! 19:63

2,4-, and 2,6-PhCH3(NO2)2 þ dil: acids

All three possible toluene nitration outcomes are separately carried throughthe reduction and phosgenation stages to give the corresponding diisocyanatemixtures, or pure 2,4-toluene diisocyanate. Reduction to the diamines withhydrogen (ca. 50 atm) is conducted catalytically using Raney nickel in theliquid phase at about 908C, to avoid the considerable explosion risk of gasphase operation (Eq. 19.64).

2,4-, or 2,6-PhCH3(NO2)2 þ 6 H2 ! 2,4-, or 19:64

2,6-PhCH3(NH2)2 þ 4 H2O

Before the catalytic route had been developed, iron in hydrochloric acid wasused to reduce the dinitrotoluenes to the diamines.

The second stage, phosgenation of the mixed diamines, or the 2,4-diami-notoluene is conducted in an inert (aromatic, or chlorinated) solvent at 20–508C. This uses an excess of phosgene in one, or preferably two (for betteryields) stages (Eq. 19.65).

R(NH2)2 þ 2 ClCOCl ! R(NHCOCl)2 ! 19:65

R(N¼¼C¼¼O)2 þ 2 HCl

The intermediate carbamoyl chloride is dissociated to the diisocyanate withthe aid of second stage heating of the reaction mixture to 100–1108C plussparging with natural gas or nitrogen to remove the hydrogen chloride as itforms. Material for sale is produced by reduced pressure distillation; puretoluene-2,4-diisocyanate has a b.p. of 1208C at 10 mmHg pressure.

The largest volume product, and the least expensive from this process, isthe 80:20 2,4-, to 2,6-toluenediisocyanate blend, which is the compositionobtained without any intermediate separations of nitrotoluenes. The 65:352,4-, to 2,6-TDI blend, and the pure 100% 2,4-toluenediisocyanate are pro-gressively more expensive and are produced in lower volumes than the 80:20blend since they each require one nitrotoluene isomer separation step. However,regardless of composition essentially all commercial TDI is consumed in theproduction of a wide variety of polyurethanes (Chap. 21). Diphenylmethane-4,4’-diisocyanate (MDI), with a somewhat lower volatility than TDI, is alsoused in some coating, elastomer, and polyurethane fiber applications.



19.8.6. p-Xylene to Dimethyl Terephthalate (Dimethyl Benzene-1,4-dicarboxyate

(DMT))

Catalytic oxidation of p-xylene with air is the chief commercial method usedto produce terephthalic acid. A solution of p-xylene in acetic acid, togetherwith manganese or cobalt derivative and heavy metal bromides, which serveas cocatalysts, is fed to a continuous reactor, vigorously stirred, and heated to2008C while under about 25 atm pressure. Air is continuously fed into thereactor at the same time as a small stream of partially reacted solution isremoved (Eq. 19.66).

C6H4p(CH3)2 þ 7/2 O2 ! C6H4p(COOH)2 þ 2 H2O 19:66

The pressure is released on the exit stream, which simultaneously flashes offmuch of the excess p-xylene and the acetic acid, and cools the residualsolution causing terephthalic acid to crystallize out. Residual acetic acid andp-xylene are removed from the crystals by centrifugation. The crude productacid is then slurried in hot water first for washing, and then for hydrogenationto decolorize any residual traces of colored impurities. It is then recrystallizedand dried to give ‘‘fiber-grade’’ material (m.p. >300 8C) in yields of about90%.

p-Xylene is also oxidized to terephthalic acid by systems, which replacethe bromide component of the catalyst system by acetaldehyde or methyl ethylketone. These systems function at lower temperatures and pressures, presum-ably via peroxide-derived radicals.

Terephthalic acid is usually converted directly to the dimethyl esterfor polymer synthesis. This is prepared by superficially conventional tech-nology using methanol and a mineral acid under moderate conditions(Eq. 19.67).

C6H4p(CO2H)2 þ 2 CH3OH ! C6H4p(CO2CH3)2 þ 2 H2O 19:67

Proportions and exact conditions required for optimum conversions andyields of diester are proprietary. Recovery of the dimethyl terephthalateproduct from unreacted starting materials, etc., is by distillation using a seriesof four or five columns. Polymer-grade material (m.p. 1428C; b.p. 2888C) isobtained by distillation under reduced pressure from the top of the lastfractionating column.

Almost all of the dimethyl terephthalate (DMT) output is consumed forthe production of poly(ethylene terephthalate), PET, by transesterificationwith ethylene glycol (ethane-1,2-diol), mostly for fiber, film, and beveragepackaging applications.

19.8.7. m-Xylene to Isophthalic Acid

Isophthalic acid is produced from m-xylene by processes analogous to thoseused for terephthalic acid except that five to six times higher pressures arerequired. The product (m.p. 3428C) is chiefly used for the preparation of thehigh thermal stability aramid polymer, Nomex (Dupont), used for electricalinsulation in thermally aggressive environments.



19.8.8. o-Xylene to Phthalic Anhydride

Air is sufficient to oxidize the methyl groups of o-xylene, under the rightconditions, like it is with p-, or m-xylene just described. However, here thesimilarity ends since commercial o-xylene oxidation is a vapor phase process[27]. ortho-Xylene vapor, mixed with a large excess of air to ensure operationoutside the explosive range, is fed to a reactor containing a supportedvanadium pentoxide catalyst and heated to about 5508C. Using about a0.1-second contact time under these conditions produces exit gases composedof phthalic anhydride, water, and carbon dioxide (Eq. 19.68).

C6H4O(CH3)2 þ 3 O2 (from air) ! C6H4(CO)2O þ 3 H2O 19:68

Cooling the exit gases causes condensation and crystallization of phthalicanhydride, which is collected and recrystallized to yield >99.5% pure product(about 75% yield). Phthalic anhydride is also made by catalytic oxidation ofnaphthalene with air.

About one-half of the phthalic anhydride production is consumed for thepreparation of plasticizers, mostly for the various flexible grades of poly(vinylchloride). The remainder is roughly split between alkyd resin preparation usedfor many types of surface coatings, and for polyester resin composites withfiberglass reinforcement, the so-called ‘‘fiberglass’’ resins used in boats andother sporting equipment as well as for corrosion-resistant vessels and ductsused in chemical processing, some automotive parts, and as a convenientmeans of field repair of many of these items.

19.9. ENVIRONMENTAL CONCERNS

The principal objectives of a modern petrochemical complex are good toexcellent yields to minimize waste production and reuse or disposal costs,and good containment throughout to minimize losses of raw materials andproducts to air, water, or soil. Many newer facilities are now able to operatewith only make-up water requirements and have no aqueous waste streams(see [28]). Aqueous streams containing volatile organics may be sparged withair to remove these, and the organic vapor–air stream produced used for feedair to a boiler to eliminate air pollution from this source. Bacterial treatmentof the residual waste water stream under anaerobic and/or aerobic conditionscan do much to consume and remove the residual impurities [29]. By-productorganics that are not amenable to recycle or combustion for energy recoveryon site may be cleanly consumed for this purpose in cement kilns [30].

Let us use as an example one recent environmental case history relevantto petrochemicals production. Nitrous oxide (N2O) is implicated as a con-tributor to stratospheric ozone damage, and is also a potent greenhouse gas(Table 2.7). Recent work indicated that about 10% of the nitrous oxidecontributions to the atmosphere was from the world’s adipic acid plants,slightly more than the fraction contributed by biomass burning [31, 32]. Ithas been estimated that about 1 mol of N2O is produced per mole of adipicacid, or about 0.3 kg of N2O per kg of adipic acid.



Nitrous oxide control options at various stages of development includedthermal catalytic reduction of N2O in the presence of methane, conversion ofN2O to recoverable NO and use of this to prepare nitric acid, and catalyticdissociation of N2O to nitrogen and oxygen (Eq. 19.69–19.73) [33, 34].

CH4 þ 4 N2O ! 4 N2 þ CO2 þ 2 H2O 19:69

CH4 þ 4 NO ! 4 N2 þ CO2 þ 2 H2O 19:70

N2O þ M ! N2 þ [O] þ M 19:71

N2O þ [O] ! 2 NO (to use for nitric acid, Chap:11) 19:72

N2O þ [O] ! N2 þ O2 19:73

It could also be recovered as nitrous oxide for sale, but this has not beeneconomically attractive. The major adipic acid producers, worldwide, haveagreed to implement N2O abatement measures using one or the other of theseoptions by 1998. Feasibility studies of a possible longer range solution havebeen conducted of an alternate enzymatic route that converts glucose tomuconic acid, which could then be catalytically reduced to adipic acid, butthis has not as yet been proven on a commercial scale (Eq. 19.74 [35]).

C6H12O6 ��!enzymeHO2C---CH¼¼CH---CH¼¼CH---CO2H

cis, cis-muconic acid��!H2,Pt

HO2C(CH2)4CO2

adipic acidH 19:74

REVIEW QUESTIONS

1. (a) What would be the mass (kg) of carbon theoretically possible fromthe processing of 1:00� 104 m3 (standard conditions) of natural gas(standard conditions are 15.68C, 1 atm pressure)?(b) Compare the percent yields reported for channel black and thermalblack in this chapter with the percent yields calculated using the massratio determined in part (a).

2. (a) What mass of isopropanol (100% basis) would be expected fromthe passage of 1,000 kg of propylene through the two-step process,ester formation and hydrolysis, assuming a 52% conversion and 71%selectivity (industrial yield)?(b) Assuming the same conversion and yield as in part (a), what massof propylene would be required to produce 1,000 kg of isopropanol(100% basis)?(c) What happens to the unreacted propylene?(d) Explain some of the possible causes of the relatively low selectivity.

3. (a) By using plausible reactions of ethyl radicals with ethylene andrelated reactions, sketch reasonable schemes leading to the variouspossible C4 hydrocarbon products from butane, which applies thebasic mechanisms to ethylene outlined in Section 19.5.


REVIEW QUESTIONS 665

(b) Sketch plausible propagation and termination reactions for theproducts observed from the cracking of propane.

4. (a) What pentanol isomer(s) would be possible from the oxo reactionusing isobutylene (CH2¼¼C(CH3)2) as the feed olefin? Outline theequations for the steps involved.(b) Describe and explain plausible methods, which could be used toisolate and purify the pentanol product(s).

5. (a) Calculate the research (academic) yield and the conversion andselectivity (industrial yield) on ethylene from the following datacollected from an autoclave (pressure vessel) experiment on thedirect hydration of ethylene.

Feed to reactor Recovered from reactor

Ethylene 280.0 g 268.3 gWater 300.0 g 292.6 gAcid catalyst trace Ethanol 19.17 g

(b) Based on the research yield, would you authorize construction of aplant to use this process? Explain.(c) Consider how knowledge of the selectivity of the process mightaffect your decision given in part 2 (b) and explain your answer.(d) Outline positive and negative selection features of the directhydration ethylene process in comparison to the esterification(indirect) route (Section 19.10.5).

6. (a) Calculate the theoretical masses of propylene, chlorine, andcalcium hydroxide required to produce 1,000 kg of propylene oxidevia the chlorohydrin process, and the mass of calcium chloride (100%basis) that would be coproduced.(b) What actual masses of starting materials would be required andmass of 12% by weight calcium chloride in water that would beproduced for each 1,000 kg of propylene oxide when the yield(selectivity) on each of the starting materials is 75%?(c) What would be the theoretical, and actual (same selectivity), baserequirement for 1,000 kg of propylene oxide if the process wasswitched to use sodium hydroxide instead of calcium hydroxide as thebase? What mass of sodium chloride (100% basis) would also result?(d) Using the theoretical raw material requirements, at what pricewould sodium hydroxide have to be available to equal the base costwhen slaked lime (Ca(OH)2) is purchased at $66 per metric tonnes(1,000 kg).(e) What environmental factor(s) might influence the selection of thebase, apart from equivalent raw material cost?

7. Compare the contact times (in seconds) and the respective spacevelocities for each of the three following process conditions.

Ethylene oxidation: 1.0-second contact time at 2808C, 1.0 atmEthylene hydration: 1800 hr�1 space velocity at 3008C, 70 atmPropylene ammonoxidation, 20-second contact time at 4008C, 1 atm.



8. (a) Use either a web search engine or a computer-based sciencedatabase to compile a brief list of the antiknock features and thedocumented environmental problems of methyl t-butyl ether (MTBE)as a gasoline additive.(b) Explain any two possible technological fixes, which might reduceor eliminate the environmental problems of this application of MTBE.

9. (a) To avoid the capital cost of an oxychlorination unit, and assumingperfect (100%) conversions and yields, what fraction of the chlorineconsumed in the initial addition to ethylene is ultimately present in thevinyl chloride product?(b) Explain the details of an alternate method to oxychlorination forconversion of hydrogen chloride back to chlorine.(c) How might the hydrogen chloride be used to produce a valuablefertilizer ingredient?

10. (a) Demonstrate by calculation the theoretical mass oft-butylhydroperoxide, ethylbenzene hydroperoxide, and cumenehydroperoxide required to oxidize 1 tonne (1,000 kg) of propyleneto the epoxide.(b) Explain briefly any two other considerations that would beimportant to consider in the decision regarding the most appropriateoxidant to use.

FURTHER READING

A. Chauvel and G. Lefebvre, ‘‘Petrochemical Processes’’, Vols. 1 and 2, Gulf Publ. Co., Houston,

TX, 1989.

W.H. Hedley, Potential Pollutants From Petrochemical Processes, Corporate Author: MonsantoResearch Corporation, Technomic Publ. Co., Westport, Conn., 1975.

S. Matar and L.F. Hatch, Chemistry of Petrochemical Processes, Gulf Professional Publ., Boston,

2001.

S. Matar, M.J. Mirbach, and H.A. Tayim, Catalysis in Petrochemical Processes, Kluwer AcademicPublishers, Dordrecht & Boston, 1989.

Organisation for Economic Co-operation and Development, ‘‘Petrochemical Industry: Energy

Aspects of Structural Change’’, OECD, Paris, 1985.P.H. Spitz, ‘‘Petrochemicals: The Rise of An Industry’’, Wiley, New York, 1988.

REFERENCES

1. G.T. Austin, ‘‘Shreve’s Chemical Process Industries’’, 5th ed., p. 75. McGraw Hill, New York,

1984.2. Facts and Figures for the Chemical Industry, Chem. Eng. News, 74(26), 38–80, June 24

(1996).

3. W.L. Faith, D.B. Keyes, and R.L. Clark, ‘‘Industrial Chemicals’’, 3rd ed., p. 205, Wiley, NewYork, 1966.

4. A.M. Thayer, Carbon Black Industry Rattled by Exit of Two Established Producers. Chem.Eng. News, 73(29), 33–40, July 17 (1995).

5. F.A. Lowenheim and M.K. Moran, ‘‘Faith Keyes and Clark’s Industrial Chemicals’’, 4th ed.,p. 210, Wiley, New York, 1975.


REFERENCES 667

6. M.Srivastava, I.D. Singh, and H. Singh, . . . Petroleum Based Feedstocks for Carbon Black

Production, Petr. Sci. Technol. 17(1–2), 67–80 (1999).

7. G.D. Ulrich, Flame Synthesis of Fine Particles. Chem. Eng. News, 62(32), 22–29, Aug. 6(1984).

8. M.S. Reich, Demand for Carbon Fibers Rebounds, Chem. Eng. News, 72(48), 23–24, Nov.

28 (1994).9. P. Beardmore, J.J. Harwood, K.R. Kinsman et al., Fiber-Reinforced Composites: Engineered

Structural Materials, Science, 208, 833–840 (1990).

10. P.K. Bachmann and R. Messier, Emerging Technology of Diamond Thin Films. Chem. Eng.

News, 67(20), 24–39, May 15 (1989).11. J. Andryiszyn, . . . A New Competitive Benchmark for Ethylene Production, Can. Chem.

News, 52(9), 27–30, Oct. (2000).

12. A.A. Lemonidou, I.A. Vasalos, E.J. Hirschberg et al., Catalyst Evaluation and Kinetic Study

for Ethylene Production. Ind. Eng. Chem. Res. 28, 524–530 (1989).13. P.K. Frolich and P.J. Wiezevich, Cracking and Polymerization of Low Molecular Weight

Hydrocarbons. Ind. Eng. Chem. 27(9), 1055–1062 (1935).

14. D. Netzer and O.J. Ghalayini, Improve Benzene Production from Refinery Sources, Hydro-carbon Process. 81(4), 71, Apr. (2002).

15. A. Kareem, S. Chand, and I.M. Mishra, Disproportionation of Toluene to Produce Benzene

and p-xylene: A review, J. Sci. Ind. Res. India, 60(4), 319–327, Apr. (2001).

16. T. Kinnunen and K. Laasonen, . . . Catalytic Carbonylation of Methanol . . . J. Molec. Struc.Theochem. 540, 91–100, May 4 (2001).

17. A. Faliks, R.A. Yetter, C.A. Floudas et al., Optimal . . . Catalytic Methanol Conversion to

Formaldehyde, J. Phys. Chem. A 105(10), 2099–2105, Mar. 15 (2001).

18. S. Linic, J. Jankowiak and M.A. Barteau, . . . Bimetallic Ethylene Epoxidation, J. Catal.224(2), 489–493, Jun. 10 (2004).

19. J.A. Orejas, Model Evaluation for. . . Direct Chlorination of Ethylene . . . , Chem. Eng. Sci.56(2), 513–522, Jan. (2001).

20. M.K. Naqvi, A.K. Kulshreshtha, Vinyl-chloride Manufacture: Technology Trends and anEnergy Economic-Perspective, Polym-Plast Technol. 34(2), 213–226 (1995).

21. J. Krieger, Propane Route to Acrylonitrile Holds promise . . . Chem. Eng. News, 74(39),

18–19, Sept. 23 (1996).22. S.J. Ainsworth, Propylene Oxide Producers Look for Ways to Counter Sluggish Market.

Chem. Eng. News, 70(9), 9–12, Mar. 2 (1992).

23. Arco Expands PO and SM. Chem. Brit. 32(8), 9, Aug. (1996).

24. T. Hayashi, L.-B. Han, S. Tsubota et al., . . . Propylene Oxide by the Gas-Phase Reaction ofPropane and Propene Mixture with Oxygen, Ind. Eng. Chem. 34, 2298–2304 (1995).

25. F.A. Lowenheim and M.K. Moran, ‘‘Faith, Keyes and Clark’s Industrial Chemicals’’, 4th ed.,

p. 201, Wiley-Interscience, New York, 1975.

26. K.J. Saunders, ‘‘Organic Polymer Chemistry’’, 2nd ed., Chapman & Hall, London, 1988.27. C.R. Dias, M.F. Portela, M. Galan Fereres et al., Selective Oxidation of o-Xylene to Phthalic

Anhydride, Catal. Lett. 43(1–2), 117–121 (1997).

28. D. Dembicki and K. Tsang, Off the river. Hazard. Mater. Manag. 8(2), 4–9, April–May

(1996).29. D. Dempster, Bacterial Bed Consumes Phenol. Can. Chem. Proc. 65(1), 36–37, Feb. (1981).

30. D. Gossman, The Reuse of Petroleum and Petrochemical Waste in Cement Kilns. Envir. Prog.

11(1), 1–6 Feb. (1992).31. M.H. Thiemens and W.C. Trogler, Nylon Production: an Unknown Source of Atmospheric

Nitrous Oxide. Science, 251, 932–934 (1991).

32. W.R. Cofer III, J.S. Levine, E.L. Winstead et al., New Estimates of Nitrous Oxide Emissions

from Biomass Burning, Nature (London), 349, 689–691 (1991).33. R.A. Reimer, C.S. Slaten, M. Seapan et al., Abatement of N2O Emissions Produced in the

Adipic Acid Industry. Envir. Prog. 13(2), 134–137, May (1994).

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Mar. (1995).



20CONDENSATION (STEP-GROWTH)POLYMER THEORY

Mr. McGuire: I want to say just one word toyou . . . just one word.Benjamin Braddock: Yes, sir.Mr. McGuire: . . . Plastics.

—The Graduate, Embassy Pictures, 1967

. . . each primordial BeanKnew cellulose by heart: Nature alone of CollagenAnd Apatite compounded Bone.

—John Updike, 1968

20.1. BACKGROUND

Natural polymers with a wide variety of fascinating properties have beenaround for a very long time. Materials such as wood, cotton, hides, wool,muscle, collagen, and starch, all comprise examples of natural polymers, mostof which have been used by humans since before historical records were kept,for heat, shelter, tools, food, and other purposes. For all of these applicationsthe natural materials were used in the chemical form in which they originallyoccurred. It was not until the 19th century when our understanding of thenature of very basic chemical transformations began to develop that techno-logists began to experiment with the modification of natural polymers to yieldproducts with more versatile properties. By these means the applicationspossible with natural polymeric materials were gradually expanded beyondthose possible with the native materials.

Public awareness of natural rubber began as a scientific curiosity, when itwas discovered by Priestley that it could be used to ‘‘rub out’’ pencil marks.This novel capability gave the material its name, but still gave rubber littleutility because of its dimensional instability and poor durability. The discov-ery of vulcanization by Charles Goodyear in 1839 changed all this. Vulca-nization, or the heating of natural rubber mixed with small amounts of sulfur,


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Handbook of Chemical Technology and Pollution