06 PP PGP Lecture 6 2014-2015

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1Petroleum and Gas Properties Lecture NO. 67. Petroleum Analysis (Assay)Crude assay is a detailed report which describes the properties of the whole crude, as well as the major fractions into which a crude is distilled at the refinery to gasoline, naphtha, kerosene, jet fuel, middle distillates, gas oils and residual.Crude oils and petroleum fractions are the most important feedstock for refining processes. To properly follow the refining processes, we must have good understanding of the compositional information and thermo-physical properties of crude oils and petroleum fractions.However, the complexity of molecular composition of crude oils and petroleum fractions makes it hardly possible to identity individual molecules. Instead, modern refiners use assay to characterize crude oils and petroleum fractions.1

2Petroleum and Gas Properties Lecture NO. 6

2British thermal unit per pound (BTU)/lbThe lower calorific value or Net calorific value (NCV) which supposes that the products of combustion contain the water of combustion to the vapor state. The heat contained in this water is not recovered. The higher calorific value or Gross calorific value (GCV) which supposes that the water of combustion is entirely condensed. The heat contained in this water is recovered.


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4Petroleum and Gas Properties Lecture NO. 6assess the potential quality of the oil,supply preliminary engineering data,indicate whether any difficulties might arise in handling, refining, or transporting petroleum or its products. Typical crude assay includes two types of information for an oil sample:bulk properties (preliminary assay); and fractional properties (full assay)The table in the previous page gives examples of both properties of a crude assay.Assay of crude oil helps refiner with methods of analysis that would provide information sufficient to:4Potential

5Petroleum and Gas Properties Lecture NO. 6It is suggested that assay data should not be two years older than the process data used to build process simulation. For design and modelling purposes, it is always the best practice to have process data obtained in the same period as assay data, since the properties and composition of crude in the well changes over time.Here is an explanation of both bulk and fractional properties.The preliminary assay (Bulk) provides general data on the oil and is based on simple tests such as specific gravity, sulphur content, nitrogen content, metal (Ni, V, Fe etc.) content, asphaltene content, C/H ratio, pour point, flash point, freeze point, smoke point, aniline point, cloud point, viscosity, carbon residue, light hydrocarbon yields (C1C4), acid number, refractive index and boiling point curve. 5

6Petroleum and Gas Properties Lecture NO. 6The tests in the preliminary assay are relatively simple and can be completed in a short time. This assay gives a useful general picture of the quality of a crude, but it does not cover the work necessary to provide adequate data for the design of refinery equipment.Bulk properties provide a quick understanding of the type of the oil sample such as sweet and sour, light and heavy, etc. Full assay (Fractional) of crude oil reflects the property and composition for specific boiling point range. This assay is necessary to properly refine crude oil into different end products such as gasoline, diesel and raw materials for chemical process. 6Adequate

7Petroleum and Gas Properties Lecture NO. 6It usually contains paraffin, naphthenes and aromatics contents, sulphur content, nitrogen content for each boiling-point range, octane number for gasoline, freezing point, cetane index and smoke point for kerosene and diesel fuelsThe following is an explanation of both bulk and fractional properties:API gravityGenerally the API gravity (American Petroleum Institute) used to specify the specific gravity (SG) of the crude oil as API = (141.5/SG) 131.5.SG is the specific gravity defined as the ratio of the density of the crude oil to the density of water both at 15.6 C (60 F). 7

8Petroleum and Gas Properties Lecture NO. 6Higher API crudes usually contain higher amount of paraffin, lower CH weight ratio, less sulphur and metals, and have lower carbon residues and viscosity. For this reason API gravity is used as the primary parameter to quantify quality of a crude.2. Sulfur content The sulphur content is expressed as a percentage of sulphur by weight, and varies from less than 0.1% to greater than 5%. Sweet crude oil contains relatively little sulfur amount (< 0.5 wt%) while sour crude oil contains considerable amounts of sulfur.3. Viscosity and Pour point Viscosity and pour point determination are performed principally to find out how easy or difficult to pump the crude oil especially in cold weather. 8From book : Characterization and properties of petroleum fractions

9Petroleum and Gas Properties Lecture NO. 6The pour point is the lowest temperature at which a crude oil will flow or pour when it is chilled without disturbance. The lower the pour point of a crude oil the more the naphthenic and aromatic it is, and the higher the pour point the more paraffinic it is.4. Flash pointIt is the lowest temperature at which sufficient vapor is produced above the liquid to form a mixture with air that a spontaneous ignition can occur if a spark is present. It indicates fire and explosion potential of a liquid hydrocarbon or an oil fraction.Liquids with a flash point below 38oC are defined flammable, while less-flammable liquids with a 38oC - 93oC are defined as combustible liquids9Pour Viscosity is a measure of a fluid's resistance to flow. It describes the internal friction of a moving fluid.A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion.

10Petroleum and Gas Properties Lecture NO. 6The freeze point is the temperature at which the hydrocarbon liquid solidifies at atmospheric pressure.5. Freeze and Melting point:Its an important property for kerosene and jet fuels, because of the very low temperatures encountered at high altitudes in jet planes.Similarly the melting point, is the temperature that a solid substance liquefies at atmospheric pressure.A pure substance has the same freezing and melting points.However, for petroleum mixtures, there are ranges of melting and freezing points versus percent of the mixture melted or frozen. Melting point increases with molecular weight.10Encountered, altitudes =

11Petroleum and Gas Properties Lecture NO. 6For a mixture, the initial melting point is close to the melting point of the lightest compound in the mixture.In contrast, the initial freezing point is close to the freezing point of the heaviest compound in the mixture. The smoke point of aviation turbine fuels and kerosene is the maximum height, in millimeters, of a smokeless flame of fuel burned in a wick-fed lamp of specified design6. Smoke point:The higher the smoke point is, the less sooting the fuel would be.Generally the more aromatic the fuel the smokier the flame. A high smoke point of a fuel indicates low smoke producing tendency.11

12Petroleum and Gas Properties Lecture NO. 67. Aniline point:Aniline, phynelamine or aminobenzene is an organic compound with formula C6H5NH2. Consisting of a phenyl group attached to an amino group. Aniline is the prototypical aromatic amine.

Equal volumes of aniline and desired oil are stirred continuously in a test tube and heated until the two components unify into a homogeneous solution. Thus, aniline point represents the minimum temperature for complete miscibility of equal volumes of aniline and petroleum oil. Heating is stopped and the tube is allowed to cool. The temperature at which the two phases separate out is recorded as aniline point.12In organic chemistry, the phenyl group or phenyl ring is a cyclic group of atoms with the formula C6H5Prototypical = ideal

13Petroleum and Gas Properties Lecture NO. 6Its an important property of diesel fuels and used to estimate the aromatic content of mixtures. Since, a lower content of aromatics in oil requires a higher temperature for aniline to be miscible, the greater the aniline point, the lower the aromatics in the oil. For example: Diesel with aniline point 50 0C have higher aromatic percentage than the one with 60 0C , the first one get quicker miscible than the second because (Like dissolve Like). Aromatics exhibit the lowest aniline points and Paraffins the highest aniline points. Cycloparaffins and olefins exhibit values between these two extremes.13

14Petroleum and Gas Properties Lecture NO. 6The cloud point refers to the temperature at which solidable components (waxes) present in the oil sample begin to crystallize or separate from solution. 8. Cloud point:In the petroleum industry, cloud point refers to the temperature which diesel forms a cloudy appearance. The presence of solidified waxes thickens the oil and clogs fuel filters and injectors in engines. Therefore, cloud point indicates the tendency of the oil to plug filters at cold operating temperatures.The wax also accumulates on cold surfaces (e.g. pipeline) and forms an emulsion with water. 14Crystallization is a chemical solidliquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occursTypical cloud points values: 10 0F to 50 0F Paraffin waxes are semi-crystalline in nature and tend to crystallize/ precipitate from crude oils at and below the equilibrium solid-liquid temperature. Crystallization is the process whereby an ordered solid structure is produced from a disordered phase, such as a melt or dilute solution (e.g. crude oil).

15Petroleum and Gas Properties Lecture NO. 69. Conradson Carbon Residue (CCR):It determines the amount of carbon residue left after evaporation or pyrolysis of an oil and to indicate relative coke-forming tendencies. CCR is expressed as the weight percentage of the original sample. A crude oil with a high CCR has a low value as a refinery feedstock.The acid number determines the organic acidity of a refinery stream.10. Acid number:15

16Petroleum and Gas Properties Lecture NO. 6The refractive index represents the ratio of the velocity of light in a vacuum to that in the oil. It is useful properties for concentration measurement, purity determination and chemical identification, since each component has different refractive index angles11. Refractive index:The gross heat of combustion or high heating value (HHV) is the amount of heat produced by the complete combustion of a unit quantity of fuel. It can be measured with calorimeter.12. Gross heat of combustion or High heating value (HHV):Determining the amount of water or sediment in petroleum is important, because they lead to difficulties in the refinery. 13. Water and Sediment16 ( ..) . Gross : ,

17Petroleum and Gas Properties Lecture NO. 6Example of some difficulties: corrosion of equipment, uneven running on the distillation unit, blockages in heat exchangers, and adverse effects on product quality.14. Boiling pointThe boiling point of a pure compound at a given pressure is the temperature at which vapor and liquid exist together at equilibrium. The boiling point, is one of the most important characterization parameters for hydrocarbons and is frequently used in property estimation methods.The initial boiling point (IBP) is defined as the temperature at which the first drop of liquid leaves the condenser tube of the distillation apparatus. 17

18Petroleum and Gas Properties Lecture NO. 6The final boiling point or the end point (EP) is the highest temperature recorded in the test.15. Distillation (True Boiling Point test TBP):The distillation tests give an indication of the types of products and the quality of the products that can be obtained from petroleum.The tests are used to compare different petroleum types through the yield and quality of the residuum fraction.A standard laboratory technique used to predict the refining qualities of crude petroleum; gives distillation cuts for gasoline, kerosene, distillate (diesel) fuel, etc.The boiling range gives information on the composition, the properties, and the behavior of petroleum and derived products during storage and use.18

19Petroleum and Gas Properties Lecture NO. 6Volatility is the major determinant of the tendency of hydrocarbon mixtures to produce potentially explosive vapors.The mainly products of crude oil distillationProductBoiling range oCGas< 15.5Gasoline (light naphtha)15.5 - 149Kerosene (medium naphtha)149 - 232Gas oil232 343Light vacuum gas oil343 371Heavy vacuum gas oil371 556Residuum> 56619explosiveVacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapor pressure (usually less than atmospheric pressure) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points).[1] This distillation method works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure. Vacuum distillation is used with or without heating the mixtureFrom a technical spec, the only difference between Gasoil and Diesel is the sulphur content. Gasoil can contain up to 0.1% sulphur content, while Diesel can only contain 0.001% sulphur.

20Petroleum and Gas Properties Lecture NO. 6In the refining process, the atmospheric distillation unit (ADU) separates the lighter hydrocarbons from the heavier oils based on boiling point. The ADU is capable of boiling crude oil fractions to temperatures of 400 0C.Above this temperature, the oil will thermally crack, or break apart, which impedes the distillation process. Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits. This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst.With other words there is different between ADU and cracking where the first one is physical while the second one is a chemical process, and they have different conditions.20Impedes Bit = parts, pieceVacuum distillation is a method of distillation whereby the pressure above the liquid mixture to be distilled is reduced to less than its vapor pressure (usually less than atmospheric pressure) causing evaporation of the most volatile liquid(s) (those with the lowest boiling points).[1] This distillation method works on the principle that boiling occurs when the vapor pressure of a liquid exceeds the ambient pressure. Vacuum distillation is used with or without heating the mixtureFrom a technical spec, the only difference between Gasoil and Diesel is the sulphur content. Gasoil can contain up to 0.1% sulphur content, while Diesel can only contain 0.001% sulphur.

21Petroleum and Gas Properties Lecture NO. 6As lighter products are boiled off, the heavier oils, called bottoms, remain at the bottom of the ADU. To increase the production of high-value petroleum products, these bottoms are run through a vacuum distillation column to further refine them. The name vacuum distillation implies, the distillation column is under a vacuum, or significantly less than atmospheric pressure of 760 millimetres of mercury (mmHg). At low pressures, the boiling point of the ADU bottoms is low enough that lighter products can vaporize without cracking, or degrading the oil. Vacuum distillation produces several types of gas oil. These are slightly heavier than middle distillates such as jet fuel, kerosene, and diesel. 21


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Bubble cap tray consists of a slotted cap on a central riser.The gas flows up through the riser, reverse flow under the cap, passes downward through the annulus between riser and cap, and finally passes into the liquid through a series of openings or "slots" in the lower side of the cap. 25Disengagement = separationSlot


A key result from a distillation test is the boiling point curve, that is, the boiling point of the oil fraction versus the fraction of oil vaporized. 26Cumulative

27Petroleum and Gas Properties Lecture NO. 616. Octane number (Antiknock Rating):Thus octane number is the measure of the ability of a fuel to resist knocking when ignited in a mixture with air in the cylinder of an internal-combustion engine. Detonation, or spark knock or ping, is defined as an uncontrolled and abrupt explosion of the fuel/air mixture in the engine cylinder(s) due to excessive pressure and/or temperature.Normally the fuel/air mixture in an engines cylinder(s) burns and expands in a controlled and linear fashion, spreading outwards from the spark at the spark plug at the time of ignition. This is considered normal combustion. When the fuel/air mixture burns/explodes instantaneously, you get detonation which creates shock pressure waves and thus an audible knock. 27Ping = ringing , Spark = , Abrupt = Excessive = too much, linear fashion , Outwards Instantaneously = , Audible Octane is a hydrocarbon and an alkane with the chemical formula CH, and the condensed structural formula CH(CH)CH2,2,4-trimethylpentane is the correct name for isooctane

28Petroleum and Gas Properties Lecture NO. 6If left unchecked, knock can do all kinds of damage to engines parts, sometimes quite quickly.Pure n-Heptane has zero octane rating. It is undesirable in gasoline, because it burns explosively, causing engine knocking.

Octane isomers, which burn more slowly and give better performance has octane number of 100.

The octane number is determined by comparing, under standard conditions, the knock intensity of the fuel with that of blends of two reference fuels: iso-octane, which resists knocking, and heptane, which knocks readily. 28Readily = easily

29Petroleum and Gas Properties Lecture NO. 6The percentage by volume of iso-octane in the iso-octaneheptane mixture that matches the fuel being tested in a standard test engine, is the measure of octane number.Thus, if the matching reference blend is made up of 15% n-heptane and 85% iso-octane, the test sample is rated 85 Motor or Research octane, according to the test method used.It was discovered that different labs gave different results therefore a number of methods have variety of engine conditions were used. The most two used methods are Research (RON) or Motor (MON) test methods. Motor Octane Test (MON)Research Octane Test (RON)Inlet air temperature148.9 C65.6 CEngine jacket temp100 C100 CEngine RPM90060029

30Petroleum and Gas Properties Lecture NO. 6MONRON8390859287958896909891.51009510599110Typical value compassion between RON and MON.The test condition for the RON are less severe than for the MON. Accordingly the gasoline have a higher octane number by RON than by MONTherefore, in some country the Road Index is used which is the average of Research Octane Number and Motor Octane Number; one measure of the combustion quality of gasoline. Road Index = (RON+MON)/2 30

31Petroleum and Gas Properties Lecture NO. 616. Cetane number: CNCetane (Hexadecane) is an alkane hydrocarbon with the chemical formula C16H34

Isocetane (2,2,4,4,6,8,8-heptamethylnonane) is a highly branched alkane used as a reference in determining the cetane number of diesel.. It is given a cetane number of 15.Cetane Number is a measure of the readiness of a fuel to auto-ignite when injected into a diesel engine. It relates to the delay between when fuel is injected into the cylinder and when ignition occurs. Cetane Number is usually measured directly using a test engine. 31

32Petroleum and Gas Properties Lecture NO. 6When a fuel has the same ignition delay period as a mixture of the two primary reference fuels, its cetane number is derived from the volume percent of cetane and Cetane number = % cetane + 0.15 (% heptamethylnonane)A diesel fuels cetane number, however, is actually a measure of the fuels ignition delay; the time period between the start of the injection of the fuel and the start of the combustion of the fuel .The octane number of a gasoline measures its ability to resist auto-ignition commonly referred to as pre-ignition, knocking or pinging. Then, what is the different between Octane and Cetane number?Normal modern highway diesels run best with a fuel rated between 45 and 55.32

33Petroleum and Gas Properties Lecture NO. 6In general, a higher cetane fuel will have a shorter ignition delay period than a lower cetane fuel. Usually, the method for determining cetane requires the use of an industry standard test engine called a Cooperative Fuel Research (CFR) engine. The disadvantages of this test methods are:The high purchase cost ($500,000 plus), ongoing maintenance, and operating costRequirement for trained staff and expertise for operation and maintenanceAn easer test by using API gravity and the distillation mid-point can be used to calculate cetane index instead of cetane number.33


Cetane Index Equation by ASTM D473734

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06 PP PGP Lecture 6 2014-2015