Properties of Crude Oil and Petroleum Products

8/17/2019 Properties of Crude Oil and Petroleum Products

1/54

Reproduced by Solomon Associates with the expressed permission of Haverly Systems, December 2007

© Copyright 1987 - 2007 Haverly Systems Inc.All Rights Reserved

Haverly Systems Inc. 12 Hinchman Avenue

P.O. Box 1110Denville, New Jersey 07834

Tel (201) 627-1424 Fax (201) 625-2296 E-mail [email protected]

PROPERTIES OF

CRUDE OILS and

PETROLEUM

PRODUCTS


2/54

Table of Contents

INTRODUCTION..................................................................................................................................... 3

DISTILLATION ..................................................................................................................................... 11

GRAVITY & DENSITY .......................................................................................................................... 14

SULFUR ............................................................................................................................................... 16

MERCAPTAN SULFUR ........................................................................................................................ 19

HYDROGEN SULFIDE ......................................................................................................................... 19

THIOPHENES ....................................................................................................................................... 19

NITROGEN ........................................................................................................................................... 21

OCTANE ............................................................................................................................................... 23

FLASH POINT ...................................................................................................................................... 26

REID VAPOR PRESSURE ......................... ......................... ........................... ......................... .............. 27

SMOKE POINT ..................................................................................................................................... 28

LUMINOMETER NUMBER ................................................................................................................... 28

ANILINE POINT .................................................................................................................................... 30

REFRACTIVE INDEX............................................................................................................................ 32

COLD PROPERTIES ............................................................................................................................ 33

POUR POINT .................................................................................................................................... 33 CLOUD POINT .................................................................................................................................. 35 FREEZE POINT ................................................................................................................................ 35 COLD FILTER PLUG POINT ............................................................................................................. 35

CETANE NUMBER ............................................................................................................................... 37

CETANE INDEX.................................................................................................................................... 38

DIESEL INDEX ..................................................................................................................................... 38

VISCOSITY ........................................................................................................................................... 40

VISCOSITY INDEX ............................................................................................................................... 43

NEUTRALIZATION & TOTAL ACID NUMBER ........................ .......................... ......................... .......... 45

WAX...................................................................................................................................................... 46

METALS ............................................................................................................................................... 47

CARBON RESIDUE .......................... .......................... .......................... ......................... ....................... 49

SULFUR IN CARBON RESIDUE ....................... .......................... ......................... ........................... ..... 49

ASPHALTENES & RESINS .................................................................................................................. 51

n-PENTANE INSOLUBLES ....................... ......................... ........................... ......................... .............. 53

PENETRATION .................................................................................................................................... 53

SOFTENING POINT ............................................................................................................................. 53

DUCTILITY ........................................................................................................................................... 53


3/54

Page -3-

© Copyright 1987 - 2006 Haverly Systems Inc.

All Rights Reserved

INTRODUCTION

The principal elements in petroleum fuels are carbon and hydrogen. Sulfur, nitrogen and oxygen are alsopresent in lower concentrations and a range of other elements, notably metals, are found in tracequantities. These elements are linked together in a wide variety of molecular forms: for example, morethan 600 different hydrocarbons have been identified in petroleum.

Except for a few of the lightest compounds (boiling temperatures below several hundred degrees F) themixture is never separated into pure compounds. Rather the crude oil is separated by atmospheric andvacuum distillation into fractions consisting mostly of those compounds boiling between initial and finalboiling point temperatures for the fraction.

There are four principal categories in which the molecules can be grouped.

1. Saturated Hydrocarbons

The term saturated is applied to hydrocarbons that contain only single carbon-carbon bonds.

Normal Paraffins are molecules in which carbon atoms are arranged in a straight chain. In most

crude oils they are present in a continuous homologous series CnH2n+2 in which the maximumnumber of carbon atoms n is usually around 40. The members with carbon atoms 1 to 4 are gases,(methane, ethane, propane butane) under ambient conditions; those with carbon number 5 to 18are liquids, with n>18 are solids.

Iso-paraffins are branched structures with side chains attached to the main carbon atombackbone. In crude oil, the highest number of carbon atoms in the molecule rarely exceeds 25.

Naphthenes (cycloparaffins) are molecules in which the carbon atoms are arranged in a ring. Theyare very important constituents of petroleum and account for about half the mass of an averagecrude oil. Practically all the naphthenes found in fuels are based on species having five and six-membered rings. The types found in distillate fuels consist of one or two fused rings with paraffinicside chains. The larger naphthenes, which are found in residual products, comprise up to five fused

rings and have longer paraffinic side chains than mono and bicyclic types.

2. Unsaturated Hydrocarbons

The term Unsaturated is applied to hydrocarbons that contain one or more carbon-carbon double bond.

Olefins contain on double bond. They are relatively unstable and as a result are generally notpresent in crude oils. However, they are produced in crude oil processing, especially in conversionunits.

Aromatics are compounds with one or more benzene rings such as toluene (one benzene ring) ornaphthalene (two benzene rings sharing a common bond). Benzene is the simplest aromaticmolecule and has its carbon atoms arranged in a six-membered ring. More complex aromatics

consist of several fused benzene rings with side chains attached. Molecules comprising of up tofive fused rings have been identified in heavier fuels although single and double-ringed species arealways predominant.

Naptheno aromatics are a combination of fused aromatic and naphthenic rings with side chainsthat are predominantly methyl, CH3, groups; they are a major constituents of heavier fuel fractions.The number of fused rings varies from two to five.


4/54

Page -4-


All Rights Reserved

Saturated Hydrocarbon Constituents

Normal Paraffins

Iso-paraffins

Naphthenes


5/54

Page -5-


All Rights Reserved

Unsaturated Hydrocarbon Constituents

Olefins

Butylene

Aromatics

Naphtheno Aromatics


6/54

Page -6-


All Rights Reserved

Hetro-Atomic Constituent


7/54

Page -7-


All Rights Reserved

3. Hetro-Atomic Molecules

Some constituents of petroleum fuels contain elements in addition to carbon and hydrogen, notablysulfur, nitrogen or oxygen.

Sulfur compounds form the most important group with respect to both quantity and their effect onfuel performance.

Nitrogen is present in all crude oils, up to a maximum of about 1% by weight. Molecules in whichthe nitrogen is bound can constitute 15% by weight of the oil.

Oxygen compounds are present in low concentrations in crude oils. During processing, the majoritydecompose to form ring compounds with a carboxylic acid group, COOH, attached in a side chainand a re generally called naphthenic acids.

More details on these elements are covered later in this course manual.

4. Complex Species

The structure of this group of compounds is chemically less well defined and are broken down into twobroad groups; Resins and Asphaltenes.

They are aromatic materials with polar groups attached which can be precipitated by the addition ofliquid propane. The part of the precipitate that is dissolved by n-heptane is defined as the resins; theinsoluble part is defined as the asphaltenes.

Both asphaltenes and resins are confined to residual streams. The asphaltenes are a particularlyimportant class of compound and give residual products unique characteristics in relation to distillatefractions. When precipitated they form dark brown to black solids. Asphaltenes are composed of anumber of sheets that comprise an arrangement of condensed aromatic and naphthenic rings with anumber of side chains. Sulfur, nitrogen and oxygen are also contained within the structure. Severalsheets link together to form the asphaltene molecule. Bonding of the sheets is accomplished either bycovalent bonding, or by strong associative forces.Asphaltenes have high molecular weight and typically contain seven to eight unit sheets. The unit sheetscomprise up to 16 condensed aromatic rings which mean that asphaltenes, as a class, are very aromaticmaterials. The total number of sulfur, nitrogen and oxygen atoms associated with each unit sheet isnearly always less than five. Additionally, a significant fraction of a crude oil’s inherent content ofvanadium and nickel is likely to be associated with its asphaltenes.

When resins are precipitated, their appearance varies from dark yellow, viscous liquids to amorphous,dark-colored solids. Their structure is broadly similar to that of the asphaltenes but they are smaller andless aromatic and typically consist of only one unit sheet. Resins generally contain more oxygen, andless sulfur and nitrogen than asphaltenes; their hydrogen content is higher owing to their loweraromaticity.

CATEGORIZING CRUDE OILS

Crude oils are often grouped into types. There is no standard industry definit ion of crude oil types.Frequently used types are: (1) heavy vs. light crudes, (2) low or “sweet” vs. high or “sour” sulfur crudesand (3) paraffinic vs. naphthenic crudes.


8/54

Page -8-


All Rights Reserved

Heavy crudes are ones with a high proportion of high-boiling, high-specific-gravity components and alarge percent of residuum. Light crudes have a high proportion of naphthas and middle distillates andlittle residua.Industry sometimes uses 1 wt% Sulfur as the criteria of sweet (less that 1%) versus sour (greater than1%) crude oil.

A crude oil predominantly of paraffin type compounds is called a paraffinic crude oil. One withpredominantly ring compounds is called a naphthenic crude oil. Actually some crudes may have morearomatic than naphthene type compounds but it is still called a naphthenic crude. Crude oils with higharomatics content are not typically spoken of as aromatic crudes. Of course a crude oil may be largelyparaffinic in one fraction while largely naphthenic in another.

The proportion of paraffins, naphthenes and aromatics strongly influence many of the properties. Forexample, for the same number of carbon atoms in a molecule the aromatics have the highest boilingpoint, cycloparaffins in between boiling points and paraffins the lowest. For compounds of similar boilingpoints paraffins have the lowest density, the highest smoke point, the highest pour and cloud points, thehighest viscosity index, the highest aniline point, and the lowest viscosity.

In general aromatics are the opposites of paraffins with naphthenes in between. Paraffins are the easiestto crack, aromatics the hardest. Paraffins make good waxes and lube oils while aromatics make good

asphalt. Crudes that are excellent for making asphalts are generally naphthenic crudes and they may behigh in sulfur, nitrogen and metals. In naphthas, the naphthenes can be converted to aromatics bycatalytic reforming. Also, the structure of the paraffin may affect some properties significantly.Branched-chain paraffins in the gasoline boiling range have much higher octanes than the straight-chainparaffins. Iso-octane has an octane number of 100 while normal heptane has an octane number of zero.Both are paraffins. Also branched paraffins tend to have lower smoke points than straight chainedparaffins. In general aromatics are desirable in gasoline because of their octane and undesirable indiesel fuels because of their low Cetane. However, air-pollution regulations now limit the content ofaromatics in gasoline.

CRUDE OIL PRODUCTS

Lower boiling fractions are typically used for refinery fuel gas, LPG, gasoline and naphtha solvents.Medium boiling fractions (300 to 700 degrees F) are known as mid-distillates and have uses as kerosene,

jet fuel, diesel fuel and heating oil. Heavier fractions (boiling between 700 and 1000 F) are separated bya vacuum distillation unit and find uses as fuels, waxes and lubricating oils. Residual fractions fromvacuum distillation (material not distilled off at 1000 F) are used in heavy fuels and asphalt products.

Lighter fractions, such as mid-distillates, may be blended with heavier fractions to improve the propertiesof products being made.

Many of the fractions also are used as feeds to various refinery processes. A cracking process changesthe chemical composition and boiling range of the mixture. A naphtha fraction may be fed to a catalyticreformer as a means of improving the octane and making a better gasoline blending stock. All distillatesboiling above 400 F are potential feed stocks to a cracker, although the most common cracker feedstock

is vacuum gas oil, boiling between 700 and 1000 F. Even deasphalted oil “bright stocks” have been fedto crackers with some deasphalting units having been designed specifically to produce this type ofcracker feedstock. Residuals may also be fed to a coker unit producing coke for metallurgical use,electrodes or just common fuel. By-products from cracking include a whole range of boiling pointmaterials which can be further processed to add to the supply of materials used to make products.


9/54

Page -9-


All Rights Reserved


10/54

Page -10-


All Rights Reserved


11/54

Page -11-


All Rights Reserved

DISTILLATION

TBPTBP stands for the true boiling point data. The tests are run in a column with high reflux and goodseparation. This is often done in a column with fifteen theoretical plates and a reflux ratio of 5 to 1according to ASTM D2892. TBP represents an accurate measure of the volume which will distill vs.

temperature. TBP data is used for the crude assay input. When used in connection with a distillate cutone may want data for the initial temperature, the final temperature and the temperatures at whichspecified amount of the cut has distilled over (typically 5%, 10%, 30%, 50%, 70%, 90% and 95%). Inrefinery production equipment one would not expect to get as accurate separation as the TBP data.

ASTM Distillations Typically in an operating refinery a simpler, quicker distillation test is used to help monitor operation and

to conform to product specifications. Two ASTM tests are in common use. One is the ASTM D86 test,the other the ASTM D1160 test.

D86: The D86 test is done at atmospheric pressure with little reflux ratio. It is basically a batchdistillation where 100 ml of sample is distilled under prescribed conditions and observations aremade of the temperature readings and volumes of condensate. A mercury-in-glass thermometer

(or equivalent in automatic equipment) records the vapor temperature at the vapor outlet. Thistemperature is actually 0-32 degree’s F below true temperature for observed ASTM D86temperatures between 200 and 700-degree F, respectively. The standard test procedure (andproduct specification based thereon) provides for using the temperature as recorded without anysuch adjustment. Adjustments to temperatures are made when pressure is not 760 mm Hg.

D1160: In this test the distillation is done at predetermined and accurately controlled reducedpressure. It would be used for fractions which may decompose when distilled at atmosphericpressure. A thermocouple is used to measure temperatures. The results are likely to be closer toTBP than the D86 test. Observed temperatures are converted to atmospheric pressure equivalentby use of a formula or chart as given in the ASTM Manual of Hydrocarbon Analysis for D1160.

D2887: Simulated distillation (SD) by gas chromatography appears to be the most simple,

reproducible, and consistent method to describe the boiling range of a hydrocarbon fraction. Thismethod is applicable to all petroleum fractions with a final boiling point of at least 1000 deg F orless at atmospheric pressure. The method is also limited to samples having an initial boiling pointof at least 100 deg F. Simulated distillations are plotted in weight percent.

Conversion of Distillation Results. Methods are available for estimating ASTM distillation data fromTBP data and vice versa. One method for D86 is the API Procedure 3A1.1 (1987). It coverts eachtemperature (initial, 5%, etc.) from one system to the other without regard to data points at the othertemperatures. The method does not give consistently good results.

Another method for D86 is the API Procedure 3A1.1 (1980). It was adapted from Edmister and Pollock,Chem. Engr. Progr. 44 905 (1948). One first converts the 50% point and then calculated the differencesto other points based on corresponding differences in the originating data. For example, convert the50% TBP temperature to 50% ASTM. Then take the difference in temperatures between the 30% and50% TBP data, convert it to ASTM using the charts and apply this difference to the 50% ASTM point toget the 30% ASTM point.

The basic approach in the second method appears to be sounder than the first. However some believethat a better method for D86 is based on Edmister-Okamoto correlation in Petroleum Refiner, August1959. This approach is similar to the second method but uses different correlations. For example the50% point has a much bigger adjustment for higher temperatures. CAL II uses this latter method.


12/54

Page -12-


All Rights Reserved

Volume distilled for corrected D86 ASTM temperatures (add 0-32) can be correlated to TBP volume atthe same temperature.

To convert D1160 ASTM data to TBP and vice versa one can use the API procedure 3A2.1. In it, the50% points for ASTM and TBP are the same. The 50% to 70% and the 70% to 90% differences are thesame. The 50% to 30% and 30% to 10% differences are only slightly dif ferent while the 10% to 0% havesignificant differences (up to 18 degree’s F). The basic approach is similar to the second and thirdmethods above but with less adjustment.


13/54

Page -13-


All Rights Reserved


14/54

Page -14-


All Rights Reserved

GRAVITY & DENSITY

Description These relate to the weight per unit volume. This may be expressed as Specific Gravity (weight ofmaterial compared to an equal volume of water), Density (weight per standard volume) or API Gravity.All of these measures vary with temperature so the temperature of the sample is part of the definition.

API gravity is defined at 60 degrees F. Density may be measured at 0 or 4 degrees C or 60 degrees F oranother temperature. Specific gravity is the ratio of the weights of a standard volume of the material at agiven temperature compared to the weight of the same volume of water at a temperature. The twotemperatures are often, but not always, specified the same. API gravity is related to specific gravity (orvice versa) by the following formula:

API = (141.5/Sp.gr at 60F/60F) - 131.5

Since the specific gravity of water is 1.0, its API gravity is ten (10).

Range Gravity is widely used in crude assay calculation and is needed for whole crude and over the full range ofdistillates and residues.

Typical ValuesMost petroleum fractions and crude oils are lighter than water, i.e., have API gravities greater than 10and specific gravities less than 1.0. However, many crude residuals and some highly cracked heavycycle oils are heavier than water.

Whole crude oils in the marketplace range from 10 to 66 API. However, benchmark crude oil has agravity around 33 API. Two-thirds of all crudes of commerce are between 25 and 40 API. Generally theAPI gravity is an indication of the proportion of lighter distillates to resid in the crude. High API indicatesa higher proportion of light material. Also a crude oil (or portion of the crude oil) with a high proportion ofaromatics and naphthenes will have a higher density (lower API) than a crude with mostly paraffins.

Test Methods

ASTM D 1298 Standard Test Method for Density, Relative Density (Specific Gravity),or

API Gravity of Crude Petroleum and Liquid Petroleum Products byHydrometer Method.


15/54

Page -15-


All Rights Reserved


16/54

Page -16-


All Rights Reserved

SULFUR

Description This is the weight percent of sulfur in the material. Sulfur may be present in Crude Oils and petroleumproducts as dissolved sulfur and hydrogen sulfide or as organic compounds such as thiophenes, sulfonicacids mercaptans, alkyl sulfates and alkyls sulfides. See the diagram on following page which depicts the

structural formulas for some of these compounds. Many of these compounds occur naturally in crudepetroleum whereas others are formed during processing.For any given crude the higher boiling fractions almost always have higher sulfur content than lowerboiling fractions. Residues have higher sulfur contents than distillates. See an attached example ofsulfur curve.

Sulfur in Petroleum is undesirable for a number of reasons: corrosion, odor, air pollution, poor burning orexplosive characteristics, and catalyst poisoning. Sulfur compounds are not only corrosive to refineryequipment but can cause corrosion and wear in engines, boilers, and furnaces. In the case of motor andaviation gasoline, sulfur inhibits the effectiveness of lead antiknock as octane boosters and contributes tothe depletion of lubricating oil additives.Legal limits of the sulfur content of fuel products for environmental reasons makes high sulfur crude oilsmore costly for a refiner to process.

Range Of interest for whole crude and over the full range of distillates and residues. Whole crudeconcentrations range from less than 0.1 wt% to 7 wt%.

Typical ValuesThere is no general accepted criterion for classifying a crude oil as either high- or low-sulfur crude but thefollowing are guidelines proposed by Nelson as a criterion for low-sulfur crudes:

Crude Oil, API Sulfur Content, Wt% 12 < 0.9315 < 0.8820 < 0.7525 < 0.60

30 < 0.4635 < 0.3540 < 0.2545 < 0.15

Note that high-sulfur crudes are not necessarily “sour” crudes. The term “sour” can only be applied tothose crudes which contain more than 0.05 cu. ft of dissolved hydrogen sulfide per gallon of oil (0.374liters/liter).This level of dissolved H2S makes “sour” crudes dangerously toxic.

Test Methods ASTM D 129/IP 61 Test for Sulfur in Petroleum Products (General Bomb Method)

ASTM D 1551/IP 63 Test for Sulfur in Petroleum Oils (Quartz-Tube Method)

ASTM D 1552 Test for Sulfur in Petroleum Products (High-Temperature Method)

ASTM D 2662 Test for Sulfur in Petroleum Products (X-Ray SpectrographicMethod)

ASTM D 1266/ IP 107 Test for Sulfur in Petroleum Products (Lamp Method)


17/54

Page -17-


All Rights Reserved


18/54

Page -18-


All Rights Reserved


19/54

Page -19-


All Rights Reserved

MERCAPTAN SULFUR

Description Mercaptans often have an objectionable odor, can be corrosive and have an adverse effect on some fuelsystems. As an example, the smell of skunk is butyl mercaptans. Methyl mercaptan is added toodorless natural gas so customers can smell when gas may be leaking. Mercaptans are undesirable in

aviation fuels because they react with certain elastomers.

Range Mercaptan sulfur compounds are generally found concentrated in the gasoline boiling rangefractions. They may be present in kerosene and light mid-distillates.

Typical Values See Sulfur.

Test Methods ASTM D 1219/IP 104 Test for Mercaptan Sulfur in Aviation Turbine Fuels

(Color-Indicator Method)ASTM D 3227 Test for Mercaptan Sulfur in Gasoline, Kerosine, Aviation Turbine

and Distillate Fuels (Potentiometric Method)ASTM D 484/IP 30 Doctor Test Method

HYDROGEN SULFIDE

Description The hydrogen sulfide gas associated with some crude oils within the reservoir is normally removed alongwith light hydrocarbon gases during the gas separation stage of production. Some oil companiesmeasure Hydrogen sulfide both “dissolved” and “evolved.” Dissolved Hydrogen sulfide in crude oil isstripped at room temperature with nitrogen and absorbed in a cadmium sulfate scrubber. The crude oilsample is then heated and the hydrogen sulfide evolved is absorbed in a second scrubber. Hydrogensulfide found in the first scrubber is reported as dissolved Hydrogen sulfide and the total in the twoscrubbers is reported as evolved Hydrogen sulfide.Hydrogen sulfide was used in the past as a refinery fuel but when it burned in furnaces, sulfur dioxide isformed. Air quality regulations now limit SO2 emissions to the extent that most of the H2S must be kept

out of the fuel systems.

Test Methods ASTM D 130/IP 154 Detection of Copper Corrosion from Petroleum products

(Copper Tarnish Test)ASTM D 853 Test for Hydrogen Sulfide and Sulfur Dioxide Content of

Industrial Aromatic Hydrocarbons.ASTM D 2385 Test for Hydrogen Sulfide in Natural Gas

(Cadmium Sulfate-Iodometric Titration Method)ASTM D 2420 Test for Hydrogen Sulfide in Liquefied Petroleum Gases

(Lead Acetate Method)

THIOPHENESDescription Thiophene is a ring compound comprising one sulfur atom and four carbon atoms in the ring plus fourhydrogen atoms. It has a boiling point and some chemical properties similar to benzene.


20/54

Page -20-


All Rights Reserved


21/54

Page -21-


All Rights Reserved

NITROGEN

Description The importance of nitrogen in petroleum is due to its adverse effect on processing catalysts and on thestability of finished oils. High nitrogen content can result in high hydrogen consumption in hydro-

processes such as residual hydrodesulfurization.

The nitrogen content of crude oils ranges between 0.01 and 0.9 weight percent. Most of the compoundscontaining nitrogen have boiling points above 750 F. A distinction is made between those compounds inwhich the nitrogen can be made to react chemically as a base, called basic nitrogen, and those whichdo not do so.

The basic nitrogen compounds include pyridines and quinolines, e.g.,

Non-basic nitrogen containing series include pyrroles, indoles, carbazoles and benzcarbazoles, e.g.

Although the nitrogen contents of California crudes are generally the highest in the world, there are veryfew crudes in which the nitrogen content is negligible. In general, the more asphaltic crude oils containgreater amounts of nitrogen and the bulk of the nitrogen is in the high molecular weight portion of theoils.

Range Of interest for heavy distillates and resids.

Typical Values The higher boiling fractions contain most of the nitrogen. Residues contain more nitrogen thandistillates.

Test Methods ASTM D 3228 Standard Test for Total Nitrogen in Lubricating Oils and Fuel Oils

By Modified Kjeldahl Method ASTM D 4629 Standard Test for Organically bound Trace Nitrogen in Liquid Petroleum


22/54

Page -22-


All Rights Reserved

Hydrocarbons by Oxidative Combustion and Chemiluminescence


23/54

Page -23-


All Rights Reserved

OCTANE

Description The power obtained from a conventional reciprocating engine is limited by two distinct types of abnormalcombustion known as “knock” and “rumble.” When the fuel-air mixture in the cylinder of a spark-ignition

engine burns spontaneously in localized areas instead of progressing from the spark, this explosivedecomposition produces a characteristic noise or “knock.” Rumble, on the other hand, is caused bymultiple pre-ignition of the fuel-air mixture during the compression stroke and is also recognized by acharacteristic noise sometimes referred to as “wild ping.” In both cases, the accompanying pressuresurge cannot be converted into mechanical work by the piston, which must move in a fixed time/positionrelationship, and is lost as heat to the engine cooling system and the exhaust gas. In addition to the lossof power and fuel economy, knocking can result in engine damage and may burn a hole in the piston.For these reasons, the antiknock quality of gasolines is one of their most important properties.

Octane number is a measure of the resistance of the petroleum fraction to knock in a gasoline engine.Octane numbers may be measured by the Research method (RON by ASTM D 908) or the Motormethod (MON by ASTM D 357) and may be done Clear (i.e., without any lead additive) or with somelead added.

The test fuel is compared to blends of two pure hydrocarbons, normal heptane and isooctane (2, 2, 4-trimethylpentane). Normal heptane is quite low in its resistance to knock and has been arbitrarilyassigned an octane value of zero; isooctane has good antiknock properties and has, therefore, beenassigned a value of 100. The octane number of a fuel is defined as the volume percentage of isooctanein a blend of n-heptane which is equal to the test fuel in knock intensity under standardized testconditions.

Because some hydrocarbons have better antiknock properties than pure isooctane, it became necessaryto extend the octane scale above 100. In these cases, the antiknock ratings are expressed as eitherperformance numbers or quantities of tetraethyl lead (TEL) in isooctane and converted to equivalentoctane numbers via the Wiese scale. The performance number is an indication of the relative powerobtainable from an engine using the test fuel as compared with operation of the same engine with leaded

isooctane, operating at equal knocking intensity.

The Research method involves testing at lower engine speeds than the Motor method. The researchoctane number (RON), which is also referred to as F-1 octane number, is representative of the fuelperformance during city driving when the speed is generally low and acceleration frequent. On the otherhand, the motor octane number (MON), or F-2 number, indicates the relative fuel performance at highspeeds. Generally, RON is greater than the MON and the difference between the two ratings is knownas the “sensitivity” or “spread” of the fuel. Commercial gasoline often have motor octane values about 8numbers below their research octane values.

There is also a Road Octane test which often gives values between the Research and Motor numbers.Road Octane may also be approximated by (RON+MON)/2. In the USA the published octane at thepump is the average of RON and MON.

Sensitivity Of the two types of octane numbers, the research number is most often reported and correlationsdeveloped for estimating octane numbers from other physical and chemical properties are usually basedon the research number. Since the RON and MON are related by chemical composition, the MON canbe estimated from the RON of the gasoline.


24/54

Page -24-


All Rights Reserved

Susceptibility The octane number response to lead alkyls varies with the hydrocarbon composition of the gasoline andis known as the TEL or lead susceptibil ity. Although the octane number usually increases with increasingconcentrations of lead alkyls, this response is not linear, i.e., it is not proportional to the lead level. Asthe lead level concentration increases, its effectiveness as an octane booster decreases, i.e., themarginal gain in octane number per unit of additional lead alkyl decreases.

Addition of lead to the gasoline (tetra-ethyl lead, or in some cases, tetra-methyl lead) reduces the effectof the free radicals and improves the octane rating of the gasoline. The amount of change in the octanefor a compound (or mixture of compounds) from addition of lead is called susceptibility. Lead increasesthe octane most for low octane paraffin compounds. The effect of lead is reduced in the presence ofsulfur (particularly mercaptans, mono sulfides and disulfides) and Olefins.

Octane Blending Values When gasoline components are blended together, the octane number of the blends may be greater than,equal to, or less than that calculated from the volumetric average of the octane numbers of the blendcomponents. Blending deviations become more pronounced with increasing differences in thecomponent properties such as antiknock rating and hydrocarbon type. Deviations of several octanenumbers between observed and calculated octane numbers have occurred when blending common fuelcomponents. Thus, economic calculations designed to optimize refinery operations or refinery blendingwould always be subject to question without the preparation and testing of the blends being considered.Before the development of octane prediction equations, operating personnel relied on correction factorsbased on their experience. Although these corrections are useful in certain situations, they are notuniversally applicable.

One octane prediction equation is the DuPont Interaction Blending approach which uses the followingmodel (equation) to describe nonlinear gasoline blending behavior:

Octane No. = a1 X1 + a2 X2 + b1,2X1X2

where:a1 = octane number of component 1a2 = octane number of component 2X1 = Volume fraction of component 1

X2 = Volume fraction of component 2b1,2 = Interaction coefficient for components 1 and 2.

The interaction equation is accurate over the entire range of composition. The curve was developedusing only the data from the two components and the 50:50 blend. Octane measurements for the 25:75and 75:25 blends were predicted almost exactly by the curve which is described by the followingequation:

MON = 70.1X1 + 84.4X2 + 10.4X1X2

Interaction octane blending equations describe the octane blending behavior of gasoline componentsquite accurately as evidenced by the small residual standard errors obtained in blending studies for 15different refineries. In these studies the standard error for the research octane number ranged from 0.17

to 0.45 and for the motor octane it varied from 0.14 to 0.49.

The principal advantages of the interaction approach over previous gasoline blending methods aresummarized below:

The interaction approach provides a complete description of blending behavior over the entirecomposition range.


25/54

Page -25-


All Rights Reserved

Accuracy of the interaction model approaches experimental error quite closely for octane number,RVP, ASTM distillation, and V/L ratio.The model can be expanded easily to include new gasoline components.The equations can be made self-consistent so that the octane number calculated for a blendcontaining light and heavy cat cracked gasoline will be identical to the octane number calculatedfor the same blend containing the equivalent amount of full-boiling cat cracked gasoline.

Generalization of octane blending behavior is facilitated by separating the total nonlinearity intomany small parts - the interactions between all the pairs of the major component types.

Range Research Octane is normally higher than Motor Octane. Octanes are higher for leaded naphthas. LeadedOctane is not of interest where lead is not being added to gasoline. Octane is only of interest for gasolineblending materials (roughly C4 through 405 degrees F).

Typical Values Straight chained paraffins have low octane numbers and branched paraffins have high octanes. n-Heptane has an octane number of zero while iso-octane has an octane number of 100. Aromatics canhave very high octanes (over 100). For example, toluene has an octane of 105.3.

Test Methods

ASTM D 908 Research Octane Gasoline engines

ASTM D 357 Motor Octane Gasoline Engines

ASTM D 2700 Motor Octane for Aviation fuels

ASTM D 909 Motor Octane Super Charge Method


26/54

Page -26-


All Rights Reserved

FLASH POINT

Description The Flash Point of a petroleum fraction is that temperature at which its vapors, existing above thesurface of the liquid, will ignite by an open flame but not sustain continued combustion. The flash point ofa fuel, therefore, indicates the maximum temperature at which the oil can be stored and handled without

it being a serious fire hazard.

The test may be conducted using either an open cup or a closed cup method. Closed cup (ASTM D56)is normally used for light materials, Pensky-Martens (ASTM D93) for middle distillates and Clevelandopen cup (ASTM D92) for the heaviest materials. The closed cup method will give lower temperaturesthan the open cup method. The flash point of a material is close to the flash point of the lowest flashmaterial present in an appreciable amount and therefore is related to the initial boiling point of thematerial. Flash point is related to safety (likely explosion) or ease of igniting the material in use.

Fire Point is also related and is the temperature at which oil in an open container gives off vapors at arate to continue burning after a flame is applied.

Product specifications involving flash or fire point based on user requirements and climatic conditions in

consumption areas are often set by regulatory agencies. For example, the Canadian Railroads require aminimum of only 125 F flash point; but most consumers around the world require 150 F minimum. Eitherspecification is easily met and exceeded by most refiners. Most jet fuel consumers (JP-1 and JP-1A)require the old kerosene specification of 110 F since this level has been accepted by regulatoryagencies. But most refiners make much higher, usually about 125 F because it is economical to do so.This is because the fraction which makes the lower flash is more valuable in gasoline. This situationmay change as new environmental regulation in the USA force lower endpoint gasoline blends. USmilitary requirements for JP-5 is 140 F minimum. JP-5 usually meets arctic diesel specifications.

Range Of interest especially on whole crude, naphthas, kerosene, mid distillates and fuel oils. Generally ofinterest for distillates up to about 650 degrees F.

Typical ValuesThe flash and fire points of most whole crude oils and naphthas are at room temperature or below. Theflash point of distillates (but not whole crude oils) can be estimated from the ASTM 10% temperature byprocedure 2B7.1 of the API Technical Data Book. The associated chart gives the following:

ASTM 10% temperature degrees F 200 250 300 350 400 450 500Flash, Closed cup degrees F 15 58 98 132 163 195 220

Petroleum ether (boiling range 95-140)= -60 flash; Hexane (boiling point 155)=


27/54

Page -27-


All Rights Reserved

REID VAPOR PRESSURE

Description Reid Vapor Pressure (RVP) is used to characterize the volatility of gasoline and crude oils. It is also aconvenient approximation of the absolute vapor pressure. RVP is the pressure of a 4/1 ratio of vapor toliquid heated to 100 degrees F. True vapor pressure is generally 5% to 9% higher the RVP. The vapor

pressure of a material is an important consideration for transport safety, storage tank requirements,probability of losses, gasoline vapor lock and the starting characteristics of the fuel. It is also now amandatory gasoline specification that is being lowered by air pollution authorities in some countries. Inthe USA RVP of gasoline is now 9 psi in the summer and the limit will decrease.

Range Of interest for naphthas (to 450 deg F, 230 deg C) and for whole crude.

Typical Values.Lower boiling materials have higher values.

C3 190 psi (1310 kpa)nC4 52 psi ( 359 kpa)nC8 0.74 psi ( 5.1 kpa)

Test Methods

ASTM D 323 Standard Test Method for Vapor Pressure of Petroleum Products.


28/54

Page -28-


All Rights Reserved

SMOKE POINT

Description The combustion characteristics of turbine fuels and kerosenes are directly related to the hydrocarboncomposition of fuels. For example, aromatics tend to burn with a smoky flame and release a greaterportion of their chemical energy as undesirable thermal radiation than other hydrocarbon types.

Smoke Point is the maximum flame height, expressed in millimeters, at which a fuel can be burned in astandard wick-fed lamp without smoking. A high smoke point indicates a fuel of low smoke-producingtendency.

The Smoke Point for the same boiling range distillate is greatest with straight chain paraffins, lower withbranched paraffins, considerably lower with naphthenes and much lower still with aromatics.Naphthalenes or bicyclic aromatics produce more soot, smoke, and thermal radiation than monocyclicaromatics.

Range Of interest for all burning oils such as kerosene and jet fuels. Jet fuel usually requires a smoke point ofat least 20 mm.

Typical ValuesMixtures of Toluene (an aromatic) and iso-octane (a branched paraffin) have smoke points as follows:

Vol. % Paraffin 60% 75% 85% 90% 95% 100%Smoke Point, mm 14.7 20.2 25.8 30.2 35.4 42.8

Test Methods ASTM D 1322 Test for Smoke Point of Aviation Turbine fuels.

LUMINOMETER NUMBER

Description The Luminometer number measures the flame -radiation characteristics of a fuel. The test wasdeveloped because combustion chamber life is shortened in certain jet engines if a fuel producesluminous flames that result in high-liner temperatures. A low Luminometer number indicates that a largeportion of the chemical energy of the fuel is released as thermal radiation and therefore, a highernumber indicates a fuel of good combustion quality.

Range Kerosene and jet fuel fractions.

Typical ValuesAs given in ASTM 1322, the smoke point in mm (SP) can be estimated from luminometer numbers (LN) ,or vice versa, by the following equations:

SP = 4.16 + .331 * LN + .000648 * LN ** 2LN = -12.03 + 3.009 * SP - .0104 * SP ** 2

LN between 10 and 80 gives SP between 7.5 and 35 respectively.

Test Methods ASTM D 1740 Test for Luminometer Number of Aviation Turbine fuels.


29/54

Page -29-


All Rights Reserved


30/54

Page -30-


All Rights Reserved

ANILINE POINT

Description Aniline point is the lowest temperature at which a petroleum fraction is completely miscible with anequal volume of aniline. Mixed aniline point is a mixture of one volume sample, one volume n-heptaneand two volumes aniline. The mixed aniline point test is used for lighter materials where the aniline point

is below the temperature where aniline crystallizes out of the mixture. Aniline point is inversely related tothe amount of aromatics in the material. Paraffins have the highest aniline point, cycloparaffins andolefin in the middle and aromatics the lowest. Aniline Point also increases with molecular weight. Dieselindex can be calculated and heating value estimated from a combination of the aniline point and gravity.

Aniline point is used to characterize the quality or chemical nature of naphthas and some heavierdistillates. It is often used to help predict the behavior of a feed in a cracker (fluid or hydro) and thequality of the streams produced by the cat cracker. Feeds with higher aniline numbers (less aromaticand therefore less refractory) are generally considered more desirable.

Range May be desirable over the entire range of distillates

Typical ValuesHexane 146Heptane 127Benzene 57* ( * by the mixed aniline test)Low Aromatics Naphtha (145-175 F boiling range) 134Low Aromatics Naphtha (200-220 F boiling range) 12030 % Aromatics Naphtha (320-380 F boiling range)` 105High Aromatics Naphtha (360-540 F boiling range) 76*Low Aromatics Kerosene (350-575 F boiling range) 160Low Aromatics Kerosene (400-480 F boiling range 190

.Test Methods

ASTM D 611 Test Methods for Aniline Point and Mixed Aniline Point of PetroleumProducts and Hydrocarbon Solvents


31/54

Page -31-


All Rights Reserved


32/54

Page -32-


All Rights Reserved

REFRACTIVE INDEX

Description The Refractive Index is the ratio of the velocity of light in air to its velocity in the material. It can beused, together with density and viscosity, to calculate the paraffin to naphthene ratio in white oils. It alsois a measure of aromaticity and unsaturation and some refiners use it as a means of process control.

Typical ValuesRefractive index can be estimated for petroleum fractions from their mean average boiling point andspecific gravity by the method given in procedure 2B5.1 of the API Technical Data Book. Care must betaken that Refractive Index results are at consistent temperatures..Test Methods

ASTM D 1747 Test for Refractive Index of Viscous Materials.

ASTM D 1218 Test for Refractive and Dispersion of Hydrocarbon Liquids.


33/54

Page -33-


All Rights Reserved

COLD PROPERTIES

The congealing properties of an oil are related to its hydrocarbon composition. In general, symmetricalmolecules, e.g., normal paraffins, have high congealing temperatures whereas the presence of sidechains, i.e., branching discourages crystallization. Since petroleum oils contain components with a widerange of molecular sizes and configurations, they do not have sharply defined freezing points. They

become semi-plastic when cooled to sufficiently low temperatures.

Under low-temperature conditions, the paraffinic constituents of a fuel tend to precipitate as wax. Thetemperature at which the precipitation occurs depends upon the origin, type, and boiling range of thefuel. The more paraffinic the fuel, the higher the precipitation temperature and the less suitable for lowtemperature operation. Therefore, the freeze, pour and cloud are a relative measure of wax in an oil.

POUR POINT

Description The pour point is the temperature below which the liquid no longer pours freely (i.e., no noticeable flowwhen the sample is held horizontal for a period of five seconds).

After preliminary heating, the sample is cooled at a specified rate and examined at 3 deg C intervals forflow characteristics. The lowest temperature at which movement of the oil is observed is recorded as thepour point.

For material from waxy crudes, pour point is primarily a function of wax crystallizing out of solution andforming a matrix of wax crystals which trap the lower freeze point oils, making it difficult for the entiremass to flow. Some heavier and higher viscosity materials will exhibit a pour point which is primarily afunction of the viscosity rather than actual freezing out of components. As temperature is lowered, thematerial becomes more viscous and harder to pour. Pour point can vary with the previous thermalhistory of the oil--particularly when wax crystallization is a major factor and especially for wide boilingcuts such as whole crude oil.

Range

Values are of interest for crude oils, residues and distillates with boiling ranges starting as low as 300+degrees F.

Typical Values For a given sample, Pour Point is below Freeze Point and below Cloud Point. Pour Point may be anegative 100 degrees F or so for light distillates and occasionally as much as positive 200 degrees F forheavy Residues. The pour point/boiling point relationship curve is exponential upward in shape when theviscosity effect predominates or a straight line or slightly downward curvature when the wax effectpredominates.

Pour point can be estimated from viscosity at 100 F, specific gravity and molecular weight (which alsocan be estimated) by the method of Chapter 2 of the API Technical Data Book.

Test Methods

ASTM D 97 Test Method for Pour Point of Petroleum Oils


34/54

Page -34-


All Rights Reserved


35/54

Page -35-


All Rights Reserved

CLOUD POINT

Description Petroleum oils begin to form wax crystals and become cloudy in appearance as they are cooled towardtheir pour points. The Cloud Point temperature is that which a clear liquid becomes cloudy as it is cooled.It is caused by waxes starting to crystallize out of solution. The temperature differential between cloud

and pour depends on the nature of the petroleum components with Cloud Point typically 4 to 5 deg Cabove Pour Point In highly Paraffinic and Waxy crude oils Cloud can go below the Pour Pointtemperature.When the temperature of the oil is decreased below the Cloud Point the formation of Wax crystals isaccelerated. These crystals can clog fuel system lines and filters which can cause aircraft and dieselengines to stall which make’s Cloud Point a very important measurement particularly in cold climates.

The Cold Test is the temperature at which an oil becomes solid and is generally considered to be 5 degF lower than Pour Point.

Range Primarily of interest for distillates 200-720 degrees F.

Typical Values

For a given sample, Cloud Point is almost always below Freeze Point and usually 4 to 5 (occasionally upto 8) degrees C above Pour Point.

Test Methods ASTM D 2500 Test Method for Cloud Point of Petroleum Oils

FREEZE POINT

DescriptionThe Freezing Point of a pure compound is the temperature at which the compound will freeze (i.e.,becomes a solid). The Freezing Point of a mixture is the temperature at which crystals formed bycooling disappear as the temperature rises.The Freeze Point test is particularly important property for aviation and jet fuel since it must be low

enough to ensure adequate flow of fuel to the engine during long flights at high altitudes. MaximumFreezing point values are specified for all aviation and jet fuels as an indication of the lowesttemperature at which the fuel can be used without risk of separation of solidified hydrocarbons (wax).

Range Primarily of interest for lighter distillates such as jet fuels (200-720 degrees F).

Typical Values For a given sample, the Freeze Point will be above the pour point for a mixture. The Freeze Point isalmost always above the Cloud Point.

Test Methods ASTM D 2386 Test Method for Freeze Point of Petroleum Oils.

COLD FILTER PLUG POINT

Description The CFPP is the temperature at which a standard filter would become blocked by wax crystals. TheCFPP temperature is lower than Cloud Point but usually above Pour Point. CFPP can be reduced by theaddition of additives which stop the growth of wax crystals that plug the filters.


36/54

Page -36-


All Rights Reserved


37/54

Page -37-


All Rights Reserved

CETANE NUMBER

Description In most diesel engines, the ignition delay period is shorter than the duration of injection. The totalcombustion period can be divided into four stages;

a. ignition delay

b. rapid pressure risec. constant pressure or controlled pressure rised. burning on the expansion stroke

Because the rapid pressure rise represents uncontrolled and inefficient combustion, it is desirable to limitignition delay to a minimum. This can be achieved mechanically by selection of a spray patternconfiguration properly tailored to the combustion chamber. Ignition delay also can be reduced by the useof high - fuel injection pressures and high - fuel/air turbulence to promote rapid fuel jet breakup andthorough fuel distribution.The nature of the fuel is also an important factor in reducing the ignition delay. Viscosity, gravity, andmid boiling point are influential. Composition is also important since straight chain paraffins ignite readilyunder compression, but branched chain and aromatics react poorly. It is therefore desirable to have anumerical basis for evaluating the fuel ignition delay and measuring or predicting this property.

Cetane Number is determined in a diesel test engine much like octane numbers are determined forgasolines. It is the numerical result of an engine test designed to evaluate fuel ignition delay. This is ameasure of the anti-knock ignition quality of Diesel fuels. To establish the Cetane number scale, tworeference fuels were selected. One, normal Cetane C16H34 which has excellent ignition qualities andconsequently, a very short ignition delay. The second fuel, alphamethylnaphthalene, has poor ignitionqualities and was assigned a cetane number of zero. In 1962, alphamethylnaphthalene was replaced asa primary reference fuel by heptamethylnonane which has a cetane number of 15 as determined by useof the two original primary reference fuels.

The cetane number of a diesel fuel is defined as “the whole number nearest to the value determined bycalculation from the percentage by volume of normal cetane (Cetane No.=100) in a blend withheptamethylnonane (Cetane No.=15) which matches the ignition quality of the test fuel when comparedby this method.” The matching blend percentages to the first decimal are in serted in the following

equation to obtain the cetane number.

Cetane No. = (percent n-cetane) + 0.15 * (percent heptamethylnonane)

Low to medium cetane number fuels offer better fuel economy but fuels with higher cetane numbersprovide easier starting, lower temperature starting and smoother operation. Lower cetane numberedfuels are poor burning in a diesel engine and may cause engine deposits and smoke.

Range Diesel fuels with boiling temperatures ranging from 300 to 715 degrees F.

Typical ValuesKerosene 50 High speed city busesPremium Diesel 47 High speed buses, trucks, tractors, light marine engines

Railroad Diesel 40 Medium speed buses, railroad, marine & stationary enginesMarine Distillate Diesel 38 Low speed buses, heavy marine and large stationary engines

Test Methods ASTM D 613 Test for Ignition Quality of Diesel Fuels by the Cetane Method.


38/54

Page -38-


All Rights Reserved

CETANE INDEX

Description Since the determination of cetane number by engine testing requires special equipment and can be timeconsuming as well as costly, alternate methods have been developed for calculating estimates of cetanenumber.

Cetane Index is calculated from API Gravity (G) and mid-boiling Point in degrees F (M) by ASTM D976which gives the formula:

Cetane Index = -420.34 + .016 G**2 + 0.192 G Log M + 65.01 (Log M)**2 - .0001809 M**2

An equation in metric units and a nomograph are also presented. They point out that calculated CetaneIndex is a useful tool for estimating Cetane Number if laboratory data is not available but may not alwaysbe a valid substitute.The calculated Cetane Index is applicable to straight-run fuels, catalytically cracked stocks and blends ofthe two. It is not applicable for fuels containing cetane-improving additives nor pure hydrocarbons,synthetic fuels, alkylates, or coal-tar products. The correlation can also be quite inaccurate when used forcrude oil, residuals and products having a volatility below 500 deg F end point.

Range Same as Cetane Number

Typical ValuesThe Cetane Index is usually within ±2 numbers of the measured cetane number.

DIESEL INDEX

Description Another scale used to predict the ignition quality of diesel fuels, the Diesel Index, was actually developed

prior to the adoption of the cetane number scale. The Diesel index is defined as the API gravity times theaniline point in degrees F divided by 100.

DI = (API * AP) / 100

Diesel Index and Cetane Number correlate but Diesel Index tends to be the higher above 38 and lowerbelow 38.

Range Same as Cetane Number

Typical ValuesCetane Number 30 35 40 45 50 55 60

Diesel Index 26 34 42 49 56 64 72


40/54

Page -40-


All Rights Reserved

VISCOSITY

Description The viscosity of an oil is a measure of its resistance to flow, that is, its readiness to flow when acted uponby an external force. The coefficient of absolute viscosity or, simply, the absolute viscosity of a fluid is ameasure of its resistance to internal deformation or shear. Molasses, for example, is a highly viscous

fluid whereas water is comparatively less viscous. On the other hand, the viscosity of gases is quitesmall compared to that of water. As noted below, the viscosity is an important property of crude oils andmost petroleum products.

The absolute viscosity may be defined as the shear stress at a point divided by the velocity gradient atthe point. Stated in another way, the viscosity is in force in dynes required to move a plane of 1 squarecentimeter in area, at a distance one centimeter from another plane of 1 square centimeter in area,through a distance of 1 centimeter in 1 second. In the centimeter-gram-second (cgs) system, the unit ofabsolute viscosity is called a poise and is equal to 1 g/(cm)(sec) or 100 centipoises. The English unitscommonly employed are “slugs per foot second” or “pound force seconds per square foot”.

The kinematic viscosity is the ratio of the absolute viscosity to the mass density, both at the sametemperature and pressure. In the metric system, the unit of kinematic viscosity corresponding to the

poise is the stoke, which is equal to 1 square centimeter per second, or 100 centistokes. The conversionfrom absolute viscosity to kinematic v iscosity is given by the following equation:

= ____

where

= kinematic viscosity, stokes= absolute viscosity, poises

= density (in vacuo), grams per cubic centimeter

There are a number of methods of measuring Viscosity. These include Kinematic (ASTM D 445),

Saybolt Universal (SSU), Saybolt Furol (SSF), Redwood 1 and 2, and Engler. Kinematic is reported incentistokes. It is generally the current preferred method for crude assays. Saybolt Universal andSaybolt Furol are reported in seconds--the time to flow out of a specific size container with a specific sizeorifice. The Furol size orifice is larger than the Universal size orifice and therefore SSF is more suitablefor higher viscosity material (the heavier cuts) and the lower temperatures. Redwood is reported inseconds, Engler in degrees. The Redwood and the Engler instruments are not considered as accurate.Kinematic viscosity is usually preferred today but test results are often converted to Saybolt units forreporting by use of the standard ASTM charts. The Kinematic test measures the time for the liquid toflow under gravity through a glass viscometer. Because some residues deposit wax from solution around100 degrees F there are some who prefer to measure viscosity at 180 degrees F. It is important that thetemperature chosen for viscosity measurement be sufficiently warmer than the pour point to insure thatthe liquid is Newtonian. Redwood no. 1 is normally at 140 degrees F.

A log-log function of kinematic viscosity vs. the log of absolute temperature plot (or the equivalentformula as contained in ASTM Standard D341-87) can be used to convert available viscosity data fromthe temperature measured to the temperature required in the crude assay library.


41/54

Page -41-


All Rights Reserved

Crude Oils Viscosity measurements on crude oils are used principally in the design of field gathering systems andthe lines and pumps between refinery storage and the processing facil ity. In these systems viscosity andpour point measurements provide the data for solving transportation problems associated with crude oils.

Aviation Fuels The viscosity of aviation fuels is limited to ensure that adequate fuel flow and pressure are maintainedunder all operating conditions and that fuel injection nozzles and system controls will operate down todesign temperature conditions. Viscosity can also affect significantly the lubricating properties of the fuelwhich has an influence on the pump service life.

Diesel Fuels The viscosity of diesel fuels is important primarily because of its effect on the handling of the fuel by thepump and injector system. Diesel fuel viscosity exerts a strong influence on the shape of the fuel sprayand, when the viscosity is either below or above that required for good engine operation, the fuel is notproperly distributed. This results in poor combustion, accompanied by loss of power and economy, andcan contribute to excessive engine wear.

Heating Oils Viscosity is one of the more important heating oil characteristics. It is indicative of the rate at which theoil will flow in the fuel systems and the ease with which it can be atomized in a given type of burner.Since the viscosities of heavier residual fuel oils are high, this property tends to be particularly relevantto its handling and utilization characteristics.

Lube Oils To meet a particular application, viscosity is generally the most important controlling property formanufacture and selection of lubricating oils. The viscosity of a new oil is of fundamental importance


42/54

Page -42-


All Rights Reserved

with respect to performance in a specific type of equipment or machine element and is always describedor specified by the buyer, the seller, or both.

Range Viscosity data is generally of most interest for the middle and heavy distillates (say 400+ degrees F) andresidua. Viscosity increases exponentially as the mid temperature of the cut increases.

Typical ValuesThe kinematic viscosity of whole crudes are often in the range of 2 to 6 centistokes at 104 degrees F. Afew crudes have lower values. A significant number of crudes have values 6 to 10, others 10 to 100, stillothers in the hundreds and a few heavy crudes have viscosities in the thousands.

Test Methods To measure the absolute viscosity of fluids, especially gases and vapors, requires elaborate equipmentand considerable experimental skill. On the other hand, a rather simple instrument can be used formeasuring the kinematic viscosity of oils and other viscous liquids. The viscosity of oils is usuallymeasured by recording the time required for a given volume of fluid at a constant temperature to flowthrough a small orif ice of standard dimensions. The two standard test methods in the USA are:

D 445 ASTM Standard Test Method for Kinematic Viscosity of Transparent andOpaque Liquids (and the Calculation of Dynamic Viscosity)

D 2170 ASTM Standard Test Method for Kinematic Viscosity of Asphalts(Bitumens)


43/54

Page -43-


All Rights Reserved

The older, empirical procedures such as the Saybolt Universal and Saybolt Furol systems, and theSaybolt thermoviscometer is being superseded by the kinematic system in the United States. Otherviscometers somewhat similar to the Saybolt, but not used to any extent in the U.S., are the Engler, theRedwood Admiralty, and the Redwood.

VISCOSITY INDEX

The viscosity of petroleum base oils decreases with a rise in temperature, but this rate of changedepends on the composition of the oil. The viscosity index is an empirical number which indicates theeffect of change of temperature on the viscosity of an oil. It compares the rate of change of viscosity ofthe sample with the rates of change of two types of oil having the highest and lowest viscosity indices atthe time (1929) when the viscosity index scale was first introduced. A standard paraffinic oil was given aviscosity index (VI) of 100 and a standard naphthenic oil a VI of 0. Equations were evolved connectingthe viscosity and temperature for these two types of oil and, from these equations, tables were preparedshowing the relationship between viscosities at 100 F (37.8 C) and 210 F (98.9 C) for oils with a VIbetween 0 and 100. With these tables and the viscosities at 100 F and 210 F of an oil, the viscosityindex can be calculated. A high viscosity index denotes a low rate of change of viscosity withtemperature.

VI is of particular interest to the lubricating oil manufactures, the automotive industry and to some of themore sophisticated and informed consumers. The VI scale was developed to compare relativeperformance of different lube oils, particularly in automotive engines which encounter many cold startsand high operating temperatures after starting, as opposed to stationary engines where lube oiltemperatures can be maintained relatively constant.

The VI scale was an arbitrary development where 100 was assigned to a lube oil which showed relativelylittle change in viscosity with temperature. This was a highly paraffinic lube oil made from a highlyparaffinic Pennsylvania crude oil. Zero VI was assigned to a low cold-test lube oil that showed a largechange in viscosity with temperature. This was a naphthenic lube oil made from a highly naphtheniccrude oil produced in the US Gulf Coast. Today some lube oils have been developed which exceed 100VI. These are the so-called multi-grade oils which are actually blends of lighter grades of lube distil latebase stocks plus additives which make the oils perform at higher temperatures like a heavier grade.


45/54

Page -45-


All Rights Reserved

NEUTRALIZATION & TOTAL ACID NUMBER

Description Neutralization number is the milligrams of potassium hydroxide required to neutralize the total acidity.The acidity is primarily from carboxylic acids which are predominantly in naphthenic crude oils and are

sometimes called naphthenic acids. Naphthenic type acids corrode carbon steel badly and especially atthe flash zone temperature of 700F encountered in crude distillation. Crude oils with substantialnaphthenic acids may require use of austenitic 318 or 347 stainless steel in the flash zone.

Total Acid number (TAN) is the quantity of base (KOH) to neutralize the acid within a sample. TotalBase number is the quantity of acid required to neutralize any bases within a sample. The Neutralizationnumber includes both the Acid Number and the Base number. This was carried out according to ASTM D664which involved two titrations, one with acid and one with a base using Potentiometric Titrations.ASTM D 664 was renamed from Neutralization number to Total Acid Number where only the total acidnumber is measured and ASTM Test Method D 4739 was developed as an alternative to the basenumber portion of Test Method d 664. Base numbers obtained by this method may or may not benumerically the same as those obtained by the base number portion of D 664.

Range Used especially on whole crude and on cuts used to make transportation fuels because there arespecifications on the products. The data is useful for the full range of distillate and residua.

Typical Values

A crude is considered highly Acidic with a TAN of around 3 mg. Between levels of 0.5 and 3 mg crudesare considered Acidic. Below 0.5 mg crudes are considered normal and with levels below 0.05 mg theyare considered to have very low acidity.

Test Methods

ASTM D 664 Standard Test for Acid Number of Petroleum Products (Potentiometric Titration).


46/54

Page -46-


All Rights Reserved

WAX

Description This is the amount of wax (wt%) in the petroleum fraction. The wax content affects the pour, cloud andfreeze points and viscosity (if not Newtonian) of the material. A petroleum fraction's wax value is afunction of the solvent used to extract it and the temperature at which the wax content is measured. A

determination or test conducted at a relatively low temperature will yield a much greater wax contentthan one conducted at a higher temperature.

Lighter fuel products should exhibit a clear and bright appearance at the lowest ambient temperature thatthe fuel may be expected to encounter. In diesel it is important to prevent fuel-filter plugging with wax.In many cold climates kerosene is added to diesel by oil marketers and/or consumers in order to keepwax in solution and thereby minimize possible problems. Likewise, wax is not desirable in lubricating oils;therefore, product specifications are established to prevent any possible problems. Specifications areusually established to provide for maximum product pour points rather than wax content per se.

Range For light distillates, cloud point may be the preferred inspection. For home heating oil and automotivediesel fuel, wax should normally be below 15%. Wax content is of interest generally for vacuum distillate

cuts.

Typical ValuesIn distillates, the wax content for most crudes tends not to exceed a few percent (sometimes essentiallyzero) for cuts below 550 F. For cuts above 550 F, many crudes have percent wax exceeding 10%, quitea few exceed 20% and some exceed 40%. For a majority of crudes looked at, the highest concentrationof wax occurred in cuts around 650 F with cuts higher than that still at wax percent levels nearly as highas the peak. This tended to be true up into the heavy distillate range.

In resids, the wax content varies considerably among crudes and values below 1% and above 50% areseen with many different crudes in the 5 to 30% range. There is a general tendency in about 3/4ths ofthe crudes looked at for wax percent in the resid to be less for higher temperature resids. But the waxpercent for about 1/5th of the crudes were higher at higher resid cut points and some crudes had about

the same wax percent over a range of resid cut temperatures.


47/54

Page -47-


All Rights Reserved

METALS

Description Traces of many metallic elements can be found in most crude oils although many are contaminantspicked up as emulsified formation with water, particles of soil from the reservoir etc. Vanadium andNickel compounds, however, have been identified in Petroleum.

The metals content in crude oils ranges from a few parts per million to over 1,000 ppm, and, in-spite oftheir relative low concentrations , the organo-metallic are of considerable importance. Small quantities ofsuch metals as arsenic, iron, nickel, vanadium and copper can have a deleterious effect on refineryprocessing catalysts, such as reforming and catalytic cracking catalysts. Vanadium in gas turbines fuelscan also form low melting compounds which cause severe corrosive attack on the high temperaturealloys for the turbine blades. Sodium can cause problems in furnace brickwork.

Vanadium and Nickel occur principally as vanadyl and nickel complexes which are stable and distill attemperatures above 500 deg C (930 deg F). Since most of the organo-metallic compounds are found inthe higher-boiling fractions, distillation concentrates these metallic constituents of the crude in residue.Vacuum gas oils up to 1000 deg F TBP cut point contain less than one part per million of volatile nickeland vanadium. Any higher values than this are caused by entrained residium.

For calculation purposes it can be assumed that all of the vanadium, nickel, iron and copper are in the600+ deg F residue. Whenever possible, the metal contents of catalytic cracking feed stocks should bedetermined experimentally due to the possibility metallic compounds either volatilized or entrainedduring crude distillation and appear in the higher-boiling distillates.

Range For calculation purposes it can be assumed that all of the vanadium, nickel, iron and copper are in the600+ deg F residue. When ever possible, the metal contents of catalytic cracking feed stocks should bedetermined experimentally due to the possibility metallic compounds either volatilized or entrainedduring crude distillation and appear in the higher-boiling distillates.

Typical Values

From a few parts per million to over 1000 ppm are possible.

Test Methods

ASTM D 5863 Determination of Nickel, Vanadium, Iron and Sodium in Crude Oils andResidual Fuels by Flame Atomic Absorption Spectrometry.

ASTM D 5708 Determination of Nickel, Vanadium and Iron in Crude Oils and ResidualFuels by Inductively coupled Plasma Atomic Emission Spectrometry.

ASTM D 2788 Test for Trace Metals in Gas Turbine Fuels.


49/54

Page -49-


All Rights Reserved

CARBON RESIDUE

Description The Carbon Residue tests give the weight percent of the residue left after vaporization and pyrolysis of apetroleum fraction. The test is done by heating the sample in a crucible or other container to drive off allthe volatiles. Some of the residue will crack giving off more volatile material and if oxygen is present

carbon will be oxidized to gas. The residue may not be all carbon as it would include non-volatile ashand metals in the sample.

The Conradson and Ramsbottom carbon test procedures limit, by the design of the test equipment, thepresence of air which would oxidize the carbon. The MCRT test method is done in a nitrogenatmosphere to exclude the presence of air.

All of the tests serve as an approximation of the carbon or coke yield from cracking. A reasonableamount of carbon is desirable and necessary in a heat-balanced unit such as fluid cat cracking since thecoke on the catalyst is burned in the regenerator thus heating the catalyst which provides the heat inputfor the endothermic cracking reactions. The test also is a rough approximation of the tendency of thefuel to form deposits in vaporizing type burners.

Range Of interest for heavy distillates and residues.

Typical ValuesASTM provides (D524) a conversion chart between the first two test values which is suitable for somematerials. Some representative values from the curve are:

CONRADSON 20.0 10.0 4.0 2.0 1.00 .40 .20 .10 .040 .020 .010RAMSBOTTOM 20.0 8.7 3.1 1.6 .80 .38 .24 .16 .092 .070 .057.

Test Methods ASTM D 189 Test Methods for Conradson Carbon Residue of Petroleum Products

ASTM D 524 Test Methods for Ramsbottom Carbon Residue of Petroleum Products

ASTM D 4530 Test Methods for Micro Carbon Residue of Petroleum Products

SULFUR IN CARBON RESIDUE

Description This is the weight percent sulfur in the carbon residue.


51/54

Page -51-


All Rights Reserved

ASPHALTENES & RESINS

Description The residue of a crude consists of asphaltenes, resins and oil. Asphaltenes are heavy hydrocarbonmolecules that are in colloidal suspension in the oil, stabilized by resins adsorbed on their surface. Theoil can be roughly thought of as the part that might be distilled off without cracking it first or, more

accurately, the part which is not asphaltenes or resins or the part of the residue which is soluble inpropane. The asphaltene content of residual oils is important in determining yields and product qualitiesfor solvent deasphalters, thermal visbreakers and hydrodesulfurization units.

Asphaltenes are very complex polyaromatics--with a molecular weight between 3000 and 10,000(typically 7000). They have high carbon to hydrogen ratios and are sometimes spoken of as "chickenwire or coal like" structures. The molecular structure is one of 3 to 11 unit sheets. Unit sheets are heldtogether by either covalent bonding or by strong associative forces. Each sheet may have 7 to 16condensed aromatic rings, 2 to 6 naphthene rings, several sulfur atoms, a nitrogen atom and perhapsother atoms such as oxygen, nickel or vanadium. Some paraffinic side chains may be present. Polargroups are attached. Asphaltenes exist in crude oils and residuals therefrom as dark brown to blackcolloidal suspensions. They can be precipitated from the oil by adding a light hydrocarbon (propane) in aratio of several times the volume of the oil. The amount of Asphaltenes is defined as that part of theprecipitate which is insoluble in hot normal heptane.

Resins is that part of the propane precipitate which dissolves in normal heptane. The structure is broadlysimilar to that of the asphaltenes but the molecules are less complex and less aromatic and may containmore oxygen and less sulfur and less nitrogen than asphaltenes. They typically consist of only one unitsheet so have lower molecular weights. When precipitated by propane their appearance may vary froma dark yellow, viscous liquid to an amorphous, dark-colored solid.

Resins can be of type A or type B. The amounts of these are determined by thin layer chromatographyon the residue using three solvents. N-heptane first elutes the saturates, then toluene elutes thearomatics and finally a chloroform/methanol or toluene/ethanol mixture separates resins A from resinsB. Resins A contain lower molecular weight polar compounds. Resins B are higher molecular weightand more like asphaltenes.

The asphaltene content of a resid is a measure of the quality of asphalt that might be expected from thatcrude oil. High asphaltene content is not desirable for cat cracking feed stocks. Asphaltenes and resinscan be separated from the heavier oils by adding a light solvent which causes them to precipitate. Thisprocess is used on vacuum residua to separate the lube oil bright stocks from asphaltenes and resins. Itcan be used to improve the quality of cat cracker feedstock. Propane is the solvent normally used in theprocess; and, dewaxing can also be accomplished with the same solvent.

Range A property of residues--particularly of interest regarding asphalt production or use of residue (orprocessing for use) in cat cracking or lube manufacture.

Typical ValuesSince asphaltenes and resins are in the "bottom of the barrel", the percent in the residue will increase asthe resid is cut deeper. Asphaltenes for residues cut not over 1000 F run from under 1 wt% in some

residues, to 15% or over in a modest number of residues and to over 30% in a very few residues.Generally to make asphalt, one looks for a crude oil with a substantial yield of residue with low wax, highasphaltene percent and low penetration for deep cut resids.

Test Methods ASTM D 3279 Standard Test Method for n-Heptane Insolubles


53/54

Page -53-


All Rights Reserved

n-PENTANE INSOLUBLES

Description This is the amount of insolubles after a residue is extracted with n-pentane. We observe crudes wherethis amount is three or more times greater than the amount of insolubles from n-heptane (asphaltenes)and others where the amount is less.

PENETRATION

Description This indicates the softness of heavy petroleum materials such as asphalt. The penetration test measuresthe distance a needle of specified size penetrates into the material under a load of 100 grams for 5seconds at 77

oF typically.

Range Resid Materials being used to make asphalt.

Typical Values 1050 F + resids from different crudes can have penetration values over a wide range such as between13 (or lower) and >300. A wide range of grades may be requested by the market in the 40 to 250

penetration range. A refinery might make two runs--one of 40 and one of 250 penetration and thenindividual orders blended directly in the tankcar or truck to fil l specific orders.

Test Methods ASTM D 5, 1321 Standard Test Method for Penetration of Bit

Date post:	06-Jul-2018
Category:	Documents
Upload:	mihaelapaval
View:	223 times
Download:	0 times

Properties of Crude Oil and Petroleum Products

Documents