OIL SPILL SCIENCE chapter 3 – introduction to oil chemistry and properties OIL SPILL SCIENCE chapter 3 – introduction to oil chemistry and properties OIL SPILL SCIENCE chapter 3 – introduction to oil chemistry and properties OIL SPILL SCIENCE chapter 3 – introduction to oil chemistry and properties OIL SPILL SCIENCE chapter 3 – introduction to oil chemistry and properties OIL SPILL SCIENCE chapter 3 – introduction to oil chemistry and properties
Chapter Introduction to Oil Chemistry and Properties Merv Fingas Chapter Outline 3.1 Introduction 3.2 The Composition of Oil 51 51 3.3 Properties of Oil 54 3.1 INTRODUCTION Oil is a general term that describes a wide variety of natural substances of plant, animal, or mineral origin, as well as a range of synthetic compounds.1 This section covers mineral oil or petroleum oil The many different types of crude oil are made up of hundreds of major constituents and thousands of minor ones As their composition varies, each type of oil or petroleum product has certain unique characteristics or properties These properties influence how the oil behaves when it is spilled and determines the fate and effects of the oil in the environment These properties also influence the efficiency of cleanup operations This section deals specifically with crude oils and petroleum products derived from crude oils and describes the chemical composition and physical properties 3.2 THE COMPOSITION OF OIL Crude oils are mixtures of hydrocarbon compounds ranging from smaller, volatile compounds to very large, nonvolatile compounds.2 This mixture of compounds varies according to the geological formation of the area in which the oil is found and strongly influences the properties of the oil For example, crude oils that consist primarily of large compounds are viscous and dense Petroleum products such as gasoline or diesel fuel are mixtures of fewer compounds, and thus their properties are more specific and less variable Crude oil contains many compounds of different sizes and different classes In fact, Oil Spill Science and Technology DOI: 10.1016/B978-1-85617-943-0.10003-6 Copyright Ó 2011 Elsevier Inc All rights reserved 51 52 PART | II Types of Oils and Their Properties there are so many that as time goes by more and more compounds are identified in oil.3 Figure 3.1 shows the number of compounds that are identified and quantified in oils by year as well as the prediction for the future Some analysts have preliminarily identified up to 17,500 compounds in an oil Hydrocarbon compounds are composed of hydrogen and carbon, which are therefore the main elements in oils Oils also contain varying amounts of sulphur, nitrogen, oxygen, and sometimes mineral salts, as well as trace metals such as nickel, vanadium, and chromium In general, the hydrocarbons found in oils are characterized by their structure A common and older method of classification is by SARA dsaturates, aromatics, resins, and asphaltenes Figure 3.2 illustrates the SARA classification along with classes of compounds typically found in this overall classification The saturate group of components in oils consists primarily of alkanes, which are compounds of hydrogen and carbon with the maximum number of hydrogen atoms around each carbon Thus, the term saturate is used because the carbons are “saturated” with hydrogen The saturate group includes straight-chain alkanes and branched-chain alkanes and also includes cycloalkanes, which are compounds made up of the same carbon and hydrogen constituents, but with the carbon atoms bonded to each other in rings or circles Straight-chain saturate compounds from C18 and up are often referred to as waxes The aromatic compounds include at least one benzene ring of six carbons Three carbon-to-carbon double-bonds float around the ring and provide Compounds Identified 4000 3000 Prediction 2000 1000 1970 1980 1990 2000 2010 2020 Year FIGURE 3.1 The number of compounds identified and quantified in crude oils by year, including prediction in the future Chapter | 53 Introduction to Oil Chemistry and Properties Groupings Example Classes, Names, and Compounds Saturates alkanes Chemical class Alternate name Description paraffins Example compound dodecane C12H26 cycloalkanes waxes Aromatics naphthanates decalin n-alkanes C18-C80 Benzenes BTEX benzene Benzene, Toluene, Ethylbenzene, Xylenes PAHs Naphthenoaromatics Resins Asphaltenes anthracene combinations of aromatics and cycloalkanes tetralin class of mostly anomalous polar compounds carbazole sometimes containing oxygen, nitrogen, sulphur, or metals N class of large anomalous compounds structures not known sometimes containing oxygen, nitrogen, metals, or sulphur FIGURE 3.2 An overview of the classification of compounds with specific examples stability Because of this stability, benzene rings are very persistent and can have toxic effects on the environment The most common smaller aromatic compounds found in oil are often referred to as BTEX, or Benzene, Toluene, Ethyl-benzene, and Xylenes Polyaromatic hydrocarbons or PAHs are compounds consisting of at least two benzene rings PAHs make up between and 60% of the composition of oil The olefins, or unsaturated compounds, are another group of compounds that contain less hydrogen atoms than the maximum possible Olefins have at least one double carbon-to-carbon bond that displaces two hydrogen atoms Significant amounts of olefins are found only in refined products Polar compounds are those that have a significant molecular charge as a result of bonding with compounds such as sulphur, nitrogen, or oxygen The “polarity” or charge that the molecule carries results in behavior that may be different from that of other compounds In the petroleum industry, the smallest polar compounds are called resins, which are largely responsible for oil adhesion The larger polar compounds are called asphaltenes because they often make up the largest percentage of the asphalt commonly used for road construction Asphaltenes often have very large molecules and, if in abundance in an oil, they have a significant effect on oil behavior.4 Bitumen, which comes from heavy oil deposits or tar sands, consists largely of asphaltenes that must be broken down to smaller compounds before refining Crude oil is processed in refineries to yield petroleum products that are used for heating, transport, and chemical synthesis Table 3.1 lists some of the 54 PART | II Types of Oils and Their Properties TABLE 3.1 General Characterizations of Product Distillation Ranges Product Distillation Temperature Range ( C) Approximate Carbon Number Range Gasoline 30e200 5e12 Naphtha 100e200 8e12 Jet Fuel & Kerosene 150e250 11e13 Diesel fuel 160e400 13e17 Gas-Oil 220e350 Heavy fuel oils 315e540 20e45 Atmospheric residue >450 30ỵ Vacuum residue >600 60ỵ products produced by distillation, a primary refinery process Table 3.2 gives the general composition of some typical fuels and oils.5 The following are the oils or fuels that be used to illustrate the fate, behavior, and cleanup of oil spills: l l l l l l gasolinedas used in automobiles diesel fueldas used in trucks, trains, and buses a light crude oil a heavy crude oil an intermediate fuel oil (IFO)da mixture of a heavy residual oil and diesel fuel used primarily as a propulsion fuel for ships (the intermediate refers to the fact that the fuel is between a diesel and a heavy residual fuel) bunker fueldsuch as Bunker C, which is a heavy residual fuel remaining after the production of gasoline and diesel fuel in refineries and often used in heating plants 3.3 PROPERTIES OF OIL The properties of oil discussed here are viscosity, density, specific gravity, solubility, flash point, pour point, distillation fractions, interfacial tension, and vapor pressure These properties for the oils noted as examples above are listed in Table 3.3.5 Viscosity is the resistance to flow in a liquid The lower the viscosity, the more readily the liquid flows For example, water has a low viscosity and flows readily, whereas honey, with a high viscosity, flows slowly The viscosity of the (% e except for metals) Group Compound Class alkanes cyclo-alkanes Diesel Light Crude 50 to 60 65 to 95 55 to 90 25 to 80 25 to 35 20 to 30 45 to 55 35 to 45 to 20 to 10 to 10 to 15 waxes Olefins Aromatics BTEX IFO Bunker C 30 to 50 to to 10 to 10 25 to 40 to 25 10 to 35 15 to 40 40 to 60 30 to 50 15 to 25 0.5 to 2.0 0.1 to 2.5 0.01 to 2.0 0.05 to 1.0 0.00 to 1.0 to 10 to 35 15 to 40 30 to 50 30 to 50 to to 15 to 40 15 to 25 10 to 30 to to 10 to 25 10 to 15 10 to 20 to 10 to 20 to 10 to 20 30 to 250 100 to 500 100 to 1000 100 to 2000 to to 0.5 to 2.0 to PAHs Polar Compounds resins asphaltenes Metals (in parts per million) Sulphur Heavy Crude 0.02 0.1 to 0.5 Introduction to Oil Chemistry and Properties Saturates Gasoline Chapter | TABLE 3.2 Typical Composition of Some Oils and Petroleum Products 55 56 TABLE 3.3 Typical Oil Properties Property Viscosity Units mPa.s at 15 C Gasoline Diesel 0.5 Light Crude to 50 Heavy Crude 50 to 50,000 0.72 0.84 0.78 to 0.88 0.88 to 1.00 Flash Point C À35 45 À30 to 30 À30 to 60 Solubility in Water ppm 200 40 10 to 50 Pour Point NR À35 to À10 À40 to 30 65 35 27 100 C 200 C C API Gravity Interfacial Tension mN/m at 15 C 1000 to 15,000 10,000 to 50,000 0.94 to 0.99 0.96 to 1.04 80 to 100 >100 to 30 10 to 30 to À40 to 30 À10 to 10 to 20 30 to 50 10 to 30 10 to 20 to 15 27 10 to 30 15 to 30 25 to 30 25 to 35 70 to 15 to 10 e e 100 30 15 to 40 to 25 to to 85 30 to 60 15 to 45 15 to 25 to 15 100 45 to 85 25 to 75 30 to 40 15 to 25 15 to 55 25 to 75 60 to 70 75 to 85 Distillation Fractions % distilled at 300 C 400 C residual NR ¼ not relevant Types of Oils and Their Properties g/mL at 15 C Bunker C PART | II Density Intemediate Fuel Oil Chapter | Introduction to Oil Chemistry and Properties 57 oil is largely determined by the amount of lighter and heavier fractions that it contains The greater the percentage of light components, such as small saturates, and the lesser the amount of asphaltenes, the lower the viscosity As with other physical properties, viscosity is affected by temperature, with a lower temperature giving a higher viscosity For most oils, the viscosity varies as the logarithm of the temperature, which is a very significant variation Oils that flow readily at high temperatures can become a slow-moving, viscous mass at low temperatures In terms of oil spill cleanup, viscosity can affect the oil’s behavior Viscous oils not spread rapidly, not penetrate soil as readily, and are difficult to pump and skim Density is the mass (weight) of a given volume of oil and is typically expressed in grams per cubic centimeter (g/cm3) It is the property used by the petroleum industry to define light or heavy crude oils Density is also important as it indicates whether a particular oil will float or sink in water As the density of fresh water is 1.0 g/cm3 at 15 C and the density of most oils ranges from 0.7 to 0.99 g/cm3, most oils will float on water As the density of seawater is 1.03 g/cm3, even heavier oils will usually float on it The density of oil increases with time, as the light fractions evaporate Occasionally, when the density of an oil becomes greater than the density of freshwater or seawater, the oil will sink Sinking is rare, however, and happens only with a few oils, usually residual fuels such as Bunker C Significant amounts of oil have sunk in only about 25 incidents out of thousands However, as heavier and heavier oils are being used more frequently, this may become more common in the future Another measure of density is specific gravity, which is an oil’s relative density compared to that of water If the oil-specific gravity is greater than 1, it sinks; if it is less than 1, it floats Another gravity scale is that of the American Petroleum Institute (API) The API gravity is based on the density of pure water that has an arbitrarily assigned API gravity value of 10 (10 degrees) Oils with progressively lower specific gravities have higher API gravities The following is the formula for calculating API gravity: API gravity ¼ [141.5 O (oil density at 15.5 C)] À 131.5 Oils with high densities have low API gravities and vice versa Solubility in water is the measure of how much of an oil will dissolve in the water column on a molecular basis Solubility is important in that the soluble fractions of the oil are sometimes toxic to aquatic life, especially at higher concentrations As the amount of oil lost to solubility is always small, this is not as great a loss mechanism as evaporation In fact, the solubility of oil in water is so low (generally less than 100 parts per million) that it would be the equivalent of approximately one grain of sugar dissolving in a cup of water Yet, even this small amount is important to the environment as even small amounts may be toxic to certain biota The flash point of an oil is the temperature at which the liquid gives off sufficient vapors to ignite upon exposure to an open flame A liquid is considered to be flammable if its flash point is less than 60 C There is a broad range of flash points for oils and petroleum products, many of which are 58 PART | II Types of Oils and Their Properties considered flammable, especially when fresh Gasoline, which is flammable under all ambient conditions, poses a serious hazard when spilled Many fresh crude oils have an abundance of volatile components and may be flammable for as long as one day until the more volatile components have evaporated On the other hand, Bunker C and heavy crude oils generally are not flammable even when spilled The pour point of an oil is the temperature at which it takes longer than a specified time to pour from a standard measuring vessel As oils are made up of hundreds of compounds, some of which may still be liquid at the pour point, the pour point is not the temperature at which the oil will no longer pour The pour point represents a consistent temperature at which an oil will pour very slowly and therefore has limited use as an indicator of the state of the oil In fact, pour point has been overused in the past to predict how oils will behave in the environment For example, waxy oils can have very low pour points, but may continue to spread slowly at that temperature and can evaporate to a significant degree It is important to note that pour point is not the solidification temperature As produced crude oils become heavier, pour point becomes less relevant Distillation fractions of an oil represent the fraction (generally measured by volume) of an oil that is boiled off at a given temperature This data is obtained on most crude oils so that oil companies can adjust parameters in their refineries to handle the oil This data also provides environmentalists with useful insights into the chemical composition of oils For example, while 70% of gasoline will boil off at 100 C, only about 5% of a crude oil will boil off at that temperature and an even smaller amount of a typical Bunker C The distillation fractions correlate strongly to the composition as well as to other physical properties of the oil Equations to predict evaporation can use distillation fraction data as input The oil/water interfacial tension, sometimes called surface tension, is the force of attraction or repulsion between the surface molecules of oil and water Together with viscosity, surface tension is an indication of how rapidly and to what extent an oil will spread on water The lower the interfacial tension with water, the greater the extent of spreading In actual practice, the interfacial tension must be considered along with the viscosity because it has been found that interfacial tension alone does not account for spreading behavior The vapor pressure of an oil is a measure of how the oil partitions between the liquid and gas phases, or how much vapor is in the space above a given amount of liquid oil at a fixed temperature Because oils are a mixture of many compounds, the vapor pressure changes as the oil weathers Vapor pressure is difficult to measure and is not frequently used to assess oil spills Again as oil is a mixture of hundreds of compounds, vapor pressure is not entirely relevant Although there is a high correlation between the various properties of an oil, these correlations should be used cautiously as oils vary so much in composition For example, the density of many oils can be predicted based on their Chapter | Introduction to Oil Chemistry and Properties 59 viscosity For other oils, however, this could result in errors For example, waxy oils have much higher viscosities than would be implied from their densities There are several mathematical equations for predicting one property of an oil from another property, but these must be used carefully as there are many exceptions REFERENCES Neumann H-J, Paczynska-Lahme B, Severin D Composition and Properties of Petroleum New York: Halsted Press; 1981 Speight JG The Chemistry and Technology of Petroleum 4th ed Boca Raton, FL: CRC Press; 2007 Marshall AG, Hendrickson CL High-Resolution Mass Spectrometers, chapter in Annual Review of Analytical Chemistry, Volume 1, 2008, Young ES and Zare RN, editors., Annual Reviews, Palo Alto, CA, p 579e99, 2008 Groenzin H, Mullins OC Asphaltene Molecular Size and Weight by Time-Resolved Fluorescence Depolarization, Chapter in Asphaltenes, Heavy Oils and Petroleomics In: Mullins OC, Sheu EY, Hammami A, Marshall AG, editors New York: Springer Publications; 2007 p 17 Fingas MF The Basics of Oil Spill Cleanup 2nd ed Boca Raton, FL: CRC Press; 2000 ... 15 to 25 0.5 to 2.0 0.1 to 2.5 0.01 to 2.0 0.05 to 1.0 0.00 to 1.0 to 10 to 35 15 to 40 30 to 50 30 to 50 to to 15 to 40 15 to 25 10 to 30 to to 10 to 25 10 to 15 10 to 20 to 10 to 20 to 10 to. .. 1000 to 15,000 10,000 to 50,000 0.94 to 0.99 0.96 to 1.04 80 to 100 >100 to 30 10 to 30 to À40 to 30 À10 to 10 to 20 30 to 50 10 to 30 10 to 20 to 15 27 10 to 30 15 to 30 25 to 30 25 to 35 70 to. .. 55 to 90 25 to 80 25 to 35 20 to 30 45 to 55 35 to 45 to 20 to 10 to 10 to 15 waxes Olefins Aromatics BTEX IFO Bunker C 30 to 50 to to 10 to 10 25 to 40 to 25 10 to 35 15 to 40 40 to 60 30 to