The Basics of Oil Spill Cleanup - Chapter 3

CHAPTER 3 Types of Oil and their Properties 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. The many different types of oil are made up of hundreds of major compounds 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 determine the effects of the oil on living organisms in the environment. These properties also influence the efficiency of cleanup oper-ations. This book deals specifically with crude oils and petroleum products derived from crude oils. The chemical composition and physical properties of these oils are described in this chapter. THE COMPOSITION OF OIL Crude oils are mixtures of hydrocarbon compounds ranging from smaller, vol-atile compounds to very large, non-volatile compounds. 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. 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. The hydrocarbon structures found in oil are the saturates, olefins, aromatics, and polar compounds, some examples of which are shown in Figure 5. ©2000 by CRC Press LLC Figure 5 Chemical compounds in oils. 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 also includes cyclo-alkanes, 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. Larger saturate compounds are often referred to as waxes. The olefins, or unsaturated compounds, are another group of compounds that contain fewer hydrogen atoms than the maximum possible. Olefins have at least one ©2000 by CRC Press LLC double carbon-to-carbon bond that displaces two hydrogen atoms. Significant amounts of olefins are found only in refined products. The aromatic compounds include at least one benzene ring of six carbons. Three double carbon-to-carbon bonds float around the ring and add stability. Because of this stability, benzene rings are very persistent and can have toxic effects on the environment. The most common smaller and more volatile 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 0 and 60% of the composition of oil. 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 behaviour that, under some circumstances, is different from that of unpolarized 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 behaviour. This will be discussed in Chapter 4. The following are the oils used in this book to illustrate the fate, behaviour, and cleanup of oil spills: · gasoline — as used in automobiles · diesel fuel — as used in trucks, trains, and buses · a light crude oil — as produced in great abundance in western Canada or Louisiana · a heavy crude oil — as imported to North America from Arabic countries or similar to that produced off the coasts of Newfoundland and California · an intermediate fuel oil (IFO) — a 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 fuel — such 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 · crude oil emulsion — such as an emulsion of water in a medium crude oil Typical amounts of hydrocarbon compounds found in these oils are shown in Table 4. Properties of Oil The properties of oil discussed here are viscosity, density, specific gravity, sol-ubility, flash point, pour point, distillation fractions, interfacial tension, and vapour pressure. These properties for the oils discussed in this book are listed in Table 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 poorly. The viscosity of the oil is largely determined by the amount of lighter and heavier fractions that it contains. The greater ©2000 by CRC Press LLC Table 4 Typical Composition of Some Oils and Petroleum Products Compound Group Class (%) Light Heavy Bunker Gasoline Diesel Crude Crude IFO C Saturates Olefins Aromatics alkanes cyclo-alkanes waxes 50 to 60 65 to 95 45 to 55 35 to 45 5 30 to 50 0 to 1 5 to 10 0 to 10 25 to 40 5 to 25 55 to 90 25 to 80 25 to 35 20 to 30 0 to 20 0 to 10 2 to 10 5 to 15 10 to 35 15 to 40 40 to 60 30 to 50 BTEX 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 Polar Compounds PAHs resins asphaltenes 0 to 5 10 to 35 15 to 40 40 to 60 30 to 50 0 to 2 1 to 15 5 to 40 15 to 25 10 to 30 0 to 2 0 to 10 2 to 25 10 to 15 10 to 20 0 to 10 0 to 20 5 to 10 5 to 20 Metals 30 to 250 100 to 500 100 to 1000 100 to 2000 Sulphur 0.02 0.1 to 0.5 0 to 2 0 to 5 0.5 to 2.0 2 to 4 Photo 18 This shows the appearance of highly weathered Bunker C 25 years after it was spilled and washed up onto this beach. (Environment Canada) the percentage of light components such as 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 tem-peratures. In terms of oil spill cleanup, viscosity can affect the oil’s behaviour. Viscous oils do not spread rapidly, do not penetrate soil as readily, and affect the ability of pumps and skimmers to handle the oil. ©2000 by CRC Press LLC Table 5 Typical Oil Properties Light Property Units Gasoline Diesel Crude Heavy Intemediate Bunker Crude Fuel Oil C Crude Oil Emulsion Viscosity mPa.s at 0.5 15°C 2 5 to 50 50 to 1000 to 50,000 15,000 10,000 to 50,000 20,000 to 100,000 Density g/mL at 0.72 15°C 0.84 0.78 to 0.88 0.88 to 0.94 to 0.99 0.96 to 0.95 to 1.0 1.00 1.04 Flash Point °C –35 45 –30 to 30 –30 to 60 80 to 100 >100 >80 Solubility in ppm 200 40 10 to 50 5 to 30 10 to 30 1 to 5 – Water Pour Point °C NR –35 to –40 to 30 –40 to 30 –10 to 10 5 to 20 >50 –1 API Gravity 65 35 30 to 50 10 to 30 10 to 20 5 to 15 10 to 15 Interfacial Tension mN/m at 27 27 10 to 30 15 to 30 25 to 30 25 to 35 NR 15°C Distillation Fractions % distilled at 100°C 70 200°C 100 300°C 400°C residual 1 2 to 15 30 15 to 40 85 30 to 60 100 45 to 85 15 to 55 1 to 10 – – NR 2 to 25 2 to 5 2 to 5 15 to 45 15 to 25 5 to 15 25 to 75 30 to 40 15 to 25 25 to 75 60 to 70 75 to 85 NR = not relevant Photo 19 Emulsified oil is very viscous and dense. (Environment Canada) Density is the mass (weight) of a given volume of oil and is typically expressed in grams per cubic centimetre (g/cm3). It is the property used by the petroleum industry to define light or heavy crude oils. Density is also important because it indicates whether a particular oil will float or sink in water. As the density of 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. ©2000 by CRC Press LLC ... - tailieumienphi.vn