The components of crude oil

The plants, animals and micro-organisms in wetlands are generally adapted to survival in wet habitats. One example is the species of the moss Sphagnum which thrive in such waterlogged, nutrient-poor and acidic environments because of various adaptations. The accumulation of biomass occms because of this saturation which provides a medium that is imsuitable for decomposer organisms (detrivores, see Section 3.6.3). The medium is even more unfavourable if conditions are acidic. Thus the rate of breakdown of organic matter is lower than its rate of accumulation and so organic 

Although wetlands occupy only 4 to 6 percent of the Earth s surface, they account for c. 20 to 25 percent of the carbon stored at the Earth s surface in soils (IPCC, 2001). A great deal of this is in peat. According the Irish Peatland Conservation Council (2003) Peatlands may well contain 3 to 3.5 times the amount of carbon stored in tropical rain forests . Table 4.4 lists the extent of peatland by continent. 

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The separation of the components of crude oil into useable products is known as refining. Each of the crude oil fractions finds its way into consumer products. A typical list of fractions is gasoline, kerosene and fuel oil, gas oil, wax distillate, and bottoms or asphaltics. Refineries must be designed to handle... 

A summary of the components of crude oil and their approximate compositions, based on the data of Goldstein (55) and Boyd (7), is presented in Table III. 

The components of crude oil can be classified into a few broad categories. Some of these components have properties desirable in a lubricant whilst others have properties which are detrimental. 

The various components of liquid air can be separated by boiling because each component has a different boiling point. For example, the nitrogen in liquid air boils away before the oxygen. This is called fractional distillation, and it is the basic method of separating the components of crude oil. 

Fractional distillation is as important in industry as it is in the laboratory. The petroleum industry employs fractional distillation on a large scale to separate the components of crude oil. More will be said of this process in Chapter 24. 

Figure 14. Modern fractionating tower for separating the components of crude oil, Fawky Refinery, England (32)...

The concentration of hydrocarbon and non-hydrocarbon components in crude oil from different sources differ greatly (Brunnock et ah, 1968). The components of crude oil that go... 

When there is delay in clean up action for any reason, after spaUage has occurred, the water soluble components of crude oil seep into the aquatic ecosystem. The components of crude oil that go into solution make up the WSF. Concave (1979) reported that pane hydrocarbon yield 4.2mgH of WSF. Baker (1970a) observed that water soluble fraction (WSF) is produced during a long period of oil water contact. 

The non-hydrocarbon components of crude oil may be small in volume percent, typically less than 1 %, but their influence on the product quality and the processing requirements can be considerable. It is therefore important to identify the presence of these components as early as possible, and certainly before the field development planning stage, to enable the appropriate choice of processing facilities and materials of construction to be made. 

The primary process for separating the hydrocarbon components of crude oil is fractional distillation i.e. separation according to the boiling points of the components. These separated fractions are processed further by catalytic reformers, cracking units, alkylation units, or cokers which have there own fractional distillation towers for its products. 

Distillation is probably Ihe most widely used separation (mass transfer) process in the chemical and allied industries. Its applications range from the rectification of alcohol, which has been practiced since antiquity, lo the fractionation of crude oil. The separation of liquid mixtures by distillation is based on differences in volatility between the components. The greater the... 

Single-stage flash distillation processes are used to make a coarse separation of the light components in a feed often as a preliminary step before a multicomponent distillation column, as in the distillation of crude oil. 

Mehlman MA. 1994. Dangerous and cancer-causing properties of products and chemicals in the oil refining and petrochemical industry. Part VII Adverse health effects and toxic manifestations caused by exposure to hydrogen sulfide, a component of crude oil. Advances in Modem Environmental Toxicology 23 321-340. 

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

The first step in the treatment of crude oil at a refinery is fractional distillation. The mixture is separated into various groupings of compounds, called fractions, by making use of the different boiling points of the components of the mixture. The main fractions obtained from the initial distillation of crude oil are shown below. 

Alicyclic hydrocarbons are saturated carbon chains that form ring structures. Naturally occurring alicyclic hydrocarbons are common (Chap. 1). For example, alicyclic hydrocarbons are a major component of crude oil, comprising 20-67 vol.%. Other examples of complex, naturally occurring alicyclic hydrocarbons include camphor (a plant terpene) and cyclohexyl fatty acids (components of microbial lipids). Anthropogenic sources of alicyclic hydrocarbons to the environment include fossil-fuel processing and oil spills, as well as the use of such agrochemicals as the pyrethrin insecticides (Chap. 1, and references therein). 

Wilson and Madsen [152] used the metabolic pathway for bacterial naphthalene oxidation as a guide for selecting l,2-dihydroxy-l,2-dihydronaphthalene as a unique transient intermediary metabolite whose presence in samples from a contaminated field site would indicate active in situ naphthalene biodegradation (Fig. 26). Naphthalene is a component of a variety of pollutant mixtures. It is the major constituent of coal tar [345], the pure compound was commonly used as a moth repellant and insecticide [345], and it is a predominant constituent of the fraction of crude oil used to produce diesel and jet fuels [346]. Prior studies at a coal tar-contaminated field site have focused upon contaminant transport [10,347], the presence of naphthalene catabolic genes [348, 349], and non-metabolite-based in situ contaminant biodegradation [343]. 

Single-ring aromatics. Aromatic constituents are characterized by the presence of rings with six carbon atoms and are considered to be the most acutely toxic component of crude oil constituents because of their association with chronic and carcinogenic effects. Many low-molecular-weight aromatics are also soluble in water, increasing the potential for exposure to aquatic resources. 

Cracking the thermal processes by which the constituents of petroleum are converted to lower-molecular-weight products a process whereby the relative proportion of lighter or more volatile components of crude oil is increased by changing the chemical structure of the constituent hydrocarbons. 

Reduced crude a residual product remaining after the removal, by distillation or other means, of an appreciable quantity of the more volatile components of crude oil. 

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