Petroleum constituents, table

Since the term total petroleum hydrocarbons (total petroleum hydrocarbons) includes any petroleum constituent that falls within the measurable amount of petroleum-based hydrocarbons in the enviromnent the information obtained for total petroleum hydrocarbons depends on the analytical method used. Therefore, the difficulty associated with measurement of the total petroleum hydrocarbons is that the scope of the methods varies greatly (Table 8.1). Some methods are nonspecific, whereas others provide results for hydrocarbons in a boiling-point range. Interpretation of analytical results requires an understanding of how the determination was made (Miller, 2000, and references cited therein Dean, 2003). 

Coal asphaltene constituents are quite different in nature from petroleum asphaltene constituents (Table 18.7). The molecular weight of asphaltene constituents from coal liquids may be some 8-10 times lower than the observed molecular weight of petroleum asphaltene constituents, although this latter can be revised to lower values for a variety of reasons (Steedman, 1985). 

Liquefied Petroleum Gas (LPG). Certain specific hydrocarbons, such as propane, butane, pentane, and their mixtures, exist in the gaseous state under atmospheric ambient conditions but can be converted to the Hquid state under conditions of moderate pressure at ambient temperature. This is termed Hquefied petroleum gas (LPG). Liquefied petroleum gas (qv) is a refinery product and the individual constituents, or light ends (Table 4), are produced during a variety of refining operations. 

The equihbrium shown in equation 3 normally ties far to the left. Usually the water formed is removed by azeotropic distillation with excess alcohol or a suitable azeotroping solvent such as benzene, toluene, or various petroleum distillate fractions. The procedure used depends on the specific ester desired. Preparation of methyl borate and ethyl borate is compHcated by the formation of low boiling azeotropes (Table 1) which are the lowest boiling constituents in these systems. Consequently, the ester—alcohol azeotrope must be prepared and then separated in another step. Some of the methods that have been used to separate methyl borate from the azeotrope are extraction with sulfuric acid and distillation of the enriched phase (18), treatment with calcium chloride or lithium chloride (19,20), washing with a hydrocarbon and distillation (21), fractional distillation at 709 kPa (7 atmospheres) (22), and addition of a third component that will form a low boiling methanol azeotrope (23). 

TABLE 18.2 Hydrocarbons Hydrocarbon Constituents of Petroleum Boiling range (°C) Fraction... 

Hexanc is a very volatile aliphatic hydrocarbon. It is a constituent in the paraffin fraction of crude oil and natural gas and is also used as an industrial chemical and laboratory reagent. Laboratory grade -hexane contains approximately 99% w-hexane. "Hexane" or "hexanes" is a commercial and industrial product consisting of a mixture of hydrocarbons with six carbon atoms and includes -hexane and its isomers 2-methylpentane and 3-methylpentane as well as small amounts of other hydrocarbons (Brugnone et al. 1991). Laboratory and industrial solvents such as "hexane" and petroleum ether contain -hexane from <0.1% to as much as 33% (Creaser et al. 1983). Information regarding the chemical identity of -hexane is located in Table 3-1. 

Considerable care must be exercised in the selection of the rate constant for each constituent to avoid significantly over- or underpredicting actual decay rates. It is usually most effective to evaluate the results of several analytical events, several weeks apart. Half-lives for common petroleum hydrocarbons and organic compounds encountered in groundwater are presented in Table 13.1. 

Nitrogen, carbon dioxide, and hydrogen sulfide are common nonhydrocarbon constituents of petroleum. All three are light molecules and mainly are part of the gas at the surface. Hydrogen and helium are found in some natural gases. Table 1-1 shows the quantities of these nonhydrocarbons typically found in naturally occurring petroleum gases. 

Sulfur compounds are perhaps the most important nonhydrocarbon constituents of petroleum and occur as a variety of structures (Table 3-3). During the refining sequences involved to convert crude oils to salable products, a great number of the sulfur compounds that occur in any particular petroleum are concentrated in the residua and other heavy fractions. 

Distillation concentrates the metallic constituents in the residua (Table 3-5) some can appear in the higher-boiling distillates but the latter may, in part, be due to entrainment. Nevertheless, there is evidence that a portion of the metallic constituents may occur in the distillates by volatilization of the organometallic compounds present in the petroleum. In fact, as the percentage overhead obtained by vacuum distillation of reduced crude is increased, the amount of metallic constituents in the overhead oil is also increased. The majority of the vanadium, nickel, iron, and copper in residual stocks may be precipitated along with the asphaltenes by low-boiling alkane hydrocarbon solvents. Thus, removal of the asphaltenes with n-pentane reduces the vanadium content of the oil by up to 95% with substantial reductions in the amounts of iron and nickel. 

The composition of the various feedstocks may, at first sight, seem to be of minor importance when the problem of the hydrodesulfurization of heavy oils and residua comes under consideration. However, consideration of the variation in process conditions that were outlined in the previous section (Table 6-6) for different feedstocks (where the feedstocks are relatively well-defined boiling fractions of petroleum) presents some indication of the problems that may be encountered where the feedstocks are less well defined. Molecular composition is as important as molecular weight (or boiling range). Such is the nature of the problem when dealing with various residua and heavy oils which are (to say the least) unknown in terms of their chemical composition. In fact, the complexity of these particular materials (Chapter 3) has allowed little more than speculation as to the molecular structure of the constituents. 

Sulfur removal, as practiced in various refineries, can take several forms for instance, concentration in refinery products such as coke (Table 7-1), hydrode-sulfurization, or chemical removal (acid treating and caustic treating, i.e., sweetening or finishing processes). Nevertheless, the desulfurization of petroleum is almost universally accomplished by the catalytic reaction of hydrogen with the sulfur-containing constituents of petroleum to produce hydrogen sulfide that can be readily separated from the liquid products (Chapter 9). 

As the basic elements of crude oil, hydrogen and carbon form the main input into a refinery, combining into thousands of individual constituents, and the economic recovery of these constituents varies with the individual petroleum according to its particular individual qualities, and the processing facilities of a particular refinery (Fig. 13.1). In general, crude oil, once refined, yields three basic groupings of products that are produced when it is broken down into cuts or fractions (Table 13.1). 

Natural gas is an odorless and colorless naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found in porous geologic formations beneath the earth s surface, often in association with petroleum or coal. The principal constituent is methane (CH4) and its composition is regionally dependent. Table 2.2 summarizes the composition of natural gas by region.8... 

Note that aliphatic compounds other than the above straight-chain alkanes were not listed by the TPHCWG [1997b] as constituents of petroleum and petroleum-based fuels that are the focus of the fraction-selection approach. See Appendix D, Table D-l.) Petroleum products such as mineral-based crankcase oil and mineral-based hydraulic fluids, however, contain branched and cyclic... 

Correlative methods have long been used as a way of dealing with the complexity of petroleum fractions. Relatively easy to measure physical properties such as density, viscosity, and refractive index (ASTM D-1218) have been correlated to hydrocarbon structure (Table 7.3) with the potential to relate refractive index data to the nature of the constituents of a petroleum product. 

The studies described above give evidence that the XAD-2 method provides a useful determination of the hydrocarbon components in dilute seawater-oil suspensions. The quantity of "total oil reported in Table I is in sharp contrast to the total hydrocarbons found in the water by the combined helium extraction/XAD extraction techniques. The discrepancy between total oil by IR and hydrocarbons found in water by component analysis was previously reported (5,11) and can be explained by the low contribution to the IR absorbance at 2927 cm 1 of the soluble aromatic constituents relative to the saturate hydrocarbons. The difference between IR analytical result and component analysis by GC becomes much greater in the filtered systems, where the total hydrocarbons found are three times that reported by the IR method. It is clear that the IR analytical technique is only useful in systems where there is a preponderance of particulate, bituminous petroleum or where it is used as a monitoring tool. It provides no information about actual levels of hydrocarbons in systems where there is a preponderance of water-soluble aromatic compounds. 

With reference to the alkyd eompositions in Table 2, phthalic anhydride was the only petroleum based ehemieaL while the other constituents could be eonsid-ered as natiual materials. As portion of the phthalic anhydride was replaced by fumaric acid, the natural eontent of the alkyd has increased, and the tack strength has also improved. Figure 5 is an empirical fit of the tack strength with the fumaric acid content in the alkyd. The tack strength achieved a maximum for AlkFA25 which contained around 5% by weight of fumaric acid in the alkyd. 

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