Compounds in Petroleum

Nickel and vanadium in petroleum exist as soluble organometallic complexes that fall into two categories metal porphyrins and nonporphyrin metal complexes. Both the porphyrins and the nonporphyrins may be distributed over a wide boiling range (350-650°C+), reflecting significant variations in molecular weight, structure, and polarity. Metal porphyrins and nonporphyrin metal complexes also tend to precipitate as part of the asphaltene materia] to an extent that varies with the source of the crude oil. 

This section will review the nature of nickel and vanadium compounds present in petroleum oil, beginning with a detailed discussion of the metal compound categories and their molecular structure. The final section of this discussion will consider the manner in which these two classes of metal-bearing compounds are distributed or associated in the oil. 

Crude oil origin Asphaltenes (wt. %)d Nickel Vanadium Iron 

0 Sources Speight (1981), Yen (1973), and Chevron (unpublished data). b Ar atmospheric resid. c 1000°F + vol % of atmospheric resid. d Heptane insoluble. 

Metal-Bearing Compounds in Petroleum 1. Porphyrin Metal Compounds 

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The principal direct appHcation of furfural is as a selective solvent. It is used for separating saturated from unsaturated compounds in petroleum refining, for the extractive distillation of butadiene and other hydrocarbons in the manufacture of synthetic mbber and for the production of... 

Fig. 1. Structures of compounds in petroleum cmde oils. See Table 1.

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

The presence (and concentration, if known) of corrosive materials, other than the typical concentrations of sulfur compounds in petroleum hydrocarbon streams. 

With comprehensive GC, we can now choose a rational set of columns that should be able to tune the separation. If we accept that each column has an approximate isovolatility property at the time when solutes are transferred from one column to the other, then separation on the second column will largely arise due to the selective phase interactions. We need only then select a second column that is able to resolve the compound classes of interest, such as a phase that separates aromatic from aliphatic compounds. If it can also separate normal and isoalkanes from cyclic alkanes, then we should be able to achieve second-dimension resolution of all major classes of compounds in petroleum samples. A useful column set is a low polarity 5 % phenyl polysiloxane first column, coupled to a higher phenyl-substituted polysiloxane, such as a 50 % phenyl-type phase. The latter column has the ability to selectively retain aromatic components. 

A fractional distillation tower is used to separate different compounds in petroleum. The fuels condense at different enfi efttures and produce different products. 

During the early 1990s IGT collaborated with EBC to develop the BDS process. The combined results from the two companies produced a series of patents describing the process for desulfurization of fossil fuels [237-240], Compared with the patent described in the earlier paragraph [235], these later patents propose a more realistic approach to desulfurization. The basis of these patents is the fact that some of the organosulfur compounds in petroleum are not desulfurized during hydrodesulfurization (HDS), but may be susceptible to BDS. 

Engineered biocatalysts with altered specificity have been developed. A Rhodococcus strain capable of DBT as well as BT desulfurization has been developed by cloning dsz genes into a strain-containing BT desulfurization pathway. The variety of sulfur compounds in petroleum feedstocks and complexity of the problem may require use of a consortium rather than a single bacterial strain. Alternately, use of multiple bioreactors each with a single dominant strain may be employed to achieve maximum desulfurization [299],... 

Dispersants are being increasingly used to combat oil spills in the marine environment. The new generation of dispersants are commonly fatty acid-polyethoxylate esters (25) and are relatively non toxic. The specific compounds in petroleum responsible for MFO induction in fish have not been defined. Dispersed oil could increase the availability of inducing components, either the particulates or solubles, but alternatively, soluble compounds may be rapidly lost from dispersed oil (26). Preliminary experiments have been carried out to assess the effectiveness of dispersed oil in AHH induction. Venezuelan crude and bunker (distillation cut above 300-400°C).and two polyethoxylate oil spill dispersants,... 

Our knowledge of the composition of nitrogen compounds in petroleum is due largely to the investigations at the University of Texas, including the work of Bailey and coworkers from 1928 to 1941, and the more recent work of Lochte and coworkers. These and other pertinent data have been summarized recently by Lochte (30). Approximately half of the nitrogen in California petroleum is present in the form of nitrogen bases, and... 

Petroleums also contain compounds in which sulfur, oxygen, and/or nitrogen atoms are combined with carbon and hydrogen. These elements usually are combined with the complex ring structures that make up the larger molecules of petroleums. These larger nonhydrocarbon compounds form a class of chemicals generally called resins and asphal-tanes. The quantity of these compounds in petroleum is often very small however, as much as 50% of the total molecules in some heavy crude oils are resins and asphaltines. 

Seemingly, T. thiooxidans is able to attack the sulfur-sulfur bond quite readily and the sulfur-carbon bond with some difficulty, if at all. Since a large portion of the sulfur compounds in petroleum are of the monosulfide-aromatic type, more attention is paid to this facet. 

In Section II, the nature of the metal compounds in petroleum oils is discussed to establish a basic understanding of the targeted reactants. The chemical composition of the host petroleum and residuum is described, including a discussion of the two classes of metal compounds (1) metal-loporphyrins and (2) nonporphyrin metals. The troublesome asphaltenes will also be described. Comparison is made between the characteristics of vanadium and nickel complexes and their distribution in residua. 

The relative importance attached to sulfur compounds in petroleum may, at first, seem unwarranted, but the presence of sulfur compounds in any crude oil can only result in harmful effects. For example, the presence of sulfur compounds in finished petroleum products such as gasoline will cause corrosion of engine parts, especially under winter conditions when water containing sulfur dioxide (from the internal combustion) may collect in the crankcase. On the other hand, mercaptans cause the corrosion of copper and brass in the presence of air and also have an adverse effect on the color stability of gasoline and other liquid fuels. 

Table 3-3 Types of Organic Sulfur Compounds in Petroleum... 

Schaub, T. M., Rodgers, R. R, Marshall, A. G., Qian, K., Green, L. A., and Olmstead, W. N. (2005). Speciation of aromatic compounds in petroleum refinery streams by continuous flow field desorption ionization FTICR mass spectrometry. Energy Fuels 19,1566-1573. 

Request tentative identification of unknown individual compound peaks with GC/MS, particularly when they are sizable or recurring. (Exceptions are tentatively identified compounds in petroleum fuels, which are fuel constituents, such as aliphatic and aromatic hydrocarbons.)... 

A number of reviews related to the identification of sulfur compounds in petroleum should be mentioned. Dean and Whitehead (30) summarized work on separation and identification of sulfur compounds in petroleum and shale oil in 1967. Drushel (7) reviewed sulfur compound types with an emphasis on the available analytical methods as of 1970. Mehmet (31) and Gal pern (32) also reviewed sulfur compounds in petroleum in 1971 with some speculation on their origin. The major contributions of API Project 48 reported by Coleman et al. in 1971, Rail et al. in 1972, and Thompson in 1981 will be discussed below (33-35) More recent summaries of sulfur compounds by Aksenov and Kamyanov in 1981 (36) and by Gal pern in 1985 (37), discuss OSC in petroleum, processed petroleum fractions, shale oil, coal derived liquids and related products. These reviews include much of the Soviet literature. In 1975 and 1978 Orr (28-291 discussed sulfur in the petroleum system with somewhat... 

Figure 1. Examples of non-thiophenic sulfur compounds in petroleum and related materials.

Some of the first studies on the biodegradation of sulfur compounds focused on their fate and removal from oil-contaminated environments. Another major area of study is the microbial process of "biodesulfurization" which has been suggested as a means of selectively removing sulfur compounds from petroleum prior to refining. Information gathered from these two areas of research provide the basis of the present knowledge of metabolism of organosulfur compounds in petroleum. This information is reviewed with emphasis on the metabolism of dibenzothiophenes and n-alkyl tetrahydrothiophenes (n-alkyl thiolanes). 

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