Sulfur compounds, in oils

Sulfur Compounds in Oils From the Western Canada Tar Belt... 

Removal of sulfur compounds from fuel oils is usually accomplished at the refinery. Although most of the sulfur in oil is in the high boiling fraction, some middle distillates have high sulfur contents. A better understanding of the chemistry of sulfur compounds in oil will also facilitate their efficient removal. 

Fossil fuels nonnally contain sulfur, as sulfur compounds in oil and in the case of raw natural gas, as H2S, COS, and mercaptans from traces to... 

Rail, H.T., C.J. Thompson, H.J. Coleman and R.L. Hopkins (1972), "Sulfur compounds in crude oil". Bureau of Mines Bull. No. 659. Distributed by National Technical Information Service (NTIS), US Dpt of Commerce, Springfield, VA. 

Figure 14.20 GC cliromatogram of the total sulfur compounds in a heavy gas oil sample.

Sulfur Compounds. All crude oils contain sulfur in one of several forms including elemental sulfur, hydrogen sulfide, carbonyl sulfide (COS), and in aliphatic and aromatic compounds. The amount of sulfur-containing compounds increases progressively with an increase in the boiling point of the fraction. A majority of these compounds have one sulfur atom per molecule, but certain aromatic and polynuclear aromatic molecules found in low concentrations in crude oil contain two and even three sulfur atoms. Identification of the individual sulfur compounds in the heavy fractions poses a considerable challenge to the analytical chemist. 

Sulfur in crude oils is mainly present in the form of organosulfur compounds. Hydrogen sulfide is the only important inorganic sulfur compound found in crude oil. Its presence, however, is harmful because of its corrosive nature. Organosulfur compounds may generally be classified as acidic and non-acidic. Acidic sulfur compounds are the thiols (mercap-tans). Thiophene, sulfides, and disulfides are examples of non-acidic sulfur compounds found in crude fractions. Extensive research has been carried out to identify some sulfur compounds in a narrow light petroleum fraction.Examples of some sulfur compounds from the two types are ... 

Identifying sulfur compounds in crude oils and their products is of little use to a refiner because all sulfur compounds can easily be hydro-desulfurized to hydrogen sulfide and the corresponding hydrocarbon. 

Sulfur in cmde oil is mainly present in organic compounds such as mercaptans (R-SH), sulfides (R-S-R ) and disulfides (R-S-S-R ), which are all relatively easy to desulfurize, and thiophene and its derivatives (Fig. 9.2). The latter require more severe conditions for desulfurization, particularly the substituted dibenzothiophenes, such as that shown in Fig. 9.2. Sulfur cannot be tolerated because it produces sulfuric add upon combustion, and it also poisons reforming catalysts in the refinery and automotive exhaust converters (particularly those for diesel-fueled cars). Moreover, sulfur compounds in fuels cause corrosion and have an unpleasant smell. 

Among the bacteria that can inhabit an oil reservoir are the sulfur bacteria that use sulfur compounds in their metabolism. These bacteria produce hydrogen sulhde, which has been responsible for extensive corrosion in the oil field. Thus exclusion of these bacteria from MEOR is highly desirable. The net effect of souring a reservoir is a decrease in the economic value of the reservoir [1835]. 

It is more than likely that when sulfur occurs in a crude oil or in coal (other than the pyrites), it is organically bound in one of the three forms listed in Table 8.3—the thiols, sulfides, or disulfides. The combustion of these compounds is very much different from that of other sulfur compounds in that... 

Aliphatic sulfur compounds, in particular disulfides such as methyl propyl disulfide, dipropyl disulfide, and especially cis- and /ran -propenyl propenyl disulfide are mainly responsible for the typical odor of onion oil [235]. The presence of 2-hexyl-5-methyl-3(2H)-furanone [33922-66-6] is a characteristic of authenticity [235a]. 

Plants to process alternate sources of energy will make low-sulfur fuels from high-sulfur feeds such as coal, oil shale, tar sands, or heavy oil. Elemental sulfur will be a normal byproduct. Nearly all processing schemes first produce H2S from the sulfur compounds in the raw material, and then convert H2S to elemental sulfur. Usually this conversion step is labelled "Claus Process". 

A summary of the work on the identification of sulfur compounds in crude oils has been given recently by Ball, Rail, Waddington, and Smith (31), who list the sulfur compounds isolated from petroleum by earlier investigators and, in addition, give several new compounds which have recently been isolated from a Wasson, Tex., crude petroleum by the API Research Project 48. Birch and Norris (5) isolated a substantial number of the thiol (mercaptan) type of sulfur compounds from an Iranian crude petroleum. 

These results show that, in equimolar concentrations, naphthalene would not be considered as a strong inhibitor toward direct sulfur extraction (A Do) for PASCs. However, as discussed earlier, the content of di- and trinuclear aromatics in diesel fuels and gas oils can be as high as 20-30%, whereas the level of sulfur compounds in today s diesel fuels is only 0.2% sulfur, or about 1 wt% PASCs. So the competition for the active site by aromatic hydrocarbons is very strong. Their effect on the direct desulfurization route will lower the rate to about one-third of the noninhibited rate in the case of dibenzothiophene and would lower that of 4,6-DMDBT even more. 

There have been a few investigations of selective sorbents for trace amounts of aromatic sulfur compounds in gas oils. It has been claimed that certain active carbons exhibit the required selectivity and may be regenerated easily (152). More research in this area is encouraged. 

Turpentine oils extracted from pine resins are now marginal sources of terpenes pinenes, carene and some other monoterpenes are essentially obtained from the paper oils produced in the KRAFT process. Nevertheless this process is based on a treatment of wood chips in sodium sulfide, which leaves significant fractions of sulfur compounds in the paper oils. For the use of terpenes, these sulfur compounds must be eliminated. The process requires ... 

The positive identification of the sulfur compounds in crude oils is a difficult problem often complicated by the lack of reference compounds. This difficulty has been overcome by hydrodesulfurization (see Section VIII), which converts the sulfur compounds into known hydrocarbons. Treatment of a petroleum oil fraction with calcium hexammine converts the benzo[6]thiophenes present into aryl mercaptans, which are readily separable from accompanying aromatic hydrocarbons (e.g., naphthalene) and then identified by hydro-... 

Sulfur compounds in the gas oil fractions from two bitumens (Athabasca oil sand and Cold Lake deposit)> a heavy oil (Lloydminster) from Cretaceous reservoirs along the western Canada sedimentary basin, and a Cretaceous oil from a deep reservoir that may be mature (Medicine River) are investigated. The gas oil distillates were separated to concentrates of different hydrocarbon types on a liquid adsorption chromatographic column. The aromatic hydrocarbon types with their associated sulfur compounds were resolved by gas chromatographic simulated distillation and then by gas solid chromatography. Some sulfur compounds were further characterized by mass spectrometry. The predominant sulfur compounds in these fractions are alkyl-substituted benzo- and dibenzothiophenes with short side chains which have few dominant isomers. 

Tn this work the sulfur compounds in the gas oil of three Cretaceous - heavy oils from the edge of the Alberta sedimentary basin were investigated. These crude oils were obtained from the Athabasca, Cold Lake, and Lloydminster deposits and are believed (I) to belong to the same oil system which implies like modes of origin. The geographic location of these deposits is shown in Figure 1. This investigation was conducted to develop the analytical capability used to follow the maturation of the sulfur compounds in these oils (2). 

The dominant sulfur compounds in the gas oils of the heavy oil and bitumens are alkyl substituted benzo- and dibenzothiophenes, with a limited number of isomers. While some of these thiophenes have long side chains, those in the major fractions have short side chains. The dominance of short side chains might be ascribed to the maturation effects. The benzothiophenes in the deeper Medicine River oil are similar to those from the heavy oils, however, the same dibenzothiophenes are not found in significant amounts. 

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