Sulfur-containing organic compounds in coal

This chapter reviews research on the abundance of sulfur in major coal basins in the U.S., the forms of sulfur in coals, the distribution of sulfur in coal lithotypes and macerals, and the nature of sulfur-containing organic compounds in coal. Next, the origin of sulfur in coal is reviewed based on the evidence from the distribution and speciation of sulfur in peat, and from stratigraphic, isotopic, and trace element data. Finally, the origin of sulfur in coal is explained by a geochemical model. 

Studies of sulfur-containing organic compounds in coal provide information on the origin of organic sulfur and the transformation of sulfur compounds during coal maturation. The distribution and types of organic sulfur compounds in coal have profound implications for desulfurization processes. 

In summary, considerable progress has been made in recent years in the characterization of sulfur-containing organic compounds in coal. Much of this progress is attributed to the development of GC-MS. However, systematic study of many coal samples from different seams is needed to establish a firm relationship between the nature of organosulfur compounds and either coal rank or depositional environment. 

Most of the hydrogen sulfide in the atmosphere—approximately 90%— comes from natural sources through nonspecific and anaerobic bacterial reduction of sulfates and sulfur-containing organic compounds (ATSDR 1999). These sources include stagnant or polluted waters and manure or coal pits with low... 

World sulfur reserves. The earth s crust contains about 0.6% S, where it occurs as elemental S (brimstone) in deposits associated with gypsum and calcite combined S in metal sulfide ores and mineral sulfates as a contaminant in natural gas and crude oils as pyritic and organic compounds in coal and as organic compounds in tar sands (Tisdale and Nelson, 1966). The elemental form commonly occurs near active or extinct volcanoes, or in association with hot mineral spings. Estimates by Holser and Kaplan (1966) of the terrestrial reservoirs of S suggest that about 50% of crustal S is present in relatively mobile reservoirs such as sea water, evaporites, and sediments. The chief deposits of S in the form of brimstone and pyrites are in Western European countries, particularly in France, Spain, Poland, Japan, Russia, U.S.A., Canada, and Mexico. World production of S in the form of brimstone and pyrites was approximately 41 Tg in 1973 other sources accounted for about 8 Tg, making a total of 49 Tg (Anon, 1973). Byproduct S from sour-gas, fossil fuel combustion, and other sources now accounts for over 50% of S used by western countries, as shown in Fig. 9.1. This percentage may increase as pollution abatement measures increase the removal of SO2 from fossil fuel, particularly in the U.S.A. Atmospheric S, returned to the earth in rainwater, is also a very important source of S for plants. 

Generally, coal treated with bacteria shows an improvement in quality. Apart from the reduction of the sulfur content, the mineral matter content (measured as ash production) in bacteria-treated coals are substantially reduced. However, the removal of organic sulfur depends on the structure and type of the sulfur-containing organic compounds present in coal. 

Sulfur also is found as sulfide minerals in combination with iron or base metals (e g-, pyrites) and as sulfates in combination with alkali metals and alkaline earths (e.g., gypsum). Hydrogen sulfide, with its rotten egg odor, is the primary sour component of sour gas. Crude oil and coal contain a variety of complex sulfur-containing organic species. These sulfur compounds are removed from the liquid fuels by treatment with hydrogen to convert the sulfur to hydrogen sulfide, which is taken off in the gas stream. The recovery of sulfur from sour fuels for environmental reasons is the largest source of sulfur today. 

As we can see from Table III, 86% of the sulfur contained in all of the oxidation products resides in the soluble oxidation products even though this product fraction only represents 52% by weight of the combined oxidation products. This indicates that organic sulfur compounds have been preferentially depolymerized from the coal matrix and that this oxidative procedure may be a possible desulfurization process. 

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