Reactions of Sulfur-Containing Functional Groups

Sulfur occurs in coal as both organic (Chapter 10) and inorganic sulfur (Chapter 7) and the reactions of both forms of sulfur are quite important for coal combustion and conversion. During coal combustion, both of the sulfur forms appear as sulfur dioxide, which is the most significant pollutant from sulfur-containing coals. Thus, one of the major objectives of many coal conversion programs is to bring about the facile separation of sulfur from the combustible fraction of the coal. 

Organic sulfur in coal can undergo oxidation reactions and can be involved in reduction reactions. Thus sulfur is contained in a variety of groups (Chapter 10) that are susceptible to further 

The formation of sulfones, followed by elimination of sulfur as sulfuric acid, has been proposed as a means of removing the organic sulfur from coal prior to combustion. Unfortunately, the formation of a sulfone from sulfur in a thiophene group is rather difficult. However, up to 40% of the organic sulfur in bituminous coal can be removed when the coal is subjected to 1000 psi air at 200°C (390°F) for 1 h, implying that there exists within the coal an appreciable fraction of nonthiophene sulfur from which sulfuric acid is produced  

Aromatic groups bound to the sulfur form phenols and aliphatic groups normally form carboxylic acids. 

Because of the nature of coal, some consideration must also be given to the reactions of the inorganic sulfur (Chapter 7). This particular type of sulfur is often difficult to remove completely and 

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