SH Radical: The Key Intermediate in Sulfur Transformation during Thermal Processing of Coal

Abstract

To uncouple the complex behavior of sulfur transformation during thermal processing of coal and to elucidate the main mechanism, typical organic and inorganic sulfur compounds impregnated on or mixed with a low-ash char are studied through temperature-programmed decomposition coupled with online mass spectrum analysis (TPDMS) and followed by temperature-programmed oxidation coupled also with online mass spectrum analysis (TPOMS) in a temperature range of up to 800 degrees C. It is evident that the cleavages of Cal-S and Car-S bonds, where the subscripts al and ar stand for aliphatic and aromatic carbon, respectively, in the organic compounds result in the formation of SH radicals, which then undergo secondary reactions with the char to form various sulfur compounds such as H2S, SO2, COS, and elemental sulfur, as well as sulfur structures in the char. H2 has the ability to stabilize the -* SH radicals and weaken the interactions between the -* SH radicals and the char. For the sulfur compounds, which do not generate the *SH radical, the only sulfur products detected are those formed directly from the decomposition of the starting sulfur compounds, H2S from FeS2 in H2 or SO2 from Fe2(SO4)3 in He, for example, and no sulfur structure is formed in the char. Minerals have significant effects on the bond cleavage temperature and the reactions of the *SH radicals with the char. It is clear that the *SH radical is a key species interacting with the char to form secondary sulfur compounds, while H2S and SO2 play no role in the sulfur transformation to the carbon structure.