Changes in sulfur functionality during solvent extraction of coal in HyperCoal production

Abstract

In this paper, the structural changes of the chemical forms of sulfur in coal, as induced by thermal extraction with industrial solvents (HyperCoal [HPC] production), were examined using X-ray photoelectron spectroscopy (XPS). In raw coal, thiophenic sulfur is more common than alkyl sulfides, and the observed structural changes during solvent extraction depend on the initial chemical form of sulfur. The majority of sulfur remains in the residue after extraction, and inorganic sulfur is found only in the residue. Only thiophenic sulfur (~84%) and sulfoxides (~16%) were found in the resulting HPC; no other types of sulfur (e.g., alkyl sulfides) were detected. These results demonstrate that, during HPC extraction, sulfates are not extracted and that some or most of the extracted alkyl sulfides, sulfoxides, and sulfones are likely decomposed and eliminated as gases. It was found that thiophenic and sulfate sulfur are unaffected by the extraction process and are found in the HPC and/or the extraction residue.