Organosulfur compounds in sulfur-rich Rasa Coal

Abstract

The organosulfur compounds in the extract and pyrolysate of the unusually organic sulfur-rich (11.4 wt %) Upper Palaeocene Raa coal have been identified by gas chromatography-high-resolution mass spectrometry. The major organosulfur compounds (OSC) present in the extract are alkylated benzo[b]- and dibenzothiophenes and in the pyrolysates alkylated thiophenes and benzo[b]thiophenes. In addition, a large suite of sulfur-containing polyaromatics were identified, which sometimes contain more than one sulfur atom per molecule. The degree of alkylation of many homologous series was found to maximize at either three, four, or five alkyl carbons. The dominance of polyaromatic sulfur compounds is consistent with the relatively mature stage of the coal (Ro 0.7%), and their abundance at this rank indicates that the initial peat must have been extremely organic sulfur-rich (atomic Sorg/C ratio 0.15). This together with the very low abundance of lignin-derived components in the coal pyrolysate indicates that Raa coal should not be considered a typical coal. Nevertheless, our results represent a starting point that can be used as a guide for analysis of other coals.