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Distribution of tiophenic organosulphur compounds in some venezuelan coals

Abstract:

Some tiophenic organosulphur compounds (OSC) distribution in coal bitumen of four different localities in Venezuelan coalfields was studied in order to establish if they could be used as geochemical peat accumulation environment markers, as well as the possibility of using these to establish organic matter maturity in coals. Typical coal organic geochemistry analyses were carried out, including proximate, ultimate and total sulphur analysis, mean vitrinite reflectance %Rm, yield extraction and bitumen fractionation. Saturates and aromatics fractions were analyzed by gas chromatography using FID and FPD detection, respectively. Results indicate that coals range between high volatile bituminous and anthracite. It was found that the degree of maturation of the studied coals was early catagenesis, except the Cerro Saroche coals that are in metagenesis. The sedimentary paleoenvironments were inferred as fresh or low saline water with slightly reducing conditions not free of oxygen. Organic matter precursor in all cases is associated principally to higher plant contribution. FPD chromatograms are characterized by a lack of signs of benzothiophene and their alkylhomologues; The dibenzothiophene and monosustituted alkyl isomers are enriched with regard to the isomers dy and trisustituted. Organosulphur compoundsdistribution indicates a continental siliciclastic origin. The variation of 4-MDBT, (2+3)-MDBT, 1-MDBT y 4-EDBT, is associated to thermal processes, while DMDBT and TMDBT isomers reflects biogenic precursor materials. In general, organosulphur compounds ratios could be used as a degree maturation index, in the same way that crude oil and source rock bitumen; however, some coelution problems point to limits in their applicability.