Identification of homologous series of alkylated thiophenes, thiolanes, thianes and benzothiophenes present in pyrolysates of sulphur-rich kerogens

Abstract

The ability of flash pyrolysis-gas chromatography with dual flame ionization and flame photometric detection, and flash pyrolysis-gas chromatography-mass spectrometry, to afford detailed information about the organic sulphur pyrolysis products of kerogens is exemplified through analysis of five different sulphur-rich, type II kerogens. The pyrolysates of these kerogens are extremely complex mixtures. The technique with flame photometric detection yields a chromatogram that shows the distribution of only organic sulphur products in the pyrolysates. However, a considerable loss of sensitivity in flame photometric detection was apparent for higher-molecular-weight compounds. The use of the mass spectrometer as a detector, using characteristic m/z values of organic sulphur compounds for appropriate mass chromatograms, was therefore preferable. Identification of the organic sulphur products was accomplished by sulphur-selective flame photometric detection and comparison of their mass spectral and chromatographic data with those of standard reference compounds. Chromatographic retention time data for 48 standard sulphur compounds (alkylated thiophenes, thiolanes and benzo[b]thiophenes) were determined. Homologous series of 2-alkylthiophenes, 2-alkyl-5-methylthiophenes, 2-alkyl-5-ethylthiophenes, 2-alkylthiolanes, 2-alkylthianes, 2-alkyl-5-methylthiolanes, 2-alkyl-4-methylbenzo[b]thiophenes, 4-alkyl-2-methylbenzo[b]thiophenes and 2-alkyl-benzo[b]thiophenes, through a total carbon number of 22, have been identified through linear Kováts plots and comparison of mass spectral and chromatographic data of the C18 members of these series with those of standard compounds.