Sulphur functionality study of steam pyrolyzed “Mequinenza” lignite using reductive pyrolysis technique coupled with MS and GC/MS detection systems

Abstract

Atmospheric pressure–temperature programmed reduction (AP-TPR) and its analogous in oxidative atmosphere coupled “on-line” with a mass spectrometer (MS) were used to study the behaviour of organic sulphur forms of “Mequinenza” lignite during their mild steam pyrolysis. The obtained data were confirmed and completed by the AP-TPR-GC/MS “off-line” analysis. Samples under study were pyrolyzed at different processing parameters (temperature and flow gas). Some peculiarities in the distribution of non-thiophenic sulphur forms depending on experimental conditions were found. Namely, their amounts decreased with temperature increase at the steam treatment. The experiment performed at 500 °C in water vapor flow proved the C–S bond splitting in dibenzothiophene with biphenyl formation. Sulphonic acid compounds were also systematically removed. At higher temperature of the steam pyrolyzed treatment, this effect was more pronounced. At the same time, a relative increase in sulphones was found. The following organic sulphur species in demineralised lignite were detected by the “off-line” AP-TPR-GC/MS technique: methyl- and benzenethiols; mono- and disulphides; alkylthiolanes; alkenyl thiophenes; alkylbenzo[ b]thiophenes and alkyldibenzo[ bd]thiophenes. Their relative intensities as a function of temperature were followed. A strong preponderance of benzo[ b]thiophene and its alkylated homologues above 450 °C were observed. Thiophene presence was temperature independent.