Identification of some sulphur species in a high organic sulphur coal

Abstract

In this paper, a preliminary study is described concerning the characterization of sulphur forms in a subbituminous coal rich with organic sulphur deposited in a lacustrine carbonate environment (Upper Cretaceous, Provence, France). Two American high organic sulphur coals were studied for comparison with the Provence coal. Optical microscopy, scanning electron microscopy and electron microprobe approaches offered a global view of the relations between sulphur, metals and coal petrography. Sulphur occurs in all the macerals and most minerals. Vitrinite contains the major part of organic sulphur and metals. This common occurrence of organic sulphur and metals in vitrinite suggests the presence of organosulphur-metallic species. X-Ray photoelectron spectrometry showed that mineral and organic sulphur is very much reduced (divalent). It would mainly include pyrite, sulphides and thiophenes. Programmed temperature oxidation and programmed temperature reduction (Attar's test) revealed fragile sulphur compounds such as aliphatic thiols and sulphides and thermal stable sulphur compounds such as aromatic and high molecular weight compounds. Curie-point pyrolysis in combination with mass spectrometry, gas chromatography, and gas chromatography-mass spectrometry indicated the absence of free organic sulphur compounds and of elemental sulphur. Pyrolysis yielded large amounts of low molecular weight products (H2S, COS, etc.) and smaller amounts of thiopenes, benzothiophenes, dibenzothiophenes and their alkylated homologues. These sulphur compounds could result from the thermal degradation of organic sulphur moieties of the coal as well as from secondary reactions. © 1987.