DETERMINATION OF ORGANIC SULFUR FORMS IN SOME COALS AND KEROGENS BY HIGH-PRESSURE TEMPERATURE-PROGRAMMED REDUCTION

The principal inherent drawbacks associated with temperature-programmed reduction (TPR), for specifying the distribution of organic sulfur forms in solid fuels, in that first, thiophenic sulfur is largely undetectable and second, sulfides interconvert readily into thiophenes, have been overcome by the use of a well-swept, fixed-bed reactor, operating at relatively high hydrogen pressure (15 MPa). The high pressure technique was applied previously to two high sulfur lignites, Rasa (Croatia) and Mequinenza (Spain), and indicated that thiophenic forms account for approximately 70% of the total organic sulfur. The study has now been extended successfully to samples of varying organic sulfur content which include three of the Argonne Premium coals i.e. Wyodak-Anderson, Illinois No. 6 and Upper Freeport; a UK bituminous coal i.e. Gedling; two kerogens i.e. Goynuk (Type I, Turkey) and Kimmeridge Dorset-Cuddle (Type II, UK); and a liptinite concentrate of Mequinenza lignite. For those samples in which pyritic sulfur represents a significant proportion of the total sulfur, treatment with lithium aluminium hydride was necessary, in order to obtain any meaningful information on the organic sulfur forms present. From the subsequent H2S evolution profiles, the relative contributions from thiophenic and non-thiophenic forms have been resolved satisfactorily. In common with other pyrolysis techniques and X-ray techniques (XPS and XANES), high pressure TPR indicates that thiophenic sulfur increases with rank. However, the proportions of thiophenic sulfur derived from high pressure TPR are consistently higher than by other techniques.