AP–TPR study of sulphur in coals subjected to mild oxidation. Part 1. Demineralised coals

Five samples of coal characterised by different degree of coalification and different content of sulphur have been subjected to oxidation in the dry phase and in aqueous media in order to determine the effect of oxidation on the sulphur groups. The transformations were studied by the classical chemical methods and by atmospheric pressure–temperature programmed reduction. It has been shown that the greatest changes in sulphur groups occurs in the case of the oxidation with HNO3 and peroxyacetic acid, while the air oxidation and the oxidation in the O2/Na2CO3 system is much less effective. The oxidation leads to formation of sulphoxides, sulphones and sulphonic acids. The non-thiophene groups have been found much more susceptible to oxidation than the thiophene ones.