Thermal reactivity of sulphur forms in coal

X-Ray absorption near edge structure spectroscopy (XANES), X-ray photoelectron spectroscopy (XPS) and temperature programmed decomposition (TPD) have been used to follow the chemical transformation of sulphur that takes place during the low temperature pyrolysis of coals of varying rank. This chemistry takes place under milder pyrolysis conditions than those required for the production of almost all of the other organic volatile matter of coal. The results provide evidence for the conversion of aliphatic sulphides to aromatic forms below 400 °C in addition to the elimination of some of the aliphatic sulphur forms as H 2S. Results between temperatures of 400 and 750 °C indicate that a considerable amount of the aromatic sulphur forms identified by XPS and XANES in the chars made at 400 °C subsequently react (by 750 °C) to produce H 2S. For some low rank coals, a direct relationship cannot be made between the initial aliphatic sulphur content and the total amount of H 2S produced below 750 °C. A comparison of the TPD pattern of H 2S evolution for high rank coal with those of chars made from lower rank coals at 400 °C shows that they are remarkably similar and suggests that the thermal reactions induced in sulphur species in laboratory pyrolysis experiments could be related to those that occur as a result of thermal reactions during coal metamorphism.