Chemical Structure and Properties of Heat Treated Coal in the Early State of Carbonization (VII)

Abstract

Many studies concerning the oxygen containing functional group in coal substance and its extracts have been done to investigate its chemical properties and structure. On the other hand, little has been known of the behaviours of functional oxygen groups in coal by heat-treatment. Present authors determined the contents of carboxyl, hydroxyl and carbonyl groups in twelve Japanese coals, five foreign coals and the heat-treatment products of these coals, and attempted to clarify the behaviours of oxygen containing functinal groups in the early state of carbonization (200-500°C).As for the analytical methods of carboxyl, hydroxyl and carbonyl groups, ion exchange method in aqueous calcium acetate solution, acetylation method in acetic anhydride-pyridin solution and oximation method with hydroxyl amine hydrochloric acid in pyridine were adpoted respectively.The results of determination of carboxyl and hydroxyl groups in original coals agreed with those reported by Blom etal., Friedman etal., Halleux etal., Takeya etal., and so on. As for carbonyl groups in original coals, relatively good agreements were obtained when comparing our results with those reported by Halleux etal. and Takeya etal., but there were large differences between our results and those reported by Blom etal. especially in the range from 70%°C to 80%°C.The carboxyl, hydroxyl and carbonyl groups in original coal decreased almost lineally with coal rank.The behaviours of functional oxygen groups by heat treatment were characteristic of the coal rank of original coals. In low rank coals, the functional oxygen groups decreased gradually above a certain heat treatment temperature (HTT), and the higher the coal rank, the higher the temperature where the functional groups began to decrease.In caking or coking coal, however, the functional oxygen groups began to increase at about 350°C and had a maximum at about 400°C.The rest oxygen of all coals investigated, with the exception of that of Tempoku coal (the lowest rank coal), decreased slightly at first and then abruptly with HTT and had a minimum at about 400°C and again increased abruptly at 450-500°C. The rest oxygen of Tempoku coal began to increase at about 250°C and continued to increase with HTT.These tendencies agreed qualitatively with those reported by Angelova etal.Considering the yields of heat treated coals, discussion about the oxygen balance by heat treatment was also made.