CHANGES IN THE MACROMOLECULAR STRUCTURE OF COALS WITH PYROLYSIS TEMPERATURE

This paper describes a study of the effect of pyrolysis temperature on the macromolecular structure of coal, using solvent swelling techniqu es. Heat treatment initially dissociates the intermolecular interactio ns in the coal and cleaves some cross-links, leading to increase in th e solvent swelling of the coal, which indicates a decrease in the cros s-link density. The solvent swelling reaches a maximum before cross-li nking reactions predominate, causing a progressive increase in cross-l ink density and a decrease in solvent swelling. For lower-rank coals t here appears to be an overlap (near the temperature of minimum cross-l ink density) of the dissociation of intermolecular interactions and th ermal decomposition. Appreciable decrease in the apparent cross-link d ensity of high-rank coals as indicated by increase in solvent swelling was observed only after thermal decomposition had commenced. Major de composition involves cross-linking reactions leading to the formation of chars. However, the solvent swelling characteristics continue to ch ange above the resolidification temperature, eventually ceasing at sim ilar to 600 degrees C. The results are discussed in relation to measur ements of thermoplastic properties and devolatilization characteristic s. Copyright (C) 1997 Elsevier Science Ltd.