Dependence of solvent swelling on coal concentration: A theoretical investigation

An empirical equation for the dependence of coal concentration on coal solvent swelling was theoretically investigated on the basis of the associated structural model of coal. Swelling results of previously reported concentration dependence were analyzed by following this theory. It was reasonably derived that coal molecules are physically associated, and the covalently cross-linked macromolecular model is questionable. The swelling ratios of high-molar-mass fractions were larger than those of low-molar-mass fractions. This was interpreted as intermolecular association is superseding intramolecular association, and that the size of molecules in associated complexes is a determining factor for swelling ratios. The average molar mass of coal is apparently comparable to those of high-molar-mass fractions in coal extracts. The average molar mass of coal decreases with an increase in the rank of coal. Extraction and swelling kinetics follow the first-order process, and are controlled by the solvation of associated sites.