EFFECTS OF SOLVENT STERIC PROPERTIES ON THE EQUILIBRIUM SWELLING AND KINETICS OF SOLVENT SWELLING OF COAL

The effects of solvent molecular size on the equilibrium swelling ratio and kinetics of the swelling of a high-volatile bituminous coal in straight-chain amines were examined. The swelling ratio increases with amine size up to a critical level, above which the swelling ratio decreases. This decrease is attributed to reduced access of the solvent to the coal structure with increasing molecular size. The maximum swelling is evidently limited by the density of covalent cross-links, which prevents the coal structure from swelling further to accommodate larger molecules. Rate constants for solvent swelling decrease with increase in molecular size of the amine. Values of the apparent activation energy show that the energy barrier for the swelling process increases with amine size. Clearly, molecular size is a factor which must be considered when choosing solvents for solvent swelling studies on coal.