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 rati o and kinetics of the swelling of a high-volatile bituminous coal in s traight-chain amines were examined. The swelling ratio increases with amine size up to a critical level, above which the swelling ratio decr eases. This decrease is attributed to reduced access of the solvent to the coal structure with increasing molecular size. The maximum swelli ng is evidently limited by the density of covalent cross-links, which prevents the coal structure from swelling further to accommodate large r molecules. Rate constants for solvent swelling decrease with increas e in molecular size of the amine. Values of the apparent activation en ergy show that the energy barrier for the swelling process increases w ith amine size. Clearly, molecular size is a factor which must be cons idered when choosing solvents for solvent swelling studies on coal.