In order to increase the extract yield of coal and decrease the loss of extraction solvent due to the condensation between the solvent molecules, Wandoan, Wabamun and Illinois No.6 coals were kneaded with a half amount of solvent such as tetralin prior to supercritical extraction of coal. The solvent added coals were swollen during preheating process, and then extracted with a supercritical solvent such as toluene under pyrolysis condition. As a result, the extract yield of Wandoan coal was remarkably increased and the condensation of toluene was suppressed. Wandoan coal swollen with a hydrogen-donor solvent including nitrogen, such as tetrahydroquinoline and piperidine, gave a high extract yield over 88 wt% during extraction with supercritical toluene. However, these solvents were also taken into the residue in fairly mass. The extract yield was further increased by raising the extraction temperature above 653 K which was the temperature giving the maximum extract yield in the usual supercritical extraction without swelling. The effect of solvent addition was more significant for a coal having a higher solvent swelling property, in the order of Wabamun < Wandoan<Illinois.
