Thermal extractions of subbituminous coals were performed to obtain "HyperCoal" (ashless-coal) in a high yield. The extraction yield reached 60% for Pasir coal with an industrial solvent, crude methylnaphthalene oil (CMNO). Acid-treatment prior to the extraction was carried out to enhance the thermal relaxation of the coals. The extraction yield increased; especially the effect was significant when a polar industrial solvent was used.
