In order to produce ashless coal (HyperCoal) in a high-yield, thermal extraction with several organic solvents under hot filtration at 360 degreesC using a flow-type extractor was performed, and the effect of the extraction solvent on the extraction yield and ash content in the HyperCoal was investigated. Crude methylnaphthalene oil (CMNO), a cost-effective industrial solvent, gives much higher extraction yield ( similar to 80%) than light cycle oil (LCO), which was previously reported as a useful solvent for HyperCoal production. The high extraction yield can be obtained due to the solvent-induced relaxation of coal aggregates by the nitrogen-containing compounds, in addition to the thermal-induced relaxation of them. Gas chromatography/mass spectrometry (GC/MS) analysis of the solvent showed that the polar compounds contained mainly consisted of quinoline-type ones. The effect of addition of some polar compounds into non-polar extraction solvent on the extraction yield was investigated. The addition led to an increase in the extraction yield, while, the quantities of solvent remained in the extract and residue also increased. The extraction yield did not reach the same level as the industrial solvents used here, even when the nitrogen content in the mixture of solvent/additives was almost identical to that in those solvents. (C) 2004 Elsevier B.V. All rights reserved.