Supercritical water extraction of Japanese sub-bituminous (Taiheiyo) coal was conducted with semi-batch type reactor (380°C, 25-40 MPa) and the results were compared with that for supercritical toluene extraction (380°C, 15-30 MPa). Higher coal conversion (55wt%) and liquid yield (45wt%) were obtained for supercritical water extraction, and this is found to be because of (1) the inhibition of polymerization or recombination of the primary products of thermal decomposition of coal and possibly due to the radical quenching with H or OH, and (2) the hydrolysis of ether or ester bond in coal.
