in comparison with the liquefaction (420 degrees C, with tetralin and elemental sulfur) of the proton-exchanged Adaro subbiturninous coal with complex (metallocene or metal carbonyl) of cobalt, nickel or iron, the coal liquefaction was enhanced significantly on the liquefaction of cation (Co2+, Ni2+ or Fe2+) exchanged Adaro coal. However, for several kinds of subbiturninous coal, metal cations hardly exchange due to the small content of carboxyl group in coal. Therefore, the simultaneous liquefaction of subbiturninous coal and cobalt-exchanged coal were carried out in this study. Further, the simultaneous liquefaction of lower rank and subbiturnitious coals with Co,(CO)(8) was carried out to compare the catalytic effect of cobalt derived from either the exchanged coal or Co-2(CO)(8). The catalytic effect of cobalt in the exchanged Morwell brown coal was appeared as the decrease of residue yield on the liquefaction with Yilan subbituminous coal. On the other hand, there was little enhancement on the simultaneous liquefaction of cobalt-exclianged Adaro and Yilan subbiturninous coals. Accordingly, it is clarified that the hydroliquefaction of subbiturninous coal, which was exchanged cation hardly, was enhanced by the addition of cobalt-exchanged brown coal. (c) 2007 Elsevier Ltd. All rights reserved.