“…Widely used coal liquefaction methods can be divide into two categories: direct and indirect. In order to increase yield of oils (n-pentane solubles), direct catalytic liquefaction method was preferred (Charcosset et al, 1986;Hewu, 1986;Joseph, 1991). Various catalysts and different preparation methods have been used to increase the yield of oils (Artok et al, 1992;Brannan et al, 1996;Liu et al, 1996;Song et al, 2000;Watanabe et al, 1984).…”