Effects of pore diameter and catalyst loading in hydroliquefaction of coal with CoO/MoO3/Al2O3 catalysts

The effect of catalyst pore size has been studied for the hydroliquefaction of a West Virginia coal in the presence of Co/Mo/Al2O3 catalyst. The alumina supports used for catalyst preparation had relatively sharp, unimodal pore size distribution with average pore diameters in the range of 100 A to almost 1000 A. Loading of MoO3 and CoO on the Al2O3 supports was in the constant weight ratio of 5:1, but the absolute loading was in direct proportion to the surface area of the support. Two series of catalyst were studied: “High loading”, with 9.7 × 10−4 g MoO3/m2 Al2O3, and “low loading”, with 4.5 × 10−4 g MoO3/m2 Al2O3; both loadings were less than the amount necessary for monolayer distribution of MoO3 on Al2O3. The weight of catalyst charged in each autoclave run was varied so that the same weight of MoO3 and CoO was present for each experiment. The principal results were: (1) Al2O3 alone is not catalytic, even in large amount; (2) conversion of coal increases as catalyst pore diameter increases; from 100 A to at least 500 A; (3) the increased conversion with increasing pore size is manifested mainly as increased yield of asphaltenes at 400°C, so the ratio of oil to oil-plus-asphaltenes decreases as pore diameter increases; and (4) catalysts with “low loading” of MoO3 and CoO on the Al2O3 surface give higher liquefactions than their counterparts with “high loading”. Most of the results are consistent with an expected low diffusion rate of large, coal-derived molecules through the catalyst pore system. The higher liquefaction with “low loading” of the Al2O3 surface might result from slow desorption of large product molecules (asphaltenes) exhibiting multiple-site adsorption to Mo neighbors on the surface.