Effect of catalyst size on coal liquefaction reactions and kinetics

Abstract

Diffusion of reacting coal species through catalyst pores is an important factor in the kinetics of coal liquefaction reactions. The effect of diffusion was studied using a model naphthalene system and using Illinois #6 coal and asphaltenes and preasphaltenes derived from Illinois #6 solvent refined coal. These reactions were performed with four different presulfided NiMo/Al 2O 3 extrudate sizes (1/10″, 1/16″, 1/32″, and 1/64″) and with each catalyst in powdered (−200 mesh) form. Thermal reactions were also performed. The naphthalene reaction showed definite diffusional limitations at a reaction temperature of 300°C. The selectivity of naphthalene to intermediate product followed the theoretical prediction with decreasing particle size for a first order series reaction. Diffusional limitations were also observed in the coal liquefaction reactions. The upgrading of coal and preasphaltenes with large catalyst pellets produced much more conversion to products soluble in pentane, benzene, and methylene chloride/methanol than did the thermal reactions for each of the materials; however, little improvement was observed in the asphaltene reaction. Reducing the catalyst size significantly increased the degree of upgrading of all three materials. A kinetic model has been developed for the reaction and rate constants have been calculated.