SOLVENT AND TEMPERATURE EFFECTS ON RESTRICTIVE DIFFUSION UNDER REACTION CONDITIONS

The effects of decalin and mesitylene solvents and reaction temperatures of 573 and 623 K on restrictive diffusion were investigated for the catalytic hydrogenation of nickel porphyrins over three NiMO/gamma-Al2O3 catalysts, of average micropore sizes in the range 62-174 angstrom. It was found that the solvents and temperatures used had little effect on restrictive diffusion under reaction conditions, except that less restrictive effect was observed when reaction temperature approached the solvent critical temperature. Because the adsorption strength of reactants under reaction conditions was relatively weak due to high temperature, the restrictive effect was not noticeably influenced by solvent and temperature. However, the effect was even less prominent when temperature approached the solvent critical temperature. It is proposed that the solvent behaved as gaslike liquid when the reduced temperature was close to 1. Under such a condition, viscous drag on diffusing solutes was less important in comparison with inertial forces and, thus, a lower restrictive effect would be expected.