The influence of intraparticle mass transfer on the activity of a gel-form polymer-bound transition metal catalyst

Abstract

A mathematical model was developed to investigate the influence of substrate intraparticle mass transport limitations on the hydrogenation rate of cyclohexene and cyclooctene at 25 to 50 °C, 1 atm hydrogen pressure, over RhCl(PPh 3) 3 bound to polystyrene-divinylbenzene (DVB) polymer beads. Initial solute concentrations of ca. 0.16 M were used for the reaction rate studies. Intraparticle transport limitations were determined to be negligible within the 200–400 mesh, 1, 2, and 3% DVB catalyst beads under the reaction conditions employed. Changes in the reduction rate of cyclooctene relative to cyclohexene were not caused by differences in intraparticle diffusion rates. Alterations in selectivity were related to the catalyst bead swelling ratio implying that steric effects induced by the presence of the polymer support in the vicinity of active rhodium affected intrinsic activity. Intrinsic activity was found to depend on polymer crosslink density and functionalized swelling ratio. Studies of the equilibrium distribution of substrate between the solvent-swollen polymer phase and the surrounding bulk phase solution indicated that the substrate distributed uniformly for the low DVB crosslinked beads used. The mathematical model was used to study the measured reaction rate for an intraparticle mass transport influenced system: hydrogenation of cyclohexene and cyclooctene over Wilkinson's complex supported on 18–20 mesh, 3% DVB polymer beads.