The hydrogenation of cinnamaldehyde by supported aqueous phase (SAP) catalyst of RhCl(TPPTS)3: Selectivity, kinetic and mass transfer aspects

The hydrogenation of trans-cinnamaldehyde catalysed by a supported aqueous phase catalyst of RhCl(TPPTS)3 [TPPTS: trisodium salt of tris(m-sulfophenyl)phosphine] on silica was investigated in terms of the product selectivity, reaction kinetics and mass transfer characteristics. The hydrogenation is selective at the CCCC bonds in cinnamaldehyde giving hydrocinnamaldehyde as the main product. To achieve high selectivity (99.9%), it is necessary to employ a low initial concentration of cinnamaldehyde (0.076 M). The selectivity also depended on the reaction operating conditions (pressure, temperature, catalyst loading) and the water content property of the SAP catalyst. Optimum water content of the SAP catalyst giving maximum activity was obtained when the pore volume of the supports was completely filled with water. The overall order of reaction was first-order and therefore the conventional three-phase slurry model was applied to the SAP system for the mass transfer analysis. The gas–liquid mass transfer and the reaction resistances were the controlling steps of comparable significance, while liquid–solid mass transfer resistance was negligible in this system. Under similar conditions, the SAP catalyst gave a lower reaction rate than the analogous biphasic catalyst.