Investigation of External Mass Transfer in a Micropacked Bed Reactor with a Pd/Al₂O₃/Nickel Foam

External mass transfer performance of micropacked bed reactors (μPBRs) with Pd/Al₂O₃/nickel foam catalysts is investigated by the hydrogenation of α-methylstyrene (AMS). The external mass transfer limitation region for AMS hydrogenation can be determined by means of the apparent activation energy and internal effectiveness factor. Parametric studies for external mass transfer are conducted by varying temperatures, operating pressures, liquid viscosities, gas and liquid superficial velocities, and pore diameters of foam packing. The external volumetric mass transfer coefficients [(ka)_OV] of μPBRs with the Pd/Al₂O₃/nickel foam range from 0.06 to 0.71 s^-1. An empirical correlation of (ka)_OV is developed. Based on the gas-liquid-solid process analysis, the external mass transfer of μPBRs with the Pd/Al₂O₃/nickel foam is limited by liquid-solid mass transfer under the experimental conditions. Moreover, μPBRs with the Pd/Al₂O₃/nickel foam exhibit the best energy efficiency in comparison with that of other multiphase reactors.