Operating characteristics and performance of a monolithic downflow bubble column reactor in selective hydrogenation of butyne-1,4-diol

The effects of flow condition, bubble dispersion level, and liquid flow rate on the behavior of a novel monolithic downflow bubble column (M-DBC) were investigated using a reaction model, the palladium-catalyzed hydrogenation of butyne-1,4-diol. The stable and closely packed homogeneous bubble dispersion present in the bulk region of the M-DBC allowed effective introduction of the gas-liquid phase for formation of Taylor flow inside the monolith channels. The condition defined as the minimum level dispersion was required in order to obtain high selectivity towards the intermediate product, cis-2-butene-1,4-diol. Enhanced reaction rates were obtained at increasing the dispersion level and lowering the liquid flow rate. Comparison with the DBC employing 5 % Pd/C powder catalyst and 1 % Pd-on-Raschig-ring revealed a better performance of the M-DBC (1 % Pd loading) with the advantage of smaller reaction volume and intensified reaction rate. As an alternative to conventional three-phase reactors, the M-DBC was so simple due to its inherent characteristic operation and no specially designed device is required.