An Electrochemical Membrane Reactor for Selective Hydrogenation of Acetylene in Abundant Ethylene

A membrane reactor, where acetylene and ethylene were separated from hydrogen by a phosphoric acid containing silica-wool disk, was applied to hydrogenation of acetylene in abundant ethylene at 353K. The hydrogen supplied onto the d-metal cathodes (Pt, Ir, Pd, Rh, and Ru) by electrochemical pumping through the membrane hydrogenates both ethylene and acetylene. The relative rate of hydrogenation of ethylene over all the d-metal cathodes was much greater than that of acetylene because ethylene was abundant compared to acetylene [P(C2H4)/P(C2H2) = 51]. However, the hydrogen pumped to Cu-cathode hydrogenates acetylene to ethylene very selectively with only a slight production of ethane. The gas mixture of hydrogen, acetylene, and ethylene did not cause any catalytic hydrogenation over the Cu cathode. This can be ascribed to the inability of Cu for hydrogen activation under the reaction conditions in this work. However, the electrochemical pumping of hydrogen easily generates active hydrogen onto this inactive catalyst. The results of kinetic studies on electrocatalytic hydrogenations of ethylene and acetylene over the Cu cathode have suggested that both hydrogenations occur independently each other. It is suggested that a stronger adsorption of acetylene than ethylene on Cu enables the preferential hydrogenation of acetylene.