Selective dehydrogenation of unsaturated alcohols and hydrogen separation with a palladium membrane reactor

The dehydrogenation of cis-3-hexen-1-ol was studied with a hydrogen permeable palladium membrane reactor from 443 to 503 K. The main products were cis-3-hexenal, hexanal and 1-hexanol. The reaction was determined to proceed through consecutive reactions as follows: (1) dehydrogenation of cis-3-hexen-1-ol to cis-3-hexenal and hydrogen, (2) hydrogenation of cis-3-hexenal to hexanal, (3) hydrogenation of cis-3-hexen-1-ol to 1-hexanol, and (4) dehydrogenation of 1-hexanol to hexanal and hydrogen. The formation of hexanal was dominant in the system. Separation of hydrogen was studied experimentally by depressurizing the permeate side of the membrane reactor. The selectivity of cis-3-hexenal during hydrogen removal was significantly higher than that without hydrogen separation, which can be attributed to the suppression of cis-3-hexenal hydrogenation. The selectivity of cis-3-hexenal exhibited a maximum with temperature. The balance of reaction rate and hydrogen permeation rate are important for controlling intermediate formation with palladium membrane reactors.