Catalytic dehydrogenation of ethanol in Pd-M/gamma-Al2O3 composite membrane reactors

Alumina membranes modified by Pd-M (M=Ru, Rh, Ni, Ag) and Pd were prepared by the sol-gel method, and characterized by SEM, XRD and N-2 adsorption. The single or binary metals were highly dispersed in alumina. The average pore diameters of binary metals modified membranes were 4-7 nm, which was a bit smaller than that for Pd single metal modified alumina membrane. The H-2/N-2 gas separation tests showed that the separation factor of the gaseous mixture exceeded the Knudsen value (3.74). The dehydrogenation of ethanol to acetaldehyde was carried out in membrane reactors incorporating Pd-M and Pd modification. The yield of acetaldehyde in Pd-Ru, Pd-Ag, Pd-Rh modified membrane reactors was higher than that in single metal Pd modified membrane reactor, while the yield in the Pd-Ni/gamma-Al2O3 membrane reactor was lower than that in Pd/gamma-Al2O3 membrane reactor. At moderate reaction conditions, the yield increased by 15% in Pd-Ru modified membrane reactor compared with the thermodynamic equilibrium value. The properties and characteristics of all modified membranes were compared and discussed in this paper.