PREPARATION OF SOL-GEL DRIVEN ALUMINA MEMBRANE MODIFIED BY SOAKING AND VAPOR-DEPOSITION METHOD

Porous alumina membrane for hydrogen separation was prepared by a two-step process. The gamma-alumina layer was first formed in an asymmetric porous alpha-alumina support from alumina sol mixed with a palladium precursor H2PdCl4. The membrane pore was then modified by two consecutive procedures; soaking palladium acetate solution into the pores at room temperature, followed by drying, evaporation, and decomposing palladium acetate on the pore surface by gradually increasing temperature upto 573K for 1 hour. This modification, named soaking and vapor-deposition (SVD) method, enhanced both the permeability and the hydrogen selectivity relative to those for the membrane prepared only by the sol-gel method. The permeability of hydrogen through the membrane was an increasing function of the transmembrane pressure and varied from 8.5 to 15.7 in 10(-8) m(3) (STP) m(-2) Pa-1 s(-1). The selectivity of hydrogen was maintained above 5 at 673 K even when the transmembrane pressure was 18 Wa. The effect of pore modification became pronounced as both the transmembrane pressure and the temperature were increased. The novel feature of the present membrane lay in the formation of thin intermediate layer of palladium inside of the support which was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).