Preparation and characterization of Pd-zeolite composite membranes for hydrogen separation

Zeolite A membranes have been synthesised by secondary growth on the surface of macroporous, alpha-alumina and stainless steel tubular supports, previously seeded with zeolite A crystals. The membranes thus obtained were used in the separation of H-2/N-2 and H-2/C3H8 mixtures. Stainless steel supports appeared to be more adequate for the development of zeolite A membranes by secondary growth, as evidenced by the results of XRD analysis and by higher values of selectivity and gas permeance obtained. The resulting membranes were further modified by CVD of a Pd compound or impregnation with a Pd salt solution, in order to minimize the non-selective defects by Pd deposition. Permeation measurements carried out under pressure gradient did not show any apparent beneficial effect of Pd over H-2/N-2 separation. However, in permeation tests carried out using a sweep gas, higher separation factors were achieved (e.g., ideal selectivity H-2/C3H8 of 17.35 at 323 K, and H-2/C3H8 separation factor of 7.28 at the same temperature).