Metallic membranes hydrogen separation

Siriwardane, R.V., J.A. Poston, E.P Fisher, T.H. Lee, S.E. Dorris, and U. Balachandran, Characterization of ceramic-metal composite hydrogen separation membranes consisting of barium oxide, cerium oxide, yttrium oxide, and palladium, Appl. Surf. Sci., 217, 43-49, 2003. 

Ceramic, Metal, and Liquid Membranes. The discussion so far implies that membrane materials are organic polymers and, in fact, the vast majority of membranes used commercially are polymer based. However, interest in membranes formed from less conventional materials has increased. Ceramic membranes, a special class of microporous membranes, are being used in ultrafHtration and microfiltration appHcations, for which solvent resistance and thermal stabHity are required. Dense metal membranes, particularly palladium membranes, are being considered for the separation of hydrogen from gas mixtures, and supported or emulsified Hquid films are being developed for coupled and facHitated transport processes. 

FIGt 22-48 Transport mechanisms for separation membranes a) Viscous flow, used in UF and MF. No separation achieved in RO, NF, ED, GAS, or PY (h) Knudsen flow used in some gas membranes. Pore diameter < mean free path, (c) Ultramicroporoiis membrane—precise pore diameter used in gas separation, (d) Solution-diffusion used in gas, RO, PY Molecule dissolves in the membrane and diffuses through. Not shown Electro-dialysis membranes and metallic membranes for hydrogen. 

D.J. Edlund, D. Friesen, B. Johnson and W. Pledger, Hydrogen-permeable Metal Membranes for High-temperature Gas Separations, Gas Sep. Purif. 8, 131 (1994). 

Metallic membranes for hydrogen separation can be of many types, such as pure metals Pd, V, Ta, Nb, and Ti binary alloys of Pd, with Cu, Ag, and Y Pd alloyed with Ni, Au, Ce, and Fe and complex alloys of Pd alloyed with more than one metal [3], Body-centered cubic metals, for example, Nb and V, have higher permeability than face-centered cubic metals, for instance, Pd and Ni [26-29], Even though Nb, V, and Ta possess a permeability greater than that of Pd, these metals develop oxide layers and are complicated to be used as hydrogen separation membranes [29], Especially, the Pd and Pd-based membranes have in recent times obtained renovated consideration on account of the prospects of a generalized use of hydrogen as a fuel in the future [26], We emphasize on these types of membranes in this chapter. 

Roughly, hydrogen separation membranes can be classified in four classes, based on the used materials polymer, metallic, carbon, and ceramic membranes [6],... 

Because Pd-based metal membranes, commonly used for hydrogen separation [11] are not resistant towards sulphur, not much research has been performed on the use of such membranes in H2S dehydrogenation reactors. Some success has, however, been reported by Edlund and Pledger [12], They developed a platinum-based layered metal membrane that could resist irreversible attack by H2S at 700°C. At this temperature a conversion of 99.4% was achieved in the membrane reactor. Without hydrogen removal the conversion was only 13%. No permeance data is provided, but platinum-based metal membranes are known for their low hydrogen permeance [14], Johnson-Matthey developed palladium composite membranes with a hydrogen permeance of about 1 10 mol/m sPa [14], but these are most probably not resis-... 

Peachey, N. M. Snow, R. C. Dye, R. C. Composite Pd/Ta Metal Membranes for Hydrogen Separation Journal of Membrane Sciences (in press). 

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