Ni-based amorphous alloy membranes for hydrogen separation at 400°C

Amorphous alloy membranes composed primarily of Ni and early transition metals (ETMs) are an inexpensive alternative to Pd-based alloy membranes, and these materials are therefore of particular interest for the large-scale production of hydrogen from carbon-based fuels. Catalytic membrane reactors can produce hydrogen directly from coal-derived synthesis gas at 400 degrees C, by combining a commercial water-gas-shift (WGS) catalyst with a hydrogen-selective membrane. In order to explore the suitability of Ni-based amorphous alloys for this application, the thermal stability and hydrogen permeation characteristics of Ni-ETM amorphous alloy membranes has been examined. A fundamental limitation of these materials is that hydrogen permeability is inversely proportional to the thermal stability of the alloy. Alloy design is therefore a compromise between hydrogen production rate and durability. Amorphous Ni60Nb40-XZrX membranes have been tested at 400 degrees C in pure hydrogen, and in simulated coal-derived gas streams with high steam, CO and CO2 levels, without severe degradation or corrosion-induced failure. Ni-Nb-Zr amorphous alloys are therefore prospective materials for use in a catalytic membrane reactor for coal-derived syngas. (C) 2008 Elsevier B.V. All rights reserved.