Permselectivity of a nickel/ceramic composite membrane at elevated temperatures: A new prospect in hydrogen separation?

The objective of this study was to develop a metal/ceramic membrane with high permeability and selectivity to hydrogen at elevated temperatures, able to replace the high cost conventional palladium-based membranes. The intent was to use the effect of the interaction between hydrogen and a metal surface existing for the metals from group VIII of the Periodic Table, such as Pd, Ni and Pt. Thus, a composite membrane consisting of a thin and pure nickel layer (thickness approximate to 1-1.5 mu m) deposited on an asymmetric tubular alumina support was prepared by electroless plating using hydrazine as reducing agent. In comparison to a Ni-P amorphous alloy membrane, this composite membrane showed unique permeability characteristics for both separate (H-2 or N-2) and mixed (H-2 + N-2) gases. Indeed, despite not being dense, the nickel layer was selective to hydrogen and its permselectivity increased with temperature. Moreover, both the microstructure and the permselectivity of the Ni/ceramic membrane were stable up to 600 degrees C. The use of a sweep gas provides an optimal H-2/N-2 (mixture) separation factor of 28 at 600 degrees C, the main diffusion mechanism of hydrogen being surface diffusion through the pores. (c) 2006 Elsevier B.V. All rights reserved.