Asymmetric layered vanadium membranes for hydrogen separation

Abstract Layered alloy membranes, with sub-micron Pd catalyst layers over a highly permeable vanadium alloy core, provide a low-cost alternative to supported Pd-alloy membranes. Despite the minimal Pd consumption, Pd still comprises a significant fraction of the overall membrane costs, and further cost reductions can be achieved by replacing Pd with suitable alternative catalytic layers. Ni is an obvious candidate, exhibiting high catalytic activity for a range of reactions while being relatively inexpensive, but its instability in syngas renders it unsuitable as a feed-side catalyst. The permeate surface of an alloy membrane is exposed to H 2 only during operation, making Ni of interest as a permeate-side catalyst. Asymmetric Pd/V/Ni alloy membranes have been fabricated with varying Ni thickness, and hydrogen permeance has been examined over a wide range of pressures and temperatures. Hydrogen permeance increases with decreasing Ni thickness, down to a limiting thickness of 150 nm, beyond which permeance degraded due to incomplete Ni coverage. The permeance was 65% that of a symmetrical Pd/V/Pd membrane with 500 nm Pd layers. The cost-effectiveness is dependent on raw Pd price and manufacturing costs.