Hydrogen transport through tubular membranes of palladium-coated tantalum and niobium

Palladium-based membranes have been used for decades in hydrogen extraction because of their high permeability and good surface properties and because palladium, like all metals, is 100% selective for hydrogen transport. We describe experiments with hydrogen-extraction membranes made of palladium-coated niobium and tantalum heat-exchanger tubes. The cost was about $45/ft of 3/8 in. tubular membrane, and the fluxes were as high as 0.001 47 mol/m(2)s Pa-1/2 at 420 degrees C. The main transport resistance is in the refractory metal substrate. Durability tests showed a 15% reduction in flux for 31 days of continuous membrane operation. Assuming durability is maintained for at least 1 year, this price and flux should allow competitive application for hydrogen recovery in petrochemical plants and for membrane reactors.