HYDROGEN TRANSPORT THROUGH NONPOROUS MEMBRANES OF PALLADIUM-COATED NIOBIUM, TANTALUM AND VANADIUM

Experiments are reported for hydrogen transport in palladium-coated membranes of niobium, tantalum, and vanadium . Two geometries are studied, coated discs 2 mm thick, and coated tubes of 0.25 mm wall thickness. The hydrogen is extracted at 100% purity. Fluxes are much higher than with current palladium alloy and polymeric membranes at these pressures, and are somewhat higher than with palladium-coated porous ceramics. Palladium-coated niobium discs show effective permeabilities about 0.32 mumol/m-sec-Pa1/2 at 425-degrees-C and 2 atm pressure (including gas-phase resistance). The coated tubes have about 1/2 this permeability, and thus mass transport resistances about 1450 m2-sec-Pal/2/mol. Coated tantalum discs have effective permeabilities about 0.1 mumol/m-sec-Pa1/2, but are less susceptible to hydrogen embrittlement. Since these coated-metals are stronger and more durable than palladium, ceramics or polymers, considerable design flexibility is possible. Based on these measurements, the flux for advanced membranes would be 2000 scf/hr-m2 for a driving force of 3 atm, suggesting attractive economics for petrochemical plant use.