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

Experiments are reported for hydrogen transport in palladium-coated me mbranes of niobium, tantalum, and vanadium . Two geometries are studie d, 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 tha n with current palladium alloy and polymeric membranes at these pressu res, and are somewhat higher than with palladium-coated porous ceramic s. 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 permeabili ty, and thus mass transport resistances about 1450 m2-sec-Pal/2/mol. C oated tantalum discs have effective permeabilities about 0.1 mumol/m-s ec-Pa1/2, but are less susceptible to hydrogen embrittlement. Since th ese coated-metals are stronger and more durable than palladium, cerami cs 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 fo r petrochemical plant use.