Diffusion membrane and process for separating hydrogen from gas mixture

Abstract

For separation of hydrogen and its isotopes by diffusion through a membrane irtually impermeable to other gases, a non-porous hydrogen-permeable metallic membrane is provided on the gas access side with a coating of an alloy of palladium with at least 45 atomic % Cu or at least 50 atomic percent Ag or at least 7 atomic % Y, the membrane itself containing Cu, Ag or Y respectively in a concentration at least equilibrated with the coating at operation temperature. Preferably the membrane consists of a metal of niobium and/or tantalum bases especially of an alloy containing from 10 to 30 % Ti, 3 to 10 % V, 0 to 25 % Nb and at least 30 % Ta, all by weight, and preferably it is of a composition of 20 to 25 % Ti, 5 to 7,5 % V, 0 to 25 Nb, and at least 50 % Ta, being saturated with copper and or silver, while a copper and/or silver palladium alloy coating is used. Such inherently oxidation sensitive membranes can be stabilized by provision of an internal intermediate layer in the form of a melt forming or containing an alkaline metal hydride and/or an alkaline earth metal hydride. A melt containing alkaline metal and/or alkaline earth metal which forms a hydride, brought into contact on the secondary side of a membrane in accordance with the invention, provides a hydrogen sink on the secondary side and inhibits internal hydride formation and secondary side oxidation of the membrane.