Supported and laminated Pd-based metallic membranes

Composite metallic membranes for the separation and the production of hydrogen have been prepared by using thin Pd–Ag foils (with silver content 23–25 at%) reinforced by metallic (stainless steel, nickel, niobium) structures. Essentially, the cost reduction for the Pd-based membranes has been achieved through two different methods used in the production of composite membranes. A procedure of diffusion welding was used to join Pd–Ag thin foils with expanded metals (stainless steel) and perforated metals (nickel): the thin palladium foil in these membranes assures both the high hydrogen permeability and the perm-selectivity, while the metallic support provides the mechanical strength. A second procedure investigated for the production of composite laminated membranes consists in coating non-noble metals with very thin palladium layers: in this case, Pd–Ag foils have been applied over nickel, iron and niobium sheets through the diffusion welding procedure, and then the thickness of the laminated metal has been reduced down to the desiderated value by cold rolling. tion tests carried out on these composite membranes have shown hydrogen permeability data to be in accord to previously studied literature; furthermore, the complete hydrogen selectivity, and the observed chemical and physical stability, have demonstrated the applicability of these procedures to processes for separating and producing pure hydrogen.