The membranes of V–Pd alloys: study of ultrapure hydrogen extraction from gas mixtures

Abstract

The membranes of bcc V–Pd alloys are promising alternative to commercial membranes from Pd-based alloys. An optimum content of Pd in the alloy was found as 5.1 at% and 7.0 at% for the operations with the gas mixtures contenting H₂ at 0.66 MPa and 9.0 MPa respectively. The thin-walled tubular membranes made from these alloys and electrolessly plated inside and outside with Pd served as samples for the experimental research. The effects of gaseous products of CH₄ steam-and autothermal conversion on the membrane throughput and on the hydrogen extraction ratio were studied with the binary mixtures of 0.8H₂+0.2X (X = CO, CO₂, CH₄, N₂) as well as with 5-and 6-component mixtures (including steam). The reduction in hydrogen throughput caused by CO, CO₂ and CH₄ was clearly observed, but was relatively small and completely reversible. The tubular membranes of both alloys allowed to extract ≈80 % of hydrogen from the multi-component mixtures at their pressure 1.2 MPa, providing the density of hydrogen permeation flux of ≈0.5 scc/(cm²s) and total hydrogen flux exceeding 20 scc/s. It was found with mass analytical method that the hydrogen selectivity of V–Pd alloy membrane with respect to He (H₂/He) is no less than 3⋅10¹⁰.