Design and operational considerations for a catalytic membrane reactor incorporating a vanadium-based membrane

Self-supporting vanadium-based metal membranes, comprising a vanadium core overlayed with hydrogen dissociation and recombination catalysts, are a low-cost alternative to the current benchmark Pd-based membranes. Absorption of hydrogen, however, significantly degrades the mechanical properties of the host metal, and causes significant volume expansion of the membrane. Consequently, these membranes must be operated within narrow temperature and pressure windows, and must be free to expand upon absorption of hydrogen. These conditions can be attained readily when operating these membranes as hydrogen separators, but the introduction of a catalyst to create a water-gas-shift catalytic membrane reactor (WGS CMR) introduces conditions which may be in conflict with the membrane requirements. Here we have described efforts to develop a scalable vanadium-based, packed-bed CMR which is heated only by the feed gas and the WGS reaction exotherm. Difficulty in achieving a suitable temperature profile along the length of the CMR, and membrane fractures due to the mechanical constraints of the packed catalyst bed proved to be problematic, and we conclude that the packed-bed configuration is unsuitable for this membrane type. While these initial results were less than stellar, they have clearly pointed the way for future iterations with respect to configuration and operation. Three alternative CMR configurations have been proposed.