Inorganic Membranes for Hydrogen Production from the Water-Gas Shift Reaction: Materials, Reactor Design, and Simulation

Inorganic membranes for gas separation and purification have attracted great research interest. One application utilizing these materials is for H-2 production from the water-gas shift reactions (WGS). The exothermic, reversible WGS reaction is controlled by thermodynamic equilibrium and exhibits decreased conversion with increasing temperatures. It is envisaged that the reaction conversion will surpass the equilibrium value if the reaction is conducted in a hydrogen-permselective membrane reactor, where the hydrogen product can be continuously removed from the reactor to shift the reaction equilibrium. In this article, the most recent development on material synthesis and fabrication of microporous ceramic membranes and dense palladium-based metal membranes are firstly reviewed according to their performance for H-2 permeance and permselectivity over slightly larger molecules. The modification methods for improving membrane structure integrity, hydrophobicity, and stability at high temperature operation are also discussed. Subsequently, inorganic membrane reactors for the WGS reaction are evaluated in terms of CO conversion, hydrogen purity and operation parameters. Finally, modeling on gas transport through inorganic membranes and simulation of membrane reactors are discussed. By comparing the performance of various membranes, future prospective and improvement on membrane preparation and membrane reactor design are proposed.