Hydrogen separation by dense cermet membranes

Novel cermet (i.e. ceramic-metal composite) membranes have been developed to separate hydrogen from mixed gases, particularly product streams generated during coal gasification and/or methane reforming. Hydrogen separation with these membranes is non-galvanic, i.e. it does not use electrodes or an external power supply to drive the separation, and hydrogen selectivity is nearly 100% because the membranes contain no interconnected porosity. The hydrogen permeation rate has been measured as a function of temperature (500-900 degrees C), membrane thickness (approximate to 22-210 mu m), and partial pressure of hydrogen (0.04-1.0 atm) in the feed gas. The hydrogen flux varied linearly with the inverse of membrane thickness, and reached approximate to 20 cm(3) (STP)/min cm(2) for a membrane with a thickness of = 22 mu m at 900 degrees C with 100% H-2 (at ambient pressure) as the feed gas. The results indicate that the hydrogen flux is limited by bulk diffusion and might be higher for a thinner (< 22 mu m) membrane. Some of the membranes were tested in a simulated syngas mixture containing H-2, CO, CO2, and CH4, and showed no degradation in performance. Hydrogen flux measurements made in H2S-contaming atmospheres for times approaching approximate to 270 h showed that a 200-mu m-thick cermet membrane was stable in gases containing up to approximate to 400 ppm H2S. While longer-term studies are needed, these results suggest that the cermet membranes may be suitable for practical hydrogen separation applications. (c) 2005 Published by Elsevier Ltd.