Journal of Membrane Science, 94 (1994) 299-311 Elsevier Science B.V., Amsterdam 299 Metal composite membranes for hydrogen separation zyxwvutsrqponm A.L. Athayde, R.W. Baker*, P. Nguyen Membrane Technology and Research, Inc., 1360 W illow Road, Menlo Park, CA 94025, USA (Received March 11,1993; accepted in revised form January 5,1994) A bstract Further advances in the field of gas separation membranes will require materials with higher permea- tion selectivities than the currently available polymers. Metal membranes offer such an alternative. Be- cause the mechanism for gas permeation through metals differs from that through polymers, metal mem- branes with very high selectivities can be made. Gas permeation through these membranes is very slow, however, and membranes with adequate fluxes are difficult to make. High membrane cost has also limited development because some of the best membrane materials are precious metals. Membrane Technology and Research, Inc. is pursuing a new approach to preparing metal membranes that offer the high selectivity inherent to permeation through metals with the high fluxes typical of polymeric membranes. We have prepared ultrathin metal composite membranes by sputter-deposition of a 76 atom% palladium/24 atom% silver alloy layer onto a conventional polymeric gas separation membrane. Preparation of membranes wiih different thicknesses of the metal layer (250-l,OOOA) under different deposition conditions (75-260 Almin) showed that the best membranes are obtained at high metal deposition rates. These membranes have a hydrogen flux of 1 x lo@ cm3 (STP) /cm2 s cmHg at room temperature (25’ C ) and a hydrogen/carbon dioxide selectivity greater than 100. In contrast, the best commercial polymeric membranes have a hydrogen/carbon dioxide selectivity of 6. The hydrogen flux through the membrane increases with temperature, but the fluxes of all other gases are unchanged. The net effect is an increase in membrane hydrogen flux and selectivity at high temper- ature. We have demonstrated that the membranes are stable for over 6 weeks continuous operation at room temperature, Key words: composite membranes; membrane preparations and structure; metal membranes; palladium/ silver alloys; gas separations; sputter deposition zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFED 1. Introduction Since the commercialization of the Prism@’ membrane by Monsanto in the early 19808, gas separation using membranes has gained con- siderable attention in the chemical processing and refining industries [ 11. Membranes are in *Corresponding author. Tel.: (415)328-2228; Fax: (415)328-6580. use for the recovery of hydrogen from purge streams and for the production of nitrogen-en- riched air. Membranes have failed, however, to make any significant impact on other impor- tant gas separations, such as the production of oxygen from air or the separation of hydrogen from carbon dioxide-rich streams. The main obstacle is limited membrane selectivity; the selectivity of the best polymeric membranes for 0376-7388/94/$01.00 0 1994 Elsevier Science B.V. All rights reserved. SSDZ 0376-7388(94)00042-W