Journal of Membrane Science, Vol.450, 425-432, 2014
Highly stable bilayer MFI zeolite membranes for high temperature hydrogen separation
Stable inorganic membranes perm-selective to hydrogen will find applications in a number of important industrial processes including water gas shift reaction for hydrogen production. This paper reports a highly stable bilayer MR zeolite membrane with good hydrogen separation characteristics. The membrane consists of a thin (2 mu m) ZSM-5 layer on a thick (8 mu m) silicalite base layer supported on macroporous alpha-alumina with a yttria stabilized zirconia intermediate barrier layer. The zeolitic pores of the thin ZSM-5 layer were narrowed by catalytic cracking deposition (CCD). At 500 degrees C, the bilayer zeolite membrane exhibits H-2 permeance of about 1.2 x 10(-7) mol m(-2) s(-1) Pa-1, with H-2 to CO2, CO and H2O vapor selectivity respectively of about 23, 28 and 180. The membrane shows slightly improved separation properties (H-2 permeance, H-2/CO and H-2/CO2 selectivity) as the feed side pressure increases during the test of separation of industrial relevant simulated gas mixture (25% H-2: 25% CO: 25% H2O: 25% CO2, with 400 ppm H2S) at 500 degrees C for 24 days. Membrane reactor made of the bilayer zeolite membrane shows stable performance under water gas shift reaction conditions (500 degrees C, H2O/CO=3, GHSV= 60,000 h(-1), with a ceria doped iron oxide catalyst) in terms of CO conversion, H-2 recovery, and H-2 permeance and selectivity of the zeolite membrane. The unprecedented thermal and chemical stability and good separation properties of the bilayer zeolite membrane are related to its unique bilayer structure and synthesis methods. (C) 2013 Elsevier B.V. All rights reserved.
Keywords:Microporous membranes;Zeolite;Stability;Hydrogen separation;Long-term stability;Water gas shift