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 MFI zeolite membrane with good hydrogen separation characteristics. The membrane consists of a thin (2μm) ZSM-5 layer on a thick (8μm) silicalite base layer supported on macroporous α-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°C, the bilayer zeolite membrane exhibits H₂ permeance of about 1.2×10^-7molm^-2s^-1Pa^-1, with H₂ to CO₂, CO and H₂O vapor selectivity respectively of about 23, 28 and 180. The membrane shows slightly improved separation properties (H₂ permeance, H₂/CO and H₂/CO₂ selectivity) as the feed side pressure increases during the test of separation of industrial relevant simulated gas mixture (25% H₂: 25% CO: 25% H₂O: 25% CO₂, with 400ppm H₂S) at 500°C for 24 days. Membrane reactor made of the bilayer zeolite membrane shows stable performance under water gas shift reaction conditions (500°C, H₂O/CO=3, GHSV=60,000h^-1, with a ceria doped iron oxide catalyst) in terms of CO conversion, H₂ recovery, and H₂ 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.