Synthesis and modification of ZSM-5/silicalite bilayer membrane with improved hydrogen separation performance

MFI type zeolite membrane offers good stable and high hydrogen separation performance, making it attractive for application in membrane reactors for water gas shift (WGS) reaction for hydrogen production. The hydrogen permselectivity of MFI zeolite membranes can be improved by intracrystalline pore modification. However, more than one order of magnitude reduction in H2 permeance usually accompanies with the significant improvement in H2/CO2 separation factor of MFI zeolite membranes modified by catalytic cracking deposition (CCD) of methyldiethoxysilane. In this work, a thin, high quality ZSM-5 top layer was synthesized on a thick silicalite bottom layer to form a ZSM-5/silicalite bilayer membrane. The ZSM-5/silicalite bilayer zeolite membrane was supported on a porous α-alumina support coated with an yttria stabilized zirconia (YSZ) intermediate barrier layer for membrane stability improvement. The CCD modification of the bilayer zeolite membrane resulted in an improvement of H2/CO2 separation factor of the membrane by over five-fold from 4.95 to 25.3 with only about 31% reduction in H2 permeance from 1.85 × 10−7 to 1.28 × 10−7 mol m−2 s Pa at 450 °C. The significant improvement in H2/CO2 separation factor with only moderate reduction in H2 permeance of the modified ZSM-5/silicalite bilayer membrane is due to controlled CCD modification in the thin, high quality ZSM-5 top layer instead of the entire zeolite membrane thickness. Because of the high H2/CO2 separation performance, considerable H2 permeance and good hydrothermal stability under H2S containing gas, the modified ZSM-5/silicalite bilayer membrane is very promising to be used as a membrane reactor for WGS reaction for hydrogen production.