Permeation and Separation Characteristics of Mfi Type Zeolite Membranes on Zirconia Intermediate Layer by Template-free Secondary Growth Method

MFI type zeolite membranes were synthesized on two types of supporting materials, alumina (α-alumina) and yttria-stabilized zirconia (YSZ) coated alumina. Membranes were prepared by template-free secondary growth method with multiple growth steps in order to minimize intercrystalline gaps. Gas permeation characteristics, thermal and hydrothermal stability for MFI type zeolite membranes were examined. It was found that MFI type zeolite membranes without YSZ intermediate layer showed relatively large H2 and He permeance above 10 mol⋅m⋅s⋅Pa with selectivity of around 95 (H2/SF6) at 25C. After repeated secondary growth (180C, 8 h), the temperature dependency of H2, He and CO showed little change (Knudsen type diffusion) but the behavior of CO2 was dramatically different. XRD results for MFI type zeolite membranes before and after heat treatment indicated that YSZ intermediate layer was quite effective in preventing the aluminum diffusion from alumina support to zeolite layer at high temperatures (500C). A MFI type zeolite membrane with YSZ intermediate layer showed high stability in steam at high temperature (500C, partial pressure of steam: 100 kPa).