Template-free synthesis of MFI-type zeolite membranes: Permeation characteristics and thermal stability improvement of membrane structure

MFI-type zeolite membranes have shown promise for molecular sieving applications that require high chemical and thermal stability. In this work, MFI-type zeolite membranes were prepared by template-free seeded growth method in order to minimize defects and/or intercrystalline gaps that form during the calcination step required for template removal. Membranes were synthesized on two types of supporting materials, alumina and zirconia coated alumina. Synthesized membranes were characterized by molecular probing techniques including pervaporation of xylene isomers and TIPB as well as permeation of He and SF₆. It was found that in order to obtain a high quality MFI-type zeolite film, the initial seed layer is an important factor. The quality of silicalite seed layer could be controlled by dip coating times with silicalite suspension; it was found that ideal selectivity for p/o-xylene of up to 20 could be obtained. Results also indicated that a high quality MFI-type zeolite film could be formed on zirconia intermediate layer as well. MFI-type zeolite membranes with zirconia intermediate layer prepared by annealing method showed relatively large He permeance above 10^-7 mol m^-2 s^-1 Pa^-1 with selectivity of around 50 (He/SF₆) at 25 °C. These membranes showed high thermal stability at 500 °C, however, the stability was largely affected by heating/cooling rate of membrane.