Synthesis and characterization of zeolite (MFI) membranes on porous ceramic supports

TLDR

ZSM‑5 (MFI) polycrystalline films have been grown on porous ceramic supports, providing a platform for membrane development. Hydrothermal synthesis on the ceramic support induces aluminium leaching, forming large analcime crystals, and the resulting MFI composite was subjected to gas‑permeation tests to evaluate its separation potential. The films remain thermomechanically stable after calcination, yet observed permeation rates are low and selectivities are diminished by sorption effects and the support’s low porosity, reducing the molecular‑sieving capability.

Abstract

Continuous polycrystalline films of ZSM-5 (MFI-type) crystals have been grown on porous ceramic (clay) supports. The films are thermomechanically stable upon calcination at 400 °C in air to remove template ions (tetrapropylammonium), during which process the porous support seems to have a stabilizing effect. When the hydrothermal conditions induce substantial aluminium leaching from the support, large analcime crystals are grown on the support. Gas permeation experiments with both pure gases (permanent gases, alkanes and difluorodichloromethane) and mixtures thereof have been performed on the MFI composite to investigate the separation potential of this new type of membrane. Expected selectivities as a result of large differences in diffusivity are found to be strongly reduced by differences in sorption of the same order of magnitude, and the reduced mobility of weakly adsorbing (fast moving) molecules caused by the slower moving species. However, from the observed low permeation rates it is expected that, owing to the presence of a porous support with relatively low porosity, the molecular sieving effect is reduced as well.