High-performance MFI zeolite hollow fiber membranes synthesized by double-layer seeding with variable temperature secondary growth

Hydrophobic MFI zeolite membranes are perm-selective to organic compounds over water and offer applications for organic/water separations. However, reproducible synthesis of MFI zeolite membranes with high organic selectivity remains a challenge. This paper reports a new synthesis method consisting of dual-layer seeding and varying-temperature secondary growth for the synthesis of hydrophobic MFI zeolite membranes on alumina hollow fiber supports. The effects of seeding method, seed particle size, seed size ratio, and variable temperature/time profile on the microstructure, hydrophobicity and gas perm-selectivity of the membranes are investigated leading to the identification of optimum seed structure and secondary growth conditions for synthesis of MFI zeolite membranes with high ethanol/water separation performance. The high-performance MFI zeolite membrane has a microstructure consisting of a thin, fully inter-grown, and dense top zeolite layer responsible for high selectivity, and a porous low inter-grown bottom zeolite layer minimizing resistance and retarding aluminum transfer from the support to zeolite. The best hollow fiber supported MFI zeolite membrane with a Si/Al ratio of 187 exhibits ethanol/water pervaporation separation factor of 160 with a total flux of 3 kg m⁻² h⁻¹.