Preparation of zeolite MFI membranes on defective macroporous alumina supports by a novel wetting–rubbing seeding method: Role of wetting agent

High quality zeolite MFI membranes are successfully synthesized on inexpensive defective macroporous alumina tubes by the seeded growth method. A novel seeding method of wetting assisted rubbing (wetting–rubbing, WR) technique is developed and with this new WR method alumina supports are first wetted with a liquid agent followed by rubbing dry MFI seed crystals. Effects of two typical wetting agents, i.e., alcohol solvents (n-butanol) and water on the seed layer formation and membrane performance are investigated. Experimental data suggest that n-butanol is much more effective than water for preparation of a uniform and continuous MFI seed layer on the defective alumina support, which is attributed to the hydrophobic nature of MFI crystals and their better dispersion in alcohols. The zeolite membranes synthesized at 175 °C for 4 h on the well-seeded supports have a separation layer thickness of ∼3.5 μm, and exhibit a high pervaporation performance with the ethanol/water separation factor of 62 and permeation flux of 1.82 kg m−2 h−1 for the 5:95 (wt%) ethanol/water mixture separation at 60 °C. The WR seeding method may lead to reproducible preparation of zeolite membranes on defective low-cost supports.