Synthesis and Low-Temperature Detemplation of High-Silica MFI Zeolite Membranes

Abstract

High-silica MFI zeolite membranes supported on porous α-alumina discs were prepared by a seeded secondary growth method, using tetrapropylammonium hydroxide (TPAOH) as organic template. First, nanocrystals were deposited on rough α-Al2O3 discs by a spin-on process. Then, based on controlling the H2O/ Si molar ratio of the synthetic solution, a restricting in-plane h0h-oriented growth method with an ultra-dilute precursor was designed to prepare non-defective zeolite membranes that were as thin as possible. Finally, crosslinked and dense MFI zeolite membranes were prepared after the third synthesis step, giving a membrane layer thickness of about 8 μm, including~5 μm dense layers and~3 μm intermediate layers. A novel, two-step method, coupling by low-temperature hydrocracking and oxidation, is proposed for efficient removal of the template from zeolite membranes. Compared with traditional high-temperature calcination, template removal by the two-step method could eliminate the grain boundary defects formed in response to stresses induced by heat treatment. As a result, the membranes treated by the two-step detemplation method displayed a preferable CO2/N2 separation factor (about 5.2) and high CO2 permeance (5.8 × 10-7 mol•m-2 •s-1 •Pa-1) at 30°C.