采用旋涂法在粗糙的α-Al2O3载体片上制备出较完备的分子筛晶种层;以四丙基氢氧化铵(TPAOH)为有机模板剂,通过调控合成液的H2O/Si摩尔比,实现了对分子筛晶体面内优先生长的调控;经过三次水热合成得到致密交联的hOh-轴取向高硅MFI分子筛膜,膜厚约为8μm(包括~5μm致密层和~3μm过渡层)。采用先低温加氢裂解后低温空气氧化的两步法脱除工艺,有效脱除了分子筛膜内的有机模板剂。相比于传统高温煅烧法,该法可以避免分子筛膜因脱除模板剂而形成的较大晶间缺陷。因而采用低温两步法脱除模板剂的分子筛膜片在30℃时具有较好的CO2分离效果,其CO2/N2分离因子达到5.2,CO2渗透通量高达5.8×10^-7mol·m·-2·s·-1·Pa·-1。
High-silica MFI zeolite membranes supported on porous a-alumina discs were prepared by a seeded secondary growth method,using tetrapropylammonium hydroxide(TPAOH) as organic template.First,nanocrystals were deposited on rough α-AI2O3 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 ℃.