Surface-gel-conversion synthesis of submicron-thick MFI zeolite membranes to expedite shape-selective separation of hexane isomers

表面胶转化法合成亚微米厚度MFI型分子筛薄膜应用于快速择形分离己烷异构体

Ultrathin zeolite membranes are of paramount importance in accelerating gas transport during membrane separation,and lowering down their membrane thicknesses to submicron scale is deemed to be very challenging.Herein,we develop an advanced approach of surface gel conversion for synthesis of submicron-thick pure silica MFI(silicalite-1)zeolite membranes.Viscous gel is prepared by finely adjusting the precursor composition,enabling its reduced wettability.The unfavorable wetting of the support surface can effectively prevent gel penetration into alumina support voids.Aided by the seeds,the surface gel is directly and fully crystallized into an MFI zeolite membrane with minimal water steam.A membrane with a thickness of 500 nm is successfully acquired and it is free of visible cracks.Additionally,the as-synthesized membranes exhibit rapid and selective separation of hexane isomers by virtue of unprecedentedly high n-hexane permeance of 24.5×10^−7 mol m^−2 s^−1 Pa^−1 and impressive separation factors of 13.3-22.6 for n-hexane over its isomers.This developed approach is of practical interest for sustainable synthesis of high-quality zeolite membranes.

在膜分离中,薄膜超薄化对促进气体传输至关重要,而将膜厚降至亚微米级则极具挑战性.本文中,我们提出表面胶转化法来合成亚微米厚度的纯硅MFI分子筛膜.通过精细调控前驱体化学组成制备了低浸润性的黏性胶,有效防止凝胶从氧化铝载体表面渗透至空隙中.在晶种的诱导下,辅以少量水蒸气,表面凝胶经历了直接和完全晶化过程,形成了厚度为~500 nm并且连续致密的MFI分子筛膜.合成的分子筛膜展示出对正己烷同分异构体的快速选择性分离性能:超高的正己烷渗透量(24.5×10^-7mol m^-2s^-1Pa^-1);以及可观的分离系数(13.3–22.6,正己烷对其同分异构体).此外,该方法还是一种绿色合成方法,为可持续性制备高质量分子筛膜奠定了科学基础.