离子热体系中基于磷酸铝分子筛纳米片构筑超薄小孔分子筛膜及其气体分离性能研究

Molecular sieve membranes have well-defined sub-nanometer scale pore structures，enabling precise sieving based on molecular scale and shape. However, the permeation flux of the molecular sieve membranes prepared at present is low, which can not meet the needs of practical application. Reducing the thickness of the molecular sieve membrane is an effective approach to improve its permeation flux. In this research project, we aim to develop a new strategy for the synthesis of ultra-thin small pore aluminophosphate molecular sieve membranes with high permeation flux and separation selectivity. First, two-dimensional aluminophosphate molecular sieve nanosheets with small micropores are directly prepared in an eutectic solvent by using amphiphilic dianionic ionic liquidsas structure directing agents. Then, ultra-thin aluminophosphate molecular sieve membranes are constructed by assembling the molecular sieve nanosheets on porous δ-alumina substrates with aluminophosphate gel layer by vacuum filtration, followed by gel-free secondary growth techniques in an ionic liquid. Moreover, separation performance of the prepared ultra-thin membranes in single-component and two-component gases such as H2、CO2、CH4、H2/CH4、CO2/H2、CO2/CH4 are texted. Based on the above results, the relationship between the structural parameters such as the topological structure and the thickness, and the separation performance of ultra-thin molecular sieve membranes will be established, which will provide a theoretic basis for the synthesis of target oriented ultra-thin aluminophosphate molecular sieve membranes. It is expected that this project will not only extend the synthesis of two-dimensional molecular sieves to aluminophosphate systems, but also promote the development of ultra-thin aluminophosphate molecular sieve membranes and their separation applications.

分子筛膜具有亚纳米尺度的规则孔道结构，可实现基于分子尺度和形状的精准筛分。然而，目前所制备的分子筛膜的渗透通量较低，不能满足实际应用需要，降低分子筛膜的厚度是提高其渗透通量的有效措施。本项目拟发展一种具有高渗透通量，高选择性的超薄小孔磷酸铝分子筛膜的合成策略：在低共熔溶剂中，以两亲性双阳离子型离子液体为结构导向剂来制备二维磷酸铝分子筛纳米片，采用真空过滤将其组装到具有活性磷酸铝凝胶层的δ-氧化铝基底上，再于离子液体中经无凝胶二次生长来构筑致密、无缺陷的超薄磷酸铝分子筛膜。测试其在H2、CO2、CH4、H2/CH4、CO2/H2、CO2/CH4等单、双组份气体分离性能。构建超薄分子筛膜的拓扑结构、厚度等结构参数与分离性能的关系，为合成目标导向的超薄磷酸铝分子筛膜提供理论依据。预期本项目的实施不仅可以将二维分子筛的合成拓展到磷酸铝体系，还能促进超薄分子筛膜及其应用的发展。

分子筛膜既具有分子筛规则的孔道结构和良好的稳定性，又具有膜连续分离的特点，在诸多领域具有重要的应用价值。本项目发展了多种针对纳米分子筛的合成策略，并制备了系列纳米分子筛晶种。合成了多种分子筛膜，并测试了其气体分离性能。主要研究成果如下：（1）在[Bmim]Br离子液体中添加TMAOH作为共同结构导向剂，在超短时间内（10min）合成了高结晶度的纳米LTA分子筛。以上述LTA分子筛为晶种，通过二次生长法制备了磷酸铝分子筛膜，其具有良好的气体分离性能；（2）在二乙胺盐酸盐和乙二醇组成的低共熔混合物中，通过添加1-甲基咪唑（1-MIm），在无需额外介孔模板剂/生长抑制剂的作用下，合成了片层SAPO-11分子筛；（3）在α-Al2O3载体表面涂覆一层活性γ-Al2O3，然后通过离子热合成法将γ-Al2O3膜转化为磷酸铝分子筛膜，以此方法成功合成出LTA、AFI和AFO型磷酸铝分子筛膜，其具有良好的气体分离性能；（4）以环氧丙烷参与的溶胶凝胶法制备了磷酸硅铝干凝胶，在四乙基氢氧化铵溶液中水热处理之后，转变为纳米低硅SAPO-34分子筛。上述研究工作为深入理解纳米分子筛的晶化机理，掌握分子筛膜的关键制备参数提供了理论指导意义。