自具微孔聚合物气体分离膜微孔结构及自由体积调控机制研究

Gas separation technology, such as H2 and CO2 separation can be widely used in energy and environmental field. Among the separation methods, membrane technology is extremely attractive for its energy efficiency, and simplicity and compact modular structure. The lack of membrane with both high gas permeance and high selectivity has limited the development of membrane based gas separation technology. Polymeric membrane has the advantage of flexibility, easy preparation and easy scale-up. However, it is suffered from the "Robenson Upper bond". Rubber material has high gas permeability and low selectivity, while the glassy polymer possesses high selectivity but low permeability. Inorganic materials, such as zeolite and metal organic framework, have both high gas permeability and high selectivity. However, the inorganic membrane is suffered from brittleness, the difficulty in thin film membrane preparation and scale-up. Polymer with intrinsic microporosity (PIM) has the similar pore structure with zeolite and high free volume. PIM membrane shows very high gas permeance and relative high selectivity, which is a very promising membrane material for gas separation. . This project will focus on the design and preparation of PIM materials for gas separation. The effects of micropore structure and free volume on the PIM membrane gas permselectivity will be investigated. . Firstly，we will study on how to prepare PIM material containing crown ether cavity. Amino group substituted crown ether will prepared. And the polyimide PIM will be synthesized by the condensation polymerization of amino group substituted crown ether and anhydride. The crown ether has a cavity size of 2-6 Å, which is similar to the gases. Therefore, small gas can permeate through the cavity of crown ether. Therefore, the PIM membrane contain crown ether can have high selectivity.. Secondly, the effects of material monomers on the micropore size and distribution will be investigated. Different size crown ether and different length anhydride will be applied for the synthesis of PIM. The micropore size and the distribution will be characterized by the Positron Lifetime Spectrum.. Thirdly, the effects of material monomers on the free volume will be investigated. The anhydride with different substituted group and different three-dimensional structure will investigated.. Finally, the PIM membrane material structure will be obtained by the comprehensive optimization of the micropore size and distribution as well as the free volume. And the PIM membrane with both high gas permeance and high selectivity will be prepared for gas separation.. The theory on how to control and adjusting the micropore size and distribution as well as the free volume will be formed based on the research in this project. And the technology for preparing the PIM membrane with crown ether micropore will be formed.

围绕用于气体分离的自具微孔聚合物（PIM）膜材料设计与开发，采用DFT理论模拟、PIM材料合成及PIM材料微孔结构表征结合的理论和策略，对PIM材料设计中的微孔尺寸及其分布控制、自由体积调控两个影响PIM膜材料渗透选择性的关键因素进行深入探讨。首先，通过将环状冠醚分子经化学改性引入PIM材料，在PIM材料内部构建具有特定尺寸的环状微孔来提高膜的选择性。其次，深入研究所制PIM材料微孔尺寸及其分布与单体结构的关系以及对PIM膜选择性的影响；同时，深入研究PIM材料自由体积与单体结构的关系以及对PIM膜渗透性的影响。最后，在上述研究基础上通过调控PIM膜材料分子结构优化PIM膜材料的微孔尺寸及分布、自由体积等参数，提高膜材料的气体渗透选择性。. 通过对上述问题的深入研究，形成具有高渗透选择性PIM膜材料的设计理论和制备技术，为促进气体膜分离技术在能源与环境领域的应用做出贡献。

自具微孔聚合物气体分离膜材料具有高自由体积，高气体渗透系数的优点，成为近几年研究的热点。但由于这类材料存在微孔尺寸难以精确控制，所制膜选择性较低、材料物理性能较差等缺点，限制了其工业应用。本项目基于冠醚环状分子微孔于CO2气体分子的匹配性，通过化学改性，在聚酰亚胺分子结构中引入环状冠醚，通过冠醚的微孔结构，精确调控所制膜的微孔尺寸，强化其对CO2/N2和CO2/CH4选择性。通过研究探明了含环状冠醚微孔聚酰亚胺类PIM膜材料分子主链中构建环状微孔的方法；制备出含有环状冠醚微孔结构的聚酰亚胺类PIM材料。所制的含冠醚结构的聚酰亚胺膜材料具有非常高的CO2/N2和CO2/CH4选择性；所制膜的CO2/N2选择性可达80-95；CO2/CH4选择性可达120；远高于文献报道的聚酰亚胺膜材料。探明了微孔结构分布及调控方法。本研究通过正电子湮没技术及MS分子模拟相结合，探明了材料内部自由体积分数及微孔半径；通过不同单体的匹配，调控膜内自由体己分数及微孔尺寸。在上述研究基础上，形成微孔尺寸及其孔径分布调节、自由体积调控方法，制备出具有特定微孔尺寸、窄孔径分布、高自由体积的含环状冠醚微孔结构PIM气体分离膜材料。通过结构优化，所制膜的CO2渗透系数提高90%；同时CO2/N2和CO2/CH4选择性保持基本不变。研究了引入金属有机骨架（MOFs）和多孔有机骨架（POFs）纳米粒子制备混合基质膜，强化CO2分离并提高膜的稳定性。通过MOF纳米粒子表面改性，提高MOF材料与PI聚合物基质之间的相容性，减少团聚，进而掺杂可以同时提高膜材料的CO2渗透系数及CO2/惰性气体选择性；利用聚酰亚胺膜材料的侧边基团可以穿插到多孔有机骨架材料的孔中的特性，保持聚酰亚胺膜材料结构稳定，从而提高膜在长时间使用过程中的稳定性。. 本研究合成的膜材料表现出优异的气体分离性能，对CO2/CH4混合气的分离性能均超过了2008年Robeson上限。这说明，含冠醚结构的共聚聚酰亚胺类自具微孔聚合物膜材料在气体分离领域具有巨大的应用潜力，对此类膜材料的研究与开发可有效促进气体膜分离过程的工业化进程。