溶胀聚离子液体的构筑及其催化酯交换反应性能研究

Poly(ionic liquid)s (PILs) have received increasing attention due to their solid feature to solve the problems of separation and recycle of homogeneous ionic liquid catalysts. In this project, a novel kind of PILs with swelling ability in methanol and ethylene carbonate was developed and applied as catalysts for the transesterification reaction of methanol and ethylene carbonate to prepare dimethyl carbonate. The swelling ability and catalytic efficiency of PILs can be modified by variation of the substituents on imidazolium and the nucleophilicity of the anion. And the selective enrichment of methanol in mixed substrates could be controlled by introducing functional groups such as hydroxyl and amino. The selective enrichment of methanol may provide an opportunity to prepare dimethyl carbonate with a low methanol/ethylene carbonate molar ratio. The micro-structures and morphologies of PILs after swelling in methanol and ethylene carbonate will be characterized by SEM, Cryo-SEM, etc. And the interactions between substrates and PIL catalysts will be investigated by in-situ NMR, FT-IR and DFT calculations. Based on these investigations, we will propose the activation model and reaction mechanism catalyzed by the swelling PILs. The successful implementation of the project will have an important influence on revealing the swelling rules of PILs and improving the catalytic activity of heterogeneous catalysts. The swelling PILs may provide a novel catalytic system for high efficient and low cost production of dimethyl carbonate.

聚离子液体可以解决均相离子液体催化剂的分离回收问题，使其成为离子液体研究领域的热点之一。项目利用聚离子液体结构的可设计性，研制在甲醇、碳酸乙烯酯等溶剂中溶胀的聚离子液体，考察其催化碳酸乙烯酯和甲醇酯交换反应制备碳酸二甲酯的性能。通过调变聚离子液体咪唑鎓取代基的种类和阴离子的亲核性，改善聚离子液体的溶胀性能和催化活性；通过嫁接羟基和氨基等功能基团调变聚离子液体在不同底物中的溶胀度，筛选出选择性富集甲醇的聚离子液体催化剂，实现在低醇酯比下高效制备碳酸二甲酯。利用SEM、Cryo-SEM等表征聚离子液体催化剂溶胀状态下的形貌和微观结构；利用原位NMR、FT-IR和理论计算等表征和模拟甲醇、碳酸乙烯酯等反应底物与催化剂的相互作用，推测催化剂对底物的活化模型，提出溶胀聚离子液体催化反应机理。项目的顺利实施对揭示聚离子液体溶胀性的规律，提高多相催化剂的活性以及高效、低能耗地制备碳酸二甲酯具有重要意义。

碳酸二甲酯是一种环保性能优异、用途广泛的化工原料。碳酸乙烯酯与甲醇酯交换法合成碳酸二甲酯，具有反应条件温和并能联产乙二醇的优势。离子液体作为稳定性好、溶解度高、结构可调的绿色催化剂被广泛用于催化该反应，但均相的离子液体存在催化剂难以回收的问题。因此，发展多相的离子液体催化剂仍具有重要的意义。. 项目围绕溶胀聚离子液体催化剂的构筑及其催化碳酸乙烯酯和甲醇酯交换等反应开展工作。通过自由基聚合合成了含脂肪酸根、含芳香酸根、含脲功能化溶胀聚离子液体以及酸性溶胀聚离子液体。利用固体核磁共振、傅里叶变换红外光谱、X射线光电子能谱、热重分析对上述聚离子液体的结构进行了表征。通过扫描电子显微镜、冷冻扫描电子显微镜对聚离子液体溶胀前后的微观形貌进行了观察。系统研究了聚离子液体结构与溶胀/富集性能的关系，通过改变咪唑环上取代基的亲疏水性、交联剂的种类与含量，来调控所合成聚离子液体的溶胀与富集性能。为了探索聚离子液体在常用有机溶剂中的溶胀规律，我们提出摩尔溶胀度新概念，发现聚离子液体在不同溶剂中的摩尔溶胀度与溶剂的Hansen溶度参数呈线性相关。溶胀性能可以有效促进反应底物与催化剂活性位点的接触，从而显著提高聚离子液体的催化活性。溶胀聚离子液体的富集性能提使得反应物在聚离子液体内部的浓度提高，促进了反应的进行。所合成的溶胀聚离子液体可高效催化碳酸乙烯酯和甲醇酯交换、碳酸乙烯酯水解、乙酸环己酯水解、甲酸与环己烯加成等反应。通过核磁共振波谱技术，采用核磁滴定的方法，研究了聚离子液体与反应底物、溶剂分子之间的相互作用，提出了可能的反应的机理。项目的研究成果对揭示溶胀聚离子液体结构与溶胀/富集性能的关系、探索聚离子液体溶胀度与溶剂参数之间的规律具有重要意义，将为促进碳酸乙烯酯和甲醇的酯交换反应研究以及高效、低能耗地制备碳酸二甲酯、乙二醇提供新思路。