6Li/7Li分离的多配体功能化离子液体的结构设计及性能调控

Separation of 6Li/7Li is a major strategic needs of national defense for our country, which is also a worldwide challenge. Because of the low 6Li/7Li separation coefficient of current chemical separation methods and solvent pollution issues, a new way based on the multi-ligand functionalized ionic liquids (MLILs) to the separation of 6Li/7Li is put forward for the designable ablilities of ILs and their excellent characteristics as a separation medium. The separation of 6Li/7Li can be achieved through the different interaction energy between 6Li/7Li and the ligands incorporated in the MLILs, as well as the coupling effect of electrostatic force etc. in the ILs. Quantum chemistry calculation, experimental study and molecular simulation will be used. Through the study of the interaction between 6Li/7Li and MLILs, the roles of the ligands and electrostatic force of the MLILs on the 6Li/7Li can be understood from an electron and molecular level, which provide the guidance for the design of MLILs. The structure-activity relationship of MLILs and 6Li/7Li separation effect will be set up through the liquid-liquid extraction by taking the separation coefficient of 6Li/7Li as a evaluation index. The separation mechanism of 6Li/7Li can be interpreted according to the study of the structure of extraction interface, migration and exchange behavior of 6Li/7Li. Based on above results, the way of how to optimize the structures of MLILs and tuning of the extraction interface will be obtained. A highly efficient and environmental friendly method for 6Li/7Li separation can be constructed finally. This project provides a new idea to the separation and extraction of lithium isotopes, and also provides a theoretical guidance for the interpretation of lithium isotope separation effect from the micro level.

锂6（6Li）、锂7（7Li）同位素分离是我国国防重大战略需求，是国际性难题。本项目针对化学法锂同位素分离系数低、环境污染的问题，鉴于离子液体作为分离介质的优良特性和结构的可设计性，拟采用多配体功能化离子液体（MLILs），利用6Li/7Li和MLILs包含的官能团/配体相互作用的强弱以及离子液体静电力等作用能协同耦合分离锂同位素。采用计算、实验和模拟相结合，通过对6Li/7Li和MLILs相互作用的研究，从电子、分子水平认识MLILs的配体以及静电力等和6Li/7Li的作用机制，指导MLILs的分子结构设计；以6Li/7Li的分离系数为考核指标，建立不同锂盐体系下离子液体和锂同位素分离效应的构效关系；通过对萃取界面结构以及6Li/7Li迁移、交换行为的研究，揭示MLILs对锂同位素的萃取分离机制。在此基础上，获得对离子液体结构优化和萃取界面调控的方法，最终建立高效的锂同位素绿色分离体系。

随着人口增长和经济的高速发展，能源短缺和生态环境问题日益凸显，核能等新能源开发利用日趋重要。锂作为重要的核能源材料，有6Li、7Li两种同位素，它们具有截然不同的核反应性能，锂同位素的分离是核能开发必须解决的关键技术。冠醚螯合体系是目前研究和报道最多的分离体系，其对6Li/7Li的分离效应显著，在一定条件下，可以和汞齐法相媲美，然而冠醚中性配体和Li+的结合能比较差，Li分配系数比较低，不利于6Li/7Li的多级分离和富集，如何获得较高6Li/7Li分离因子的同时提高Li分配系数是关键。针对冠醚和Li+结合性能差以及化学交换法分离同位素影响机制不清晰的问题，提出了离子对强化Li+相转移的策略，并采用Urey模型和量化计算，揭示了冠醚分离锂同位素的影响机制。具体如下：（1）将对6Li/7Li分离效应显著的12-冠-4醚功能化至咪唑基离子液体上，利用冠醚和Li+的离子-偶极作用以及离子液体咪唑环C-H的氢键作用协同提锂，和单体冠醚相比，相同条件下冠醚功能化离子液体可提高Li分配系数。（2）在冠醚分离锂同位素的过程中，引入路易斯酸FeCl3为阴离子的识别位点，冠醚作为Li+的识别位点，构建了离子对接收体促进了Li+的高效相转移，和单纯冠醚提锂相比，Li分配系数提高了3-4个数量级；和单纯的LiCl-H2O盐体系相比，B15C5对6Li/7Li分离因子提高了1.03。（3）对于溶剂萃取体系，6Li/7Li分离主要取决于Li在两相配合物的结构，冠醚屏蔽与 Li+水合的水分子能力越强，同位素分离因子越高；由于溶剂效应产生正负电荷分散和电荷离域引起了Li+配位和静电环境的改变，进而削弱Li-O键和阴阳离子间的静电作用有助于锂同位素分离。以上工作可推动冠醚用于6Li/7Li分离的工业化应用，也为更加高效的锂同位素分离交换体系的设计提供指导，也可为其他离子型同位素的分离提供借鉴。