“质子-离子化”pH响应提锂冠醚衍生物分子设计及其应用

The recovery of lithium from salt lake brine which is a multi-salt coexistence system with high ionic strength continues to be a challenge. The traditional extraction technology for lithium recovery still have problems including large consumption of synergist and acid with high concentration. This project will design and synthesize one kind of pH-response crown ether molecule which can complex and release lithium under the control of pH without any other synergists. This molecule combines the pH-response properties of “proton-ionizable” functional groups and selectivity of 14-crown 4-ether for lithium ion. The theoretical calculations will be conducted to reveal the switch mechanism of “proton-ionizable” by pH stimulation and the interaction between extractant molecule and lithium ion, which can guide the design and synthesis of pH-response crown ether molecule for lithium extraction. The controllability by pH and cyclicity of “complexation-dissociation” of extractant for lithium will be investigated by spectrum technology, which help to build a relationship between molecular structure and complexation properties of lithium. The coordination way and geometrical configuration of extractant-lithium coordination compound will be studied by combination of the structure analysis of coordination crystal and quantum chemistry calculation. The interface migration and transformation of lithium ion in the process of liquid membrane extraction will be also involved to reveal the lithium extraction mechanism with the control of pH. This project will try to design and synthesize new type of molecules for lithium extraction, and the process of lithium extraction will be pH-controllable, which can provide reference for the extraction of other metal ions.

针对高离子强度多离子共存盐湖卤水体系中微量锂离子分离富集难度大，传统萃取提锂过程中协萃剂和高浓酸用量大的问题，本项目拟结合“质子-离子化”基团对pH的响应性和14-冠4-醚对锂离子的选择性，构筑pH响应型冠醚提锂分子，通过pH调控分子的“质子-离子化”性能实现单一萃取剂分子对锂离子的精准捕获和释放。采用理论计算研究该冠醚分子“质子-离子化”结构对pH的响应性转变规律，以及与锂离子的相互作用，指导pH响应型冠醚提锂分子的设计。采用光谱技术，研究提锂分子对锂离子“络合-解离”的pH可控性和循环性，建立分子结构与提锂性能之间的构效关系。通过分析提锂分子与锂离子络合物单晶的晶体结构，结合量化计算，研究锂离子的配位方式和配位体的空间几何构型。研究液膜萃取中锂离子的界面迁移转化规律，揭示pH可控提锂机理。本项目尝试设计合成新型提锂分子，实现提锂过程的pH可控化和绿色化，可为其他金属离子的提取提供借鉴。

我国锂资源主要蕴藏于盐湖卤水中，具有锂离子浓度低、离子强度高、多离子共存、镁锂比高等特点，锂的分离富集难度大，传统萃取提锂过程中协萃剂和高浓酸用量大。针对以上问题，本项目分别设计合成了具有pH响应性的硝基苯酚-冠醚和系列磷酸二丁酯离子液体类提锂分子，并对其pH响应性、循环稳定性及选择性提锂性能进行了研究，同时优化了提锂过程及操作条件。研究表明，硝基苯酚-冠醚的pH响应性是基于酚羟基基团的“质子-离子化”性质，而磷酸二丁酯离子液体分子的pH响应性是由于分子的亲疏水性随酸碱发生互变。进一步，通过一步相转化法将硝基苯酚-冠醚分子与聚偏二氟乙烯（PVDF）共混，制备了具有pH特性的多孔聚合物复合膜，以减少提锂分子的溶损，提高提锂分子与卤水锂离子的有效接触面积。为了进一步强化锂离子的跨膜传质效率，设计搭建了相应的电驱动提锂配套装置，考察了提锂分子掺量、PVDF膜厚度、外加电场直流电压、模拟卤水元素配比等因素的影响规律，实现盐湖镁锂高效分离。项目实施过程中，发表文章5篇（SCI 2篇，EI 2篇），申报发明专利2项，授权1项，培养毕业硕士生2人，在读硕士生3人。