离子液体非水溶致液晶的构建及萃取分离性能研究

The development of environmentally benign and energy-efficient separation method for the hydrogen-bond (H-bond) donor molecules is vitally important for the production of clean energies and high-purity chemicals. Recently, considerable attention has been paid to ionic liquid (IL)-mediated extractive separation methods because of its reduced environmental impact. It has been widely used in the separation of H-bond donor molecules, such as desulfurization, denitrification, and deacidification of fuel oils and enrichment of biomolecules from edible oils and biodiesels. IL-based extraction processes generally demonstrate enhanced molecular recognition ability and selectivity compared with traditional organic solvent-based processes because of the relatively strong H-bond basicity of the anion of ILs. However, one of key drawback for IL-mediated extraction processes is the relatively low extraction capacity for organic molecules due to the intrinsically strong polarity of ILs resulting from its charged structures, which seriously limits its application. Therefore, there is a great need to design new industrial attractive IL-based extractants with high capacity for H-bond donor solutes. In this proposal, we plan to prepare a class of IL-based non-aqueous lyotropic liquid crystals (LLCs) and use it as novel extranctant for the separation of H-bond donor molecules. It is expected that the IL-based non-aqueous LLCs with self-assembled anisotropic nanostructures will overcome the strong isotropic polarity of common ILs and significantly enhance the molecular recognition ability for H-bond donor solutes, then bring out an high extraction capacity and excellent separation selectivity. The forming mechanism of IL-based non-aqueous LLCs and their nanostructure and physicochemical properties will be investigated by polarized optical microscopy (POM), small angle X-ray scattering (SAXS) and solvatochromic method in this project. The extraction performance of IL-based non-aqueous LLC will be evaluated through measuring the distribution coefficients and selectivity of various H-bond solutes in LLC-based biphasic system.

弱酸性复杂有机分子是一类重要化学品，其高效分离不仅是相关高纯化学品制备的必需途径，也是清洁能源生产和物质转化等过程的重要环节。离子液体是新型弱酸性物质萃取分离介质，其阴离子所固有的负电性使离子液体可通过氢键识别弱酸性基团，分离选择性高。但由于离子液体强静电的本质特征，存在极性强、对有机物亲和性差、萃取容量小等不足，限制其应用。本申请拟向离子液体结构中引入有序自主装结构，设计具有强氢键碱性界面、纳米疏水区域的离子液体非水溶致液晶（Lyotropic liquid crystal, LLC）萃取剂，通过氢键与疏水作用的协同增强对有机分子的亲和能力，克服均相离子液体存在的选择性和容量难以兼顾的不足。为此，拟研究离子液体非水LLC的形成机理、微观结构和物化性质，考察其对弱酸性溶质的萃取分离性能，探讨LLC结构与分离性能之间的关系。课题组在离子液体合成及应用方向已有一定研究基础，已获初步研究成果。

液-液萃取是十分重要的化工分离过程，离子液体因其独特的理化性质而被广泛应用于液-液萃取过程。针对均相离子液体存在的选择性和容量难以兼顾的问题，本项目成功向离子液体结构中引入了有序自主装结构，设计具有强氢键碱性界面、纳米疏水区域的离子液体非水溶致液晶萃取剂。本研究结论有助于发展离子液体萃取新方法，促进离子液体在分离过程中的应用。.本项目基本按计划进行，取得的主要进展有：（1）1. 合成了兼具长碳链和亲水头部的双亲性离子液体，以极性溶剂为连续相，设计及构建了一系列长链羧酸离子液体非水溶致液晶新型萃取剂，采用溶剂渗透扫描法考察了离子液体在非水溶剂中溶致液晶的形成情况及各种影响因素。（2）考察了该类萃取剂对天然活性同系物以及多种脂溶性酸性物质的萃取分离性能。该类萃取剂对生育酚不同的同系物具有较强的识别能力，萃取容量极高，并对油酸/三油酸甘油酯、环烷酸/辛烷体系表现出较高的分配系数和萃取容量，同时对酚类分子具有很强的亲和性，表现出优于传统溶剂的萃取分离性能。（3）采用溶剂化显色法、IR、XRD和POM等手段对萃取机理进行探索，该体系高效萃取能力来源于萃取剂增强的氢键碱性，以及非水溶致液晶结构提供的纳米尺度上数量丰富的碱性微表面和非极性微区域，从而实现被萃取物质的选择性高分配。通过加入其他溶剂破坏非水溶致液晶聚集结构，可以将离子液体与被萃取分子进行分离，实现离子液体的循环再生。（4）在Green Chem.、ACS Sustain. Chem. Eng.、Chem. Eur. J.、Chem. Comm.、Chem. Eng. J等期刊发表标注资助的SCI收录论文22篇，其中影响因子3.0以上的17篇；在项目实施期间，“天然活性同系物的分子辨识分离新技术及应用”获国家发明进步二等奖（2018，第二完成人）。