电渗析/反电渗析无电极集成系统的设计构建及自脱盐机制研究

Fresh water supply is the most important issue for the residents living in remote islands, and it's mainly relies on groundwater. However, the groundwater is easily influenced by saltwater intrusion. Conventional desalination technology requires a large scale plant and stable power input, which is difficult for many small islands to achieve. There is an urgent need for a compact and low power consumption desalination system to obtain effective supply of fresh water. This project designs and ultimately achieves a novel desalination system based on thermodynamic theory. We establish a new mechanism of the desalination and resolve the problem of thermodynamic driving force of this energy self-sufficiency system. The two electrochemical membrane processes of electrodialysis and reverse electrodialysis are integrated in a unit. Reverse electrodialysis collects salinity energy in the form of the ion current during the spontaneous diffusion process of high concentration seawater to the low concentration salt water. The collected energy is directly applied to drive the electrodialysis process and the desalination process of brackish water is completed. The innovation of this project is from the thermodynamic theory level to design and ultimately achieve an energy self-satisfied desalination system with no transformation between the ion current and electron currents. Through the optimization of ion channel and connector between the membrane stack, it is expected to completely eliminate the external circuit components, and for the first time achieve ionized current path. Therefore the system complexity is greatly reduced and the loss of energy conversion is avoided. At the same time, the whole process only need to consume sea water and brackish water, and with no brine and chemical emissions issue. The design and implementation of the system provide a new way for fresh water supply on island and personal outdoor emergency, and it has a good prospect of commercial application.

淡水供给是偏远海岛居民最关心的问题，作为其主要来源的地下水易受到咸潮入侵的影响，不确定性很大。常规脱盐方法依赖大的规模和稳定的电能输入，微小海岛难以实现，人们迫切需要一种小巧而低耗能的脱盐系统。本课题创新地从热力学理论层面设计并最终实现一种“以盐来脱盐”的能量自给系统，建立全新的脱盐机制，解决自脱盐系统的热力学驱动力问题，探索过程中离子迁移传输的规律。系统中反电渗析和电渗析两过程集成于一体，前者以离子电流的形式收集浓差能，在膜堆内直接驱动离子迁移完成脱盐，得到淡水。课题有望首次实现完全离子化通路的无电极体系，跳脱出不同电流形式相转化的制约，彻底消除法拉第电解反应带来的能量损失，最大程度简化系统，提高效率。全过程仅消耗海水及咸水，不涉及化学品和浓度高于海水的浓盐水排放，无生态压力。本课题可为海岛居民或驻守人员以及内陆苦咸水地区人民的淡水获取提供一种可行的新思路，兼具科学意义和应用前景。

本项目的研究围绕电化学膜过程展开，主要包括电渗析/反电渗析自脱盐集成系统的研发，特种电渗析海水淡化系统的设计搭建以及混合盐溶液中特定离子的选择性去除等。因此，除了较好地完成了原定计划中的自脱盐系统的研究之外，通过类似地在溶液环境下对离子选择性跨膜的操控，实现多种其他重要的应用场景。.（1）反电渗析/电渗析自脱盐集成系统的研发。关于自脱盐系统中反电渗析(RED)子过程的功率输出特性的系统研究，经过不断地优化和改进，在优化流速1.20cm/s时，通过调控电流密度，膜堆给出的最大功率密度可达到1.302w/m2。而且成功构建出完全无电极体系，实现了纯离子电流通路的集成自脱盐系统。.（2）特种电渗析海水淡化。为了进一步优化RED-ED集成系统中ED(电渗析部分)的脱盐性能及能量效率，课题组在特种电渗析装置优化及系统设计方面进行了大量的研究工作，自主搭建了小型特种电渗析海水淡化原型系统。该系统包含四个部分：控制模块、海水预处理模块、核心ED脱盐模块、以及淡水分配模块。通过持续改进，性能的稳定性和优越性通过了时间的检验。.（3）混合盐溶液中特定离子的选择性去除，所得结果可指导溶液脱盐等相关研究。（A）湿法冶锌电解液体系除杂的难点主要是同为阴离子的硫酸根与氯离子的高选择性分离。课题组通过扩散渗析（DD）及pH调节，实现了极高的分离比。（J. Membrane Sci. 2017, J. Membrane Sci. 2018，ZL201710127073.0）。（B）为了保障产品品质，电极箔化成液中即使仅有痕量的氯离子杂质仍被作为废液处置，企业经济负担重。课题组创新地借助DD技术使用常规阴离子交换膜实现痕量氯离子/高浓度己二酸根的同电性离子高选择性分离，己二酸铵得以回用(Sep. Purif. Technol. 2020)。.（4）基于电渗析的手性氨基醇绿色合成。H2和L-丙氨酸为原料，通过催化加氢和双极膜电渗析（EDBM）成功转化为纯净的L-丙氨醇产品，具有完美的原子经济性。EDBM将催化加氢获得的盐溶液分解并转化为对应的酸和L-丙氨醇，酸可以直接回用，形成闭环。该工作具有一定普适性，环境友好，被选为inside back cover发表于Green Chemistry 2020。