阴离子交换膜的限域传质机制及其表征方法研究

With the expanding of ion exchange membrane applications, how to fabricate membranes with higher ion selectivity has been becoming a research trend. “Confined ion transport mechanism” is the key mechanism on ion exchange membrane selectivity. However, since the complication of ion interaction with membrane surface and inside membrane, and the difficulties of direct measurement of ion exchange membrane pore size and surface charge, a commonly recognized mechanism on confined ion transport and the characterization methods have not been found. This fact is a bottleneck to promote ion exchange membrane and electrodialysis in separation processes..Membranes with tunable surface potential and cross-linkage (namely four-quadrant membrane, FQM) will be developed in this project. In order to create an efficient and reliable method for characterizing confined ion transport mechanism, analytical electrochemical methods will be applied together with other measurement techniques. By this method, thickness of electro-double layer, membrane potential and transition time will be investigated, when ions with various hydration number / valences / molecular weight pass through the prepared FQMs. Furthermore, a physical model on confined ion transport mechanism in ion exchange membrane, as well as a mathematical model on calculating molecular weight cut-off (MWCO) of ion exchange membrane will be set-up. These efforts of this project are expected to establish a guidance for fabricating high-selective ion exchange membrane as well as developing ion fractionation processes.

随着离子交换膜的应用范围日益扩展，如何制备具有更高选择分离性的膜也日益成为研究热点。“限域传质机制”是离子交换膜具有选择分离性的关键机制，然而，由于离子在膜中的限域传质机制非常复杂，并且难以直接测量膜空腔、膜表面电位等重要参数，这使得对于离子膜的限域传质机制与表征手段仍然缺乏统一的认识和公认的方法。这也限制了离子膜和电渗析技术在物料分离领域的发展和推广。.本项目以制备的表面电位和交联度可控的复合阴离子交换膜为研究对象，以分析电化学及其他辅助方法为手段，通过计算不同水合数、不同价态及不同分子量离子在制备的四象限膜表面形成的双电层结构和厚度，并结合过膜电压、过渡时间等参数，研究阴离子交换膜表面电荷排斥、内部空间位阻所产生的限域传质机制，并开发有效、可靠的离子膜限域传质的表征方法和手段，建立离子膜限域传质模型和离子膜截留分子量计算模型，从而为高选择性膜的制备和离子析分膜过程的开发提供理论指导。

由于离子交换膜的传质机制由膜的性质和溶质性质等多方面共同作用产生，目前尚缺乏系统和有效的表征方法，因此对于其限域效应也没有统一的认识。本项目通过界面聚合法对离子交换膜进行修饰，进而制备出具有高的离子选择性以及较低膜面电阻的单价选择性离子交换膜和聚合物包覆膜。项目采用磺化聚砜作为膜基质材料，通过改变其磺化度来调节膜通道大小，以实现有机物的低渗透率和离子的高透过率。项目借助仪器分析表征手段和分离实验，从膜的性质和溶质性质两个角度分别出发，定量研究不同结构阴离子交换膜对不同离子溶质的限域效应，从而研究了离子膜的限域机制，实现盐与有机物分离的目的，并根据实验数据和结果建立传质机制模型和截留分子量模型，系统性的提高对于离子膜限域传质机制的了解。本项目开发了聚合物包覆膜电渗析系统，研究了电场驱动下各种金属离子在聚合物包覆膜中的迁移机制，提出了随着电场强度增加，金属离子在膜中传输会呈现出从跳跃迁移到连续迁移的转变。此外，本项目还面向资源回收需求，结合限域传质机制，研究开发了利用高离子选择性复合离子交换膜和聚合物包覆膜的废水资源化（盐析分）和动力电池中的有价金属回收技术，实现了多种金属（锂钴镍、铬锌镍等）“一步法”分离，大大提高了分离效率，降低了投资和运行成本。