Application and Modification of Ion Exchange Membranes

Abstract

Although studies on charged membranes have been widely spreading, most of ion exchange membranes, which are a typical charged membrane, are used in ion transport through the membranes in the presence of electrical potential. In some cases, transport number of counter ions should increase and new additional functions were required for the membranes. A typical example of the former is to increase current efficiency of the membranes for chlor-alkali process at the initial stage of development and one of the latter is to give permselectivity for specific ions to the membranes. In particular, many studies on providing permselectivity for specific ions to the membranes have been made in both cation and anion exchange membranes, e. g., in cation exchange membranes, to form a cationic charged layer on the membrane surface, to introduce phosphonic acid groups as ion exchange groups in the membrane and to electrodialyze mixed salt solution in the presence of chelate-forming agents; in anion exchange membranes, to form an anionic charged layer on the membrane surface and to control balance between hydrophilicity of the anion exchange membrane and hydration energy of anions. These works are summarized in this paper.