Modification of transport properties of ion exchange membrane. XI. Electrodialytic properties of cation exchange membranes having polyethyleneimine layer fixed by acid–amide bonding

Abstract

AbstractFor the purpose of preparing the monovalent cation permselective membrane for electrodialysis, the membrane having—SO2Cl groups reacted with the polyethyleneimine to form a cationic polyelectrolyte layer on the membrane surface by using the acid–amide bonding. Reaction conditions, i.e., reaction temperature, concentration of the polyethyleneimine solution and the addition of tertiary amines to the polyethyleneimine solution, were all examined in detail. As a result, all the different kinds of polyethyleneimines were effective in obtaining the monovalent cation permselective membrane if the correct reaction conditions were selected. The durability of the monovalent cation permselectivity was evaluated in a continuous electrodialytic concentration of sea water. The monovalent cation permselectivity decreased gradually during the electrodialysis in the cation exchange membrane with the polyethyleneimine layer. Therefore, the cation exchange membrane with the cationic polyelectrolyte layer was further treated with crosslinking reagents, i.e., form aldehyde–hydrochloric acid, epichlorohydrin, etc. or other alkylating reagents. The monovalent cation permselectivity of the treated membranes was almost constant for two months. The crosslinking reaction of polyethyleneimine was more effective than alkylation in maintaining the high permselectivity constantly.