Heterogeneous bipolar membranes and their application in electrodialysis

• A complex of data regarding heterogeneous BPM investigation is presented.
• Aspects of BPM structure, water splitting and ion transfer mechanisms are revealed.
• Operating parameters of BMED in novel electromembrane processes were investigated.
• Heterogeneous BPMs can be applied in novel electrodialysis applications.

Over the last 50 years, ion exchange membranes have evolved from a laboratory tool to industrial products with significant technical and commercial impacts. Bipolar membranes (BPMs), as a result of their ability to produce acid and alkali from corresponding salt, occupy a special place among them. These properties make it possible to design a number of unique electromembrane processes which have huge industrial impact. These processes include acid and base syntheses, electrochemical regeneration of acidic and basic gas sorbents and ion-exchange resins, protein separation and pH correction of natural waters and juices. The main characteristics that define the possibility of effective BPM application are total potential drop across the membrane and water dissociation current efficiency. These two parameters are closely related to each other and determined by the physical and chemical structures of monopolar layers and the nature of the water dissociation reaction catalyst located in the bipolar region. In this particular article the electrochemical properties of heterogeneous bipolar membranes, methods for investigating them and various theories developed to describe water dissociation are discussed. Comparison between Russian industrial heterogeneous bipolar membranes and various commercial and experimental foreign bipolar membranes is made. In addition, some novel electromembrane processes developed for application of heterogeneous bipolar membranes and their main characteristics are presented.