A new model for characterization of bipolar membrane electrodialysis of brine

Electrodialysis with bipolar membranes (EDB) is an attractive/promising technique of converting unnecessary salt into corresponding acid and base. The efficiency of this process depends on the quality of bipolar and monopolar (anion- and cation-exchange) membranes constituting a repeating unit of an EDB stack. Thus, the choice of membranes is essential. A new model to characterize each kind of membrane in the EDB stack individually is proposed. The model is fitted to the experimental results of laboratory-scale electrodialysis of industrial brine using commercially available membranes (Neosepta: BP-1, AMX, and CMX; and FumaTech: FAB and FKB). It was found that the efficiency of the bipolar membrane BP-1 is ca. 90%. For both sets of membranes (Neosepta and FumaTech) anion-exchange membranes showed lower selectivity than cation-exchange ones. For j = 75 mA/cm2 the ionic selectivity of monopolar Neosepta membranes was slightly better than that of the FumaTech membranes. However, because of reduced water transport the FAB anion-exchange membrane (FumaTech) was more efficient in the production of more concentrated acid. The accuracy of determination of the model parameter was better when a significantly large charge passed through the EDB stack.