Abstract
We have developed a new technique of electrodialysis with a bipolar membrane and ion-exchange membranes. The technique has a separating zone with acidic pH steps between compartments. The electrodialyzer was composed of six compartments, which were divided by an anion-exchange membrane, a bipolar membrane, and three cation-exchange membranes. The solutions including sodium chloride were circulated by chemical pumps through the compartments and reservoirs at constant flow rate. When a voltage was applied to the electrodialyzer, hydrogen ions were electrically generated by the bipolar membrane, and partially moved to cathode-side compartments through cation-exchange membranes. The hydrogen concentration in each compartment was almost equal to the concentration of coexisting anions, and formed acidic-pH steps in the electrodialyzer. All the experimental data were simulated by a mathematical model which considered ionic flux in the membrane based on the Nernst-Planck’s equation, ion-exchange equilibrium between solution and membrane, electroneutrality in the solution, hydrogen production rate, and material balances of ionic species. The model well explained the experimental results of formation of pH steps in the electrodialyzer.
