Effect of cell configurations on the performance of citric acid production by a bipolar membrane electrodialysis

The purpose of this study was to evaluate the effect of cell configurations on the energy consumption and the electroacidification parameters in the production of citric acid using a bipolar membrane electrodialysis (BPED). Three basic cell arrangements, A (anion membrane)–C (cation membrane)–BP (bipolar membrane)–A–C (type I), C–BP–C (type II) and BP–A–C–BP (type III) were discussed and compared. Type I generates acid citrate by acidification with acid sulfate produced from the dissociation of sodium sulfate, and type II produces acid citrate by replacing Na+ with H+ generated at BPED and type III generates acid citrate by direct splitting sodium citrate. The current density–voltage curves for the three configurations show the typical behaviors given by the coupling of ion transport and electrical field-enhanced water dissociation and are not completely overlapped in the two determined orders due to the change in Donnan potential at the bipolar junction and solution–membrane interface. The magnitudes of cell voltage, current efficiency and energy consumption follow the analogous order as type IItype I≈type III. From the comprehensive considerations of the energy consumption, current efficiency and concentration of the produced acid citrate, it suggests that type II seems to be a favorable cell configuration for the production of citric acid. It is not advisable to manufacture acid citrate by direct splitting its salt.