Effect of flow oscillations on mass transfer in electrodialysis with bipolar membrane

The potential of applying oscillatory flows as a method for enhancing the performance of electrodialysis with bipolar membrane has been investigated using the production of lactic acid from sodium lactate solution as an example. Up to 160% increase to the limiting current density was achieved using such intensification approach. The enhancement was found to increase with increasing the oscillation frequency and amplitude but decreased with the cell steady flow rate, likely due to flow reversal inhibition. The enhancement mechanism was mainly attributed to the increase in mass transfer rate at the cationic membrane fluid–surface interface due to the oscillatory shear and the eddies generated at the rough surface of the net spacers during flow reversals. This however, did not have any measurable effect on the mass transfer at the bipolar membrane, indicating negligible mass transfer resistance there. A correlation is developed for predicting the percentage limiting current density enhancement with an average error of 11%.