Comparison of Homogeneous Anion-Exchange Membrane Based on Copolymer of N,N-Diallyl-N,N-dimethylammonium Chloride and Commercial Anion-Exchange Membranes in Electrodialysis Processing of Dilute Sodium Chloride Solutions

In this study, we investigated the electrodialysis process for treating a dilute sodium chloride solution using various anion exchange membranes – specifically, the commercial heterogeneous MA-41 and homogeneous Neosepta AMX, along with the experimental homogeneous membrane MA-1. We observed an increase in the desalting rate and the limiting current for the studied anion-exchange membranes in the series MA-41, MA-1, and AMX. We found that with commercial membranes, the decrease of the solution concnetration leads to the development of conjugated effects of concentration polarization. For the AMX membrane, useful mass transfer due to electroconvection increases, whereas for the MA-41 membrane, the flux of salt ions decreases due to the occurrence of the water dissociation reaction. For the MA-1 membrane, a decrease in the solution concentration leads to a transition of the system to the underlimiting current mode. This behavior may be associated with a significant contribution of equilibrium electroconvection to the process of ion transfer in dilute solutions in electromembrane systems with this membrane. Due to these differences in membrane properties, the mass transfer coefficients for the MA-1 membrane are higher compared to the AMX membrane at potential drops of 1 and 2 V. Our findings suggest that the most optimal operating mode for the MA-1 membrane is at a potential drop of 1 V in the electromembrane system, which results in a specific energy consumption of 0.24 kWh/mol. Contrastingly, under comparable conditions for the AMX membrane, the specific energy consumption is 0.34 kWh/mol.