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

Abstract

This study investigates the electrodialysis processing of a dilute sodium chloride solution using commercial anion-exchange membranes—heterogeneous MA-41, homogeneous Neosepta AMX, and an experimental homogeneous membrane MA-1. The rate of desalination and the limiting current value for the examined anion-exchange membranes increase in the order of MA-41, MA-1, AMX. It has been found that for commercial membranes, the desalination process under a constant potential difference across the membrane is accompanied by a transition to an overlimiting state and the development of coupled effects of concentration polarization. For the AMX membrane, beneficial mass transfer is enhanced by electroconvection, whereas for the MA-41 membrane, the salt ion flux decreases due to the occurrence of water dissociation. For the MA-1 membrane, decreasing the solution concentration leads to a transition of the system to a pre-limiting state, which may be associated with a significant contribution of equilibrium electroconvection to ion transfer in dilute solutions in electromembrane systems with this membrane. This difference in the properties of the MA-1 and AMX membranes results in higher mass transfer coefficients for the MA-1 membrane compared to the AMX membrane at potential jumps of 1 and 2 V. The most optimal operating mode for the MA‑1 membrane is a potential jump in the electromembrane system of 1 V, where specific energy consumption is 0.24 kWh/mol. Under comparable conditions, the specific energy consumption for the AMX membrane is 0.34 kWh/mol.