Study on the production of high-concerntration inorganic alkali by bipolar membrane electrodialysis
Bipolar membrane electrodialysis(BPMED)is a promising method for producing acids and alkalis.However,the process is often hindered by co-ion leakage and water molecule migration,which complicates the attainment of high-concentration acid and alkali products.This study explored the optimization of operational parameters in a three-compartment BPMED reactor,using sodium chloride solution as the raw feed,without altering membrane performance.The research investigated the effects of current density,solution flow rate,and initial salt solution concentration on the BPMED process to identify optimal operating conditions.Key performance metrics such as current efficiency,energy consumption,and product yields were calculated at the highest achieved concentrations of acid and alkali.Under typical industrial conditions-specifically,a current density of 50 mA/cm2,a flow rate of 2.0 cm/s,and an initial salt concentration of 1.5 mol/L-the BPMED process demonstrated enhanced performance.The process achieved a current efficiency of 50％,an energy consumption of 1.68 kWh/kg NaOH,a yield of 0.41,a productivity of 0.19 g/(cm2·h),and a maximum alkali concentration of 1.68 mol/L.To further increase the alkali concentration,experimentation with a higher current density of 100 mA/cm2 was conducted,alongside an increase in the initial volume ratio between the raw feed chamber and the acid/alkali chambers.Under conditions ensuring stable BPMED operation,an alkali concentration of up to 3.84 mol/L was achieved.Subsequently,the alkali concentration was further augmented by integrating overflow-saturated solution injection and increasing the initial liquid volume of the acid chamber.Under conditions of 80 mA/cm2 current density,the maximum alkali concentration reached 7.32 mol/L.These findings highlight the potential for optimizing BPMED processes to achieve high-concentration acid and alkali production,providing valuable insights for industrial applications.
bipolar membrane electrodialysisbipolar membraneacid and alkali production from saltcur-rent density
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