Ion-injection bipolar membrane electrodialysis realizes 8+ mol/L caustic soda conversion from the brine stream

Abstract

Abstract The chlor-alkali process is currently the predominanttechnology for caustic soda production but has several major challenges,such as huge energy demand, and the emission of a large amount of chlorine, which cannot be completely consumed in downstream industries. Bipolar membrane electrodialysis (BMED) is an emerging technology to produce caustic soda with near zero chlorine emission by accelerating water splitting in bipolar membranes. However, the gradualdepletion of feedstock and the unbalanced behavior between water splitting and salt migration have led to the produced acid and base concentrations beingrelatively low for further utilization. Herein, we proposea novel ion-injection bipolar membrane electrodialysis (IJBMED) approach, which achieves a continuous feedstock supply. This IJBMED design is capable of boosting water splitting in abipolar membrane with an ultrahigh current density while avoiding concentration polarization in the anion- and cation-exchange membranes. Therefore, the IJBMED system enables one-step conversion of the NaCl-containing brine stream into 8.4 mol/L NaOH with specific energy consumptions of 870 kWh/t NaOH (24 wt.%→26 wt.%) and 2740 kWh/t NaOH (0→26 wt.%). This bench-scale experiment proved that IJBMED is a promising caustic base production technology that might be aplausible supplement or even compete with the chlor-alkali approach.