Ion injection bipolar membrane electrodialysis realizes over 8 mol/L NaOH conversion from a brine stream

Abstract

The chlor‐alkali process is currently the predominant technology for caustic soda production but has several major challenges, such as enormous energy demand and supply–demand imbalance between NaOH and Cl2 in downstream industries. Herein, we propose a novel ion‐injection bipolar membrane electrodialysis (IJBMED) system that is capable of boosting water splitting in a bipolar membrane with an ultrahigh current density while omittance concentration polarization in anion‐ and cation‐exchange membranes. The results indicate that the IJBMED approach enables one‐step conversion of the NaCl‐containing brine stream into 8.12 mol/L NaOH with specific energy consumption of 0.79 kWh/kg NaOH (23 wt.% → 25 wt.%), compared to 2.15 kWh/kg NaOH (28 wt.% → 30 wt.%) for the chlor‐alkali process. The advantages of low energy consumption and omittance of chlorine emissions suggest that IJBMED might be a promising alternative to the chlor‐alkali process, revealing a new route to reshape the chemical industry for caustic soda production.

Electrochemical Separations for Sustainability

“…Bipolar ion-exchange resin wafers also perform pH adjustment with lower ohmic losses as the resin wafer compartment augments the solution conductivity under dilute solutions. 72 Conversely, it can be challenging to generate highly concentrated acid and base streams using bipolar membrane electrodialysis, but a recent ion-injection alteration to bipolar electrodialysis resulted in a NaOH stream over 8 M. 73 Faradaic reactions are also effective for in-situ pH adjustment, but OER and HOR to generate acid requires platinum group metals, and the formation of gas bubbles within the cell can be undesirable. Faradaic reactions generating hydroxide ions can be achieved by using stainless steel, or other low-cost transition metals, for both OER and HER.…”