Online neutralization promotes water dissociation equilibrium forward in bipolar membranes to achieve 9.2 mol/L NaOH production

The bipolar membrane electrodialysis is a promising caustic soda production technique by taking advantage of the water dissociation under a reverse voltage bias. However, dissociation equilibrium is easily reached when forward water dissociation is equivalent to the back diffusion of acid and base into the salt chamber. Here, we propose manipulating the water dissociation equilibrium by introducing an online neutralization reaction for acid or base products. The results indicate that the online neutralization of the acid product could promote water splitting forward in bipolar membranes, leading to an increase in the base yield of 27.7 % and a saving of 43.7 % in time in parallel with conventional operation. The boosting water dissociation via online acid neutralization results in the production of 9.2 mol/L NaOH, the highest recorded base concentration produced by bipolar membrane electrodialysis. The present study provides a simple and unique approach for manipulating the water dissociation equilibrium, suggesting the increasingly crucial role of bipolar membranes in base production.