(670a) Designing an Electrochemical System for Simultaneous Extraction of CO2 and Rejection of Salts from Seawater

Two of the major challenges of the present times are the rapidly increasing demand for fresh water and the rise of anthropogenic CO₂ in the atmosphere and consequent acidification of the water bodies. Because approximately 70% of the earth is seawater, one of the obvious solutions to meet the freshwater crisis is desalination of seawater. However, seawater is extremely saline and must reject 99% of the salt concentration in order to be accessible for applications like irrigation and drinking. For the commercially available technologies for seawater desalination like Reverse Osmosis (RO) and Multi-Stage Flash Distillation (MSF), there is a trade-off between energy efficiency and salt rejection efficiency. Also, due to the rise in CO₂ concentrations in the atmosphere, more CO₂ gets absorbed in the water bodies leading to the formation of bicarbonates which lower the pH of seawater causing trouble for marine biota. An efficient method to extract this dissolved CO₂ would essentially enable sequestration of CO₂ from the atmosphere without the need to process large volumes of air. To counter both the issues, we propose a stack-type electrochemical cell employing bipolar membranes to desalinate seawater. The cell stack of an acidic solution, bipolar membrane, anion-exchange membrane, cation-exchange membrane, bipolar membrane, and a basic solution divide seawater into a brine stream and a clean water stream by electrodialysis. Due to the high concentration of H+ ions in the acidic chamber of the cell, the equilibrium of the carbonate buffer system shifts so that CO₂ is evolved at the acidic solution and can be sequestered at that point. The feasibility of this design was analyzed using COMSOL Multiphysics. The simulation results show that a stacked arrangement of such cell can successfully reach a desalination efficiency of 99% at near neutral pH. Effect of operating parameters such as the width of the desalination chamber, concentration of salts, and flow rate of seawater is also reported as a part of this work.