(54a) Influencing the Migration of Ions for Simultaneous Extraction of CO2 and Desalination of Seawater

Climate impacts from high anthropogenic CO₂ emission have led to the development of strategies to reduce its atmospheric concentration. One of the dominant areas of interest is CO₂ extraction from various sources. Currently, most of the CO₂ extraction techniques involve thermal cycles where CO₂ captured from a stream of gas by a nucleophilic agent in a solvent and is extracted by heating the solvent. Such processes are not only energy-intensive but also require a large solvent makeup at the end of each cycle. Alternatively, electrochemical routes to CO₂ extraction offer a more sustainable solution to this problem. Electrochemical extraction of dissolved CO₂ from seawater is an efficient method to effectively remove CO₂ from the atmosphere without processing large volumes of air. Such an electrodialysis process is not only less energy-intensive but can be used to simultaneously desalinate seawater without any extra energy penalty thereby tackling two of the major challenges of the present times: the rapidly increasing demand for freshwater and the acidification of the water bodies as a consequence of rising atmospheric CO₂ concentration. Standard electrodialysis methods have been used to extract CO₂ from aqueous solutions and are an active field of research. Here we propose a combination of a computational and experimental approach to observe the extraction of CO₂ and the rate of salt rejection from seawater. We propose a stack-type electrochemical cell employing cation and anion-exchange membranes to desalinate seawater. The cell stack of an acidic solution, anion-exchange membrane (AEM), seawater, cation-exchange membrane (CEM), 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/bicarbonate system shifts so that CO₂ is evolved at the acidic solution and can be extracted at that point. The feasibility of this design was analyzed using COMSOL Multiphysics. To efficiently extract CO₂ from seawater, it is important to study the preference of the anions for AEM. We observe the migration of anions of the simulated seawater as a function of transference number to propose design modification to the currently existing system. The 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.