Numerical Modeling and Comparative Analysis of Electrolysis and Electrodialysis Systems for Direct Air Capture

Abstract

Electrochemical systems of alkali solution electrolysis and electrodialysis are prospective candidates for large-scale direct air capture (DAC) applications. In this study, electrolysis and electrodialysis DAC systems based on the pH-swing method are modeled and compared. The attainable membrane K+ selectivity and CO2 absorption ratio are modeled to accurately predict system performance. Considering the electrolysis system has dual functions for hydrogen production and DAC, its minimum energy demand for DAC is 1255 kJ mol-1 under a current density of 0.14 A cm-2, while the electrodialysis system has a minimum energy consumption of 1451 kJ mol-1 under a current density of 0.012 A cm-2. The effects of cycle solution flow rate and concentration are analyzed, and it is found that the solution pH difference between compartments needs to be greater than 5.25 to achieve optimum performance for both systems. Finally, the systems are simulated with 100% K+ selectivity and CO2 absorption ratio, and the results show that the lower limits on DAC energy demand for electrolysis and electrodialysis systems under such ideal conditions are reduced by around 90%, to 162 and 154 kJ mol-1, respectively. The improvement of K+ selectivity in electrochemical cells, and optimization of the air contactor to obtain higher CO2 absorption ratios are promising areas deserving further research.