Alkalinity Concentration Swing for Direct Air Capture of Carbon Dioxide.

We describe a new process - the Alkalinity Concentration Swing (ACS) - for direct air capture of carbon dioxide driven by concentrating an alkaline solution that has been exposed to the atmosphere and loaded with dissolved inorganic carbon. Upon concentration, the partial pressure of \ce{CO2} increases, allowing for extraction and compression. We find that higher concentration factors result in proportionally higher outgassing pressure, and higher initial alkalinity concentrations at the same concentration factor outgas a higher concentration of \ce{CO2}. We examine two desalination technologies, reverse osmosis and capacitive deionization, as possible ACS implementations, and evaluate two corresponding energy models. We compare the ACS to incumbent technologies and make estimates for water, land, and energy requirements for capturing one million tonnes of \ce{CO2} per year. Our estimates for the lower end of the energy range for both approaches compare favorably to other methods, such as solid sorbent and calcining methods.