Demonstration of direct ocean carbon capture using hollow fiber membrane contactors

The focus of membrane carbon capture to date has been primarily on point source capture, such as power plants and industrial capture. However, membrane technology can also play a role in negative emissions technology, such as direct air capture and direct ocean capture. Direct ocean capture has a few potential advantages over direct air capture, such as avoiding land use and coupling with offshore wind and offshore storage. The use and feasibility of hollow fiber membrane contactors (HFMCs) for direct ocean carbon capture with benign aqueous basic carbon dioxide solvents is assessed here through a multifaceted approach. A 1D HFMC model incorporates fluid dynamics and the chemical kinetics of both ocean water and aqueous sodium hydroxide solvent in order to simulate CO2 flux behavior in two flow configurations. Lab scale experiments of this system then guide a model refinement and validation process until experimental behaviors are predicted through computation. A preliminary technoeconomic assessment then uses computational and experimental results to estimate the carbon capture cost when the system is scaled to remove 0.98 Mtonnes CO2/year. Computational results suggest that higher seawater flow rates and temperatures relative to the sodium hydroxide solvent improve CO2 flux. The technoeconomic assessment suggests that HFMCs may only be cost-competitive if seawater pH is decreased at the membrane interface, thereby increasing the local concentration of dissolved carbon dioxide. These findings indicate that local pH swing on the seawater side will be necessary to feasibly remove carbon dioxide from seawater using HFMCs.