(130g) Direct Ocean Carbon Capture Using Hollow Fiber Membrane Contactors

Although much research has been done on direct air capture (DAC), far less has been conducted on direct ocean capture (DOC) to-date. Whereas DAC suffers from large system sizes and high energy costs to blow large volumes of air through the system, DOC could be more compact, require less energy due to the higher CO₂ concentration per unit volume, and (at a large-scale), it could have the added benefit of controlling local ocean pH in a high-risk marine environment (i.e., coral reef or shellfishery). We propose a novel approach to removing CO₂ from sweater using a hollow fiber membrane contactor (HFMC) that flows seawater on one side, and an aqueous solvent (NaOH) on the other side. HFMCs have been investigated thoroughly for traditional carbon capture and are a promising fit for DOC due to low energy costs, compact/efficient separation, and the benign aqueous solvents. This work will present lab-scale experimental results that validate a developed 1D models. The model applies the resistance-in-series model for mass transport, and detailed reaction chemistry on both seawater and solvent sides. Then, parametric studies will be shown to demonstrate design and operating parameters for HFMCs for DOC. This work concludes that CO₂ flux increases in a HFMC as the seawater is flown on the shell side of the membrane and that flow direction, co-current or counter-current, has minimal effects on performance. Other parameters such as fiber diameter, temperature, and solvent loading times are also studied. Finally, a techno-economic assessment (TEA) was performed on a theoretical system similar to a scaled-up DAC system, as this is the first of it’s kind. The system size was matched to Carbon Engineering’s proposed DAC system, which captures 980,000 CO₂ tonnes/year. The TEA here considers both capital and operating costs for all components needed for absorption, regeneration and CO2 compression for a greenfield installation. The results found that lowering the local seawater pH to around 5-6 will be necessary to make this approach economically competitive with state-of-the-art DAC systems. Next steps involve working with experimental collaborators at Arizona State University and UC Irvine to develop a hybrid DOC/desalination membrane that locally lowers pH on the seawater side to improve CO₂ flux and therefore lower capture cost.