(18f) Direct Air Capture with Amino Acid Solvent: Operational Optimization Using a Crossflow Air-Liquid Contactor

One of the negative emission technologies, Direct Air Capture(DAC) is important technology for industrial decarbonization and CO₂ removal processes. Solvent-based DAC is a well-known process, but it requires significant initial costs and energy demand, particularly due to dilute CO₂ concentration in the air. In this study, the conventional packed bed and 3D printed Gyroid packing were utilized with 1M K-Sar (Potassium Hydroxide and Sarcosine) for passive, wind-driven, DAC. We used additive manufacturing for the prototype structured packing, Gyroid, in the vast design space accessible via advanced manufacturing and computer aided design. The effects of feed wind speed, solvent flowrate, contactor geometry and ambient temperature condition are tested to suggest optimized running condition. The tested wind speed range was 0 to 3.5 LPS and 0.06 to 0.16 GPM for the solvent flow rate. The ambient temperature and relative humidity condition were controlled by environmental chamber.

Three conditions of conventional packed bed: 360, 438 and 578 m²/m³ were tested and compared with advanced structured, Gyroid, packing: 579 m²/m³. The conventional packed bed (using Polypropylene balls) with the highest specific surface area, 578 m²/m³, showed nearly 50% CO₂ capture efficiency at optimum running condition. The optimum running condition was found at 1 LPS air flow rate and 0.1 GPM solvent flow rate. Compared to the lower specific surface area packed bed results: 25% for both 360 and 438 m²/m³, there is significant CO₂ capture efficiency shift from 578 m²/m³ packing. The Gyroid packing showed 4.5 times lower pressure drop while maintaining the same CO₂ capture efficiency, 50%, at optimum running condition.

We used Gyroid packing, 578 m²/m³ with the optimum running condition for the ambient temperature effect on CO₂ capture efficiency. The relative humidity conditions are fixed at 80% for all experiments for consistency. Three different ambient temperature conditions: 35, 65, 95 F are tested and showed 24%, 36% and 47% CO₂ capture efficiency as an average value for 1 hour test. This is because of temperature-dependent inherent solvent’s reaction kinetics. DAC technology is sensitive to ambient temperature conditions meaning that DAC performance, CO₂ capture efficiency, varies under different climate conditions.

It is essential that we locate DAC system offer the best techno-economic performance given the high cost of the DAC technology, the need to secure public and private investment, and the pressing need to meet regional net-zero to negative emissions targets. Performance can change depending on the climate, which can affect DAC operational costs and, consequently, deployment potential. To reduce the overall capital and operating costs of the passive contacting DAC systems and allow for their scalability, the design of the contactor and the adsorption operating conditions must be optimized.