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201258 https://hdl.handle.net/2286/R.2.N.201258 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2025 2027-05-01T17:04:18 181 pages Doctoral Dissertation Academic theses en Niimoto, Kacie Green, Matthew D. Lackner, Klaus S. Holloway, Julianne L. Seo, Soyoung E. Wade, Jennifer L. Arizona State University Partial requirement for: Ph.D., Arizona State University, 2025 Field of study: Chemical Engineering The increasing urgency to mitigate atmospheric CO2 concentrations has driven research into Direct Air Capture (DAC) technologies, with moisture-swing sorbents offering a promising pathway due to their energy-efficient regeneration. This dissertation focuses on the rational design and evaluation of chemically modified anion exchange resin-based sorbents for moisture-swing DAC. However, preliminary experiments revealed that standardized testing methodologies and careful control of operating conditions are essential for reliably assessing DAC performance. Because moisture-swing materials are highly sensitive to ambient conditions and influenced by more than just their chemical properties, considerable effort was dedicated to refining the experimental techniques used to evaluate their behavior. While sorbent-focused studies provide important insights, this work demonstrates that operating conditions play an equally critical role, and the effects of material properties versus system conditions are often difficult to disentangle. With reliable testing protocols established, this work then systematically evaluated how specific chemical modifications influence moisture-swing performance. The modifications explored include variations in cationic functional groups, ion exchange capacity (IEC), crosslinking chemistry, and the spatial arrangement of cationic sites. Results show that the type of cation and its substituents play a critical role in determining both capture performance and degradation behavior. While higher IECs generally enhanced CO2 loading, increased hydrophilicity led to diminishing returns, suggesting an optimal water content for effective sorption at a given humidity level. Sorbents incorporating varying spatial arrangements of cationic sites were synthesized, but the differences were not sufficiently distinct to fully elucidate their influence on performance. However, the results revealed that DAC performance was strongly influenced by IEC, sorbent morphology, and mass transfer conditions. Testing the same materials under different system configurations (closed-loop versus open-flow) revealed significant sensitivity of measured performance metrics, emphasizing the need for standardized DAC testing protocols that better reflect real-world conditions. To further interpret sorption kinetics, widely used kinetic models were applied and critically assessed using controlled numerical simulations. Although these models fit experimental data well, their parameters were shown to lack consistent physical interpretability when applied to systems with varying mass transfer or diffusion constraints, revealing their shortcomings. Overall, this work provides a framework for designing and testing moisture-swing DAC sorbents by integrating molecular-level material design, process-level evaluation, and kinetic model analysis. It emphasizes the importance of both material innovation and experimental standardization for advancing next-generation carbon capture technologies. Engineering Chemical Engineering Environmental engineering Direct Air Capture Gas Separation kinetic models moisture-swing Sorbents sorption science Moisture-Swing Direct Air Capture: Sorbent Design, Experimental Evaluation, and Kinetic Model Validation