Counter-sorption of water and carbon dioxide in moisture-swing direct air capture sorbents

Stratton, Ryan J (2023) Counter-sorption of water and carbon dioxide in moisture-swing direct air capture sorbents. Masters thesis, Northern Arizona University.

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Abstract

Direct air capture (DAC) of carbon dioxide (CO2) is a technology that could limit global warming, but its high energy demand and cost are still barriers to large-scale deployment. In this work, the focus is on the thermodynamic adsorption properties of strong base quaternary ammonium resins (QA) and state-of-the-art primary amine resins (PA), both of which are solid polymeric sorbents capable of CO2 chemisorption. The former QA structures have been identified as novel sorbents for DAC due to their excellent adsorption of CO2 at ambient concentrations (40 Pa) and the reversal with moisture. Conventional regeneration of an adsorbent requires thermal energy or a mechanical pressure swing, which is more energy intensive for regeneration over a moisture-swing process. The current work aims to investigate the simultaneous mass and energy flows in these resins by varying water vapor, CO2 and mixed H2O/CO2 experiments. The data informs solid sorbent capacities, isosteric heats of sorption, and kinetics of the varying ad/desorbing species. For the first time, this work established a method to measure the simultaneous thermogravimetric and calorimetric changes from mixed water and CO2 ad/desorption in state of the art and emerging direct air capture sorbents. The water sorption capacity and isosteric heat of sorption were established for the first time in primary amine and strong base quaternary amine resins. The QA resins exhibited the greatest water adsorption capacity due to their permanent charge in a polymeric structure. Further, an important finding is that the polymeric sorbents showed an increase in isosteric water adsorption with water vapor pressure – opposite of what has been measured elsewhere in sorbent materials. CO2 sorption behavior in the PA materials was not sensitive to water vapor activity, while the QA sorbents showed an increasing capacity with water vapor activity. It was also revealed that there are two distinct time constants in the QA counter sorption of CO2 and H2O (CO2 binds as H2O is released) that may be indicative of a fast physisorption and a slow chemisorption response.

Item Type:	Thesis (Masters)
Publisher’s Statement:	© Copyright is held by the author. Digital access to this material is made possible by the Cline Library, Northern Arizona University. Further transmission, reproduction or presentation of protected items is prohibited except with permission of the author.
Keywords:	Carbon Capture; Direct air capture; Moisture Swing; Quaternary ammonium resin; Primary amine resins
Subjects:	T Technology > TD Environmental technology. Sanitary engineering
NAU Depositing Author Academic Status:	Student
Department/Unit:	Graduate College > Theses and Dissertations College of Engineering, Informatics, and Applied Sciences > Mechanical Engineering
Date Deposited:	29 Jul 2026 20:19
Last Modified:	29 Jul 2026 20:19
URI:	https://openknowledge.nau.edu/id/eprint/6327

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