Isotherm model for moisture-controlled CO₂ sorption

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Moisture-controlled sorption of carbon dioxide (CO2) is key for moisture-swing CO2 capture using anion exchange materials.
• Existing models, like Langmuir isotherms, offer approximate fits but lack a robust analytic derivation.
• A fundamental understanding of sorption mechanisms is needed for optimizing CO2 capture technologies.

Purpose of the Study:

• To derive a novel, analytic isotherm equation for moisture-controlled CO2 sorption.
• To validate the derived equation against experimental data for strong-base anion exchange materials.
• To provide a more accurate theoretical framework for CO2 capture from air.

Main Methods:

• Developed a bottom-up theoretical approach starting from alkali liquid fundamental theory.
• Generalized the isotherm theory from alkali liquids to strong-base anion exchange materials.
• Validated the derived analytic isotherm formula using literature experimental data.

Main Results:

• Derived a simple analytic isotherm equation with a single parameter, Keq, for alkali liquids relevant to CO2 capture.
• Extended the theory to anion exchange materials, yielding Keq(AEM)eff = Keq(AEM) × [H2O]− based on mass action law.
• Demonstrated that the derived formula accurately fits experimental CO2 sorption data, outperforming Langmuir isotherms.

Conclusions:

• The novel analytic isotherm equation provides a superior description of moisture-controlled CO2 sorption compared to existing models.
• The derived Keq(AEM)eff parameter significantly varies with sorbent moisture content, offering insights into material performance.
• This work advances the fundamental understanding and predictive capability for CO2 capture materials.