A Scale-Consistent Adsorption Model for Polymer-Based Adsorbents in Direct Air Capture

Abstract Energy-efficient and cost-effective direct air capture of CO2 is considered key for carbon dioxide removal and carbon capture and utilization. However, separating CO2 from air is inherently challenging due to its low concentration and fluctuating humidity levels. Polymer-based chemisorbents combine good selectivity and capacity and are currently regarded as state-of-the-art benchmark materials. Nevertheless, their complex structure and interactions with water complicate both experimental characterization and predictive modeling. We introduce a modeling framework that combines flexibility in contactor geometry with the accurate reproduction of the physical phenomena observed for the amine-functionalized resin Lewatit VP OC 1065 under varying humidity conditions. A multi-porosity description coupled with a dual-site kinetics adsorption mechanism captures the size- and humidity-dependency of material properties and provides a comprehensive tool for experimental characterization and model-based design. The framework enables the analysis of breakthrough experiments in pellet beds and allows results to be transferred in a scale-consistent manner to structured monoliths considered for next-generation adsorbers.