Enhancing CO₂ adsorption kinetics in direct air capture: The role of steam desorption in amine-based anion exchange sorbents

Abstract

This study investigates the impact of steam desorption on the CO₂ co-adsorption kinetics of amine-functionalized sorbents for direct air capture applications. Amine-based sorbents are highly selective for CO₂ and effective in capturing it at low ambient concentrations, making them ideal for DAC. However, desorption methods, particularly under varying humidity conditions, significantly influence sorbent performance and efficiency. This research compares the effects of nitrogen and steam desorption on CO₂ adsorption kinetics, with a focus on the kinetic advantage provided by steam's residual moisture left on the adsorbent. Experimental adsorption and desorption processes were conducted in a custom-built DAC unit, using Lewatit VP OC 1065 as the sorbent material. The linear driving force model, combined with the Weighted Average Dual-Site Toth model, was applied to predict adsorption behavior, incorporating the Toth and Guggenheim-Anderson-de Boer parameters from previous studies. Results demonstrate that steam desorption significantly enhances initial CO₂ adsorption rates and equilibrium capacities across humidity levels compared to N₂ desorption. Notably, steam desorption leaves residual moisture on the sorbent, which primes the material for rapid CO₂ uptake in the subsequent adsorption phase, especially under low-humidity conditions. These findings suggest that steam desorption not only improves adsorption kinetics but also supports energy-efficient regeneration, positioning it as a favorable option for DAC systems in arid climates. The study highlights the potential of optimizing desorption methods to improve operational efficiency and capture performance in DAC applications.