Humidity-Driven Swelling and Mass Transfer in Lewatit VP OC 1065 and Purolite A110 for Direct Air CO ₂ Capture

Direct air capture (DAC) of CO2 using amine-functionalized adsorbents is a promising carbon removal strategy. We investigate how humidity influences the swelling, CO2 uptake, and mass transfer of two amine-functionalized polymeric resins, Lewatit VP OC 1065 and Purolite A110, using a combined experimental and modeling approach. Humidity-induced swelling is quantified, and a simplified diffusion model is developed to explore how swelling, humidity, and effective diffusivities affect water and CO2 transport within adsorbent beads. Swelling slows water transport, particularly at high humidities, where the effective diffusivity is 10–100 times slower. Despite this, CO2 saturation times remain comparable across humidities, supporting the use of single linear driving force constants when water diffuses faster than CO2. Furthermore, Lewatit exhibits slower kinetics, but greater swelling and CO2 capacity enhancement compared to Purolite, highlighting a trade-off between swelling, capacity, and mass transfer in adsorbent design and selection.