From powder equilibria to contactor design: An experimentally anchored material based framework for direct air capture on TEPA impregnated SBA-15

Amine-functionalized mesoporous silica remains a leading option for direct air capture (DAC) due to its strong affinity toward dilute CO2 at ambient conditions. In this study, SBA-15/TEPA at 50 wt% amine loading was characterized across the full material-to-process chain. CO2 isotherms were globally fitted with the Toth and modified Toth models, and H2O uptake by the GAB model, capturing competitive and cooperative interactions under realistic humidity. Uptake kinetics extracted with the Linear Driving Force (LDF) model were validated against five fixed-bed breakthrough experiments (R2 = 0.87 to 0.97; mean kLDF = 2.1 & times; 10-3 s-1), with the rate attributed to reaction-retarded CO2 diffusion through the viscous TEPA amine filling the mesopores. Parametric sensitivity resolves equilibrium-controlled and dispersion-controlled regimes through the bed-scale NTU and Peclet numbers, and a resistance-in-series translation shows that an Heating, Ventilation, and Air Conditioning (HVAC)-compatible monolith preserves 87% of the powder kinetics up to a 247 mu m active-layer thickness, with capacity utilization at 5% breakthrough rising from 49% to 77% at 1 m channel length across the 50 to 150 mu m washcoat range and exceeding 85% above 1.5 m.