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

Abstract

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 Tóth and modified Tóth 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 (R 2 = 0.87 to 0.97; mean k LDF = 2.1 × 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 Péclet numbers, and a resistance-in-series translation shows that an Heating, Ventilation, and Air Conditioning (HVAC)-compatible monolith preserves 93% of the powder kinetics up to a 339 μm active-layer thickness, with capacity utilization at 5% breakthrough rising from 49% to 77% at 1 m channel length across the 50 to 150 μm washcoat range and exceeding 85% above 1.5 m.