Mechanism and kinetics of CO₂ adsorption on surface bonded amines

The impact of H₂O on the mechanism and kinetics of CO₂ adsorption by amine-impregnated SBA-15 has been investigated. The H₂O-free adsorption mechanism proceeds predominantly via formation of carbamates stabilized between two amine groups. Bicarbonates and surface stabilized carbamates were formed on hydrated sorbents. Film diffusion limitations were not observed during adsorption of CO₂ at high amine loadings. Gaseous water decreased the adsorption rate but increased the maximum equilibrium uptake as well as the uptake before breakthrough of the reactor bed. A water film is formed on the adsorbent particles in gas streams containing more than 5 vol %, gaseous H₂O limiting the interaction of CO₂ with the active amine sites and constraining the rates of adsorption. The higher uptake of CO₂ in the presence of H₂O vapor is a result of a change in the adsorption mechanism that increases the amine efficiency, thus leading to a higher adsorption capacity. The adsorption was fully reversible for all adsorbents at a maximum desorption temperature of 100 °C.