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.