Grafted Amine/CO2 Interactions in (Gas-)Liquid-Solid Adsorption/Absorption Equilibria

The effects associated with the presence of liquid water on the CO2 adsorption capacity by SBA-15 silica functionalized with aminopropyltrimethoxysilane (APS) and N-(2-aminoethyl)-3-(aminopropyl)trimethoxysilane(AEAPS) were examined to evaluate the potential of this mode of contact in gas-liquid-solid scrubbing operations for CO2 partial pressures typical of atmospheric postcombustion flue gases. The results were compared to the CO2 adsorption capacity of the grafted airlines in moist and dry gas-solid conditions along with the CO2 absorption capacity in gas-liquid amine solution systems consisting of amines with almost identical structures. In these conditions, an estimation of CO2 physical adsorption was obtained through study of (bare) unmodified SBA-15. Furthermore, to assess the efficacy and long-term stability of the amine/SBA-15 association, grafted amines were subjected to up to eight successive immersion cycle tests (24 h each) in aqueous media. The recovered samples were characterized by X-ray diffraction (XRD), nitrogen sorption isotherm, and CHN elemental analysis. Up to 40% of grafted amines merely leached off in the first few regeneration cycles; thereafter, the nitrogen content of AEAPS remained quite stable, unlike APS which exhibited lower stability. Interestingly, the mesoporous structures of both APS and AEAPS were preserved after several exposures to water. The highest CO2 capture efficiency was achieved with liquid amines, while CO2 capture efficiency using grafted amines in gas-liquid-solid systems was intermediate between the ones in dry and in moist gas-solid systems for comparable conditions.