CO2 Adsorption Ability and Thermal Stability of Amines Supported on Mesoporous Silica SBA-15 and Fumed Silica

In this study, monoamine 3-aminopropyl silane (APS) grafted on silica supports were prepared either by post-modification of mesoporous template-free SBA-15 and nonporous fumed silica with 3-aminopropyl triethoxysilane (APTES) or by direct synthesis using a reaction mixture of APTES, TEOS and organic template P123. The CO2 adsorption capacities and efficiencies of amine (defined as CO2/N ratio) on APS grafted silica adsorbents as well as the thermal stability of grafted APS were analyzed and further compared with those of multiamine, tetraethylenepentamine (TEPA), loaded on mesoporous SBA-15 and nonporous fumed silica. The TEPA-loaded silica adsorbents exhibited higher CO2 adsorption capacities but lower thermal stability than the APS-grafted silica adsorbents. The low cost and commercially available nonporous fumed silica was found to be an appropriate support for amine loading. The TEPA-loaded fumed silica possessed a CO2 adsorption capacity of 3.97 mmole CO2/(g of adsorbent) and a CO2/N mole ratio of 0.37 under a 15% CO2/N-2 mixed gas flow at 75 degrees C and 1 atm, which were higher than those of the TEPA-loaded SBA-15 due to the less CO2 diffusion hindrance. Besides, a high stability of TEPA on fumed silica in cyclic adsorption-desorption of CO2 over the TEPA loaded on SBA-15 was observed as well.