CO2 Capture at Low Temperature by Nanoporous Silica Modified with Amine Groups

Abstract

MCM-41 and SBA-15 were chosen as nanoporous materials based on silica for its modification with amine groups. This modification was done by two methods: grafting method and wet impregnation method. The first method grafted-amine groups by chemical reaction between surface silanol groups in the nanoporous materials and 3-aminopropyltrimetoxilane (APTMS).In the wet impregnation method, low molecular weight polyethylenimine (PEI) is incorporated trough this method. These modified materials capture CO₂ at low temperature. CO₂ capture on the sorption sites by amine loading is believed to occur via chemisorption mechanism by formation of ammonium carbamate. The evaluation and analysis of CO₂ adsorption was carried out by two methods: static mode and dynamic mode. The static mode is a pure CO₂ adsorption-desorption isotherms at 298K. The isotherms of the functionalized materials show a behavior by chemisorption, capture at low pressure, being the desorption branch almost horizontal, while nanoporous silica isotherms is due a physical adsorption, low CO₂ capture at low pressure and dependence with pressure, a complete reversibility of the desorption process. The dynamic mode is a thermogravimetry study at different N₂/CO₂ concentrations. Isothermal CO₂ captures at 298K were carried out to evaluate the suitability of the samples for cyclic operation. The mass increase during the capture step was interpreted as CO₂ adsorption capacity of the samples. The results obtained by both methods were compared, and, its differences were analyzed.