Ultrasonic-assisted preparation of organic amine-modified SBA-15 for CO2 capture in wide temperature range: Experimental and computational investigation

Abstract

Amine-modified mesoporous silicon was widely used for CO2 capture. However, its adsorption capability was significantly affected by temperature and humidity. In this paper, tetraethylenepentamine (TEPA) modified SBA-15 adsorbents were prepared for capturing CO2. The effects of the modification method, the concentration of TEPA, the adsorption temperature, and the humidity of atmosphere on CO2 adsorption capability were studied. Moreover, combined with molecular dynamics (MD) and density functional theory (DFT) computations, the diffusion characteristics and adsorption mechanism were explored. The CO2 adsorption capability of the adsorbent prepared by the ultrasonic impregnation method was higher than those prepared by the stirring impregnation method, owing to that ultrasonic impregnation could promote the uniformity of TEPA. With the increase of TEPA concentration of SBA-15, the CO2 adsorption capability increased. SBA-15-2 had the highest CO2 adsorption capability of 1.17 mmol/g at 30 °C. This was due to the N-containing functional groups, showing good affinity for CO2, introduced by TEPA impregnation. When the temperature increased from 30 °C to 70 °C, the CO2 adsorption capability of all modified SBA-15 adsorbents decreased, since the CO2 adsorption was an exothermic reaction. SBA-15-2 showed better water vapor resistance than SBA-15-2 (Stir). This was related to the higher dispersity of organic carbon chain introduced by TEPA modification after ultrasonic impregnation. The organic carbon chain of SBA-15-2 increased the water vapor resistance by reducing the hydroxyl group. Finally, from a microscopic aspect, the MD simulation suggested that impregnated TEPA inside SBA-15 may improve CO2 capture by increasing the thickness of effective adsorption layer. Besides, the DFT simulation showed that TEPA modification increased the adsorption energy of SBA-15 on CO2. This serves as a reference for later mesoporous silicon adsorbent research and development on CO2 capture.