Functionalization of Silica SBA-15 with [3-(2-Aminoethylamino)Propyl] Trimethoxysilane in Supercritical CO 2 Modified with Methanol or Ethanol for Carbon Capture

The CO 2 adsorption process using amine-grafted silica is a promising technology for reducing the CO 2 emissions from the power and industry sectors. In this work, silica SBA-15 was functionalized using [3-(2-aminoethylamino)propyl] trimethoxysilane (AEAPTS) in supercritical CO 2 (scCO 2 ) modified with 10% mol methanol or ethanol. The functionalization experiments were carried out at 323 K and 12.5 MPa, and with reaction times of 2 and 3 h. The molar fraction of AEAPTS in scCO 2 plus 10% mol alcohol ranged from 0.5 × 10 −3 to 1.8 × 10 −3 . It was found that as the molar fraction of AEAPTS increased, the amino-grafting density steadily rose, and the pore volume, surface area and pore size of the functionalized silica SBA-15 also decreased gradually. The scCO 2 functionalization method was compared to the traditional toluene method. The diamine-SBA-15 prepared in the scCO 2 process shows a slightly lower amine-grafting density but a higher surface area and pore volume than the ones obtained using the traditional method. Finally, the excess CO 2 adsorption capacity of the materials at different temperatures and low pressure was measured. The diamine-silica SBA-15 displayed moderate excess CO 2 adsorption capacities, 0.7–0.9 mmol∙g −1 , but higher amine efficiency, ca. 0.4, at 298 K, due to the chemisorption of CO 2 . These findings show that diamine-grafted silica for post-combustion capture or direct air capture can be obtained using a media more sustainable than organic solvents.