Amino-functionalized pore-expanded SBA-15 for CO2 adsorption

Abstract

The adsorption of CO2 on pore-expanded SBA-15 mesostructured silica functionalized with amino groups was studied. The synthesis of conventional SBA-15 was modified to obtain pore-expanded materials, with pore diameters from 11 to 15 nm. Post-synthesis functionalization treatments were carried out by grafting with diethylenetriamine (DT) and by impregnation with tetraethylenepentamine (TEPA) and polyethyleneimine (PEI). The adsorbents were characterized by X-ray diffraction, N2 adsorption–desorption at 77 K, elemental analysis and Transmission Electron Microscopy. CO2 capture was studied by using a volumetric adsorption technique at 45 °C. Consecutive adsorption–desorption experiments were also conducted to check the cyclic behaviour of adsorbents in CO2 capture. An improvement in CO2 adsorption capacity and efficiency of amino groups was found for pore-expanded SBA-15 impregnated materials in comparison with their counterparts prepared from conventional SBA-15 with smaller pore size. PEI and TEPA-based adsorbents reached significant CO2 uptakes at 45 °C and 1 bar (138 and 164 mg CO2/g, respectively), with high amine efficiencies (0.33 and 0.37 mol CO2/mol N), due to the positive effect of the larger pore diameter in the diffusion and accessibility of organic groups. Pore-expanded SBA-15 samples grafted with DT and impregnated with PEI showed a good stability after several adsorption–desorption cycles of pure CO2. PEI-impregnated adsorbent was tested in a fixed bed reactor with a diluted gas mixture containing 15 % CO2, 5 % O2, 80 % Ar and water (45 °C, 1 bar). A noteworthy adsorption capacity of 171 mg CO2/g was obtained in these conditions, which simulate flue gas after the desulphurization step in a thermal power plant.