The modification of porous silica with amino functional groups is considered one of the most effective methods to develop solid sorbents for CO2 capture. In this work, several low-cost silica substrates were modified with aminosilanes using supercritical CO2 as the solvent. The optimal operating conditions of pressure and temperature required to have free aminosilane in solution were first evaluated by studying the phase behavior of the system scCO2/aminosilane. The method was demonstrated to be not only an excellent alternative to conventional liquids, but also to lead to high quality materials in regard of their thermal stability and CO2 adsorption capacity.
The Journal of Supercritical Fluids, Volume 85, 2014, Pages 68–80.
López-Aranguren a, b, J. Frailea, L.F. Vegab, c, C. Domingoa
a Instituto de Ciencia de Materiales de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Spain.
b MATGAS Research Center, Campus de la UAB, 08193 Bellaterra, Spain.
c Carburos Metálicos, Air Products Group, C/ Aragón 300, 08009 Barcelona, Spain.
The present work examines the functionalization of silica supports via supercritical CO2 grafting of aminosilanes, which is an important step in the preparation of materials used as solid sorbents in CO2capture. Four materials have been considered as solid supports: two commercially available silica gels (4.1 and 8.8 nm pore diameter), the mesoporous silica MCM-41 (3.8 nm pore diameter) and a microporous faujasite of the Y type. Mono- and di-aminotrialkoxysilane were chosen for this study. The optimal operating conditions required to have free aminosilane in solution were first evaluated by studying the phase behavior of the system scCO2/aminosilane at different pressures and temperatures. FTIR spectroscopy was used to determine the chemical structure of the grafted species. Aminosilane uptake was estimated by thermogravimetric and elemental analysis. Densities up to 3–4 molecules of monoaminosilane per nm−2 were reached by using a small amount of a cosolvent together with the supercritical CO2. The samples were characterized in regards of thermal stability, showing that aminosilane groups were covalently attached to the amorphous silica surface in the mesoporous supports, but not in the microporous zeolite. Low temperature N2 and ambient temperature CO2 isotherms were recorded to establish the adsorptive behavior of the prepared hybrid materials. The amine functionalized MCM-41 and the 8.8 nm silica gel exhibited a significant higher uptake of CO2 at low pressures compared with the bare supports. On the contrary, for the 4 nm silica gel and the zeolite the adsorption decreased after impregnation.