Insights into the Hydrothermal Stability of Triamine-Functionalized SBA-15 Silica for CO₂ Adsorption

The hydrothermal stability of triamine-grafted, large-pore SBA-15 CO₂ adsorbents was studied by using steam stripping. Following two 3 h cycles of steam regeneration, lower CO₂ uptakes, lower CO₂ /N ratios, and slower adsorption kinetics were observed relative to fresh samples, particularly at the lowest adsorption temperature (25 °C). CO₂ adsorption measurements for a selected sample exposed to 48 h of steam stripping depicted that after the initial loss during the first exposure to steam (3-6 h), the adsorptive properties stabilized. For higher adsorption temperatures (i.e., 50 and 75 °C), however, all adsorptive properties remained almost unchanged after steaming, indicating the significance of diffusional limitations. Thermogravimetric analysis and FTIR spectroscopy on grafted samples before and after steam stripping showed no amine leaching and no change in the chemical nature of the amine groups, respectively. Also, a six-cycle CO₂ adsorption/desorption experiment under dry conditions showed no thermal degradation. However, N₂ adsorption measurement at 77 K showed significant reductions in the BET surface area of the grafted samples following steaming. Based on the pore size distribution of calcined, grafted samples before and after steaming, it is proposed that exposure to steam restructured the grafted materials, causing mass transfer resistance. It is inferred that triamine-grafted, large-pore SBA-15 adsorbents are potential candidates for CO₂ capture at relatively high temperatures (50-75 °C; for example, flue gas) combined with steam regeneration.