Unprecedented improvement of the hydrothermal stability of amine-grafted MCM-41 silica for CO2 capture via aluminum incorporation

Abstract

The hydrothermal stability of amine-containing CO2 adsorbents is of paramount importance as steam stripping is often practiced for regenerating CO2-loaded materials. The impact of aluminum incorporation into the structure of MCM-41 silica on its adsorptive properties and hydrothermal stability during CO2 capture was studied. Large-pore MCM-41 silica and MCM-41 aluminosilicate (Si/Al = 15) supports with similar average pore sizes of 64 and 66 Å, respectively, were synthesized using a novel method. Amine functionalization of the supports was conducted using grafting of triamine under dry and wet conditions. Amine-tethered MCM-41 aluminosilicate adsorbents exhibited higher CO2 uptakes (up to 63% higher after 60 min of adsorption at 25 °C) and faster CO2 adsorption kinetics (up to 71% faster after two minutes of adsorption at 25 °C) relative to their MCM-41 silica counterparts. Following a three-hour exposure to steam, extensive deterioration of adsorptive properties was observed for the triamine-grafted MCM-41 silica materials, particularly at low adsorption temperatures of 25 and 50 °C, showing CO2 uptake losses as high as 73 and 56%, respectively. The triamine-grafted MCM-41 aluminosilicate materials, however, showed unprecedented hydrothermal stability with no significant drop in CO2 uptake (respective losses as high as 27 and 17%) and adsorption kinetics. After steam stripping, N2 adsorption-desorption measurements at 77 K showed significantly higher reductions in the Brunauer-Emmett-Teller surface area of the triamine-grafted MCM-41 silica materials (losses of 36–49%) compared to their MCM-41 aluminosilicate counterparts (losses of 31 to 35%). It is inferred that aluminum incorporation into the support increases the hydrothermal stability of the resulting grafted materials in the presence of steam.