Applications of Pore-Expanded Mesoporous Silicas. 3. Triamine Silane Grafting for Enhanced CO2 Adsorption

Abstract

Conventional MCM-41 and pore-expanded MCM-41 (PE-MCM-41) silicas have been used as supports for grafting 3-[2-(2-aminoethylamino)ethylamino]propyl trimethoxysilane (TRI) and tested for CO 2 adsorption. The effects of the quantity of triamine silane added to the grafting mixture on the CO 2 adsorption capacity and apparent adsorption rate have been examined. The results showed that when both supports were grafted under the same conditions, PE-MCM-41 was grafted with slightly larger quantities of amine than MCM-41, for all controlled silane additions. Based on the adsorption performance of the materials using a dry 5% CO 2 /N 2 feed mixture, the optimal quantity of triamine silane added to the grafting mixture was determined to be ca. 3.0 cm 3 /g(SiO 2 ), for both MCM-41 and PE-MCM-41. The CO 2 adsorption capacity of TRI−PE-MCM-41 was significantly higher than that of TRI−MCM-41. Furthermore, the dynamic adsorption performance of TRI−PE-MCM-41 was far superior to TRI−MCM-41. In comparison to 13X zeolite, TRI−PE-MCM-41 exhibited higher adsorption capacities in the initial time frame of exposure, even though the 13X zeolite exhibited a higher equilibrium adsorption capacity. The result of this behavior is largely due to the rapid CO 2 −amine interaction and the open pore structure of TRI−PE-MCM-41 over that of the 13X zeolite. When these adsorbents were exposed to a humid stream of 5% CO 2 /N 2 (28% relative humidity), both grafted materials exhibited a slight increase in the adsorption capacity, whereas, 13X zeolite did not retain any significant CO 2 adsorption capacity. These results suggest that the TRI−PE-MCM-41 material may be most suitable for use in a rapid cyclic adsorption process under humid feed conditions.