Effect of Amine Structure on CO2 Adsorption of Modified Poly(ethyleneimine)-Impregnated Mesostructured Silica Sorbents

Poly(ethyleneimine) (PEI) was modified to study the effect of amine type and introduced hydroxy groups on its ability to capture carbon dioxide. Amines were impregnated in as-synthesized mesostructured silica (MSU-F) to fabricate solid amines, and the resulting samples were characterized via 13C nuclear magnetic resonance spectroscopy and diffuse reflectance infrared Fourier transform spectroscopy. Nitrogen contents, structural properties, adsorption capacity, and sorbent durability during CO2 adsorption/desorption processes were measured to study the CO2 sorption performances of the sorbents. Reaction between PEI and propylene oxide (PO) altered the ratio of primary, secondary, and tertiary amines and also produced hydroxy groups on amine molecules. With a specific reactant ratio, a modified amine-impregnated sorbent (M-EP10) showed a CO2 adsorption capacity and amine efficiency of 13.90 wt % and 0.37, respectively, which were higher than that of the pristine PEI-impregnated sorbent. The new adsorbents also showed excellent stability in cyclic adsorption–desorption operations, even under pure CO2 desorption conditions in which commercial PEI adsorbents are known to lose CO2 adsorption capacity owing to urea formation. The use of modified PEI to enhance CO2 sorption characteristics of amine-based sorbents was investigated. With a specific reactant ratio, modified PEI-impregnated sorbent (M-EP10) showed better sorption capacity and amine efficiency than a pristine-PEI impregnated sorbent (M-PEI) did. This study clearly shows that the PO-modified PEI (EP)-impregnated mesoporous silica is a potential candidate for practical applications.