Effect of crosslinking on the CO2 adsorption of polyethyleneimine-impregnated sorbents

Amine-based silica sorbents for CO2 capture prepared by an impregnation method generally show high adsorption capacity, but physical and chemical degradation for long-term operation are critical problems such as leaching and evaporation of amines, and urea formation, respectively. A strategy to form crosslinks between the impregnated amines was introduced to prevent these problems. Crosslinkers with two amine-reactive groups such as epoxy and halide were used to prepare crosslinked polyethyleneimine (PEI)-impregnated sorbents. A viscosity increase was observed in all crosslinked PEIs. The structure and the amine ratio of the crosslinked PEIs were investigated by 13C NMR analysis. The highest reaction selectivity to primary amines and the formation of hydroxyl groups were observed for 1,3-butadienediepoxide (BDDE). In addition, BDDE-crosslinked PEI-impregnated sorbents exhibited the most stable long-term stability with the highest CO2 adsorption capacity and the smallest weight gain after regeneration by simulated temperature swing adsorption (TSA) operations; the hydroxyl groups produced from BDDE-crosslinked PEI enhanced the CO2 utilization by acting as proton acceptors. The effect of the BDDE content was investigated. The advanced physical stability was observed by an increase in the viscosity at high temperatures or gelation with increasing amounts of BDDE. The BDDE-crosslinked PEI-impregnated sorbents with the appropriate amount of BDDE showed an outstanding stability for the cyclic adsorption capacity (determined by simulated TSA operations) and resistance to urea formation (indicated by in situ infrared analysis).