An investigation into the adverse effects of O2, SO2, and NOx on polyethyleneimine functional CO2 adsorbents

In this study, we investigated the influence of O2, SO2, and NOx on branched and linear polyethyleneimine (PEI) functional silica CO2 adsorbents (BPEI-SiO2 and LPEI-SiO2, respectively). O2 was much more likely to oxidize BPEI-SiO2, compared with LPEI-SiO2, to form C=O and C=N groups and led to a 23.0% decrease in the CO2 adsorption capacity after 990 min of cumulative contact with 10% O2. In contrast, LPEI-SiO2 lost only approximately 3.6% of its CO2 adsorption capacity, although O2 oxidized LPEI-SiO2 to form C=O groups. SO2 can cause severe degradation of BPEI-SiO2 and LPEI-SiO2 by forming heat-stable NH3+—and/or NH2+—containing adducts and by promoting the formation of urea linkages. After cumulative contact with 10, 50, and 200 ppm SO2 for 990 min, BPEI-SiO2 lost 18.2%, 61.4%, and 89.0% of its CO2 adsorption capacity, and LPEI-SiO2 lost 18.5%, 60.6%, and 78.5% of its CO2 adsorption capacity, respectively. NO2 at 10 ppm and NO at 200 ppm caused almost no loss in CO2 adsorption capacity after cumulative contact for 990 min, but both led to degradation of adsorbents. NO2 can cause irreversible formation of NH3+—and/or NH2+—containing adducts, acid products, N-nitro compounds (N–NO2), C-nitroso compounds (C–N=O), and C-nitro (C–NO2) compounds, and can promote the formation of urea linkages. NO can lead to the formation of NH3+—and/or NH2+—containing adducts and N-nitroso (N–N = O) compounds.