Epoxy-modified polyethyleneimine for enhanced SO2-resistance during CO2 capture: Effects of propylene and butylene alkyl chains

초록

Amine-functionalized materials have attracted considerable interest as potential candidates for the selective capture of CO2; however, severe deterioration in the presence of even trace amounts of SO2 in flue gases has limited their practical application. Because SO2 mainly degrades primary amines, converting primary amines into secondary or tertiary amines can enhance their resistance to SO2. In this study, polyethyleneimine (PEI), a widely used amine for CO2 capture, was modified using two epoxides with different alkyl chain lengths. The PEI modified with propylene oxide (40PP) predominantly contained tertiary amines (ca. 93%), whereas the PEI modified with butylene oxide (40BP) had a similar fraction of secondary and tertiary amines. Both epoxy- modified PEI showed dramatically enhanced SO2 resistance compared to pristine PEI. The reversibility of 40PP was more stable than that of 40BP under flue gas conditions (2000 ppm SO2 balanced with N2), which was attributed to the weakly conjugated SO2 on 40PP, because tertiary amines have lower basicity than secondary amines. The SO2 adsorption retention of 40PP and 40BP after 10 cycles of adsorption and desorption was 94% and 91%, respectively, and much higher than that of PEI (64%) under simulated post-combustion flue gas composition (400 ppm SO2 and 15% CO2 balanced with N2). The adsorption-desorption mechanism was confirmed using diffuse reflectance infrared Fourier transform spectroscopy. Epoxy-modified PEI with superior reversibility even in the presence of SO2 can contribute to effective post-combustion CO2 capture from flue gas.

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