• Trace SO2 in flue gas significantly restrains CO2 absorption in piperazine-based amine absorbents, while promoting carbamate formation.
• Aminoethyl-substituted piperazine absorbents exhibit enhanced SO2-resistance by favoring carbamate formation, whereas hydroxyethyl-substituted ones reduce resistance by promoting bicarbonate formation.
• The study provides structure-activity relationships linking amine functional groups to SO2 resistance, guiding the design of more robust absorbents for industrial CO2 capture.
• Findings highlight the need to consider trace SO2 in practical flue gas when evaluating amine absorbent performance, with implications for CCUS process efficiency.