Deciphering the effect of SO2 on CO2 capture using enhanced biphasic solvent: Lab-scale continuous operation

Carbon dioxide (CO 2 ) chemisorption employing biphasic solvents is recognized as a method with substantial application potential. Nevertheless, under conditions of burning high-sulfur fuels or rapid load changes, SO 2 in the flue gas poses challenges to the stability and economic operation of biphasic CO 2 capture system. To tackle this, the impact of residual SO 2 on CO 2 capture performance was systematically investigated in a lab‑scale continuous absorption–desorption set-up using novel biphasic solvent. The system achieved steady CO 2 capture efficiencies of 97.8 % and 94.8 % over 20 days without SO 2 . In the presence of SO 2 , CO 2 capture efficiency declined from >90 % in the first 10 days to below 80 % after 13 days and 70 % after 17 days, owing to irreversible reactions between SO 2 and amine, pH drop, and amine loss. CO 2 loading and circulation capacity similarly decreased, while CO 2 desorption duty rose from 2.51 to over 5.0 GJ/t CO 2 , driven by increased solvent flow and amine degradation catalyzed by SO 4 2− . DFT calculations indicated that the dissolution of SO 2 formed SO 3 2− /SO 4 2− , which enhanced the hydration of CO 2 . However, SO 2 preferentially reacted with amines, acidifying the interface and hindering CO 2 absorption. Quantitative 13 C NMR indicated that the oxyanion produced by the dissolution of SO 2 reduced the concentrations of bicarbonates and carbonates in the rich phase. A mechanistic model based on film theory was proposed, delineating gas‑phase diffusion, liquid‑phase competition, and catalytic promotion by oxyanions. These findings guided recommendations for pretreatment and solvent‑management strategies to ensure stable biphasic CO 2 capture under real flue gas conditions.