Performance evaluation and mechanistic investigation of multiple organic solvents for sulfur dioxide (SO2) capture

Sulfur dioxide (SO2) is a major atmospheric pollutant that poses serious risks to human health and the environment. Developing efficient methods for SO2 removal from flue gas is therefore essential, and organic solvent absorption has emerged as a promising approach. In this study, an experimental method was established to evaluate the SO2 absorption capacity of organic solvents, and 26 solvents from five classes, including alcohols, ethers, esters, nitrogen-containing solvents, and sulfone-based solvents, were systematically investigated. The breakthrough solubility of SO2 in each solvent was measured to compare their absorption performances. The results showed that nitrogen-containing solvents exhibited the highest SO2 absorption capacity, followed by ethers, sulfone-based solvents, esters, and alcohols. These differences were further analyzed using Hansen solubility parameter (HSP) theory, which provided a theoretical basis for understanding the interactions between SO2 and the investigated solvents. Furthermore, reduced density gradient (RDG) analysis was employed to characterize the intermolecular weak interactions in representative solvent–SO2 systems. The results indicated that the chalcogen-bonding interaction between N-methylformamide (NMF) and SO2 was significantly stronger than those observed in the other four solvent systems, providing a molecular-level explanation for the superior SO2 absorption performance of NMF. The experimental results were in good agreement with the theoretical analysis, demonstrating that the combined experimental and theoretical approach can effectively support the screening of SO2 absorbents. Considering both physicochemical properties and absorption performance, N-methylformamide (NMF) was identified as a promising organic solvent for SO2 absorption. These findings provide useful insights into the development and screening of efficient organic solvents for flue-gas desulfurization.