Effect of alkalinity on absorption capacity and selectivity of SO2 and H2S over CO2: Substituted benzoate-based ionic liquids as the study platform

•Benzoate-based ILs with tunable alkalinity were designed and synthesized.•Performance for the selective absorption of acidic gases was investigated.•Relationship between absorption performance and alkalinity was figured out.•Upper bounds were drawn to show the balance between capacity and selectivity.•Guidances for designing ILs with both high capacity and selectivity were proposed.

A series of substituted benzoate-based ionic liquids (SBILs) were synthesized to investigate the effect of alkalinity of ionic liquids on the selective absorption of acidic gases. The alkalinity of SBILs can be easily tuned through altering the substitutions on the benzene ring. The performance of SBILs for selective absorption of acidic gases (e.g., solubility of SO2, H2S and CO2, selectivity of SO2/CO2 and H2S/CO2) was systematically investigated and found to be highly dependent on the alkalinity of SBILs. Some thermodynamic properties (e.g., Henry’s constants and reaction equilibrium constants) were also calculated and correlated with the alkalinity of SBILs. The optimized alkalinity for ionic liquids with maximized selectivity of SO2/CO2 or H2S/CO2 was thus figured out. Furthermore, to achieve a compromise between capacity and selectivity, upper bounds were proposed as criteria for evaluating whether ionic liquids are with both high capacity and selectivity. The results obtained in this work provide interesting clues for the future design of ionic liquids based on the insights into the effect of alkalinity.

Graphical abstractThe performance of ionic liquids for the selective absorption of SO2 or H2S from CO2 was correlated with the alkalinity of ionic liquids, to demonstrate how to design ionic liquids with both high absorption capacity and selectivity through tuning the alkalinity of ionic liquids.Figure optionsDownload full-size imageDownload as PowerPoint slide