Insight to CO2-assisted H2S removal in chelated iron-based ionic liquid composite: From COSMO-RS prediction to molecular-level understanding

Recently, the oxidative removal of hydrogen sulfide (H 2 S) using chelated iron-based ionic liquids has garnered extensive research attention owing to high H 2 S conversion efficiency and no by-salts production. Nevertheless, for natural gas, biogas, H 2 S is typically accompanied by high concentrations of carbon dioxide (CO 2 ) where excess CO 2 molecules tend to occupy the binding sites of H 2 S, thereby limiting the desulfurization efficiency. Therefore, developing H 2 S/CO 2 selective absorption materials is of great significance. In this work, the COSMO-RS method was employed to systematically screen cation–anion pairs and evaluate 13 organic solvents for their H 2 S/CO 2 selectivity and solubility. The chelated iron-based ionic liquid (HDMIFeEDTA) was identified as the most promising candidate, and its composite with NMP at a 1:2 mass ratio was selected as the optimal absorbent. This composite exhibited excellent desulfurization performance under CO 2 -rich conditions. Interestingly, the presence of CO 2 significantly enhanced H 2 S removal in the composite. FT-IR, ESI-MS, and DFT calculation revealed that after [Fe(III)EDTA] − is reduced to [Fe(II)EDTA] 2− by H 2 S, the electrons of [Fe(II)EDTA] 2− transfer to CO 2 , resulting the charge of O (CO 2 ) more negative. This negative site provides an additional binding site for H 2 S, thereby promoting its uptake through hydrogen-bond interactions. These results not only clarify the promoting role of CO 2 in the desulfurization process but also provide a new strategy for developing high-efficiency chelated iron-based ionic liquid absorbents for fuel gas purification