Experimental study and thermodynamical modelling of the solubilities of SO2, H2S and CO2 in N-dodecylimidazole and 1,1′-[oxybis(2,1-ethanediyloxy-2,1-ethanediyl)]bis(imidazole): An evaluation of their potential application in the separation of acidic gase

• Low-volatile and long-chain N-substituted imidazoles were investigated for the absorption of acidic gases.
• The solubilities of SO2, H2S and CO2 under different temperatures and pressures were reported.
• The solubility data were correlated with thermodynamic models to calculate thermodynamic parameters.
• The absorption performance were compared with other organic solvents and ionic liquids.
• The functionalization of organic solvents is another way to design efficient solvents for the selective separation of acidic gases.

Exploring low volatile solvents for the capture of acidic gases is highly valued from the viewpoint of green chemistry. In this work, the solubilities of SO2, H2S and CO2 in two long-chain N-substituted imidazoles: N-dodecylimidazole (NDI) and 1,1′-[oxybis(2,1-ethanediyloxy-2,1-ethanediyl)]bis(imidazole) (Im2TEG) at different temperatures and pressures were determined systematically. It is shown that the absorption behaviour of SO2 in NDI and Im2TEG deviates strongly from the ideality. However, the absorption behaviour of H2S and CO2 in NDI and Im2TEG deviates only slightly from the ideality. Therefore, the solubility data of SO2 were correlated using the PR-NRTL model while the solubility data of H2S and CO2 were correlated with the Krichevsky–Ilinskara (K–I) equation. Thermodynamic parameters including the Henry's constants at infinitely dilute condition and the enthalpy of absorption were calculated from the thermodynamic modelling. The potential application of the two liquid solvents in the selective separation of acidic gases (i.e., SO2/CO2 and H2S/CO2) was evaluated by comprehensively considering the absorption capacity and ideal selectivity. The results were compared with other organic solvents and ionic liquids. It is revealed that NDI and Im2TEG are two promising solvents for the selective separation of acidic gases due to their high absorption capacity of SO2 and H2S and high selectivity of SO2/CO2 and H2S/CO2.