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• The structural effects on VLE of H 2 O-IL systems was experimentally investigated. • The UNIFAC-Lei model was well extended for predicting VLE of H 2 O-IL systems. • HB interaction mechanisms in H 2 O-IL systems at the molecular level was identified. • The relationship between the VLE behaviors and the HB interactions was explored. The relationships between the structure and the thermodynamic behavior and the hydrogen bond (HB) interactions in H 2 O + ionic liquid (IL) systems were systematically investigated for the first time. Imidazolium-based ILs comprising 1-alkyl-3-methylimidazolium cations ([RMIM]+) and various anions such as acetate ([AC]-), thiocyanate ([SCN]-), tetrafluoroborate ([BF 4 ]-), and bis (trifluoromethylsulfonyl)imide ([Tf 2 N]-) were investigated. The vapor–liquid equilibrium (VLE) of H 2 O + IL systems was experimentally determined and predicted by the UNIFAC-Lei model. The results demonstrated that the vapor pressure is mainly dependent on the type of anion and increases slightly with an increase in the cation alkyl chain length. Quantum chemistry calculation and wavefunction analysis clearly revealed the relationship between the VLE and the HB interactions. This study provides theoretical guidance for designing and screening task-specific ILs for chemical processes such as gas dehydration and dehumidification. [ABSTRACT FROM AUTHOR]

The vapor-liquid equilibrium (VLE) data for water/methanol/ethanol +1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA]) binary mixtures were measured by a saturated vapor pressure device at different temperatures. The experimental results showed that the existence of ionic liquid (IL) has a significant effect on the VLE data for all the investigated systems. The thermodynamic model (i.e., modified UNIFAC model) for quantitative prediction has been extended to estimate the VLE data for water/methanol/ethanol + [EMIM][DCA] systems, and the relative mean deviations (RMDs) are 6.02%, 3.45% and 3.05%, respectively. Besides, the binding energy, excess enthalpies and σ -profiles were derived by the COSMO-RS model and density functional theory (DFT) calculation to further understand the nature of the interactions between ordinary matter and IL at the molecular scale. It was clear that the intermolecular interaction between [EMIM][DCA] and methanol/ethanol is weaker than that between [EMIM][DCA] and water; Moreover, the hydrogen bonding interaction is the dominant intermolecular force between [EMIM][DCA] and water/methanol/ethanol. • The vapor pressures for the binary systems of water/methanol/ethanol + [EMIM][DCA] were measured. • The popular UNIFAC-Lei model was extended to predict the VLE of these systems. • The binding energy, excess enthalpies and σ -profiles were used to understand the thermodynamic behavior at the molecular scale. [ABSTRACT FROM AUTHOR]