Isobaric vapor liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium trifluoromethanesulfonate (CmimTfO) with either water or short chained n-alkyl alcohols (methanol, ethanol, propan-1-ol, and butan-1-ol) are described in this study. Two different microebulliometers and a classical VLE apparatus were compared and the VLEs were determined in the composition range 0.4 ≤ x(solvent) ≤ 1 at three different pressure levels ( p = 500 mbar, 700 mbar, and 1000 mbar). The experimental data were modeled using the soft-SAFT equation of state, which was able to accurately describe the nonideal behavior of these mixtures. The combined experimental-modeling results obtained contribute to establish the structure-property relationship between the CmimTfO and n-alkyl alcohol molecules and to infer about its influence on the phase behavior of these solvents.

The isobaric vapor liquid equilibria (VLE) of different binary mixtures of the ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (C2mimTfO) with the n-alkyl alcohols, methanol, ethanol, propan-1-ol, and butan-1-ol, are studied at the pressures of p = 500, 700, and 1000 mbar, covering a composition range 0.25–0.35 ≤ x(solvent) ≤ 1.0. Complementarily, the experimental results are compared with calculations by the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS). For deriving suitable PC-SAFT parameters, experimental liquid densities were determined for the neat IL C2mimTfO and its longer homologues, 1-butyl-3-methylimidazolium trifluoromethanesulfonate (C4mimTfO) and 1-hexyl-3-methylimidazolium trifluoromethanesulfonate (C6mimTfO), in a temperature range of 288.15 K ≤ T ≤ 363.15 K (C2mimTfO) and 293.15 K ≤ T ≤ 363.15 K (C4mimTfO and C6mimTfO), respectively. The PC-SAFT EoS is found to be suitable for describing the VLEs under study with good accuracy (AARDVLE ≤ 0.4%).

No abstract

Isobaric vapor–liquid equilibria (VLE) of binary mixtures of the ionic liquid (IL) 1-hexyl-3-methylimidazolium trifluoromethanesulfonate (C6mimTfO) and the n-alkyl alcohols methanol, ethanol, propan-1-ol, and butan-1-ol at three pressures are reported. Measurements were carried out at pressures of p = 1000, 700, and 500 mbar, which allowed to cover compositions in the range of 0.24–0.35 ≤ x (n-alkyl alcohol) ≤ 1.0 and temperatures in the range of 321.8 K ≤ T ≤ 423.6 K. The experimental data are described applying two theoretical models: (1) the nonrandom two-liquid (NRTL) model as an example of a descriptive model for calculating the excess free Gibbs energy G E and (2) the perturbed-chain statistical associating fluid theory (PC-SAFT) equation of state (EoS) as an example of a model based on statistical thermodynamics. Both approaches allow a description of the phase equilibria with good accuracy (AARDVLE,NRTL ≤ 0.3% and AARDVLE,PC‑SAFT ≤ 1.1%) and redraw its details, partially quantitative, when applied as a fitting algorithm (NRTL) or when applying the PC-SAFT theory. The present work is a continuation of an ongoing study, which aims at developing the structure–property relationships of ILs. With the present results, a first systematic view on the impact of the alkyl side chain length of the C x mim+ (x = 2, 4, 6) cation on the boiling behavior of binary IL (C x mimTfO)/n-alkyl alcohol mixtures is provided by scaling the boiling temperatures of the mixtures with that of the pure alcohol master plot results. Our data reveal that increasing the alkyl chain length of the C x mim+ cation causes an enhancement of the attractive forces between the IL and the n-alkyl alcohol moieties, resulting in an increase in the relative boiling temperature of the binary mixture.

Adding imidazolium ionic liquids to polar solvents such as alkyl alcohols usually results in the dissociation of ion pairs as cation–anion interactions are replaced, e.g., by ion⋯OH hydrogen bonds. In this Communication, we apply Raman scattering and infrared absorption spectroscopy to an example binary system comprising 1-butyl-3-methylimidazolium trifluoromethanesulfonate (triflate) and propan-1-ol. The spectra are analyzed using principal component analysis (PCA), excess spectroscopy, and spectral decomposition. The results provide evidence that the ion pairs of the ionic liquid do not dissociate in propan-1-ol, even at high dilution. Moreover, there are clear signs that the propan-1-ol hydrogen bonding network is disrupted in the presence of the ionic liquid as the hydroxyl groups predominantly interact with the sulfonate oxygen atoms.