Vapor–liquid equilibria at 333.15 K and excess molar volumes and deviations in molar refractivity at 298.15 K for mixtures of diisopropyl ether, ethanol and ionic liquids
Highlights
► Diisopropyl ether (DIPE) is considered as a benign gasoline. ► VLE data for the systems {DIPE + ethanol + [P666,14][Cl]} and {DIPE + ethanol + [P666,14][TMPP]}. ► VE and ΔR for the binary systems {DIPE + [P666,14][Cl]} and {ethanol + [P666,14][Cl]}. ► VE and ΔR showed a negative deviation. ► VE and ΔR were calculated from the binary data.
Introduction
Distillation is by far the most extensively used and common industrial separation process in the petroleum, natural gas and petrochemical industries. It is also common in many other industries including air fractionation, solvent recovery and recycling processes. However, distillation is highly restricted when azeotropes appear. Azeotropes can be separated using a pressure swing method or by distillation with an entrainer (liquid additive or solid salt) that modifies the relative volatility of the distilled components. The use of salts has problems associated with the causticity and the limited solubility in organic compounds, whereas volatile organic solvents may contaminate the environment and the product streams [1].
Recently, ionic liquids (ILs) have become useful in industrial separation methods because of their extremely low vapor pressures and thermal stabilities. Additionally, ILs have a highly polar character caused by Coulomb forces acting between the ions in the liquid state, and because they are exceedingly good solvents for a wide range of materials [2], [3]. Many applications of ILs as “green solvents”, replacing volatile organic compounds, have been reported [3]. Imidazolium-, pyridinium- and pyrrolidinium-based ILs are usually of interest in laboratories as extractive solvents.
Diisopropyl ether (DIPE) is considered one of the most attractive economical gasoline octane boosters as a substitute for methyl tert-butyl ether (MTBE), which was phased out in California, USA. Some primary alcohols have also been considered as candidates for new additives of gasoline. We have studied the phase equilibria and mixture properties systematically for several mixtures with ether compounds and alcohols, due to the presence of an azeotrope and the lack of equilibrium, and the thermophysical properties for ether compounds [4], [5], [6].
In this work, we report the influence of ILs on the shift of the azeotrope for the system {DIPE + ethanol} using phosphonium-based ILs, tri-hexyltetradecylphosphonium chloride ([P666,14][Cl])} and tri-hexyltetradecylphosphonium bis(2,2,4-trimethylpentyl) phosphinate ([P666,14][TMPP]). Because imidazolium-, pyridinium- and pyrrolidinium-based ILs are barely soluble in DIPE, whereas [P666,14][Cl] and [P666,14][TMPP] are soluble in DIPE, the isothermal vapor–liquid equilibrium (VLE) data at 333.15 K for the systems {DIPE + ethanol} with different concentrations of [P666,14][Cl] and [P666,14][TMPP] were measured using headspace gas chromatography (HSGC). The experimental ternary VLE data were correlated with the Wilson equation [7]. In addition, we report the mixture properties, excess molar volumes (VE) and deviations in molar refractivity (ΔR) at 298.15 K for the binary systems {DIPE + [P666,14][Cl]} and {ethanol + [P666,14][Cl]} by a digital vibrating tube densimeter and a precision digital refractometer. These binary data were correlated with the Redlich–Kister polynomial [8].
Section snippets
Chemicals
Commercial grade DIPE (C6H14O, M = 102.18 g mol−1, CAS-RN 108-20-3), [P666,14][Cl] (C32H68ClP, M = 519.31 g mol−1, CAS-RN 258864-54-9) and [P666,14][TMPP] (C48H102O2P2, M = 773.27 g mol−1, CAS-RN 465527-59-7) were obtained from Aldrich Chemical Company. Ethanol (C2H6O, M = 46.07 g mol−1, CAS-RN 64-17-5) was supplied from J.T. Baker Chemical Company. DIPE and ethanol have no impurities as determined by gas chromatography, and the purity of ILs, [P666,14][Cl] and [P666,14][TMPP], was declared better than 99% by
Isothermal VLE
The VLE data for the ternary systems {DIPE + ethanol + [P666,14][Cl]} and {DIPE + ethanol + [P666,14][TMPP]} at 333.15 K were measured and are listed in Table 2, Table 3, where x3 is the mole fraction of [P666,14][Cl] or [P666,14][TMPP] in the liquid phase; is the recalculated liquid phase mole fraction of DIPE as an IL-free basis; y1 and y2 are the mole fraction of DIPE and ethanol in the vapor phase, respectively; and P is the calculated equilibrium pressure. The activity coefficient of each
Conclusions
The isothermal vapor–liquid equilibrium data at 333.15 K are reported for the ternary systems, {DIPE + ethanol + [P666,14][Cl]} and {DIPE + ethanol + [P666,14][TMPP]}, to verify the salting out effect of ILs. The mole fractions of [P666,14][Cl] or [P666,14][TMPP] (x3) were fixed as 0.05 and 0.1. The ionic liquids, [P666,14][Cl] and [P666,14][TMPP] were effective in shifting or breaking the azeotropic point. An azeotrope of the system, {DIPE + ethanol}, disappeared at the ionic liquid concentration of x3 ≥
Acknowledgement
This work was supported by a Korean Research Foundation Grant that was funded by the Korean Government (MOEHRD) (KRF-2008-313-D00182).
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