Elsevier

Fluid Phase Equilibria

Volume 344, 25 April 2013, Pages 32-37
Fluid Phase Equilibria

Azeotrope breaking for the system ethyl tert-butyl ether (ETBE) + ethanol at 313.15 K and excess properties at 298.15 K for mixtures of ETBE and ethanol with phosphonium-based ionic liquids

https://doi.org/10.1016/j.fluid.2013.01.022Get rights and content

Abstract

Isothermal vapor–liquid equilibria for the ternary system {ethyl tert-butyl ether (ETBE) + ethanol + trihexyltetradecylphosphonium chloride ([P666,14][Cl]) or trihexyltetradecylphosphonium bis(2,2,4-trimethylpentyl)phosphinate ([P666,14][TMPP])} have been determined at 313.15 K using headspace gas chromatography (HSGC). The addition of a small amount of ionic liquids (ILs) to the system ETBE + ethanol produced an important salting-out effect. The azeotrope disappeared by varying the mole fraction of ILs from 0.05 to 0.10. The experimental VLE data were correlated using the Wilson equation. In addition, excess molar volumes (VE) and deviations in molar refractivity ((R) data at 298.15 K are reported for the binary systems {ETBE + [P666,14][Cl]}, {ETBE + [P666,14][TMPP]} and {ethanol + [P666,14][TMPP]} by a digital vibrating tube densimeter and a precision digital refractometer. The VE and (R were well correlated according to the Redlich–Kister equation.

Highlights

Ethyl tert-butyl ether (ETBE) is considered as a benign gasoline. ► VLE data for the systems {ETBE + ethanol + [P666,14][Cl] or [P666,14][TMPP]}. ► VE and (R for the binary systems {ETBE + [P666,14][Cl] or [P666,14][TMPP]}. ► VE and ΔR showed a negative deviation. ► Ternary VE and ΔR were calculated from the binary data.

Introduction

Recently, the use of ionic liquids (ILs) as an entrainer for extractive distillation or salt distillation of azeotropic or close boiling mixtures has become important in industrial separation methods because of their extremely low vapor pressures and thermal stabilities. Additionally, ILs, as substances formed by ions, show a negligible vapor pressure at normal temperature and pressure conditions. Many applications of ILs as “green solvents”, replacing volatile organic compounds, have been reported [1]. Imidazolium-, pyridinium- and pyrrolidinium-based ILs are usually of interest in laboratories as extractive solvents.

Since MTBE (methyl tert butyl ether) was phased out in California, USA, new octane booster gasoline additives have become a focus of research for the refining industry. Some primary alcohols and heavy ethers that have a low solubility in water and some alkylate could be candidates for new octane booster additives. Among the considered compounds, ethyl tert-butyl ether (ETBE) is the most plausible candidate. We have studied the phase equilibria and mixture properties systematically for several mixtures of ether compounds and alcohols because of the presence of an azeotrope, the lack of equilibrium and the thermophysical properties of ether compounds [2], [3], [4].

In this work, we report the influence of ILs on the shift of the azeotrope for the system {ETBE + ethanol} using phosphonium-based ILs, trihexyltetradecylphosphonium chloride ([P666,14][Cl]) and trihexyltetradecylphosphonium bis(2,2,4-trimethylpentyl)phosphinate ([P666,14][TMPP]). The isothermal vapor–liquid equilibrium (VLE) data at 313.15 K for the systems {ETBE + ethanol}, varying the mole fraction of ILs from 0.05 to 0.10 of [P666,14][Cl] and [P666,14][TMPP], were determined using headspace gas chromatography (HSGC). The experimental ternary VLE data were correlated with the Wilson equation [5]. 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 {ETBE + [P666,14][Cl]}, {ETBE + [P666,14][TMPP]} and {ethanol + [P666,14][TMPP]} by a digital vibrating tube densimeter and a precision digital refractometer. These binary data were correlated with the Redlich–Kister polynomial [6].

Section snippets

Chemicals

Commercial grade ETBE (C6H14O, M = 102.18 g mol−1, CAS-RN 637-92-3, 99.9 wt%), [P666,14][Cl] (C32H68ClP, M = 519.31 g mol−1, CAS-RN 258864-54-9, 97.0 wt%) and [P666,14][TMPP] (C48H102O2P2, M = 773.27 g mol−1, CAS-RN 465527-59-7, 97.0 wt%) were obtained from Aldrich Chemical Company. Ethanol (C2H6O, M = 46.07 g mol−1, CAS-RN 64-17-5, 99.9 wt%) was supplied by J.T. Baker Chemical Company. ETBE and ethanol had no impurities as determined by gas chromatography, and the purity of the ILs, [P666,14][Cl] and [P666,14

Isothermal VLE

Isothermal VLE for the ternary systems {ETBE + ethanol + [P666,14][Cl]} and {ETBE + ethanol + [P666,14][TMPP]} at 313.15 K were determined 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; x1 is the recalculated liquid phase mole fraction of ETBE as an IL-free basis; y1 and y2 are the mole fraction of ETBE 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 313.15 K are reported for the ternary systems {ETBE + ethanol + [P666,14][Cl]} and {ETBE + 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 because the azeotrope of the binary system disappeared at the ionic liquid concentration of x3 > 0.05.

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