Elsevier

Fluid Phase Equilibria

Volume 316, 25 February 2012, Pages 11-16
Fluid Phase Equilibria

Liquid–liquid equilibria for ternary mixtures of methyl tert-amyl ether + methanol (or ethanol) + imidazolium-based ionic liquids at 298.15 K

https://doi.org/10.1016/j.fluid.2011.09.011Get rights and content

Abstract

Liquid–liquid equilibria (LLE) were determined for ternary systems {methyl tert-amyl ether (TAME) + methanol + 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4])}, {TAME + ethanol + [Bmim][BF4]}, {TAME + methanol + 1-ethyl-3-methylimidazolium ethylsulfate (EMISE)} and {TAME + ethanol + EMISE} at 298.15 K. Experiments were carried out at atmospheric pressure using stirred and thermo-regulated cells. The experimental data were correlated with the well-known non random two liquid (NRTL) and universal quasi chemical (UNIQUAC) activity coefficient models. In addition, the distribution coefficients and the selectivities of the ionic liquids of [Bmim][BF4] and EMISE for methanol and ethanol in the TAME phase were measured.

Highlights

► Methyl tert-amyl ether (TAME) is considered as a benign gasoline additive. ► LLE data for the systems {TAME + methanol (or ethanol) + imidazolium-based ionic liquids}. ► NRTL and UNIQUAC models were used for the description of the determined LLE data. ► All ternary systems were classified as Treybal's type I systems. ► The distribution coefficients and the selectivities of the ionic liquids for methanol and ethanol in the TAME phase were measured.

Introduction

Recently, there has been considerable interest in using various fuel additives as anti-knock agents to improve gasoline performance, and to reduce ground and air pollution. Methyl tert-butyl ether (MTBE) is a tertiary ether. It is the most widely used gasoline additive in the world because of its low vapor pressure and the availability of ethanol feedstock from renewable resources. However, MTBE has the drawback of easily dissolving in water and contaminating ground water.

Methyl tert-amyl ether (TAME) is considered as a suitable alternative candidate for gasoline anti-knock agents with di-iso propyl ether (DIPE) and ethyl tert-butyl ether (ETBE). We systematically studied the phase equilibria and mixture properties for some anti-knock agents because accurate design data are strongly related to the processing of the compounds and the application of a group contribution model [1], [2], [3].

Ionic liquids are an unusual class of nonvolatile chemical compounds with interesting physical properties. They are therefore studied in several fields such as separation technology, biotechnology and environmental remediation. Ionic liquids possess high ionic conductivity, electrochemical stability, and variable physical and chemical properties. They typically contain large organic cations and smaller inorganic or organic anions. The lattice energy of their crystal structure is therefore generally reduced, resulting in a lower melting point. This is the reason why ionic liquids usually remain liquid at room temperature. Unlike molecular liquids, ionic liquids have negligible vapor pressures at room temperature and a high solvating capacity for organic, inorganic, and organometallic compounds. Thus, they can effectively be used as environmental friendly solvents in liquid–liquid extractions and can be designed for particular applications [4], [5]. However, the solubility between ionic liquids and a second liquid phase is still unknown. Thus, new data concerning phase equilibrium and mixture properties would be of great use to the field of ionic liquids.

In this work, we report the ternary liquid–liquid equilibrium data for {TAME + methanol + 1-butyl-3-methyl-imidazolium tetrafluoroborate [Bmim][BF4]}, {TAME + ethanol + [Bmim][BF4]}, {TAME + methanol + 1-ethyl-3-methylimidazolium ethylsulfate (EMISE)} and {TAME + ethanol + EMISE} mixtures at 298.15 K. These data were determined at atmospheric pressure using stirred and thermo-regulated cells. Data for the binary and ternary systems were correlated using two activity coefficient models: NRTL and UNIQUAC. In addition, the distribution coefficients and selectivity of the ionic liquids [Bmim][BF4] and EMISE for methanol and ethanol in the TAME phase were measured.

Section snippets

Chemicals

Commercial grade TAME (C6H14O, M = 102.18 g mol−1, CAS-RN 994-05-8, 99.9 wt%) and [Bmim][BF4] (C8H15BF4N2, M = 226.02 g mol−1, CAS-RN 174501-65-6, 98.0 wt%) were supplied from Aldrich Chemical Co. EMISE (C8H16N2O4S, M = 236.29 g mol−1, CAS-RN 342573-75, 95.0 wt%) was obtained from Fluka Co. Methanol (CH4O, M = 32.04 g mol−1, CAS-RN 67-56-1, 99.9 wt%) and ethanol (C2H6O, M = 46.07 g mol−1, CAS-RN 64-17-5, 99.9 wt%) were provided by J.T Baker Chemical Co. Methanol, EMISE and [Bmim][BF4] were dried using molecular sieves

Results and discussion

We examined ternary liquid–liquid equilibrium phase systems for {TAME + methanol + [Bmim][BF4]}, {TAME + ethanol + [Bmim][BF4]}, {TAME + methanol + EMISE} and {TAME + ethanol + EMISE} mixtures at 298.15 K, as given in Table 2. The results are plotted in the form of Gibbs triangles in Fig. 1, Fig. 2, Fig. 3, Fig. 4. They show the broad liquid–liquid miscibility gaps. And as indicated by the slope of tie-lines, a remarkably distinct solutropic phenomenon was found only in the system {TAME + ethanol + [Bmim][BF4]}. As

Conclusions

The ternary LLE for the systems {TAME + methanol + [Bmim][BF4]}, {TAME + ethanol + [Bmim][BF4]}, {TAME + methanol + EMISE} and {TAME + ethanol + EMISE} are reported at 298.15 K. All ternary systems were classified as Treybal's type I systems, which have one partially miscible binary system. The slopes of the tie-lines illustrate that methanol and ethanol were more soluble in ionic liquids than in TAME, except {TAME (1) + ethanol (2) + [Bmim][BF4]. Only the ternary LLE system of {TAME (1) + ethanol (2) + [Bmim][BF4]

Acknowledgement

This work was supported by a Korea Research Foundation Grant that was funded by the Korean Government (MOEHRD) (KRF-2008-313-D00182).

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