Phase equilibria and interfacial tensions in the systems methyl tert-butyl ether + acetone + cyclohexane, methyl tert-butyl ether + acetone and methyl tert-butyl ether + cyclohexane

doi:10.1016/j.fluid.2008.08.012

Fluid Phase Equilibria

Volume 273, Issues 1–2, 25 November 2008, Pages 68-77

https://doi.org/10.1016/j.fluid.2008.08.012 Get rights and content

Abstract

Isobaric vapor–liquid equilibrium (VLE) data have been measured for the ternary system methyl tert-butyl ether + acetone + cyclohexane, and for its methyl tert-butyl ether based binaries, at 94 kPa and in the temperature range 323–340 K. Equilibrium determinations were performed in a vapor–liquid equilibrium still with circulation of both phases. The dependence of interfacial tensions of these mixtures on concentration was also determined, at atmospheric pressure and 303.15 K, using the maximum bubble pressure technique.

From the experimental results, it follows that the investigated mixtures exhibit positive deviation from ideal behavior and azeotropy is present for the methyl tert-butyl ether + acetone system at 94 kPa. The application of a model-free approach allows concluding about the reliability of the present vapor–liquid equilibrium data for all the indicated mixtures. Furthermore, the determined interfacial tensions exhibit negative deviation from linear behavior for all the analyzed mixtures.

The vapor–liquid equilibrium data of the binary mixtures were well correlated using the NRTL, Wilson and UNIQUAC equations, while their interfacial tensions were smoothed using the Redlich–Kister equation. Scaling of these models to the ternary mixture allows concluding that both the VLE data and the interfacial tensions can be reasonably predicted from binary contributions.

Introduction

The experimental characterization of the phase and interface behavior of mixtures containing branched ethers (e.g. methyl tert-butyl ether or MTBE, ethyl tert-butyl ether or ETBE, tert-amyl methyl ether or TAME, 2,2′-oxybis[propane] or DIPE) is of fundamental importance for commercial gasoline blending and distribution [1], [2]. On the one hand, phase equilibrium behavior is a clear indicator of the combustion evolution during the vaporization of fuels and, additionally, it allows estimating the Reid’s vapor pressure (RVP), which is the widely accepted volatility indicator of fuels [1], [2]. On the other hand, the interfacial tension of fuel droplets may be conveniently modified by adding new agents to fuels, so as to control the ignition kinetics and the atomization of fuels inside the engine’s combustion chamber [3], [4]. Furthermore, from an environmental protection viewpoint, interface tensions and phase equilibrium behavior (particularly, liquid phase miscibility) also play an important role in assessing risks related to the pollution of aquifers during gasoline distribution [5], [6].

Despite of the practical relevance of both phase equilibrium and interface tensions in fuel processing and handling, experimental research has been mainly focused to the determination of phase equilibrium data only (vapor–liquid and liquid–liquid equilibrium), at several thermo-mechanic conditions (see, for instance: Marsh et al. [7], Chamorro et al. [8], and references therein). Thus, for the case of the system MTBE + cyclohexane, isothermal vapor–liquid equilibrium (VLE) data have been measured over the temperature range 298–333 K [9], [10], [11]. These isothermal data allow concluding that the mixture is not azeotropic, and exhibits moderate positive deviation from ideal behavior. For the case of the system MTBE + acetone, which is not directly related to gasoline production, Churkin et al. [12] reported isobaric VLE data at atmospheric pressure, while Gmehling and Bölts [13] characterized its azeotropic behavior over the range 302.65–324.35 K and 46.85–102.19 kPa. According to these experimental results, the MTBE + acetone system exhibits clear positive deviation from ideal behavior and azeotropy is present. Finally, the reported interface tension measurements are constrained to some few gasoline mixtures [14], [15], [16], [17] and, to the best of our knowledge, no data have been reported for mixtures containing MTBE.

Following our ongoing research program on characterizing thermo-physical properties of fuels, this work is devoted to measure VLE data and interface tensions of systems constituted by gasoline components and potentially attractive additives. The ternary system MTBE + acetone + cyclohexane, for which no data have been reported previously, constitutes a clear example of this latter type of mixtures.

Section snippets

Purity of materials

Acetone and cyclohexane were purchased from Merck, and were used without further purification. MTBE was purchased from Aldrich, and then was dried by percolation through dry calcium chloride in a bed column (50 cm height and 5 cm diameter). The properties and purity of the pure components, as determined by gas chromatography (GC), appear in Table 1. The densities and refractive indexes of pure liquids were measured at 298.15 K using an Anton Paar DMA 5000 densimeter (Austria) and a Multiscale

Vapor–liquid equilibrium

The equilibrium temperature T, liquid-phase x and vapor-phase y mole fraction measurements at P = 94 kPa are reported in Table 2, Table 3, Table 4 and Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 together with the activity coefficients (γ_i) that were calculated from the following equation [21]: $\ln γ_{i} = \ln \frac{y_{i} P}{x_{i} P_{i}^{0}} + \frac{(B_{i i} - V_{i}^{L}) (P - P_{i}^{0})}{R T} + \frac{P}{2 R T} \sum_{j = 1}^{3} \sum_{k = 1}^{3} y_{j} y_{k} (2 δ_{j i} - δ_{j k})$ where P is the total pressure and $P_{i}^{0}$ is the pure component vapor pressure. $V_{i}^{L}$ is the liquid molar volume of component i, B_ii and B_jj are the second

Conclusions

Isobaric vapor–liquid equilibrium data at 94 kPa and atmospheric interfacial tensions at 303.15 K have been reported for binary and ternary mixtures that contain MTBE, acetone, and/or cyclohexane. Experimental results revealed that the phase equilibrium data of ternary mixture and its MTBE based binaries exhibit positive deviations from ideal behavior, and azeotropy was observed for the MTBE with acetone binary mixture. The interfacial tensions of the analyzed mixtures exhibit negative deviation

Acknowledgment

This work was financed by FONDECYT, Santiago, Chile (Project 1080596).

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Phase equilibria and interfacial tensions in the systems methyl tert-butyl ether + acetone + cyclohexane, methyl tert-butyl ether + acetone and methyl tert-butyl ether + cyclohexane

Abstract

Introduction

Section snippets

Purity of materials

Vapor–liquid equilibrium

Conclusions

Acknowledgment

Fuel

Toxicol. Lett.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Chem. Eng. Sci.

Fuel

J. Energy Inst.

J. Braz. Chem. Soc.

J. Chem. Eng. Data

Phys. Chem. Chem. Phys.

Promst. Sint. Kauch.

J. Chem. Eng. Data