Isothermal vapour–liquid equilibria and excess enthalpies for the binary mixtures containing an isomeric chlorobutane and diisopropyl ether

doi:10.1016/j.fluid.2011.06.001

Fluid Phase Equilibria

Volume 308, Issues 1–2, 25 September 2011, Pages 8-14

https://doi.org/10.1016/j.fluid.2011.06.001 Get rights and content

Abstract

Isothermal vapour–liquid equilibria for the four binary mixtures formed by an isomer of chlorobutane (1-chlorobutane, 2-chlorobutane, 2-methyl-1-chloropropane, or 2-methyl-2-chloropropane) and diisopropyl ether has been studied at T = 288.15 K, 298.15 K, and 308.15 K. The experimental data have been satisfactorily checked for thermodynamic consistency using the method of van Ness. The isothermal vapour–liquid equilibrium data have been correlated using the Wilson equation and excess Gibbs energies have been calculated. Moreover, we have measured excess enthalpies at T = 298.15 K using an isothermal flow calorimeter; combining these excess enthalpies with excess Gibbs energies the corresponding entropic contributions to excess Gibbs energy have been obtained. The group contribution method UNIFAC has been used to predict the phase equilibrium behaviour of the mixtures at isothermal conditions.

Highlights

► We study isothermal vapour–liquid equilibria of four systems chloroalkane + ether. ► We measure the corresponding excess enthalpies. ► A donor–acceptor type interaction can explain the thermodynamic behaviour. ► We check the VLE predictive ability of the UNIFAC method.

Introduction

The study of vapour–liquid equilibria (VLE) at isothermal conditions provides experimental data of great interest in thermodynamics and chemical engineering and contributes decisively for the development of accurate methods to predict and correlate phase equilibria.

In the past years our research group has been involved in a systematic and comprehensive study about phase equilibria and thermodynamic properties of mixtures formed by a cyclic ether and a halogenated compound [1], [2], [3], [4]. From a theoretical point of view, binary mixtures of ethers and chloroalkanes are particularly interesting due to their complexity, a consequence of the presence of specific Cl–O interactions. Moreover, the study of ether mixtures is very important since oxygenated compounds are added to improve the octane rating and the pollution-reducing capability of gasoline. Between these compounds, diisopropyl ether could be a suitable and alternative candidate as gasoline additive [5], [6].

Recently we have reported densities, speeds of sound, refractive indices, and viscosities of binary mixtures formed by isomeric chlorobutanes (1-chlorobutane, 2-chlorobutane, 2-methyl-1-chloropropane, or 2-methyl-2-chloropropane) and diisopropyl ether in the temperature range 283.15–313.15 K [7], [8]. In this work, the isothermal vapour–liquid equilibria for the same mixtures has been studied at the temperatures of 288.15 K, 298.15 K and 308.15 K. Thermodynamic consistency of the experimental VLE data has been satisfactorily checked by the method of van Ness. We have also correlated activity coefficients of the components of the mixtures using the Wilson equation [9], from these activity coefficients the corresponding excess Gibbs energies have been calculated. The results presented here have been used to test the reliability of the UNIFAC predictions [10], [11]. Moreover, excess enthalpies have been determined at the temperature 298.15 K using an isothermal flow calorimeter and finally from excess enthalpies and excess Gibbs energies we have estimated the corresponding entropic contributions to excess Gibbs energy.

Section snippets

Experimental

The liquids used were 1-chlorobutane, 2-chlorobutane, 2-methyl-2-chloropropane, and diisopropyl ether (better than 99% mass) obtained from Aldrich and 2-methyl-1-chloropropane (better than 99% mass) provided by Fluka. No additional purification has been carried out.

The vapour–liquid equilibrium was studied using an all-glass dynamic recirculating type still that was equipped with a Cottrell pump. It is a commercial unit (Labodest model) built in Germany by Fischer. The equilibrium temperature

Results and discussion

The pressure–composition diagrams, p–x₁–y₁, are shown in Fig. 1, Fig. 2, Fig. 3, Fig. 4. The Wilson equation has been used to correlate the activity coefficients of the components in the liquid phase. Estimation of the adjustable parameters of the equation was based on minimization of the following objective function in terms of experimental and calculated pressure values [13]: $F = {\sum_{i = 1}^{n} (\frac{p^{exp} - p^{c a l}}{p^{exp}})}_{i}^{2}$

The calculated pressure is obtained taking into account both the non-ideality of the vapour phase

UNIFAC predictions

The group contribution UNIFAC method was used to predict the isothermal vapour–liquid equilibrium of all the systems studied. In this method the activity coefficient is the sum of a combinatorial part and a residual part $ln γ_{i} = ln γ_{i}^{C} + ln γ_{i}^{R}$

The combinatorial part is: $ln γ_{i}^{C} = 1 - {V^{'}}_{i} - 5 q_{i} (1 - \frac{V_{i}}{F_{i}} + ln (\frac{V_{i}}{F_{i}}))$ the parameters ${V^{'}}_{i}$ , $V_{i}$ and $F_{i}$ can be calculated by using the relative van der Waals volumes, R_k, and molecular surfaces areas, Q_k, of the different subgroups. ${V^{'}}_{i} = \frac{r_{i}^{3 / 4}}{\sum_{j} x_{j} r_{j}^{3 / 4}}$ $V_{i} = \frac{r_{i}}{\sum_{j} x_{j} r_{j}}$ $r_{i} = \sum_{k} ν_{k}^{(i)} R_{k}$ $F_{i} = \frac{q_{i}}{\sum_{j}}$

Conclusions

In this work, a thermodynamic study of mixtures formed by an isomeric chlorobutane (1-chlorobutane, 2-chlorobutane, 2-methyl-1-chloropropane, or 2-methyl-2-chloropropane) and an alkyl ether (diisopropyl ether) has been performed throughout the determination of excess Gibbs energies at several temperatures (T = 288.15 K, 298.15 K, and 308.15 K) and excess enthalpies at T = 298.15 K. The small values of these properties indicate a quasi-ideal thermodynamic behaviour due to the counterbalance of two

Acknowledgements

We are grateful for financial assistance from Diputación General de Aragón and Universidad de Zaragoza.

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In the last few years, our research group has been carrying out a comprehensive thermodynamic study about mixtures formed by chlorobutanes and ethers [1–4] in order to go deeply into the effect of energetic and structural factors in their behaviour.
We report in this work, experimental surface tensions for binary mixtures of isomeric chlorobutanes with butyl ethyl ether or diisopropyl ether from T = 283.15 K to 303.15 K measured with a drop volume tensiometer. The surface tension data have been correlated with a Redlich–Kister type equation. More information about the surface behaviour can be obtained combining these results with previously reported VLE measurements to calculate the excess surface composition of ether in the mixture. Finally, the results have been compared to the predictions obtained using a group contribution method.
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In many chemical engineering areas such as process design and purification techniques, a reliable estimation of thermodynamic properties as a function of composition, temperature and pressure is particularly important. In the last years our research group has made a considerable effort on the measurement of thermodynamic properties of liquid mixtures containing ethers and halogenated compounds [1–4]. In this contribution, we report densities over the temperature range (283.15 to 313.15) K and isothermal (vapour + liquid) equilibrium data at T = (288.15, 298.15 and 303.15) K for the four binary mixtures formed by an isomeric chlorobutane and butyl ethyl ether.
Densities of the binary systems containing an isomer of chlorobutane (1-chlorobutane, 2-chlorobutane, 2-methyl-1-chloropropane, or 2-methyl-2-chloropropane) and butyl ethyl ether have been measured over the temperature range (283.15 to 313.15) K. Moreover, isothermal (vapour + liquid) equilibria have also been determined at three temperatures (T = (288.15, 298.15, and 308.15) K). Excess properties have been obtained from the experimental data and correlated. Finally, the VTPR model has been used to predict densities and (vapour + liquid) equilibria of the binary systems studied.
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Isothermal vapour–liquid equilibria and excess enthalpies for the binary mixtures containing an isomeric chlorobutane and diisopropyl ether

Abstract

Highlights

Introduction

Section snippets

Experimental

Results and discussion

UNIFAC predictions

Conclusions

Acknowledgements

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

J. Phys. Chem. B

J. Chem. Phys.

J. Chem. Eng. Data

Report; Interagency Assessment of Oxygenated Fuels. Chpt. 2

Int. J. Thermophys.

J. Chem. Eng. Data

J. Am. Chem. Soc.

AIChE J.

Ind. Eng. Chem. Res.