Isobaric VLE of the mixture {(±)-linalool + ethanol}: A case study for the distillation of absolute and volatile oils

doi:10.1016/j.jct.2013.05.022

The Journal of Chemical Thermodynamics

Volume 64, September 2013, Pages 182-186

https://doi.org/10.1016/j.jct.2013.05.022 Get rights and content

Highlights

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Distillation of linalool, the main component of absolute and volatile oils from Lippia alba (Uruguay).
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Isobaric VLE for the mixture (±)-linalool + ethanol is reported at (26.66, 40.00 and 53.33) kPa.
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The mixture (±)-linalool + ethanol shows positive deviations from Raoult’s law.
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COSMO-RS calculations predict rather well the VLE behavior.
•
PR, PRSV-VT and SAFT are tested. PRSV-VT provides the best prediction and correlation.

Abstract

This paper presents the isobaric vapor + liquid equilibrium data at pressures of (26.66, 40.00 and 53.33) kPa for the mixture {(±)-linalool (1) + ethanol (2)} in the whole composition range. Also a comparative study about the capability of several models to describe the experimental behavior is reported. Three models of activity coefficients, namely, Wilson, NRTL and UNIQUAC were used to correlate the experimental data and to check their thermodynamic consistency. The equations of Peng–Robinson (PR), Peng–Robinson–Stryjek–Vera with volume translation (PRSV-VT) and the Statistical Associating Fluid Theory (SAFT) were used to, first, predict and then, to adjust the VLE of the system. The adjusted interactions parameters, k_ij, show a linear dependence with temperature and the best correlations were obtained with the PRSV-VT model. Additionally, COSMO-RS calculations were performed using σ-profiles based on Density Functional Theory (BP86 DFT) with triple valence polarization (TZVP) basis sets. Taking into account the very small number of parameters used, COSMO-RS model leads to good results for this system.

Graphical abstract

Introduction

Supercritical fluids are being actively investigated in extraction and advanced separation processes, especially in the case of supercritical CO₂ because of the sustainable character of the processes based in this solvent [1]. Referring to the extraction of polar compounds it is necessary the use of modifiers to overcome the non polar character of CO₂. For this purpose, light alkanols as ethanol or propan-1-ol have been proposed. Then, to optimize the extraction and the subsequent separation (using either conventional or supercritical techniques) of alkanol and a target compound or compounds, it is advisable to obtain as much information as possible of the mixtures {alkanol + target compound}.

With this aim, in the last few years our research group has studied the thermophysical behavior of several mixtures of alkanol with a compound present in volatile oils that are obtained through supercritical CO₂ extraction. Among these systems, several properties of the mixture {(±)-linalool (1) + ethanol (2)} have been measured [2], [3], [4], [5]. Linalool (3,7-dimethyl-1,6-octadien-3-ol) is a monoterpene often found as the main component of volatile oils in several species of medicinal plants. Specifically, it is the main component of a chemotype of Lippia alba native of Uruguay whose volatile oil we intend to extract and fractionate with supercritical CO₂ technologies.

In this work we follow our study about the mixture {(±)-linalool (1) + ethanol (2)}. The isobaric vapor + liquid equilibrium (VLE) of the mixture was determined at the pressures (26.66, 40.00 and 53.33) kPa. The activity coefficients and the excess molar Gibbs function were determined. These results were correlated using the Wilson, Nonrandom Two-Liquid (NRTL), and Universal Quasichemical Activity Coefficient (UNIQUAC) equations.

On the other hand, the COSMO-RS method [6], [7], [8], [9], [10], a tool for simulation of fluid phase equilibria, was used to predict the VLE of (±)-linalool + ethanol mixture. This method is one of the more accurate variants of the COSMO (COnductor-like Screening Model) solvation model [11], that is, in its turn, an efficient modification of the dielectric continuum solvation methods in quantum chemical programs. COSMO-RS is an extension to “real solvents” (RS) which is a statistical thermodynamics approach based on the results of COSMO calculations.

Furthermore, three equations of state (EOS) were used to predict VLE behavior considering that there was no effect due to the mixture, that is, setting the interaction parameters equal to zero for each model. Two of the EOS were cubic in the molar volume (Peng–Robinson and Peng–Robinson–Stryjek–Vera used with volume translation (VT) according to Peneloux) and the other one based on perturbation models (Statistical Associating Fluid Theory). In sight of the deviations obtained in the predictions, the interaction parameters were adjusted to provide a best fitting of the experimental data. The EOS were selected taking into account previous studies of our research group [4], [12] that showed that the EOS are a good tool for the prediction and correlation of the thermodynamic behavior of such mixtures.

Section snippets

Materials

The liquids used were (±)-linalool and ethanol provided by Aldrich and Scharlau, respectively. All the chemicals were used without further purification and their description appears in table 1.

Equipment

The VLE experiments were performed at constant pressure using an all-glass, dynamic re-circulating still, equipped with a Cottrell pump. It is a commercial unit (Pilodist model VLE 100) capable of handling pressures from (0.25 to 300) kPa and temperatures up to 523.15 K. The procedure followed is very

Vapor + liquid equilibrium data and their correlation

VLE data for binary mixture {(±)-linalool (1) + ethanol (2)} were experimentally determined at the pressures of (26.66, 40.00 and 53.33) kPa. Table 2 shows the VLE data (T, x₁, y₁), the activity coefficients and excess molar Gibbs energies. The activity coefficients (γ_i) were calculated taking into account the non-ideality of the vapor phase, through the following equations: $γ_{i} = \frac{{Py}_{i} \exp [\frac{(V_{i}^{0} - B_{ii}) (P - P_{i}^{sat}) - {(1 - y_{i})}^{2} P δ_{ij}}{RT}]}{P_{i}^{sat} x_{i}},$ and $δ_{ij} = 2 B_{ij} - B_{ii} - B_{jj},$ where x_i and y_i are the liquid and vapor phase compositions,

Conclusions

The isobaric vapor + liquid equilibrium of {(±)-linalool + ethanol} mixture was determined at pressures of (26.66, 40.00 and 53.33) kPa. The activity coefficients were evaluated with Wilson, NRTL and UNIQUAC equations that show a good correlation of the experimental data. These data are thermodynamically consistent.

Three EOS, namely, Peng–Robinson, Peng–Robinson–Stryjek–Vera with volume translation and SAFT have been used, in first place, to predict (k_ij = 0, l_ij = 0) the VLE behavior. All EOS give good

Acknowledgements

The authors thank the financial support from MICINN-FEDER (Project CTQ2009-14629-C02-02), MINECO-FEDER (CTQ-2012-38219-C03-02), and from Gobierno de Aragón-Fondo Social Europeo (Group E-52). SMGA and LH thank GATHERS Group for their research position.

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In the last years our research group is carrying out a study of the thermophysical behavior of binary mixtures constituted by a compound present in volatile oils from plants and an alkanol (references to this work can be found in the literature cited in the papers of Ribeiro et al. [1], Gimeno et al. [2] and García-Abarrio et al. [3].
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View full text

Isobaric VLE of the mixture {(±)-linalool + ethanol}: A case study for the distillation of absolute and volatile oils

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Materials

Equipment

Vapor + liquid equilibrium data and their correlation

Conclusions

Acknowledgements

J. Chem. Thermodyn.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

Fluid Phase Equilib.

J. Chem. Thermodyn.

Fluid Phase Equilib.

J. Chem. Eng. Data

J. Chem. Eng. Data

J. Phys. Chem.

J. Phys. Chem. A

AIChE J.

COSMO-RS: From Quantum Chemistry to Fluid Phase Thermodynamics and Drug Design

J. Chem. Soc. Perkin Trans.

AIChE J.