Isobaric VLE of the mixture {(±)-linalool + ethanol}: A case study for the distillation of absolute and volatile oils Sandra M. García-Abarrio, Luisa Haya, Juan I. Pardo, José S. Urieta, Ana M. Mainar ⇑ Group of Applied Thermodynamics and Surfaces (GATHERS), Aragon Institute for Engineering Research (I3A), Facultad de Ciencias, Universidad de Zaragoza, Zaragoza 50009, Spain article info Article history: Received 16 March 2013 Received in revised form 10 May 2013 Accepted 13 May 2013 Available online 22 May 2013 Keywords: (±)-Linalool Ethanol VLE Cubic EOS SAFT COSMO-RS 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 compar- ative 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 r-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. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Supercritical fluids are being actively investigated in extraction and advanced separation processes, especially in the case of super- critical CO 2 because of the sustainable character of the processes based in this solvent [1]. Referring to the extraction of polar com- pounds it is necessary the use of modifiers to overcome the non po- lar character of CO 2 . 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 super- critical techniques) of alkanol and a target compound or com- pounds, 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 stud- ied the thermophysical behavior of several mixtures of alkanol with a compound present in volatile oils that are obtained through supercritical CO 2 extraction. Among these systems, several proper- ties of the mixture {(±)-linalool (1) + ethanol (2)} have been mea- sured [2–5]. 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 CO 2 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 Quasi- chemical Activity Coefficient (UNIQUAC) equations. On the other hand, the COSMO-RS method [6–10], 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 pre- dict 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 vol- ume translation (VT) according to Peneloux) and the other one based on perturbation models (Statistical Associating Fluid The- ory). 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 0021-9614/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2013.05.022 ⇑ Corresponding author. Tel.: +34 976 761 195; fax: +34 976 761 202. E-mail address: ammainar@unizar.es (A.M. Mainar). J. Chem. Thermodynamics 64 (2013) 182–186 Contents lists available at SciVerse ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct