Experimental and theoretical study of quaternary (liquid + liquid) equilibria for mixtures of (methanol or water + ethanol + toluene + n-decane) Mohsen Mohsen-Nia * Thermodynamic Research Laboratory, Kashan University, Kashan 87317-51167, Iran Received 2 November 2005; received in revised form 16 February 2006; accepted 25 February 2006 Available online 5 May 2006 Abstract Experimental (liquid + liquid) equilibrium data were obtained for the extraction of toluene from n-decane by mixed-solvents (etha- nol + water) and (ethanol + methanol) at three temperatures (298.15, 303.15, and 313.15) K and ambient pressure. The measured tie-line data for two quaternary mixtures of {(ethanol + water) + toluene + n-decane} and {(ethanol + metha- nol) + toluene + n-decane} are presented. The experimental quaternary (liquid + liquid) equilibrium data have been correlated using the NRTL activity coefficient model to obtain the binary interaction parameters of these components. The NRTL models predict the equilibrium compositions of the quaternary mixtures with small deviations. The partition coefficients and the selectivity factor of the mixed-solvents used were calculated and presented. From our experimental and calculated results, we conclude that for the extraction of toluene from n-decane mixtures the mixed-solvent (ethanol + methanol) has a higher selectivity factor than the other mixed-solvent at the three temperatures studied. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Quaternary mixture; Solvent extraction; Tie-line; NRTL; Selectivity; Partition coefficient 1. Introduction There currently is a considerable interest in using suit- able solvents for extracting aromatic hydrocarbons from alkane mixtures used in chemical and oil industries [1–3]. From a practical and economical point of view, liquid to liquid extraction is an attractive field of investigation [4]. The experimental determination of (liquid + liquid) equi- libria (LLE) for quaternary mixtures has been carried out for some different mixtures [5–8]. By considering the important role of the solvents in the extraction of aromatic hydrocarbons from alkane mixtures, it is worth while to study the LLE of quaternary mixtures of {(mixed-sol- vent) + aromatic hydrocarbons + alkanes}. Due to availability, economics, and environmental aspects, light alcohols may be considered as suitable sol- vents in the recovery of aromatic hydrocarbons from refin- ery process streams. Unfortunately, the associated experimental data on the extraction by the solvent alcohol, such as methanol and ethanol, are scarce. In this work, we report the LLE results for the two quaternary mixtures of {ethanol (1 0 ) + water (1 00 ) + toluene (2) + n-decane (3)} and {(ethanol (1 0 ) + methanol (1 00 ) + toluene (2) + n-dec- ane (3)} at three temperatures (298.15, 303.15, and 313.15) K. The results of this study can lead to the evalua- tion of the effects of the water or methanol as co-solvents on ethanol for the extraction of toluene from n-decane mix- tures. The results obtained were correlated by the NRTL activity coefficient model [9] and the parameters of the model were evaluated and are reported here. Although, sol- vents with high selectivity factors and distribution coeffi- cients are considered potential candidates to carry out the 0021-9614/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2006.02.011 * Corresponding author. Tel./fax: +98 361 5552935. E-mail address: m.mohsennia@kashanu.ac.ir. www.elsevier.com/locate/jct J. Chem. Thermodynamics 38 (2006) 1285–1291