Experimental study on (vapor + liquid) equilibria of ternary systems of hydrocarbons/ionic liquid using headspace gas chromatography Babak Mokhtarani ⇑ , Leila Valialahi, Kurosh Tabar Heidar, Hamid Reza Mortaheb, Ali Sharifi, Mojtaba Mirzaei Chemistry and Chemical Engineering, Research Center of Iran, P.O. Box 14335-186, Tehran, Iran article info Article history: Received 18 December 2011 Received in revised form 19 February 2012 Accepted 24 February 2012 Available online 5 March 2012 Keywords: Ionic liquid (Vapor + liquid) equilibria Headspace gas chromatography NRTL model abstract (Vapor + liquid) equilibrium (VLE) data for ternary systems of (hexane + benzene), (hexane + cyclohex- ane), (benzene + cyclohexane), (1-hexene + cyclohexane), and (1-hexene + benzene) with an ionic liquid were measured by headspace gas chromatography. The applied ionic liquid 1-methyl 3-octylimidazolium thiocyanate, [Omim][SCN], acts as an entrainer. The comparison of the measured VLE data with the equi- librium data for the binary mixtures without ionic liquid show that [Omim][SCN] significantly improves the separation factor of these systems. The NRTL thermodynamic model is applied for correlating the experimental data. The modeling results show the NRTL model can correlate the experimental data with a good accuracy. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Ionic liquids (ILs) are new solvents, which show very interesting properties such as low vapor pressure, non-flammability, chemical stability at high temperatures, and excellent solubility with organ- ic and inorganic compounds. Due to negligible vapor pressure of ILs, these substances can be used as substitute for toxic and volatile organic compounds. As the ILs are composed of a cation and an an- ion, their physical properties can be adjusted by appropriate selec- tion of the cation or anion [1]. In spite of the promising properties of ILs, only restricted applications are defined for these new sol- vents in industry. This is partly because of the lack of their physi- cochemical data either in pure forms or as mixture with organic/ inorganic compounds. In many industrial applications, it is essen- tial to know how they interact with different solutes. Therefore, knowing the thermodynamic behavior of IL in different solute and having the reliable experimental data of phase equilibria have a great importance. As a new application for ILs, they can be used as an entrainer to facilitate the separation of close-boiling binary hydrocarbons, and can be appropriate alternatives for toxic and volatile organic sol- vents such as sulfolane, N-methylpyrrolidone (NMP), and N-form- ylmorpholine (NFM). In recent years, a number of experimental VLE data for the ILs/hydrocarbons have been reported in several publications [2–7]. Headspace gas chromatography (GC) is an efficient method for measuring VLE data of binary hydrocarbons [8]. The composition of the vapor phase is determined by gas chromatography. This method saves time and reduces the potential errors that are com- mon in other GC sample preparation techniques. The effect of IL present in the hydrocarbon binaries has not widely studied by this method. Liebert et al. [6] measured the (vapor + liquid) equilibria (VLE) of (methylcyclohexane + toluene) and (1-octene + octane) mixtures in the presence of 1-hexyl-3-methyl-imidazolium bis (trifluoromethyl-sulfonyl)imide [Hmim][BTI]. Westerholt et al. [7] investigated the effect of 1-butyl-3-methylpyrrolidinium bis (trifluoromethyl-sulfonyl)imide [Bmpyr][BTI] and [Hmim][BTI] on the separation (benzene + cyclohexane), (1-hexene + n-hexane), and (2-propanol + water) binaries. The effect of different ILs, 1-octyl-3-methyl-imidazolium bis(trifluoromethyl-sulfonyl)imide [Omim][BTI], [Hmim][BTI], 1-octyl-3-methyl-imidazolium trifluoro- methanesulfonate [Omim][OTF], and 1-butyl-3-methyl-imidazolium trifluoro-methanesulfonate [Bmim][OTF] on the VLE of(hexane + benzene), (hexane + cyclohexane), (benzene + cyclohexane), and (ethanol + water) have been studied by Mokhtarani and Gmehling [8]. Cehreli and Gmehling [9] reported the VLE data for the mixture of (cyclohexene + benzene) with different types of ILs. Recently, Matsuda et al . [10] investigated on the influence of 1-ethyl-3-methylimidazolium ethyl sulfate [Emim][EtSO 4 ] on the VLE for two binary systems of (1-propanol + water) and (methyl acetate + methanol). The literature data reveal that adding IL to the binary systems of hydrocarbons improve the separation factors in those systems. 0021-9614/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2012.02.032 ⇑ Corresponding author. Tel.: +98 21 44580751; fax: +98 21 44580781. E-mail address: mokhtaranib@ccerci.ac.ir (B. Mokhtarani). J. Chem. Thermodynamics 51 (2012) 77–81 Contents lists available at SciVerse ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct