Fluid Phase Equilibria 360 (2013) 392–400 Contents lists available at ScienceDirect Fluid Phase Equilibria j our na l ho me pa ge: www.elsevier.com/locate/fluid Liquid–liquid equilibria studies on ammonium and phosphonium based ionic liquid–aromatic–aliphatic component at T = 298.15 K and p = 1 bar: Correlations and a-priori predictions C.V. Manohar, Dharamashi Rabari, A. Ananth Praveen Kumar, Tamal Banerjee ∗ , Kaustubha Mohanty Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India a r t i c l e i n f o Article history: Received 3 April 2013 Received in revised form 1 October 2013 Accepted 3 October 2013 Available online 12 October 2013 Keywords: Aromatic extraction Ionic liquid COSMO-RS LLE NRTL a b s t r a c t The commercial ionic liquids (IL), namely tris (2-hydroxyethyl) methylammonium methylsulfate and tributyl methyl phosphonium methyl sulphate were used for the separation of three systems namely benzene–hexane, toluene–heptane and thiophene–cyclohexene at ambient conditions. Liquid–liquid equilibrium (LLE) data were measured for the ternary systems namely, [TEMA][MeSO 4 ] (1)–benzene (2)–hexane (3); [TEMA][MeSO 4 ] (1)–toluene (2)–heptane (3) and [P4441][MeSO 4 ] (1)–thiophene (2)–cyclohexene (3) at T = 298.15 K and p = 1 bar. The selectivity and distribution coefficient were further calculated from the tie line data. It was observed that the IL required for the extraction will be less and the cross contamination is nearly zero in both the phases. A comparison was made with the available LLE data of imidazolium and pyridinium cations where the distribution ratios for the present work were the lowest irrespective of cation. Similarly, the experimental selectivity values for benzene–hexane separa- tion were higher than the reported selectivities of different cations. Further the experimental tie line data for ternary systems were correlated with NRTL and UNIQUAC models. For all three ternary systems, the RMSD value ranges from 0.22% to 0.88% and 0.31% to 1.05% for NRTL and UNIQUAC model, respectively. Finally, the quantum chemical based COSMO-RS predictions gave RMSD values of 2.9%, 5.78% and 10.3% for IL–benzene–hexane, IL–thiophene–cyclohexene and IL–toluene–heptane systems, respectively. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The separation of mixtures by liquid–liquid extraction is applied in many industrial procedures. This operation has advantages such as mild processes conditions which includes lower temperature and pressure [1]. The separation efficiency in liquid–liquid extrac- tion depends on the suitable solvent. The aromatic compounds are key chemicals in petrochemical, petroleum industries. The aromatic compounds are also basic raw materials for many inter- mediate and fine chemicals. In most cases, aromatics extracted from hydrocarbon feed stocks remains as a mixture of aromatic and aliphatic compounds. The aromatic compounds extracted from hydrocarbon feed stocks are useful in the catalytic cracking feed stocks having commercial importance in the oil industry [2]. The separation of aromatics from aliphatic mixtures is a very chal- lenging job in oil industry. These compounds have close boiling points which leads to the formation of azeotropic mixtures [3]. The ∗ Corresponding author. Tel.: +91 361 2582266; fax: +91 361 2582291. E-mail address: tamalb@iitg.ernet.in (T. Banerjee). conventional separation process for aromatics and aliphatic hydro- carbon mixtures are liquid–liquid extraction [4]. The aromatics are separated from aliphatic by extractive distillation. This process is usually applied when the aromatic content ranges from 20 wt% to 60 wt%. For higher aromatic content (∼90%) separation, azeotropic distillation is preferred. However, treating feed consisting of aro- matic content ranging from 65 wt% to 90 wt% becomes energy intensive. Thus liquid–liquid separation process is generally favor- able as cost and energy requirement is very less. Further the LLE data obtained provide important technical information in devel- oping processes for separation of desired products (extract) from mixtures of hydrocarbons. The commercial solvents which are used for aromatic separation from naphtha or gasoline are acetonitrile, sulfolane, N-methylpyrolidine(NMP), N-formylmorpholine, glycols and poly propylene carbons [5–9]. Organic solvents are basically toxic, flammable, volatile compounds and easily evaporate to atmo- sphere. The cost of the solvent thus becomes very high without the absence of any recovery of the evaporated solvent [10]. Further the capacity and selectivity with these solvents neces- sitates high investments and exhibit large energy consumption. The high energy consumption is mainly due to the need of addi- tional steps for the solvent recovery and purification of product 0378-3812/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2013.10.005