(Liquid + liquid) equilibrium of (NaNO 3 + PEG 4000 + H 2 O) ternary system at different temperatures Yecid P. Jimenez, Héctor R. Galleguillos ⇑ Departamento de Ingeniería Química, Universidad de Antofagasta, CICITEM, Chile article info Article history: Received 30 October 2010 Received in revised form 3 May 2011 Accepted 6 May 2011 Available online 24 May 2011 Keywords: Aqueous two-phase system (Liquid + liquid) equilibrium Polyethylene glycol Sodium nitrate abstract Phase diagram and (liquid + liquid) equilibrium (LLE) data for the (NaNO 3 + polyethylene glycol 4000 (PEG 4000) + H 2 O) system have been determined experimentally at T = (288.15 and 308.15) K. The effects of temperature on the binodal curves and tie-lines have been studied and it was found that an increasing in temperature caused the expansion of two-phase region. The Chen-NRTL, modified Wilson and UNI- QUAC models were used to correlate the experimental tie-line data. The results show that the quality of fitting is better with the UNIQUAC model. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Aqueous two-phase systems (ATPS), consist of two immiscible aqueous solutions, it can contains two polymers and water or a polymer, an inorganic salt and water. The first reported in the lit- erature was in 1896 by Beijerinck [1], later Alberston [2] applied the ATPS for recovery of biomolecules. (Polymer + salt) aqueous two-phase systems have more advantages than (polymer + poly- mer) systems. These advantages are low price, low viscosity and a short time for phase splitting. The high viscosity and high cost of (polymer + polymer) system restricts its use in the industrial scale [3]. Chile is the largest world producer of sodium nitrate and potas- sium nitrate; thus it is interesting to explore the possibility of parti- tioning sodium perchlorate and sodium nitrate in ATPS formed by aqueous sodium nitrate and sodium perchlorate solutions, respec- tively. As part of a long-term study, we report here (liquid + liquid) equilibrium composition data for aqueous mixtures of sodium nitrate and PEG 4000 at T = (288.15 and 308.15) K. These (liquid + liquid) equilibrium (LLE) data allow us to plan the sodium perchlorate partition experiences from known compositions of the midpoints of each tie-line. On the other hand, in a previous article the LLE of the (NaClO 4 + PEG 4000 + H 2 O) system was reported [4]. Graber et al. [5,6] reported the phase diagram of the (NaNO 3 + PEG 4000 + H 2 O) system at T = 298.15 K and in a later article the influence of molecular weight of the polymer on the LLE also at T = 298.15 K was studied. As far as we know, there is no report on the phase diagram of this system at T = (288.15 and 308.15) K. In addition to the equilibrium measurements, the refractive indices, densities and kinematic viscosity of solutions of each phase were measured. There are mainly three kinds of models proposed in literature, either based on the osmotic virial expansion, or lattice theories as on the local composition models. Osmotic virial expansions, using the pressure of a solvent in the solution, have been used in the describing the phase behavior of two-phase systems in various versions [7–19]. The models based on the lattice theories, the Flo- ry–Huggins theory, and on the local composition concepts and theirs modifications [20–23] are among the most familiar ones used to represent LLE phase diagram of (polymer + salts) ATPS. In the present work the Chen-NRTL [24], modified Wilson [25] and extended UNIQUAC [23] models were applied for the correlation of experimental LLE data of the (aqueous NaNO 3 + PEG 4000 + H 2 O) system. In this correlation, the experimental data re- ported by Graber et al. [5,6] have also been included. The Flory– Huggins expression [26] and Pitzer–Debye–Hückel equation [27] were used for the entropy of mixing molecules of different sizes and to account for the long-range electrostatic interactions of the ions, respectively. Additionally, the effect of temperature on the LLE of the system above mentioned has also been study. 2. Experimental 2.1. Materials Synthesis grade samples of polyethylene glycol with an average molar mass of 4000 (3500–4500) and analytical reagent grade 0021-9614/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2011.05.007 ⇑ Corresponding author. Tel.: +56 55 637313; fax: +56 55 637801. E-mail address: hgalleguillos@uantof.cl (H.R. Galleguillos). J. Chem. Thermodynamics 43 (2011) 1573–1578 Contents lists available at ScienceDirect J. Chem. Thermodynamics journal homepage: www.elsevier.com/locate/jct