Fluid Phase Equilibria 405 (2015) 132–140 Contents lists available at ScienceDirect Fluid Phase Equilibria journal h om epage: www.elsevier.com/locate/fluid Experimental isobaric vapor–liquid equilibrium at sub-atmospheric and local atmospheric pressures, volumetric properties and molar refractivity from 293.15 to 313.15 K of water + triethylene glycol Vineet Aniya, Ashish Singh, Debiparna De, Rupesh Reddy, B. Satyavathi ∗ Chemical Engineering Division, CSIR—Indian Institute of Chemical Technology, Hyderabad 500 007, Telangana, India a r t i c l e i n f o Article history: Received 21 May 2015 Received in revised form 14 July 2015 Accepted 14 July 2015 Available online 22 July 2015 Keywords: Triethylene glycol Water Vapor–liquid equilibrium Volumetric properties Refractive indices a b s t r a c t Experimental isobaric vapor–liquid equilibrium data for the binary system of water + triethylene glycol were obtained at sub-atmospheric pressures of 53.33, 66.66, 79.99 kPa and local atmospheric pressure of 95.99 kPa over the entire composition range using a modified Sweitoslawsky-type ebulliometer. The experimental data was correlated using Wilson and NRTL models. Wilson model was found to better rep- resent the calculation results. The measured densities and refractive indices over the entire composition range of water + triethylene glycol are reported from 293.15 to 313.15 K at local atmospheric pressure of 95.99 kPa. Excess molar volume, partial molar volume and deviations in molar refractivity were eval- uated and fitted to the Redlich–Kister equation. Excess molar volumes were found to be negative at all temperatures and the deviation from ideality decreased with increase in temperature. Different mixing rules were also investigated for predicting the refractive indices of the binary mixture and are reported in terms of their average percentage deviation. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Family of glycols (ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol) is widely used for the dehydration of alcohols such as isopropyl alcohol, tert-butyl alcohol and ethanol [1]. The common applications of glycols lie in extractive distilla- tion where they are used as an extractive agent to alter the relative volatility of the component to be separated. Glycols are also widely used in natural gas dehydration [2]. Aqueous glycol mixtures have multiple industrial applications including manufacturing of sol- vents, as lubricants, hygroscopic agents and conditioning agents. In the modeling and design of such chemical processes the knowledge of the phase equilibrium and the elementary physico-chemical properties are crucial. So in the present scope of work, the binary system investi- gated is water + triethylene glycol (TEG). The system is studied at sub-atmospheric (53.33, 66.66, 79.99 kPa) and local atmo- spheric (95.99 kPa) pressures in the entire composition range. Densities and refractive indices of the binary mixture at various ∗ Corresponding author. Tel.: +91 040 27191399/+91 040 27193141; fax: +91 04027193626. E-mail address: drsatyavathib@gmail.com (B. Satyavathi). compositions have been measured from 293.15 to 313.15 K. A lit- erature survey reveals that although the vapor–liquid equilibrium (VLE) data and volumetric properties of this system are available [3–8], most of these works have been reported data at limited pressures, composition and temperature conditions. Moreover as per author’s knowledge, the phase equilibrium data at the different pressures studied and refractive indices of the binary mixture are not available in the literature at the moment. 2. Experimental 2.1. Materials Triethylene glycol (TEG > 99.5% by mass, Analytical grade) pro- vided by FINAR, India was further purified by simple vacuum distillation and thereafter used for experimentation. TEG was stored in desiccator to prevent moisture absorption. Water used in the present work was double distilled. The final purity of water and TEG was confirmed using gas chromatography and titration methods as described by Rahimpour et al. [3]. The density of the pure components used in the present work was measured at dif- ferent temperatures and are compared with the reported literature [3,5–12] in Table 1. http://dx.doi.org/10.1016/j.fluid.2015.07.030 0378-3812/© 2015 Elsevier B.V. All rights reserved.