Fluid Phase Equilibria 233 (2005) 47–55 Estimation of isobaric vapor–liquid–liquid equilibria for partially miscible mixture of ternary system Hitoshi Kosuge ∗ , Koichi Iwakabe DepartmentofChemicalEngineering,GraduateSchoolofScienceandEngineering,TokyoInstituteofTechnology,2-12-1, Ookayama,Meguro,Tokyo152-8552,Japan Received 12 October 2004; received in revised form 6 April 2005; accepted 15 April 2005 Available online 17 May 2005 Abstract The NRTL and UNIQUAC parameters for ethanol–2-butanol–water and ethanol–water–1-butanol systems are determined from the vapor–liquid equilibrium (VLE) data of the constituent binary mixtures and the vapor–liquid–liquid equilibrium (VLLE) data of the ternary mixtures. Those parameters are used to calculate the isobaric ternary VLLE, and the effect of parameters on the calculated VLLE is discussed. The isobaric ternary VLLE are calculated by the parameters determined from the isobaric VLE data of the constituent binary mixtures, but the binodal curves are quite different from the experimental data. Then, the parameters for VLE and LLE calculations are separately determined using the VLE and LLE data on the ternary binodal curve. The LLE parameters are determined by a newly developed method, where the parameters for partially miscible binary mixture are preliminary determined from the pseudo-binary LLE data that are obtained from the ternary LLE data, and then the rest of LLE parameters of the ternary systems are determined. The isobaric VLLE of ethanol–2- butanol–water and ethanol–water–1-butanol systems are calculated by the parameters determined from the present method, and show good agreement with the experimental data, compared with those by Katayama’s method. The proposed method is also successfully applied to ethyl acetate–ethanol–water system. © 2005 Elsevier B.V. All rights reserved. Keywords: Vapor–liquid–liquid equilibrium; NRTL parameter; UNIQUAC parameter; Estimation; Ternary system 1. Introduction Heterogeneous distillation process is widely used to separate azeotropic and close-boiling point mixtures. In the separation of a binary azeotropic mixture, third component is usually added as an entrainer that forms two liquid phases with one component of the binary mixture, and the minimum or maximum azeotropic mixture is taken from the top or the bottom of the distillation column. Meanwhile, another component in the feed mixture is concentrated in the reverse side of the column. Therefore, the isobaric vapor–liquid–liquid equilibrium (VLLE) as well as vapor–liquid equilibrium (VLE) is indispensable to design and analyze the heterogeneous distillation process. ∗ Corresponding author. Tel.: +81 3 5734 2151; fax: +81 3 5734 2151. E-mailaddress: hkosuge@chemeng.titech.ac.jp (H. Kosuge). VLLE of partially miscible liquid mixtures is the three- phase equilibrium conditions that VLE and liquid–liquid equilibrium (LLE) are simultaneously realized in the two- liquid phase region. Assuming the vapor phase to be ideal, the condition of VLLE is expressed as follows: y i  P S i P 0  = (γ i x i ) I = (γ i x i ) II (1) where I and II represent the liquid phases, P S i the saturated vapor pressure of the component i and P 0 is the total pressure. Thus, VLLE calculation of partially miscible liquid mixtures is usually carried out by calculating VLE and LLE with the same set of parameters in activity coefficient models. Re- cently, binary and ternary VLLE were measured at atmo- spheric pressure [1–8], and parameters in activity coefficient models were determined from the experimental VLE and/or 0378-3812/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fluid.2005.04.010