Liquid-Liquid Equilibria, Density, Viscosity, and Surface and Interfacial Tension of the System Water + n-Butyl Acetate + 1-Propanol at 323.15 K and Atmospheric Pressure Henrique F. Costa, † He ´lio Lourenc ¸o, † Irudayaraj Johnson, ‡ Filipa A. M. M. Gonc ¸alves, † Abel G. M. Ferreira,* ,† and Isabel M. A. Fonseca † Departamento de Engenharia Quı ´mica, Faculdade de Cie ˆncias a Tecnologia, Universidade de Coimbra, Po ´lo II, Rua Sı ´lvio Lima, 3030-790 Coimbra, Portugal, and Department of Physics, St. Joseph’s College, Trichy-620 002, India Liquid-liquid equilibrium (LLE) data are reported for the system water + n-butyl acetate + 1-propanol at 323.15 K and atmospheric pressure. The densities, viscosities, and surface tensions have been measured in the homogeneous liquid range for the binary and ternary liquid mixtures, and the liquid interfacial tensions of the conjugate phases located in the isothermal binodal curve have been determined at the same temperature and pressure. The experimental tie-line data were predicted by the UNIFAC method with good results. The empirical method of Othmer and Tobias was used for tie-line correlation, and the method of Pick et al. was applied for binodal data correlation. The molar volumes, V m , the dynamic viscosity, η, and the surface tension, γ, of the binary systems were correlated in terms of composition using rational functions. The dilute regions of these systems deserved particular attention due to the physicochemical effects taking place in these regions. To describe the ternary system, binary pair additivity and a rational function were considered for the ternary contributions. The surface tension data of binary mixtures were correlated with the models of Fu et al. and Li et al., and the same models were applied for the prediction of ternary data. The liquid interfacial tension measured for the tie-lines was correlated using the relation proposed by Li and Fu. Introduction Extensive information on the thermodynamic and transport properties of water + alkanol + ester liquid mixtures and their binary subsystems is needed in multiple industrial process areas such as fluid flow, heat and mass transfer, and also for the development of theoretical research on molecular interactions in solutions. The knowledge of density, viscosity, and surface and interfacial tensions of aqueous systems containing aliphatic esters is essential in many fields, such as food, flavor, and fragrance industries. The systems alkanol + alkanoate are also of great interest from a theoretical point of view since in the mixing process the breaking of H-bonded structures of the alcohol occurs and the formation of new H-bonded molecular species between the alcohol and the ester takes place. 1 Ternary mixtures, especially those exhibiting liquid-liquid immiscibility, represent an appropriate testing ground for the application of correlation and prediction models. The importance of liquid-liquid extraction in separation technology has increased over the last 30 years, and it is now usually used in pharmaceutical and food industries for recovering valuable organic materials, for example, the alcohols from aqueous solutions. The present work is part of a research program which has been developed in our laboratory that aims to provide density, viscosity, surface tension, and interfacial tension for water + ester + alcohol. 2-6 These systems show a large liquid-liquid immiscibility area, the water + alkanoate being practically immiscible in all the composition ranges. The measurements of densities of the pure esters in a wide range of temperature and pressure are another task taking part of our recent work. 7,8 In the present work, we report on the density, F, on the dynamic viscosity, η, and on the surface tension, γ, measured in the miscible range of the water + n-butyl acetate + 1-propanol liquid system at 323.15 K and atmospheric pressure. From the density data, the excess molar volume, V E , was determined. The rational functions of Myers and Scott 9 and Pando et al. 10 have been used to correlate the above-mentioned properties. The surface tension data of binary mixtures were correlated with the models of Fu et al. 11 and Li et al. 12 The same models were applied for the prediction of this property for the ternary homogeneous liquid mixtures. On the other hand, the published studies on liquid-liquid equilibrium and on interfacial property data of ternary systems of practical interest are scarce when compared with the wide variety of binary systems which have been investigated. The surface and interfacial tensions of solutions have a great effect on the efficiency of the extraction. Since the aqueous solutions of alkanols can be efficiently extracted with esters, accurate thermodynamic properties and LLE data are needed for extrac- tion processes. Some LLE measurements on ternary systems of the type water + aliphatic ester + alkanol can be found in the literature at temperatures below 323 K. 13-16 Therefore, we decided to determine the liquid-liquid equilibria for the water + n-butyl acetate + 1-propanol system at that temperature and to study the interfacial tension between equilibrated liquid phases at the same temperature. The binodal curve was found by the cloud-point method, using a solubility cell assembled for this purpose. The tie-lines were determined by sampling the liquid phases from a cell carefully designed for LLE, and the composition was determined by gas chromatographic techniques. The experimental tie-line data were compared with the predic- * Corresponding author. Fax: +351 239 798 703. Tel.: +351 239 798 729. E-mail: abel@eq.uc.pt. † Universidade de Coimbra. ‡ St. Joseph’s College, India. J. Chem. Eng. Data 2009, 54, 2845–2854 2845 10.1021/je900337a CCC: $40.75  2009 American Chemical Society Published on Web 07/10/2009