DISQUAC Predictions on Thermodynamic Properties of Ternary and Higher Multicomponent Mixtures. 3. Results for H E of Ternary Mixtures Containing One Alcohol, One Polar Compound, and One Hydrocarbon or Two Alcohols and One Hydrocarbon or a Polar Compound, or Three Alkanols Juan Antonio Gonza ´ lez,* Ismael Mozo, Isaı ´as Garcı ´a de la Fuente, and Jose ´ Carlos Cobos GETEF, Departamento Termodina ´ mica y Fı ´sica Aplicada, Facultad de Ciencias, Universidad de Valladolid, Valladolid, 47071 Spain DISQUAC predictions on molar excess enthalpies, H E , are shown for a set of 67 ternary mixtures formed by one alcohol, one active compound (not self-associated), and one hydrocarbon; two alkanols and one hydrocarbon; two alkanols and one polar compound; or three alkanols. DISQUAC provides reliable predictions on H E (≈8%) for the ternary mixtures considered using binary interaction parameters only, i.e., neglecting ternary interactions. Differences between experimental results and theoretical calculations are of the same order for the ternary mixtures and for the constituent binaries. On the other hand, predictions are practically independent of the mixture compounds or of the number of contacts present in the solution. The poorer results are obtained for systems with a binary that shows strongly negative deviations from Raoult’s law. A systematic comparison between DISQUAC results and those from the Dortmund UNIFAC model is presented. DISQUAC improves UNIFAC predictions, as well as those from ERAS for 1-alkanol + oxaalkane + alkane mixtures. More complex association models yield results that are similar to those from DISQUAC. Therefore, DISQUAC should be applied when the interaction parameters used are available. The interaction parameters used are valid for the description of the thermodynamic properties of binary mixtures (vapor-liquid, solid-liquid, and liquid-liquid equilibria, H E , and the molar excess heat capacity at constant pressure, C p E ) as well as for predictions on vapor-liquid equilibria, H E , and C p E for ternary mixtures. 1. Introduction Although large amounts of data have been reported in the literature for binary mixtures, data for ternary systems and higher multicomponent solutions are scarce. This is due to the time and effort required to obtain a meaningful set of multicomponent data. For this reason, one of the most important tasks of the thermodynamics is to provide predictions on the thermodynamic proper- ties of multicomponent mixtures using data obtained from more simple systems and, in the case of vapor- liquid equilibrium (VLE), for pure substances. Of course, the most essential step is to pass from binary to ternary systems, to determine the extent to which the properties in these mixtures can be predicted on the basis of binary data, and to assess when data reflecting ternary interactions are absolutely needed. In the field of correlation and prediction of multicom- ponent data, many efforts have been developed on the basis of statistical thermodynamics methods, several theoretical solution models, and semiempirical equations. 1-21 Nevertheless, each method seems to have its own area of application limited to particular types of systems. These difficulties continue to grow with an increase in the number of components. For example, in the case of alcoholic solutions, the classical association model, 1 based on the so-called formation of polymeric species of alkanol molecules through hydrogen bonding, must be improved depending on the chemical nature of the remainder of the components. 2-15 These improve- ments affect the physical contribution to the thermo- dynamic properties 1-3,5,6,12-15 as well as the chemical contribution. 1-15 So, in ternary mixtures with two alkanols and one active nonassociating compound, complex formation should be considered in all three combinations because of the charge transfer of the self- associating and active components. The semiempirical equations more commonly used 19-21 (Redlich-Kister, Colinet, Scatchard-Hillert, and Tsao- Smith) to predict H E of ternary systems are geometrical methods to establish the contribution of each of the three binaries involved to the ternary H E . For asym- metric equations with respect to the numbering of components, it is of great importance which component is designated as component 1. An additional problem comes from the fact that H E of the constituent binaries must be known to apply these equations, and the same occurs for association models. Group contribution theories 22-27 are powerful meth- ods to predict ternary data (VLE and/or H E ), neglecting ternary interactions. That is, only information from the set of binary systems that contain the groups present in the ternary mixture analyzed is needed. However, it must be elucidated what type of information used is relevant to improve predictions. For example, it has * To whom correspondence should be addressed. Fax: + 34- 83-42-31-35. E-mail: jagl@termo.uva.es. 7622 Ind. Eng. Chem. Res. 2004, 43, 7622-7634 10.1021/ie0400696 CCC: $27.50 © 2004 American Chemical Society Published on Web 10/16/2004