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Comparatlve ebulllometry was used to measure actlvlty coefficients at lnflnlte dllutlon for the binary systems tetrahydrofuran separately wlth cyclohexane, ethyl acetate, n -pentane, n hexane, and n heptane, cyclohexme wlth ethyl acetate, 1,Cdloxane wlth n-heptane, and P-furaldehyde wlth butyl ether. To correct for dlfferences between the compodtlon of the feed solutlon and the actual llquld equlllbrlum composltlon, the evaporation factor was measured. Parameters for several Glbbs free energy models were determlned from the actlvlty coefflclents at lnflnlte dlutlon, and the predictions of the models over the whole composltlon region were compared wlth vapor-llqukl equHlbrlum data for some of the systems studled. The experlmental results were also compared to UNIFAC predlctlons. I ntroductlonIn the absence of reliable experimental vapor-liquid equilibrium data, activity coefficients at infinite dilution can be used to model vapor-liquid equilibrium phase behavior of mixtures. The relative experimental ease and rapid approach to equilibrium make ebulliometry a preferred method of measuring activity coefficients at infinite dilution (7-3). Parameters of local composition activity coefficient models such as Wilson, NRTL, or UNIQUAC can be determined directly from activity coefficients at infinite dilution. Infinite dilution activity coefficients themselves are important in separation techniques for very dilute systems, such as the production of high-purity reagents and the Separation of pollutants from the environment. Since activity coefficients at infinite dilution represent the maximum deviation from ideal solution behavior for most binary systems, model parameters determined from activity coefficients at infinite dilution can be used to accurately predict vapor-liquid equilibrium throughout the composition range. However, if an activity coefficient model has little or no theoretical basis, predictions based on activity coefficients at infinite dilution may not be optimal.Group contribution methods, such as UNIFAC (4) and TOM (5), may be used for predicting activity coefficients and other thermodynamic properties of liquid mixtures, when no experimental data are available. However, the UNIFAC group-interaction parameter table is only about 50% complete so there is a need for the evaluation of the missing parameters. Activity coefficients at infinite dilution provide information to estimate these missing group-interactlon parameters (6). Also the infinite dilution region provides an especially severe test of the UNIFAC method which is known to give questionable predictions of infinite dilution activity coefficients, especially for mixtures of molecules of very different size (7, 8). TheoryComparative ebulliometry for determining activii coefficients at infinite dilution consists of measuring the boiling temperature at constant pressure or the equilibrium pressure at constant temperature of binary mixtures as a function of gravimetrically prepared composition. By using twin ebulliometers, one a 0021-956818811733-043...

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