Ternary Ilquld-llquld equlllbrlum data have been measured for the systems acetonltrlle-benzene-cyclohexane and acetonltrlle-toluene-cyclohexane at 298.15 and 318.15 K and for the system methanol-ethanol-cyclohexane at 298.15 K. The results have been analyzed by uslng the extended UNIOUAC and UNIOUAC equatlons wlth only blnary parameters. The ablllty of the extended UNIOUAC equatlon In predlctlng ternary vapor-llquld equlllbrla from blnary data Is compared wlth that of the UNIOUAC equatlon.
I ntroductlonThe existing equations for the excess Gibbs energy function are generally used to solve phase equilibrium problems and a considerable effort has been given to obtain suitable equations which correlate liquid compositions and activity coefficients.The prediction of ternary liquid-liquid equilibria from binary data is rather more difficult than that of ternary vapor-liquid equilibria. The present work alms to compare the ability of two activity coefficient equations, the extended UNIQUAC equation and the UNIQUAC equation modifled by Anderson and Prausnitz (7), to predict the ternary liquid-liquid equilibrium data of the three investigated systems and the ternary vapor-liquid equilibrium data of four typical systems taken from the literature by using binary data alone.
Experimental SectlonMaterlsls. Pure ethanol was obtained from the Japan Monopoly Corp. and other chemicals were purchased from Wakoh Chemical Co. Acetonitrile (guaranteed reagent grade), toluene, and methanol (spectrograde) were used directly. Benzene (guaranteed reagent grade) was subjected to recrystallization 3 times. Cyclohexane (guaranteed reagent grade) was purified by fractional distillation from a I-m column packed with McMahon packing. Ethanol was refluxed wlth calcium oxide and then fractionally distilled. Densities of substances were measured with an Anton Paar (DMA-40) densimeter at 298.15 K and are in excellent agreement with literature values (2).Methods. Two separate methods were used to study liquid-liquid equilibria. The first one is to titrate binary mixtures of known composition with a third component to obtain the binodal curves. The onset of turbidity in the solution determined the end point. During titration, the sample solutions were maintained at a desired temperature within fO.O1 O C by using a water thermostat. The second one is to determine the liquid-liquid tie lines by ensuring equilibrium between two ternary liquid phases and then withdrawing portions of each sample liquid layer with a preheated hypodermic syringe. The sample liquids were analyzed with a Shimadzu (oC4C) gas chromatograph connected to a Shimadzu (ITG-PA) digital integrator.
Results and Data ReductionTables I and I 1 present solubility and tie-line data for the three systems. Two forms of the UNIQUAC equation are used Table I. Solubility Data XI x2 XI xz XI x2 x, X2 Acetonitrile (1)-Benzene (2)-Cyclohexane (3) at 298.15 K 0.to analyze the experimental data. We use the following modified form of the UNIQUAC equation for the excess Gibbs energy gE called the...