The determination of activity coefficients at infinite dilution.

Abstract

The aim of this work was to extend the theory of Everett and Cruickshank, for the determination of activity coefficients at infinite dilution, Y 13 (where 1 refers to the solute and 3 to the solvent), to accommodate solvents of moderate volatility, using the gas liquid chromatography (GLC) method. A novel data treatment procedure is introduced to account for the loss of solvent off the column, during the experiment. The method also allows us to determine the vapour pressure of the solvent. No auxiliary equipment is required, and the method does not employ the use of a presaturator. Further, the effect of a polar involatile solute is examined using various types of solutes. The activity coefficient was found to be independent of column packing and flowrate. Considering the volatile solvent, the systems investigated by the GLC method were straight chain hydrocarbons, (n-pentane, n-hexane and n-heptane), cyclic hydrocarbons (cyclopentane, and cyclohexane) and an aromatic compound, benzene. The systems were investigated at 2 temperatures, 280.15 K and 298.15 K. The results indicate a clear dependence of the activity coefficient on temperature. For the polar nonvolatile solvent, sulfolane (tetrahydrothiophene, 1,1 dioxane) was used. The systems studied were sulfolane + n-pentane, n-hexane, n-heptane, cyclopentane, cyclohexane, benzene, tetrahydrofuran, and tetrahydropyran. The systems were studied at one temperature, 303.15 K, due to the low melting point of sulfolane i.e. 301.60 K. Part of this study into the thermodynamics of solutions'\vas conducted at the Technical University of Warsaw, where the equilibria of sulfolane was studied using· two techniques, a dynamic solid-liquid equilibrium method (SLE), and an ebulliometriGI vapor-liquid method (VLE) . The main purpose of this was to apply solution theories to this data in order to predict the.activity coefficient at infinite dilution for the sulfolane mixtures. The systems measured using solid liquid equilibrium are sulfolane + tetrahydrofuran, or, 1,4-dioxane, or, I-heptyne, or, 1, 1, l,-trichloroethane, or, benzene, and cyclohexane. The results of these measurements were then described using various solution theories, and· new interaction parameters obtained. The vapour liquid equilibrium systems measured were sulfolane + I-heptyne, or, tetrahyrdofuran, or, 1,1, I-trichloroethane, and tetrachloromethane. Here as in SLE the results were described using solution theories. The results of both the VLE and SLE measurements were used in a multiple optimization procedure to produce new parameters for the interaction of sulfolane with various groups, using two group contribution method, DISQUAC and modified UNIFAC. The predicted activity coefficients compare well with the measured values using GLC.