Measurement, prediction, and application of the limiting activity coefficient and its temperature derivative
Trampe, David Mark
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https://hdl.handle.net/2142/21057
Description
Title
Measurement, prediction, and application of the limiting activity coefficient and its temperature derivative
Author(s)
Trampe, David Mark
Issue Date
1989
Doctoral Committee Chair(s)
Eckert, Charles A.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Language
eng
Abstract
Infinite dilution activity coefficients ($\gamma\sp\infty$) were measured for 54 systems using an improved differential boiling point apparatus which exhibited better temperature stability allowing more precise and accurate data to be measured. Values of $\gamma\sp\infty$ for most systems were measured at several temperatures to give an estimate of the partial molar excess enthalpy at infinite dilution (h$\sp{\rm E\infty}$). An asymmetric isothermal flow calorimeter was developed to obtain excess enthalpies (h$\sp{\rm E}$) of binary liquid mixtures of nonelectrolytes in the dilute region, and these values were used to calculate much more precise and accurate values of h$\sp{\rm E\infty}$. A variety of solutes and solvents were examined to characterize the wide range of intermolecular interactions which may occur in solution. Comparisons were made to h$\sp{\rm E\infty}$ values obtained from the temperature dependence of limiting activity coefficient data and to heats of solution at infinite dilution. These data can be used as the basis for incorporating an improved temperature dependence in the MOSCED equation for prediction of limiting activity coefficients. Weaknesses in the original formulation were noted, with suggestions made for future improvements. Current Gibbs energy expressions were examined in terms of their ability to predict liquid-liquid equilibria data using parameters determined from $\gamma\sp\infty$ data and also from h$\sp{\rm E\infty}$ data. The possibility of calculating the binary heat of mixing curve using parameters determined from h$\sp{\rm E\infty}$ data was also examined. Results showed severe inadequacies in the composition and temperature dependencies of the excess Gibbs energy models. The more sensitive derivative data of this study will provide a better basis for future formulations of Gibbs energy expressions. A final application of infinite dilution properties is the estimation of kinetic solvent effects. The prediction, based on the Bronsted-Bjerrum relationship was shown to be relatively insensitive to the values of $\gamma\sp\infty$ of the reactants for the ethyl iodide - triethylamine Menschutkin reaction. A relationship between the change in activation energy of a reaction with solvent and h$\sp{\rm E\infty}$ values of the reactants and transition state was also presented. However, the current MOSCED temperature dependence is inadequate to allow correct ordering of solvents as to the effect of temperature on the reaction rate.
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