The methanol-benzene binary mixture, which has an azeotrope with a 3:2 methanol:benzene molar ratio at 329 K, provides a useful system through which to study the computation of thermodynamic properties of non-ideal mixtures. Methanol-benzene clusters of various molar ratios up to mixed pentamers (see Fig. 1 for the azeotropic composition) are described with Density Functional Theory to model possible interactions in the binary liquid. Thermodynamic data, cluster populations, and phase transitions are then calculated using Quantum Cluster Equilibrium (QCE) theory in order to evaluate the efficacy of current computational methods in describing deviations from ideality.  Vibrational entropy, enthalpy of mixing, Gibbs free energy of mixing, and boiling points are shown to be highly dependent upon the types of normal mode deflections calculated for individual clusters, indicating that vibrational anharmonicity plays an important role in describing thermodynamic behavior. By accounting for the anharmonic characteristics of this non-ideal mixture, azeotropic behavior can be accurately and robustly modeled.

Deviations from ideality: Quantum cluster equilibrium theory and the methanol-benzene binary mixture

255th National Meeting (2018)

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