Molecular Simulation of Temperature Effects on Activity Coefficients for Binary Liquid Mixtures PDF Download

Author: James Votel
Publisher:
ISBN:
Category : Enthalpy
Languages : en
Pages : 96

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Book Description
Activity coefficients are important for modeling solubility and phase-equilibrium involving liquid mixtures, for a variety of chemical separations such as distillation and extraction. This work seeks to predict the effect of temperature on activity coefficients for binary mixtures using molecular simulations. Methanol-ethanol, methanol-water and hexane-acetone binary liquid mixtures were investigated with molecular dynamic (MD) simulations in both the isothermal-isobaric (NPT) and canonical (NVT) ensembles. From the simulations, the radial distribution function of each atom pair in the system is then used to calculate the two-body entropy term S2 as well as Smix for the mixture. The excess properties of AHEmix and AVEmix from the binary mixtures are calculated from the MD simulations as well. The excess entropic and enthalpic data was then used to calculate partial molar excess enthalpies and entropies at infinite dilution, and the subsequent temperature-dependent scaling exponent of activity coefficients of the binary mixtures at different compositions. The activity coefficients in the infinite dilute region for the binary mixtures were then compared to previous experimental work to affirm that first-principles molecular simulations can accurately predict phase-equilibrium temperature effects for different types of binary mixtures. The results of the ethanol-methanol mixture were in good agreement with the previous work. However, the methanol-water and acetone-hexane strongly suggest that the S2 term is not appropriate in predicting the excess entropy of a mixture by itself.