Abstract
Industrial applications such as batteries and bio-separations require modeling the thermodynamic properties of mixed solvent electrolytes. Thermodynamic models for electrolytes often consider the solvents as a dielectric continuum characterized by their dielectric constant. Therefore, accurate predictions require a physically sound model for the dielectric constant of mixed solvents, depending on temperature, pressure, and mixture composition. We present a physical model for the dielectric constant of pure solvents and mixtures based on perturbation theory. The analytical expression is third order in the dipole density. For each pure component, the model requires the dipole moment and two adjustable pure-component parameters. We apply the model to the binary mixtures methanol–water and ethylene glycol–water considering pure component experimental data for temperatures between 273.15 K to 823.15 K and pressures between 0.1 MPa and 1189.0 MPa. The presented model improves the prediction of the mixed solvent dielectric constant for both mixtures compared to the linear molar mixing rule, and achieves similar accuracies as the linear volume-based and mass-based mixing rules. We show that the model is suitable in the case of scarce experimental data.
Highlights
Mixed solvents are promising for electrochemical processes, e.g., batteries [1], co-electrolysis of CO2 [2], and chemical processes with electrolyte systems, e.g., amine-based CO2-capture [3]
We present a physical model for the dielectric constant of pure solvents and mixtures based on perturbation theory
This study presents a physical model for the dielectric constant εr of mixtures of real solvents based on perturbation theory
Summary
Mixed solvents are promising for electrochemical processes, e.g., batteries [1], co-electrolysis of CO2 [2], and chemical processes with electrolyte systems, e.g., amine-based CO2-capture [3]. To avoid evaluating mixture densities, the simplified Oster’s rule has been developed, which mixes the pure component polarizations pi based on the volume fraction v,i calculated from the volumes prior to mixing [19]:. Simple mixing rules, such as Equations (1), (4), or (5) have conceptual deficiencies. We apply our model to water, methanol, ethylene glycol, and their mixtures considering pure component experimental data ranging from 273.15 K to 823.15 K and from 0.1 MPa to 1189.0 MPa. Even in the case of scarce experimental data for the pure component, the presented model accurately predicts the mixed solvent dielectric constant εr.
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