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Liquid−liquid phase equilibria were comparatively studied for the aqueous mixtures of propionic acid with four structurally similar aryl compounds (2-phenylethanol, 1-phenylpropanol, propiophenone, and methyl benzoate) as a function of the mixture composition at T = 298.2 K and p = 0.1 MPa. The cloud point data were measured, and the corresponding solubility diagrams for the studied ternary systems were plotted. Tie lines were measured by the analysis of both the aqueous and organic phases. All of the ternary systems display the type-1 liquid−liquid equilibrium (LLE) behavior. The quality of tie lines was confirmed by the linear behavior of the Othmer−Tobias plot. The thermodynamic model of NRTL was successfully used to correlate the experimental tie lines, and the model binary interaction parameters were determined. Evaluation of the extracting ability of the aryl solvents was performed by the estimation of the solute distribution coefficients and selectivities. Finally, all of the studied aryl solvents are appropriate separating agents for aqueous propionic acid mixtures.

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Liquid–liquid equilibrium study was performed on the eight ternary systems containing binary azeotrope mixtures (n-heptane + n-amyl alcohol or isoamyl alcohol) and deep eutectic solvents at 298.15 K and 101 kPa. In order to evaluate the influence of structure of the constituent components on the phase equilibria, the ternary systems were systematically analyzed. In this research, four choline chloride based deep eutectic solvents (ChCl-DESs) were synthesized for separation of the amyl alcohols from a hydrocarbon (n-heptane). The prepared DESs were choline chloride + ethylene glycol (DES1; 1:2 mol ratio), choline chloride + propylene glycol (DES2; 1:3 mol ratio), choline chloride + 1,4-butylene glycol (DES3; 1:4 mol ratio), and choline chloride + diethylene glycol (DES4; 1:4 mol ratio). The Othmer–Tobias equation was applied to check the reliability of the tie-line compositions. The measured equilibrium data were correlated by the NRTL model, and the binary interaction parameters were determined. The consistency of the model parameters was validated by topological analysis connected to the Gibbs tangent principle. Distribution coefficients and separation factors were obtained from the tie-line data in order to evaluate the capacity of the studied deep eutectic solvents. The obtained solute distribution coefficients were found to be almost similar for all the studied ternary systems.