Solid-liquid phase equilibria, excess molar volume, and molar refraction deviation for the mixtures of ethanoic acid with propanoic, butanoic, and pentanoic acid

The paper reports the solid-liquid phase equilibria (SLE), excess molar volume (V^E), and molar refraction deviation (ΔR) for binary systems of ethanoic acid with the C₃ to C₅ carboxylic acids, propanoic, butanoic, and pentanoic acid, which are the main constituents of bio-butanol fermentation broth. The SLE was determined via a synthetic method using a custom-built glass tube at atmospheric pressure, whereas the thermodynamic mixture properties, V^E and ΔR were obtained from directly measured density and refractive index using a precision densitometer and refractometer, respectively. All of the SLE that were determined for binary mixtures of ethanoic acid+C₃-C₅ carboxylic acids showed a single eutectic point and regressed well with the NRTL activity model within 0.6 K of RMSD. The V^E values for the same binaries were positive for the entire composition ranges of all the systems, whereas the ΔR values were negative for all the systems. The V^E and ΔR were well regressed by polynomial equations, namely Redlich-Kister within 0.006 cm³·mol⁻¹ of the standard deviation for V^E and 0.02 cm³·mol⁻¹ for ΔR.