Ternary phase diagrams of ethyl paraben and propyl paraben in ethanol aqueous solvents

• Parabens induce a liquid–liquid phase separation in the water–ethanol solvents.
• Solubility of parabens in homogenous and LLPS solutions is well correlated by the third order polynomial equation.
• LLPS areas increase with temperature.
• Systematic change of ethyl paraben, propyl paraben and butyl paraben on melting points, LLPS points in pure water and ternary phase diagrams.

Three ternary phase diagrams of ethyl paraben, ethanol, water and propyl paraben, ethanol, water have been determined. The liquid–liquid phase separation has been reported in these three ternary diagrams. In pure water the ethyl paraben and propyl paraben solubility is both below 1 mg/g, while in pure ethanol the solubility is more than three orders of magnitude higher. While the solution saturated with propyl paraben is homogeneous at 30.0 °C, and the solution saturated with ethyl paraben is homogenous at 40.0 °C, however, the higher temperatures induce liquid–liquid phase separation in the ethanol–water mixtures, and the ternary phase diagrams contain five different regions. The size of the liquid–liquid phase separation region increases with increasing temperature. The systematic changes of thermodynamic properties between butyl paraben, propyl paraben and ethyl paraben have been investigated.

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