Experiments, Correlation, and Modeling of Curcumin Solubility in Subcritical Water (Water/Ethanol)

The solubility of curcumin in the pure water subcritical and water–ethanol solution (water + (5–10) % (v/v) ethanol) subcritical is investigated for the first time. The design approach taken from this study is the response surface methodology due to the Box Behnken. The experiments were performed in the temperature range of (90–150) °C, (0–10) volumetric percent of ethanol and the flow rate of (0.2–0.8) ml/min. As the pressure effect is ignored in the subcritical conditions, the pressure is constant in 2 MP in the experiments. All analyses were carried out employing the high-performance liquid chromatography apparatus. The curcumin solubility data were correlated with the dielectric constant of solvent mixture. Curcumin solubility modeling in subcritical conditions was done due to cubic-plus-association equation of state. The present study indicated that the rise in temperature and ethanol percentage cause an increase in curcumin solubility. Other important finding was by increasing the flow rate, curcumin solubility rate increased with a very mild slope. The optimum conditions for the curcumin solubility were in the water flow rate of 0.8 ml/min, 10% (v/v) of ethanol, and the temperature of 150 °C.