Solubility correlation of gall (Quercus infectoria) extract in supercritical CO₂ using semi-empirical equations

The present work studied the solubilities of Quercus infectoria gall extract in supercritical carbon dioxide (SC-CO₂) system with the addition of methanol as polarity enhancer. Experimentally, the galls were extracted using SC-CO₂ at different operating pressures (20 to 30 MPa) and temperatures (50 to 70 °C). Six semi-empirical equations (Chrastil, Adachi-Lu, del Valle-Aguilera, Sparks, Kumar-Johnston and Bartle) were used to explain mathematically the solubility behaviour of the Q. infectoria gall extract. The results demonstrated that the extract solubility increases as pressure increases at fixed temperature, while at constant pressure, it increases with increasing temperature. Apparently, Bartle equation provides best correlation between experimental and calculated solubility data for gall extraction with high correlation coefficient, R² (0.96), and small absolute average relative deviation (1.52%).