Measurement and calculation of solubility of quinine in supercritical carbon dioxide

Solubility of quinine in supercritical carbon dioxide (SCCO2) was experimentally measured in the pressure range of 8 to 24 MPa, at three constant temperatures: 308.15 K, 318.15 K and 328.15 K. Measurement was carried out in a semi-dynamic system. Experimental data were correlated by iso-fugacity model (based on cubic equations of state, CEOS), Modified Mendez-Santiago-Teja (MST) and Modified Bartle semi-empirical models. Two cubic equations of state: Peng-Robinson (PR) and Dashtizadeh-Pazuki-Ghotbi-Taghikhani (DPTG) were adopted for calculation of equilibrium parameters in CEOS modeling. Interaction coefficients (kij& lij) of van der Waals (vdW) mixing rules were considered as the correlation parameters in CEOS-based modeling and their contribution to the accuracy of model was investigated. Average Absolute Relative Deviation (AARD) between correlated and experimental data was calculated and compared as the index of validity and accuracy for different modeling systems. In this basis it was realized that the semi-empirical equations especially Modified MST can accurately support the theoretical studies on phase equilibrium behavior of quinine-SCCO2 media. Among the cubic equations of state DPGT within two-parametric vdW mixing rules provided the best data fitting and PR within one-parametric vdW mixing rules demonstrated the highest deviation respecting to the experimental data. Overall, in each individual modeling system the best fitting was observed on the data points attained at 318 K, which could be perhaps due to the moderate thermodynamic state of supercritical phase.