High-pressure solubility of methadone hydrochloride in supercritical CO₂: Experimental investigation and correlations

Exact drug solubility determination and modeling in supercritical carbon dioxide (SC-CO 2 ) would address the optimal experimental conditions for processing substances with supercritical fluid (SCF). In this investigation, for the first time, the solubility of Methadone hydrochloride is measured and modeled using the perturbed chain-statistical associating fluid theory (PC-SAFT) equation of state (EoS) alongside a set of eight semi-empirical models. The 24 experimental data points were obtained at pressures ranging from 120 to 270 bar and temperatures between 308 and 338 K. The minimum and maximum mole fractions observed were 1.74 × 10 -5 and 4.67 × 10 -5 , respectively, occurring within these ranges. The results indicate that both pressure and temperature significantly affect Methadone hydrochloride solubility, so that as both pressure and temperature rise, the solubility increases. Among the models, the Chrastil model and PC-SAFT EoS exhibited the lowest absolute average relative deviation (AARD) % of approximately 6.71% and 9.73%, respectively. Finally, the enthalpies of the methadone hydrochloride/CO 2 binary system were calculated as = 29.14 kJ/mol, = 23.04 kJ/mol, = 40.61 kJ/mol, = -11.47 kJ/mol, and = -17.57 kJ/mol.