Solubility estimation of high-value natural products in supercritical CO₂ based on solubility parameter

Solubilities of flavone and 6-methoxyflavone in supercritical carbon dioxide (SC-CO₂) were measured at temperatures ranging from 313 to 333 K and pressures ranging from 10 to 22MPa by a flow type apparatus. The solubilities were determined from ultraviolet-visible spectroscopic analysis of solute concentration of ethanol solution in the trap and the corresponding CO₂ amount. Solubility parameters (SP) of solutes were also estimated from correlation with a regular solution model, and these were comparable to the values obtained by solubility measurement using organic solvents under ambient conditions. The method for determining SP of solutes from solubilities in supercritical conditions is expected to be useful for SC-CO₂ extraction processing.