Solubility of flavone, 6-methoxyflavone and anthracene in supercritical CO₂ with/without a co-solvent of ethanol correlated by using a newly proposed entropy-based solubility parameter

Solubility of flavone, 6-methoxyflavone and anthracene in supercritical CO₂ with an ethanol co-solvent ranging from 0.05 to 0.40 were measured at 333 K and 22.0 MPa. Solubility of each compound increased with increasing mole fraction of ethanol. Solubility data were correlated with Chrastil equation considering a relationship between fluid density and solubility and compared with newly proposed relations that use an entropy-based solubility parameter (SSP). Among proposed relations, one relation taking temperature dependence into consideration, that included two fitting parameters had absolute relative deviation (ARD) of 3.9% compared to the experimental data and were much more reliable than a relation not taking temperature dependence into consideration within ARD of 7.6%. The expression similar to Chrastil model that included three fitting parameters and considered SSP was the best ARD within 3.6% among the proposed relations. From these correlation results, the SSP can be applied to determine the solubility of substances at high pressure with multicomponent solvent mixtures.