SOLUBILITIES OF MIXED HYDROXYBENZOIC ACID ISOMERS IN SUPERCRITICAL CARBON-DIOXIDE

Studies of the extraction of solid mixtures with supercritical fluids (SCFs) demonstrate that solute-solute interactions in the SCF phase ca n be significant. To further explore such interactions, the solubiliti es of various mixtures of hydroxybenzoic acid (HBA) isomers in supercr itical CO2 were determined. Solubility data are reported at pressures ranging from 101 to 203 bar and for temperatures of 318 K and 328 K. S ignificant solubility enhancements were observed for m-HBA and p-HBA i n systems containing the ortho isomer. The degree of solubility enhanc ement obtained is possibly the result of hydrogen bonding between the isomers in the SCF phase. The solubility data were correlated with a m odified form of the Peng-Robinson equation of state.