The experimental equilibrium solubilities of o-hydroxybenzoic acid in supercritical carbon dioxide were measured at temperatures between 35 and 55 OC and for pressures from 80 to 205 bar. Negligible solubility of m-and p-hydroxybenzoic acid was observed over the same range of temperature and pressure investigated. The solubility data was correlated by use of the thermodynamic model relating the solubility to the solvent density, an empirical model relating the enhancement factor to the density of the solvent, and a semiempirical correlation, based partly on regular solution theory and the van der Waals equation of state.

No abstract

The addition of cosolvents to supercritical fluid (SCF) solvents can have large effects on solubilities, giving engineers the ability to tailor loadings and selectivities of solutes for difficult separations. It is necessary to have a better understanding of the special intermolecular interactions that occur in SCF solutions to predict the effects of cosolvents. We use u SCF chromatographic technique to acquire a database of cosolvent effects for a variety of cosolvents and solutes; examination of the cosolvent effects shows evidence of hydrogen bonding, charge transfer complex formation, and dipole-dipole coupling between solute and cosolvent molecules. SCF solvents, carbon dioxide, ethane, and fluoroform, are compared, and then the use of the chromatograph to measure solubilities is discussed.

No abstract

The equilibrium solubilities of 0-and m-hydroxybenzoic acid in 3.5 mol ?6 acetone-C02 and 3.5 mol % methanol-C02 binary mixtures were measured at temperatures between 318 and 328 K and pressures in the range of 90-200 bar using a continuous flow apparatus. The solubility isotherms in these ternary systems exhibit a retrograde vaporization phenomenon and a common upper crossover pressure for each ternary system. Moreover, the results demonstrate that the addition of small amounts of cosolvents to C02 increase significantly the solubility of 0-and m-hydroxybenzoic acid. A molecular thermodynamic model was developed based on the Scatchard-Hildebrand regular solution and Flory-Huggins theory using the concept of component solubility parameters to obtain the unlike-pair molecular interactions between the solute and cosolvent. An effective volume fraction term that reflects the "preferential" solvation of the solute by the cosolvent molecules was included in the model development to account for differences between the bulk solvent environment and that in the immediate vicinity of the solute molecule.