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The ability to correlate and predict the solubility of solids in supercritical fluids is important in the design and evaluation of supercritical extraction processes. However, a review of the literature reveals that solid solubility data obtained by different investigators often do not agree within the reported uncertainties of the measurements. We have shown previously that a simple theory of dilute solutions can be used to check the consistency of supercritical CO 2 -solid solubility data and also that such data can be reduced to a single straight line over a significant range of solvent density and temperature. In the present work, we first show that our binary solution model is applicable to systems in which the solvent is not CO 2 . We then extend the approach to ternary cosolvent systems and show that data over a range of temperatures, pressures, and cosolvent concentrations can be correlated within experimental error using a single equation. The new model has three parameters that are independent of temperature, pressure, and cosolvent concentration. The approach may therefore be used to extrapolate limited data sets over a range of these variables.

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The solubilities of solid benzoic acid in mixtures of CO2 + hexane have been measured at temperatures ranging from (308 to 338) K, pressures ranging from (10 to 35) MPa, and cosolvent concentrations ranging from (0 to 7) mol % hexane. The consistency of the data was verified via plots of the enhancement factor versus the density as suggested by dilute solution theory. The dilute solution theory was also used to correlate and extrapolate the data using three parameters that are independent of temperature, pressure, and cosolvent concentration.

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