Solubility simple density correlation

Supercritical fluid extraction is a potential technique for the purification of pharmaceutical products containing residual solvents. The solubilities of three inhibitors of inflammatory activity, Ketoprofen, Piroxicam, and Nimesulide, in supercritical CO2, measured using a dynamic saturation technique, were reported at pressures between 100 bar and 220 bar and at two temperatures 312.5 K and 331.5 K. The solubilities exhibit a clear dependence on the solvent density, and this has been used to provide a simple and precise correlation of the data (Macnaughton et al., 1996). 

As can be noted, the correlation between the calculated and actual results, using a very simple curve fitting technique, yields good fits concerning molar volume, which is examined in terms of density, and in cloud point data, examined in terms of tai jerature. For those not familiar with the cloud point phenomena, nonionic surfactants exhibit inverse solubility characteristics per taiperature increases, i.e., as the... 

Pressure is not the best independent variable with which to represent solubilities in SCFs. The quite confused representation of Figure 2.3-l(a) can be improved if the same solubility isotherms are plotted against the vapor density (i.e. the SCF density), as in Figure 2.3-1(b). This smooth dependence is embedded in a simple equation proposed by Chrastil [7] and recently modified by Mendez-Santiago and Teja [8] to correlate solubility of solids in SCFs ... 

The empirical nature of is obvious, and it would be helpful to replace y by parameters having a sound basis in thermodynamic or statistical mechanical considerations. Recent efforts by Fowkes [40] to relate y to the dispersion forces between molecules at the interface have been especially promising in leading to tractable equations. An interesting direct correlation has been recently pointed out to us by Gar don [49] between the value of y of a solid polymer and the Hildebrand solubility parameter, 6, which is defined as the square root of the molar energy density—i.e., 6 = n/1E/p A simple consideration of the Young equation and the definition of y indicates that when cos 0=1,... 

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