SOLUBILITY ISSUES OF SUPERCRITICAL FLUIDS

For supercritical fluids, the solvent strength of a given fluid is primarily dependent upon its density and pressure. It is much easier to directly measure and control the pressure of a supercritical fluid in a given operation than to measure and control the fluid density. 

It is possible, however, to determine a relationship exists between the fluid pressure and its density, thus allowing indirect measurement and control of the density. For an ideal gas, the relationship is simply, PV/RT= 1, where Fis the molar volume (reciprocal of the molar density). From the molecular weight of the gas (M), the mass density, p, can be calculated as M/V. The simple equation breaks down at the high densities characteristic of supercritical fluids, but, the work of Pitzer et allows the ideal gas law to be extended 

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