PGSS and RESS

However, at increasing pressure, instead of tending to zero as predicted by eq (2.3-1), the solubility shows a minimum and raises up again to its asymptotic value. This solubility enhancement can be represented by the corrected isofugacity equation 

In eq (2.3-3) and q) indicate the HC fugacity coefficients in the reference state (pure vapor) and in the vapor phase, respectively, v is the molar volume of the solid phase, T the temperature and R the universal gas constant. As can be reasonably set equal to 1 and the exponential term (known as the Poynting correction) is not markedly greater than 1 for pressures below 500 bar, the enhancement effect is almost completely due to q , that is to the nonideality of the supercritical solution. 

With reference to the above points, it is important to note that  

The approach now summarized to represent solid-fluid equilibria can be profitably used in the development of both RESS and CSS processes. 

Basically, RESS takes advantage of the solubility dependence on SCF density, and that, in the supercritical region, the sensitivity of density on pressure 

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