SOLUBILITIES IN SUPERCRITICAL FLUIDS FROM THE VIRIAL EQUATION OF STATE

We present a simple treatment of supercritical fluid extraction for bi nary (solvent-solute) and ternary (solvent-solute-cosolvent) systems. Solubility predictions are made using the virial equation of state. Th e solute chemical potential is calculated up to fourth order in the fl uid density. There are no adjustable parameters: the pressure mixture virial coefficients B-alpha beta, C-alpha beta gamma and D-alpha beta gamma delta are computed directly from the potentials representing the interactions of solvent, solute and cosolvent molecules. For the purp oses of illustration we assume these are of Lennard-Jones form; howeve r, the method is considerably more general, and may be applied even wh en the potentials are anisotropic. Computer simulations have also been performed, and confirm the accuracy of this approach at densities up to twice the critical density. Our analysis of ternary systems helps t o identify the nature of the interactions primarily responsible for en trainer effects.