A simple model for the supercritical extraction of solids

The Redlich–Kwong equation of state with the Huron–Vidal mixing rules was applied to describe the solubility of solid compounds in supercritical solvents. The solute was characterized by means of two adjustable parameters only, its vapor pressure and an interaction factor in the expression for its fugacity coefficient in the gas phase. A constant value of the interaction parameter can be used, while a two-parameter expression of the solid vapor pressure is required for data at different temperatures. No significant improvement was given by introducing a volume shift according to Peneloux. Experimental literature data could be correlated with good accuracy.