THEORETICAL-MODELS OF THERMODYNAMIC PROPERTIES OF SUPERCRITICAL SOLUTIONS

Several separation processes, including supercritical extraction and supercritical fluid chromatography, take advantage of the striking solubility behavior of supercritical fluids. A general theoretical framework is presented for modeling thermodynamic properties of supercritical solutions based on the theory of J.G. Kirkwood and F.P. Buff. The theory is expressed in terms of the Kirkwood fluctuation integral from statistical mechanics and permits introduction of appropriate molecular solution approximations. Thus the solute-solvent interaction may be expressed using a local composition approximation, for example, with an accurate equation of state for the pure solvent.