SEPARATION OF ISOMERS USING RETROGRADE CRYSTALLIZATION FROM SUPERCRITICAL FLUIDS

Solubilities have been measured for a mixture of 2,3- and 2,6-dimethylnaphthalene in supercritical fluid carbon dioxide to identify retrograde regions, which have an inverse solubility versus temperature relationship. A retrograde crystallization process has been designed and tested for the separation of the two isomers at supercritical conditions. A thermodynamic framework has been developed which may be used to locate retrograde regions in order to evaluate the feasibility of retrograde crystallization processes. The complex effect of temperature on solubility at constant pressure has been expressed in terms of two approximately constant derivatives and the volume expansivity of the pure solvent.