MODELING AND SIMULATION OF COUNTERCURRENT FRACTIONAL EXTRACTION WITH SUPERCRITICAL SOLVENTS

Fractionating fluid mixtures by supercritical fluid extraction has rec eived increasing attention within the last few years. In this paper, a simulation model of a countercurrent fractional extraction column ope rated with supercritical fluids is presented. The model is based on id eal separation stages and incorporates the equation of state due to Re dlich-Kwong and Soave for describing phase equilibria. Simulation stud ies were performed on the separation of a binary feed using supercriti cal carbon dioxide as extraction solvent. The system is also used when treating a reaction mixture from an enzymatic conversion effected in supercritical carbon dioxide. To achieve a symmetric fractionation wit h equal purities in both top and bottom product flow of the column, th e reflux ratio has to be set to a distinct 'optimal' value. All other column parameters remaining unchanged, the optimal reflux ratio increa ses as the solvent flow is increased. As a consequence, product puriti es also increase.