Regeneration of loaded supercritical fluids

In a closed-cycle production plant utilizing the properties of supercritical gases, regeneration of the solute-supercritical fluid mixture is one of the two main process steps. Even though regeneration has been investigated, no systematic research has been done on the topic. In this paper, results of research activities that were performed in the last three years in Hamburg are presented.(1) Different methods for regeneration were chosen to examine the ability of each to separate a solute-supercritical fluid mixture: pressure and temperature change, adsorption, absorption, membranes, and a new method called deentrainment. Three different solutes were chosen to be separated from the supercritical fluid. New data for caffeine are presented that include caffeine-CO2 phase equilibria for pressures below 20 MPa, caffeine-water-CO2 phase equilibria, caffeine-activated carbon-CO2 phase equilibria and tocochromanol-ethanol-water-CO2 phase equilibria. Mass transport phenomena are considered to play an important role in the separator. The base of experimental data was used together with literature data to establish an evaluation system for the regeneration of supercritical fluids. This was done using membership functions mu(x) that are known in fuzzy-sets to establish the regeneration ability of a method for a certain parameter x (x: solute properties, thermodynamic conditions, operating parameters). A complete system of graphic functions are shown that allows the evaluation of the different methods according to a given case.