New aspects on adsorption from supercritical fluid phases

Adsorption from a high pressure gaseous phase, containing as one major component a supercritical fluid is discussed. The fundamentals are presented as a basis of the modelling of the adsorption equilibria. Experimental techniques for determination of adsorption isotherms are presented and examples are given. The modelling of the adsorption isotherms is an essential aspect, e.g. since during application in a chromatographic process, multiple processes of adsorption and desorption are occurring, which are influenced by kinetics, but are mainly determined by thermodynamic equilibrium. In this work the modelling is carried out using the adsorption isotherm proposed by Hill. The application of adsorption processes comprises recovery from the gas phase. Decaffeination and purification of synthetic tocopherol acetate are presented as examples. For the separation of tocopherols and sterols (from natural sources) the selective action of a sequence of adsorption and desorption steps is further discussed. Then, the application of preparative supercritical fluid chromatography (SFC) is investigated. The elution chromatography is compared to the simulated moving bed technology (SMB–SFC).