Chromatography-like propagation of water along raw material bed in supercritical fluid extraction

A chromatography-like propagation of water through the material bed was observed while performing supercritical fluid extraction of aroma plants having high moisture content. While parts of raw material bed placed at the inlet of the extraction vessel get dried after appropriate extraction time, the parts closer to the outlet not only stay wet but, in fact, gain more moisture than initial raw material. Presumably, water and other extractables with limited solubility in supercritical CO₂, get re-adsorbed onto the plant material surface along the extraction column and then desorbed further on. If the effect is of general nature, it might be important for modeling kinetics of supercritical fluid extraction of non-volatile compounds.