Adsorption equilibria of artemisinin from supercritical carbon dioxide on silica gel

Adsorption isotherms of artemisinin from supercritical CO2 on silica gel were measured at temperatures from 308.1 to 328.1 K and at pressures from 14.1 to 18.1 MPa with a frontal analysis method. The adsorption amount of artemisinin from CO2 on silica gel decreased with the increase of pressure. The adsorption amount decreased with increasing temperature at a constant CO2 density of 0.79 g cm−3; however it increased with increasing temperature at constant pressure within the range of 14.1 to 18.1 MPa. The adsorption amount of artemisinin from CO2 on silica gel was greatly affected by the solvating power of CO2. CO2 probably could not be regard as a non-adsorbed substance and it competed with artemisinin for adsorption sites on silica gel. The competitive adsorption of CO2 on silica gel enhanced as pressure increased. The isotherms of artemisinin were corrected with Freundlich model and a thermodynamic model based on the real adsorption solution theory.