Application of a gas–liquid entraining rotor to supercritical fluid extraction: Removal of iron(III) from water

Abstract

Supercritical fluid extraction (SFE) of aqueous solutions is often limited by poor mass transport. The performance of a new gas–liquid entraining device was investigated to improve mass transport and thereby increase extraction efficiency. As a test system, iron(III) was extracted from water with a β-diketone chelating agent (HL) and supercritical fluid carbon dioxide. Metal β-diketonate complexes with sufficient solubility in supercritical fluid CO 2 are often poorly extracted from aqueous solutions due to limited mass transport between the water-soluble metal ion and the CO 2-soluble chelating agent. The new entraining device maximizes contact between the ligand-rich CO 2 phase and the metal ion-rich aqueous phase. Iron(III) was extracted from water with the chelating agent 2,2,7-trimethyl-3,5-octanedione (H(tod)) and supercritical fluid CO 2 at 60 °C and 20.8 MPa. With entrainment, 79% of the iron was removed from the aqueous phase. This represents a three-fold increase in iron extraction efficiency over that of a static system.