Rate enhancement by cations in supercritical water oxidation of 2-chlorophenol

Interactions between cations and CI species in the supercritical water oxid ation (SCWO) of 2-chlorophenol (2CP) has been investigated in a high-pressu re quartz-lined reactor at 673-773 K. Experimentally, we found that the S/D ratio (defined as the amount of 2CP converted to CO2 and H2O/disappearance of 2CP) for SCWO of 2CP was enhanced by cations (such as Li+, Na+, K+, Ca2 +, Fe2+, or Fe3+). The S/D ratio increased as the charge density of cations increased (Fe3+ > Fe2+ > Li+ > Ca2+ > Na+ > K+). Due to the extremely low solubility of metal salts in the supercritical water, abstraction of CI in 2CP via an intermediate ((OH)PhCldelta- ----- Mdelta+) was postulated. Form ation of these metal chloride (such as KCl, CaCl2, and FeCl3) precipitates in the SCWO of 2CP were identified by X-ray diffraction (XRD) spectroscopy. Since the formation of toxic highly chlorinated phenols and heavy polycycl ic aromatic hydrocarbons (PAHs) was notably reduced, abstraction of Cl of 2 CP by cations may occur in the early stage of the SCWO process.