An anti-corrosive reactor for the decomposition of halogenated hydrocarbons with supercritical water oxidation

Abstract

An anti-corrosive reactor was studied, which decomposes halogenated organic compounds by way of supercritical water oxidation (SCWO). Two different types of SCWO reactor were used: a floating type reactor using a non-porous ceramic tube and a transpiring wall-type SCWO reactor using a porous ceramic tube. Reactor configurations were evaluated to protect a SCWO system from corrosion, due to halogenated hydrocarbon oxidation, and fouling, due to salt formation from the neutralizing agent. At various operating conditions (340–440 °C, 250–300 bar) and concentrations (300–3000 mg 2,4-dichloropenol/L), the system was operated to decompose 2,4-dichlorophenol (2,4-DCP) as a model compound with hydrogen peroxide (H 2O 2). Back-mixing led to corrosion of the injection part of the transpiring wall-type reactor. However, 2,4-DCP was successfully destroyed up to ≥99.99% without corrosion or fouling problems with a floating type SCWO system. As the range of the supercritical zone in the reactor was changed by the operating conditions, the conversion of 2,4-DCP increased with an increase in the reaction temperature and pressure. Therefore, residence time in the SCWO process played a key role in the decomposition efficiency of the developed system. Under the conditions of 420 °C, 250 bar and a 1 mL/min flow rate, 2,4-DCP at a concentration of 300 mg/L was completely converted using a stoichiometric amount of 100% of H 2O 2. In the case of 3000 mg/L of 2,4-DCP, complete conversion was observed under the conditions of 440 °C, 250 bar and with over 200% of H 2O 2 supply. The floating type reactor, consisted of one vertical double-wall reactor including neutralization and cooling, was successfully operated for more than 5 months for SCWO of 2,4-DCP without corrosion and fouling.