Catalytic Supercritical Water Oxidation of Coke Works Waste with Manganese Oxide.

Abstract

Heterogeneous catalysis in supercritical water oxidation (SCWO) is a new approach to improve the reaction efficiency of the treatment of hazardous waste water. In this study, the kinetic analysis of catalytic SCWO of coke works waste with manganese oxide (MnO2) was performed to obtain fundamental data for the reactor design, as well as information about interactions affecting the reaction rate between the reaction species. The major component of the coke works waste is NH3. Catalytic SCWO of NH3 solution confirmed that MnO2 is a good catalyst for the complete oxidation of NH3. SCWO of an aqueous mixture of phenol and NH3 was examined as a model solution of the real waste. The oxidation rate of NH3 in the model solution was lower than that of an aqueous solution of NH3. The presence of NH3 in the model solution did not affect the phenol conversion, but strongly suppressed the decomposition of total organic carbon (TOC). These inhibition effects between NH3 and phenol are explainable by a Langmuir-type model, in which all corresponding species are assumed to adsorb competitively on the same catalytic site. Catalytic SCWO of diluted real waste showed a similar inhibition effect especially with shorter contact times of less than 0.5s. However, very high conversions of both NH3 and TOC were achieved within 2s of contact time at 500°C. These experimental results suggest that catalytic SCWO is a promising technique for the complete decomposition of coke works waste.