Thermal abatement of nitrogen-containing hydrocarbons by non-catalytic supercritical water oxidation (SCWO)

Abstract

This work investigated the destruction of N-containing hydrocarbons namely DBU (1,8-diazobicyclo[5.4.0]undec-7-ene) and DMF (dimethyl formamide) by supercritical water oxidation (SCWO), using hydrogen peroxide as oxidant. Reactions were conducted under temperatures of (400–650 °C), pressures of (50–250 bars), oxidant stoichiometric ratio SR (0.9–12), initial concentrations of organics (0.1–8.4 mM) and residence time τ (6–17 s). Reactions took place in a plug flow continuous reactor and the results were presented in terms of the % removal (of TOC and the organic compound), C-fraction and N-fraction; all plotted as function of the above system conditions. Also, GC-MS analysis for DMF was conducted. Percent removal increased with temperature and complete organic- and >90% TOC removal, was obtained at 500 and 600 °C for DMF and DBU respectively. Conversion increased with the oxidant SR, residence time and initial organic concentration. Pressure affected conversion in the sub- and near-critical conditions but not in the supercritical region, yet an initial value of 150 bar was required to start the reaction. Pseudo first order-, integral power rate law-, and power law models successfully described the kinetic data; and the reaction constants for each model and energy of activation were evaluated.