Oxidation of Cu(II)-EDTA in supercritical water-Experimental results and modeling

Copper complex ethylenediamine tetraacetic acid (Cu(II)-EDTA) was oxidized in supercritical water in a continuous tubular reactor at temperatures 420-500°C, residence times 57-144s, and a pressure 25MPa. The major carbon-containing products were CO₂ and CO. The TOC conversions increased steadily with reaction temperature and residence time, and the yield of CO can be effectively reduced at elevating temperatures. Ammonia was determined to be the main refractory nitrogen-containing intermediate, whose oxidation was supposed to be enhanced by the copper in Cu(II)-EDTA. In addition, the copper transformed into copper oxides (CuO and Cu₂O), and was removed from the Cu(II)-EDTA solution with high efficiency. Based on the experimental results and the analysis of reaction pathways, a global Arrhenius kinetic model was proposed to predict the removal of TOC and the yield of the intermediates NH₃ and CO. With this kinetic model, a computational fluid dynamic (CFD) model of the tubular reactor was implemented to assist the experimental study. The composition profiles of TOC, CO, and CO₂ along the reactor were simulated and compared with the experimental results. Operating parameters, reaction temperature and oxygen flow rate, were optimized based on the simulation results.