PRODUCT DISTRIBUTION AND REACTION PATHWAYS FOR METHYLENE-CHLORIDE HYDROLYSIS AND OXIDATION UNDER HYDROTHERMAL CONDITIONS

The product spectrum, yields, and distribution resulting from hydrolys is of methylene chloride in sub- and supercritical water and post-hydr olysis oxidation in supercritical water have been measured and analyze d to identify and prioritize likely reaction pathways of formation and destruction and their relative importance for all species observed. R eactions with dilute feeds were carried out at 246 bar in a tubular re actor system over temperatures ranging from 25 to 600 degrees C and to tal residence times of 7 to 23 s. The products detected were formaldeh yde, hydrochloric acid, carbon monoxide, hydrogen, methanol, and carbo n dioxide, with trace amounts of methane, chloromethane, and other one - and two-carbon chlorinated hydrocarbons in the vapor phase. A comple te reaction network for CH2Cl2 and its products under hydrolysis condi tions was developed. The main route for CH2Cl2 breakdown was via subcr itical hydrolysis to formaldehyde and HCl, followed by decomposition o f formaldehyde to CO and H-2, and subsequent CO conversion to CO2 and H-2 by the water gas shift reaction. In the presence of O-2, oxidation of HCHO, CO, H-2, and CH3OH was significant, while CH2Cl2 and the chl orinated hydrocarbons exhibited no oxidation conversion below 550 degr ees C. By 600 degrees C and a 6 s residence time under oxidation condi tions, however, CO2 and HCl were the only products observed, signifyin g complete destruction of all compounds (>99.99% of total carbon) unde r these conditions. (C) 1998 Elsevier Science B.V. All rights reserved .