Product distribution and reaction pathways for methylene chloride hydrolysis and oxidation under hydrothermal conditions

Abstract

The product spectrum, yields, and distribution resulting from hydrolysis of methylene chloride in sub- and supercritical water and post-hydrolysis oxidation in supercritical water have been measured and analyzed to identify and prioritize likely reaction pathways of formation and destruction and their relative importance for all species observed. Reactions with dilute feeds were carried out at 246 bar in a tubular reactor system over temperatures ranging from 25 to 600°C and total residence times of 7 to 23 s. The products detected were formaldehyde, hydrochloric acid, carbon monoxide, hydrogen, methanol, and carbon dioxide, with trace amounts of methane, chloromethane, and other one- and two-carbon chlorinated hydrocarbons in the vapor phase. A complete reaction network for CH2Cl2 and its products under hydrolysis conditions was developed. The main route for CH2Cl2 breakdown was via subcritical hydrolysis to formaldehyde and HCl, followed by decomposition of formaldehyde to CO and H2, and subsequent CO conversion to CO2 and H2 by the water gas shift reaction. In the presence of O2, oxidation of HCHO, CO, H2, and CH3OH was significant, while CH2Cl2 and the chlorinated hydrocarbons exhibited no oxidation conversion below 550°C. By 600°C and a 6 s residence time under oxidation conditions, however, CO2 and HCl were the only products observed, signifying complete destruction of all compounds (>99.99% of total carbon) under these conditions. © 1998 Elsevier Science B.V. All rights reserved.