Thermal reactions of CH₂Cl₂ in H₂/O₂ mixtures: Implications for chlorine inhibition of CO conversion to CO₂

The thermal decomposition of dichloromethane in hydrogen/oxygen mixtures and argon bath gas was carried out at 1 atm pressure in tubular flow reactors of varied surface-to-volume ratios. The degradation of dichloromethane plus intermediate and final product formation was analyzed from 873 to 1093 K, with average residence times of 0.1-2.0 s. A detailed kinetic reaction mechanism based upon fundamental thermochemical principles and Transition State Theory was developed and used to model our experimental results. Sensitivity analysis was used to determine important reactions effective in inhibiting CO conversion to CO₂. The results indicate that the reaction: OH + HCl → H₂O + Cl is a major cause of OH loss and this decrease in OH significantly reduces CO conversion by reaction with OH. Lower temperatures result from reduced CO reaction with OH, which increases the importance of HO₂. Here, the reaction of HO₂ + Cl to the HCl + O₂ (termination) channel further inhibits combustion. A significant fraction of the CH₂Cl₂ conversion occurs through C₂ chlorocarbon formation, which results from methyl and chloromethyl combination reactions.