Formation of Chlorinated Aromatics by Reactions of Cl•, Cl2, and HCl with Benzene in the Cool-Down Zone of a Combustor

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Abstract
Conversion of benzene to chlorobenzenes and monochlorophenols by reaction with chlorine radicals (Cl•) in the cool-down zone of a plug-flow combustor has been studied, and a mechanistic analysis of the initial steps of the oxy-chlorination process is proposed. Superequilibrium concentrations of Cl• are formed during combustion of chlorocarbon species and persist at significant concentration levels even after a substantial reduction in the flue gas temperature (T = 500−700 °C). At these temperatures, Cl• attack on benzene present in trace concentrations (initial benzene concentration of 300 ppmv or 1080 ppmv were used for the experiments) in the post-flame gas is shown to result in stable chlorinated products (chlorobenzenes and chlorophenols) and loss of benzene. These results suggest that Cl• attack on trace level aromatics and possibly other organic species may be the initial step in the formation of a broad class of chlorinated and oxy-chlorinated pollutants in the post combustion zone.