An experimental and numerical study of the thermal oxidation of chlorobenzene Brian Higgins a, * , Murray J. Thomson b , Donald Lucas c , Catherine P. Koshland d , Robert F. Sawyer d a California Polytechnic University, San Luis Obispo, CA, USA b University of Toronto, Canada c Lawrence Berkeley National Laboratory, Berkeley, CA, USA d University of California, Berkeley, CA, USA Abstract A combustion-driven ¯ow reactor was used to examine the formation of chlorinated and non-chlorinated species from the thermal oxidation of chlorobenzene under post-¯ame conditions. Temperature varied from 725 to 1000 K, while the equivalence ratio was held constant at 0.5. Signi®cant quantities of chlorinated intermediates, vinyl chloride and chlorophenol, were measured. A dominant C±Cl scission destruction pathway seen in pyrolytic studies was not observed. Instead, hydrogen-abstraction reactions prevailed, leading to high concentrations of chlorinated byproducts. The thermal oxidation of benzene was also investigated for comparison. Chemical kinetic modeling of benzene and chlorobenzene was used to explore reaction pathways. Two chloro- benzene models were developed to test the hypothesis that chlorobenzene oxidation follows a CO-expulsion breakdown pathway similar to that of benzene. For the temperatures and equivalence ratio studied, hydrogen abstraction by hydroxyl radicals dominates the initial destruction of both benzene and chlorobenzene. Chlorinated byproducts (i.e., chlorophenol and vinyl chloride) were formed from chlorobenzene oxidation in similar quantities and at similar temperatures to their respective analogue formed during benzene oxidation (i.e., phenol and ethylene). Ó 2001 Elsevier Science Ltd. All rights reserved. 1. Introduction Thermal oxidation of chlorinated hydrocarbons in an incinerator is a common waste-disposal method. Under ideal conditions, chlorinated hydrocarbons oxidize to H 2 O, CO 2 and HCl. The HCl can be removed easily with exhaust gas processing. Equilibrium concentrations of parent and intermediate species are negligible (Yang et al., 1987). However, in a poorly operating hazardous waste incinerator, chlorinated hydrocarbons can escape the ¯ame zone and exist in the post-¯ame region, where chemical-kinetic limitations can lead to the production of hazardous emissions. Transient or upset conditions, cold-wall impingement, poor atomization of liquid waste, and rogue droplets are examples of poor oper- ating conditions (Oppelt, 1986). Waste-incinerator upset conditions can be replicated in a laboratory environment with a ¯ow reactor. Flow reactor studies are useful be- cause they have measurable boundary conditions, re- peatable operation, and can be operated on a scale many times smaller than a waste incinerator. For these rea- sons, ¯ow reactors are used often to investigate and to predict the reactions that occur in large-scale waste in- cinerators. Chlorobenzene decomposition is of interest as the chlorine atom is bonded strongly to the benzene ring (Tsang, 1990) and potentially contributes to dioxin formation (Ritter and Bozzelli, 1990, 1994; Sommeling et al., 1993). A number of studies have examined Chemosphere 42 (2001) 703±717 * Corresponding author. Present address: Mech. Eng. Dept., Cal. Poly., San Luis Obispo, CA 93407 USA. E-mail address: bshiggin@calpoly.edu (B. Higgins). 0045-6535/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 5 - 6 5 3 5 ( 0 0 ) 0 0 2 4 5 - 9