This paper is concerned with the formation of polychorinated organics in the gas phase in combustion systems. The results are derived from simulation studies with inputs from the fundamental kinetics of single step thermal gas phase reactions. Attention is focussed on the case where initial chlorine loading is low. It is shown that in a well mixed system high degrees of chlorination are difficult to attain due to the decrease in thermal stability with chlorination. A hypothesis for their formation as a consequence of chlorine formation during lean combustion followed by chlorination of organics as a result of the mixing and quenching of the products from rich combustion is tested. Under such conditions the competition between oxidation and chlorination of intermediates governs the final product distribution. The stability of propargyl radicals (C3H3) to oxidation makes chlorination of its products a preferred mode and results have been obtained where more highly chlorinated compounds are found in the products. Since this radical is a known precursor to benzene formation, this provides a direct route for the formation of polychlorinated benzenes. The scenario presented here extends regions for possible gas phase chlorination into the exhaust system of combustors.

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