Reactions of chlorinated benzenes in h2and in h2/o2mixtures: Thermodynamic implications on pathways to dioxin

Document Type

Article

Publication Date

11-1-1990

Abstract

Thermal Reactions of chlorobenzene and Dichlorobenzene in H2and Chlorobenzene in H2/O2mixtures were studied using tubular flow reactors between 835 to 1275K, 1 atm pressure. Complete conversion of chlorobenzenes in hydrogen required temperatures above 1100K, while in mixtures containing small quantities of O2equivalent conversion occurred at 893 K. Major products in both systems were benzene, carbon solids and HC1, with CH4and C2H6also present in low concentrations. Results from detailed kinetic mechanisms showed that displacement of the chlorine by atomic hydrogen (H addition to the ring with subsequent beta scission of the chlorine from the activated chlorocyclohexadienyl radical) was responsible for conversion of the chlorobenzene. O2can initiate the chain mechanism by H2+ O2→ HO2+ H, which explains the lower required temperature for conversion when Oxygen is present. The molecule and radical thermodynamic properties required for the kinetic models led to development of thermodynamic parameters for chlorinated aromatics including dioxins and dibenzofurans. These properties demonstrate that it is thermodynamically more favorable to form chlorinated dioxins and dibenzofurans over the analogous non-chlorinated species. The pathways presented demonstrate plausible elementary reactions to chlorinated dibenzofuran and dioxin formation in incineration and combustion processes. We suggest two regimes in incineration or high temperature reaction systems, where homogeneous dioxin formation may occur. The first is a fuel rich (pyrolysis) region where molecular weight growth may occur. The second is a region where polyphenyls and aromatics may be present with oxygen and oxy radicals at temperatures which favor addition reactions over oxidation of the ring systems. © 1990, Taylor & Francis Group, LLC. All rights reserved.

Identifier

84956440605 (Scopus)

Publication Title

Combustion Science and Technology

External Full Text Location

https://doi.org/10.1080/00102209008951684

e-ISSN

1563521X

ISSN

00102202

First Page

117

Last Page

135

Issue

1-6

Volume

74

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