- Title
- Gas phase pyrolysis of endosulfan and formation of dioxin precursors of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F)
- Creator
- Dharmarathne, Nirmala K.; Mackie, John C.; Kennedy, Eric M.; Stockenhuber, Michael
- Relation
- University of Newcastle, Australia
- Relation
- Proceedings of the Combustion Institute Vol. 36, Issue 1, p. 1119-1127
- Publisher Link
- http://dx.doi.org/10.1016/j.proci.2016.05.001
- Publisher
- Elsevier
- Resource Type
- journal article
- Date
- 2017
- Description
- This article reports the results of a computational and experimental study on the thermal degradation of endosulfan, a broad-spectrum chlorinated cyclodiene insecticide. The objective of the study was to identify its decomposition pathways, and to gain an understanding of the mechanism of formation of toxic species including polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) and their precursors. We implemented pyrolysis experiments in a tubular reactor and identified the pyrolysis products and demonstrate good qualitative agreement between the experimental species measurements and quantum chemical calculations. A sampling system intercepted the gaseous products exiting the reactor which were analysed by FTIR spectroscopy and trapped (at −10 °C) volatile organic compounds (VOC) generated from the thermal decomposition of endosulfan were analysed by GC/MS. Decomposition commences at about 573 K in a flow reactor at a residence time of 5 s. The initial primary decomposition reaction of endosulfan involves a retro Diels–Alder elimination to form hexachlorocyclopentadiene (HCCP) and 4,7-dihydro-1,3,2-dioxathiepine-2-oxide (2HDTO). Under these conditions, 2HDTO decomposes via two competing reaction channels, both eliminating SO₂. At reaction temperatures of 663 K and above, fission of a Cl atom results in the formation of endosulfan radical, which promotes further decomposition of endosulfan via a low barrier free radical pathway. As the temperature increases further, we observe a rise in secondary products including pentachlorocyclopentadiene (PCCP), tetrachlorostyrene (TCS) and pentachlorostyrene (PCS). At 823 K, chlorinated benzene products were identified comprising pentachlorobenzene and isomers of tetrachlorobenzenes which are known precursors for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans PCDD/PCDF under oxidative conditions. Under oxidative conditions (10% oxygen), PCDD/PCDF congeners are formed, dominated by mono- to octa- chlorinated dibenzofurans and tetra- to octa- chlorinated dibenzo-p-dioxins.
- Subject
- dioxin; PCDD/F precursors; endosulfan; pyrolysis
- Identifier
- http://hdl.handle.net/1959.13/1386116
- Identifier
- uon:32361
- Identifier
- ISSN:1540-7489
- Language
- eng
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