doi:10.3850/978-981-08-7724-8_11-03

ABSTRACT

The oxidation of dibenzo-p-dioxin (DD) has been studied experimentally. The objective was to identify the decomposition pathways of DD and to gain an understanding of the reactions leading to the formation of toxic species, including those that may behave in fires and combustion systems as precursors for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F). The experiments were performed in a tubular reactor equipped with sampling systems for condensable and gaseous products. The reaction conditions were characterised by a residence time of 5 s, a temperature range of 400–800 °C (673–1073K) and a total flow rate of 19 cm³ min^-1. The ratio of N₂ to O₂ was 20:1.0. DD slowly vaporised at a rate of 0.07 mg min^-1 at a temperature of 100 °C. The flow rates of DD and oxygen corresponded to the fuel equivalence ratio of 0.39. The volatile organic compounds (VOC) were trapped in an activated charcoal cartridge. Performed on a high resolution gas chromatograph-quadrupole mass spectrometer (GCMS), the analyses of VOC identified nine products, namely benzene, toluene, 2-methyl benzofuran, naphthalene, benzofuran, dibenzofuran (a suspected carcinogen), styrene, benzaldehyde and 2,3-dihydro-2-methylenebenzofuran. The first six products were confirmed by the injection of authentic standards. Gas analysis involved the application of Fourier transform infrared (FTIR) spectroscopy and micro gas chromatography (μGC). While the decomposition of DD commenced at around 450°C into 2-methylbenzofuran and 2,3-dihydro-2-methylenebenzofuran, the temperature for complete oxidation was 800 °C .

Keywords: Dibenzo-p-dioxin, Oxidation, Polychlorinated dibenzo-p-dioxins, Polychlorinated dibenzofurans, Volatile organic compounds.

© 2011 CPD Unit, University of Leeds