Journal
CHEMOSPHERE
Volume 71, Issue 1, Pages 107-113Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.chemosphere.2007.10.007
Keywords
biomass combustion; hydroquinone; semiquinone; combustion by-products; cyclopentadiene; phenoxyl radical
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Hydroquinone is considered to be one of the major, potential molecular precursors for semiquinone-type radicals in the combustion of complex polymeric and oligomeric structures contained in biomass materials. Comprehensive product yield determinations from the high-temperature, gas-phase pyrolysis of hydroquinone in two operational modes (rich and lean hydrogen conditions) are reported at a reaction time of 2.0 s over a temperature range of 250-1000 degrees C. Below 500 degrees C, p-benzoquinone is the dominant product, while at temperatures above 650 degrees C other products including phenol, benzene, styrene, indene, naphthalene, biphenylene, phenylethyne, dibenzofuran and dibenzo-p-dioxin are formed. Hydrogen-rich conditions initially inhibit hydroquinone decomposition (below 500 degrees C) but promote product formation at higher temperatures. The decomposition process apparently proceeds via formation of a resonance stabilized p-semiquinone radical. Detailed mechanisms of formation of stable molecular species as well as stable radicals are proposed. (C) 2007 Elsevier Ltd. All rights reserved.
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