Mechanisms of dioxin formation from the high-temperature pyrolysis of 2-bromophenol.
Mechanisms of dioxin formation from the high-temperature pyrolysis of 2-bromophenol.
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DOI：
10.1021/es034387s
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发表时间：
2003-10
影响因子：
11.4
通讯作者：
Catherine S Evans;B. Dellinger
中科院分区：
文献类型：
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作者：
Catherine S Evans;B. Dellinger
溴化烃是最常用的阻燃剂。含有溴化碳氢化合物的材料经常在城市和危险废物焚化炉中处置，并在意外火灾中发生热反应。这就有可能形成溴化二恶英和其他危险的燃烧副产品。与氯代烃相比，溴代烃的反应研究很少。以2-溴苯酚为模型化合物，研究了其在1cm内径的反应器中的均相气相热解热降解行为，熔融二氧化硅流动反应器，浓度为90 ppm，反应时间为2.0 s，温度范围为300 - 1000 ℃。观察到的产物包括二苯并对二恶英（DD）、1-单溴二苯并对二恶英（1-MBDD）、4-单溴二苯并呋喃（4-MBDF）、二苯并呋喃（DF）、萘、溴代萘、2，4-和2，6-二溴苯酚、苯酚、溴苯和苯。这些结果进行了比较，并与以前的结果报道的2-氯苯酚。在低于700 ℃的温度下，形成2-溴苯氧基自由基，其通过CO消除分解形成溴代萘自由基，通过自由基重组/重排反应形成萘和2-溴萘。然而，与萘是主要产物的2-氯苯酚的结果不同，DD成为2-溴苯酚热解的主要产物。DD和1-MBDD的形成归因于2-溴苯氧基自由基分别与2-溴苯氧基自由基的碳（溴）中心自由基和碳（氢）中心自由基内消旋体的自由基-自由基反应。未检测到潜在产物4，6-二溴二苯并呋喃（4，6-DBDF），在2-氯苯酚的氧化中观察到类似产物4，6-二氯二苯并呋喃（4，6 DCDF）。这归因于我们实验的热解条件（例如，更短的反应时间和更高的温度），这有利于形成DD和1-MBDD的反应中间体。
Brominated hydrocarbons are the most commonly used flame retardants. Materials containing brominated hydrocarbons are frequently disposed in municipal and hazardous waste incinerators as well as being subjected to thermal reaction in accidental fires. This results in the potential for formation of brominated dioxins and other hazardous combustion byproducts. In contrast to chlorinated hydrocarbons, the reactions of brominated hydrocarbons have been studied only minimally. As a model brominated hydrocarbon that may form brominated dioxins, we studied the homogeneous, gas-phase pyrolytic thermal degradation of 2-bromophenol in a 1-cm i.d., fused-silica flow reactor at a concentration of 90 ppm, with a reaction time of 2.0 s, and over a temperature range of 300 to 1000 degrees C. Observed products included dibenzo-p-dioxin (DD), 1-monobromodibenzo-p-dioxin (1-MBDD), 4-monobromodibenzofuran (4-MBDF), dibenzofuran (DF), naphthalene, bromonaphthalene, 2,4- and 2,6-dibromophenol, phenol, bromobenzene, and benzene. These results are compared and contrasted with previous results reported for 2-chlorophenol. At temperatures lower than 700 degrees C, formation of 2-bromophenoxyl radical, which decomposes through CO elimination to form a bromocyclopentadienyl radical, forms naphthalene and 2-bromonaphthalene through radical recombination/rearrangement reactions. However, unlike the results for 2-chlorophenol, where naphthalene is the major product, DD becomes the major product for the pyrolysis of 2-bromophenol. The formation of DD and 1-MBDD are attributed to radical-radical reactions involving 2-bromophenoxyl radical with the carbon- (bromine) centered radical and the carbon- (hydrogen) centered radical mesomers of 2-bromophenoxyl radical, respectively. The potential product, 4,6-dibromodibenzofuran (4,6-DBDF) for which the analogous product, 4,6-dichlorodibenzofuran (4,6 DCDF), was observed in the oxidation of 2-chlorophenol, was not detected. This is attributed to the pyrolytic conditions of our experiments (e.g., shorter reaction times and higher temperatures) that favor reaction intermediates that form DD and 1-MBDD.