为深入了解含多溴二苯醚(PBDE)废弃物热处置过程中多溴二苯并对二恶英(PBDD/Fs)的形成机理,本文研究了关键中间体(自由基,FRs)在PBDD/Fs的形成过程中。BDE-209,环境中最常见的PBDE,选择作为研究对象,通过模拟含PBDE的废物进入水泥窑预分解炉时的温度(850°C)和铁基材料等关键条件来分析FR的形成。使用电子顺磁共振(EPR)光谱和密度泛函理论(DFT)计算来研究反应。模拟实验的结果揭示了以碳为中心的自由基,和DMPO-OH分析进一步证实了FR的产生。这些发现证实了先前的计算,预测在由BDE-209形成PBDD/Fs期间存在自由基中间体。DFT计算显示BDE-209中存在内部邻位CBr键。BDE-209键断裂的优先顺序是醚键,内部邻位CBr键,和邻位CBr键之外。BDE-209可以进一步形成三种FR,即,单苯环的氧中心自由基,单个苯环的碳中心基团,和双苯环的碳中心基团。推断了FR形成的特定过程:化学键的高温均匀裂解,电子转移,和化学吸附,其中电子转移和化学吸附可能是更重要的途径。拟议的BDE-209内部邻位裂解为多溴二苯醚的降解和PBDD/Fs的形成提供了新的见解;关于BDE-209生成自由基的结果进一步阐明了二恶英的合成机理,这对于在处理和处置含多溴二苯醚的废物过程中控制二恶英的产生和排放非常重要。
To deeply understand the formation mechanism of polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) in the thermal disposal process of polybrominated diphenyl ether (PBDE)-containing waste, this paper studied the formation pathways of key intermediates (free radicals, FRs) in the formation process of PBDD/Fs. BDE-209, the most common PBDE in the environment, was selected as the object of
study to analyze FR formation by simulating the key conditions such as temperature (850 °C) and Fe-based materials when PBDE-containing waste entering cement kiln precalciner. Electron paramagnetic resonance (EPR) spectroscopy and density functional theory (DFT) calculations were used to
study the reaction. The result of simulation experiments revealed carbon-centered radicals, and DMPO-OH analysis further confirmed the generation of FRs. The findings confirmed previous calculations predicting the existence of radical intermediates during the formation of PBDD/Fs from BDE-209. DFT calculations revealed the existence of an inner ortho-position CBr bond in BDE-209. The priority order of the bond breaking of BDE-209 was ether bond, inner ortho-position CBr bond, and outside ortho-position CBr bond. BDE-209 can further form three kinds of FRs, namely, oxygen-centered radicals of single benzene rings, carbon-centered radicals of single benzene rings, and carbon-centered radicals of double benzene rings. The specific processes of FR formation were inferred: high-temperature homogeneous cleavage of chemical bonds, electron transfer, and chemisorption, where electron transfer and chemisorption may be more important pathways. The proposed inner ortho-position cleavage within BDE-209 provides new insights into the degradation of PBDEs and the formation of PBDD/Fs; the results regarding BDE-209 generation radicals further elucidate the synthesis mechanism of dioxins, which is important for controlling dioxin generation and emission during the treatment and disposal of waste containing PBDEs.