Abstract Brominated flame retardants (BFRs) are bromine-bearing hydrocarbons added or applied to materials to increase their fire resistance. As thermal treatment and recycling are common disposal methods for BFR-laden objects, it is essential to precisely describe their decomposition chemistry at elevated temperatures pertinent to their thermal recycling. Laboratory-level and pilot-scale investigations have addressed the thermal decomposition of pure BFRs and/or BFR-laden polymers under oxidative and pyrolytic environments, typically at temperatures of 280–900 °C. These studies shed light on the effects of various factors influencing the decomposition behaviour of BFRs such as chemical character, polymer matrix, residence time, bromine input, oxygen concentration, and temperature. Although BFRs decomposition mainly occurs in a condensed phase, gas phase reactions also contribute significantly to the overall decomposition of BFRs. Exposing BFRs to temperatures higher than their melting points results in evaporation. Quantum chemical calculations have served to provide mechanistic and kinetic insights into the chemical phenomena operating in decomposition of BFRs and subsequent emissions of polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). Under thermal conditions such as smouldering, municipal waste incineration, pyrolysis, thermal recycling, uncontrolled burning and fires, BFRs degrade and form brominated products of incomplete combustion (BPICs). Thermal degradation of BFRs often proceeds in the presence of bromine atoms which inhibit complete combustion. Major BPICs comprise brominated benzenes and phenols in addition to a wide range of brominated aromatics. Pyrolytic versus oxidative conditions seems to have very little influence on the thermal stability and decomposition behaviour of commonly-deployed BFRs. Thermal degradation of BFRs produces potent precursors to PBDD/Fs. Experimental studies have established inventories of PBDD/F emissions with alarming high yields for many BFRs. Co-combustion of BFRs-containing objects with a chlorine source (e.g. polyvinyl chlorides) results in the emission of significant concentrations of mixed halogenated dibenzo-p-dioxins and dibenzofurans (i.e. PXDD/Fs). Formation of PBDD/Fs from incomplete BFRs decomposition occurs primarily due to the condensations of gas phase precursors, including unaltered structural entities of some BFRs in their own right. Complete destruction of BFRs promotes PBDD/Fs formation via de novo synthesis. Bromination of PBDD/Fs in gas phase reactions is more prevalent if compared with chlorination mechanisms of PCDD/Fs, which is largely dominated by heterogeneous pathways. In uncontrolled burning and in simulated fly ash experiments, a strong correlation between congeners patterns of polybrominated diphenyl ethers (PBDEs) and PBDD/Fs indicate that PBDEs function as direct precursors for PBDD/Fs, even in the de novo synthesis route. In this review, we critically discuss current literature on BFRs thermal decomposition mechanisms; gather information regarding the contribution of homogenous and heterogeneous routes to overall BFRs decomposition; survey all studies pertinent to the emission of PBDD/Fs and their analogous mixed halogenated counterparts from open burning of e-waste, and finally, highlight knowledge gaps and potential directions that warrant further investigations.

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溴化阻燃剂 (BFR) 的热分解：产品和机制

摘要 溴化阻燃剂 (BFR) 是添加或应用到材料中以提高其耐火性的含溴碳氢化合物。由于热处理和回收是含 BFR 物体的常见处置方法，因此必须准确描述其在与热回收相关的高温下的分解化学。实验室级和中试规模的研究已经解决了纯 BFR 和/或含 BFR 的聚合物在氧化和热解环境下（通常在 280-900 °C 的温度下）的热分解问题。这些研究阐明了影响 BFR 分解行为的各种因素的影响，例如化学特性、聚合物基质、停留时间、溴输入、氧气浓度和温度。虽然 BFRs 的分解主要发生在凝聚相中，气相反应也对 BFRs 的整体分解有很大贡献。将 BFR 暴露于高于其熔点的温度会导致蒸发。量子化学计算有助于深入了解 BFR 分解和随后多溴化二苯并对二恶英和二苯并呋喃 (PBDD/Fs) 的排放中的化学现象。在阴燃、城市垃圾焚烧、热解、热回收、不受控制的燃烧和火灾等热条件下，BFR 会降解并形成不完全燃烧的溴化产物 (BPIC)。BFR 的热降解通常在溴原子存在下进行，溴原子会抑制完全燃烧。除了广泛的溴化芳烃外，主要的 BPIC 还包括溴化苯和苯酚。热解与氧化条件似乎对常用 BFR 的热稳定性和分解行为几乎没有影响。BFR 的热降解会产生 PBDD/Fs 的有效前体。实验研究已经建立了 PBDD/F 排放清单，许多 BFR 的产量惊人。含溴化阻燃剂的物体与氯源（例如聚氯乙烯）共同燃烧会导致大量混合卤化二苯并对二恶英和二苯并呋喃（即 PXDD/Fs）的排放。BFRs 不完全分解形成 PBDD/Fs 的主要原因是气相前体的冷凝，包括一些 BFRs 本身未改变的结构实体。BFRs 的完全破坏通过从头合成促进 PBDD/Fs 的形成。与 PCDD/Fs 的氯化机制相比，PBDD/Fs 在气相反应中的溴化更为普遍，后者主要由多相途径控制。在不受控制的燃烧和模拟飞灰实验中，多溴二苯醚 (PBDE) 和 PBDD/Fs 的同系物模式之间的强相关性表明，即使在从头合成路线中，PBDEs 也是 PBDD/Fs 的直接前体。在这篇综述中，我们批判性地讨论了关于 BFR 热分解机制的当前文献；收集关于同质和异质路线对整体 BFR 分解的贡献的信息；调查所有与电子废物露天燃烧产生的 PBDD/Fs 及其类似混合卤化对应物排放相关的研究，最后，