School of Chemical Engineering, Guizhou Minzu University, Guiyang, 550025, China.
School of Physics and Mechatronic Engineering, Guizhou Minzu University, Guiyang, 550025, China.
Environ Res. 2024 Dec 15;263(Pt 1):120061. doi: 10.1016/j.envres.2024.120061. Epub 2024 Sep 24.
Although the production and usage of polybrominated biphenyls (PBBs) as brominated flame retardants have already been prohibited, they still pose a threat to the environment and human health. However, the evolutionary behaviors and decomposition mechanisms of PBBs during thermal treatment of waste remain unclear. In the present work, the mechanism and kinetics of thermal decomposition of decabromobiphenyl (deca-BB), one of the most frequently-used PBB congeners, are studied in detail using quantum chemical calculations. Results indicate that the high bond dissociation energies and large energy gap of deca-BB make its self-decomposition reaction difficult to occur, while its reactions with several reactive radicals (including hydrogen, bromine, and hydroxyl radicals) in the combustion environment are universally carried out at low energy barriers. Hydrogen, bromine, and hydroxyl radicals all exhibit a high selectivity for the para-C/Br atoms of deca-BB, resulting in the generation of several debromination products or intermediates. This study also investigates the formation mechanism of polybrominated dibenzofurans (PBDFs) from deca-BB and the effect of polymeric materials on this process. We found that the oxidation of ortho-phenyl-type radical, followed by evolution into PBDFs, is a very exothermic and relatively low-barrier process. Thus, the emergence of ortho-phenyl-type radicals from the loss of ortho-Br atoms is a critical step in the formation of PBDFs. Influence of polymeric materials on the formation of PBDFs is reflected in that various alkyl radicals and diradicals produced by their decomposition can readily abstract ortho-Br atoms to generate ortho-phenyl-type radicals, thus facilitating the formation of PBDFs. The mechanistic pathways and kinetic parameters presented in this study can offer theoretical guidance for controlling contaminant emissions in the thermal treatment of deca-BB-containing waste.
尽管多溴联苯 (PBBs) 作为溴系阻燃剂的生产和使用已经被禁止，但它们仍然对环境和人类健康构成威胁。然而，PBBs 在废物热处理过程中的演化行为和分解机制仍不清楚。在本工作中，使用量子化学计算详细研究了十溴联苯 (deca-BB) 的热分解机制和动力学，deca-BB 是最常用的 PBB 同系物之一。结果表明，deca-BB 的高键离解能和大能隙使得其自身分解反应难以发生，而其与燃烧环境中几种活性自由基（包括氢、溴和羟基自由基）的反应普遍在低能量势垒下进行。氢、溴和羟基自由基对 deca-BB 的对位-C/Br 原子都表现出很高的选择性，导致产生几种脱溴产物或中间产物。本研究还探讨了 deca-BB 生成多溴二苯并呋喃 (PBDFs) 的形成机制以及高分子材料对这一过程的影响。我们发现，邻苯基型自由基的氧化，随后演变成 PBDFs，是一个非常放热和相对低势垒的过程。因此，邻-Br 原子的缺失导致邻苯基型自由基的出现是形成 PBDFs 的关键步骤。高分子材料对 PBDFs 形成的影响体现在其分解产生的各种烷基自由基和双自由基可以很容易地夺取邻-Br 原子生成邻苯基型自由基，从而促进 PBDFs 的形成。本研究中提出的反应机制和动力学参数可为控制含 deca-BB 废物热处理过程中污染物排放提供理论指导。
