Thermal Decomposition of Two Gaseous Perfluorocarboxylic Acids: Products and Mechanisms
Thermal Decomposition of Two Gaseous Perfluorocarboxylic Acids: Products and Mechanisms
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DOI：
10.1021/acs.est.2c08210
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发表时间：
2023-04-05
影响因子：
11.4
通讯作者：
Hanigan, David
中科院分区：
文献类型：
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作者：
Wang, Junli;Song, Mingrui;Hanigan, David
全氟烷基和多氟烷基物质（PFASs）的热分解产物和机制知之甚少，尽管使用热处理来修复PFAS污染的介质。为了确定全氟羧酸（PFCAs）的热分解产物和机理，在200至780 ℃的温度下，在氮气和氧气中分解气态全氟丙酸（PFPrA）和全氟丁酸（PFBA）。在氮气中（即，热解）时，PFPrA的主要产物为CF 2 = CF 2、CF 3CF 2H和CF 3COF。PFBA的主要产物为CF_3CF = CF_2。这些产品是通过HF消除（检测低至200摄氏度）。CF4和C2F6观察到从两个PFCA，表明形成的全氟化碳自由基中间体。热解产物是高度热稳定的，导致差的脱附。在氧气中（即，燃烧）时，PFPrA和PFBA两者在400 ℃以下的主要产物是COF 2，但由于与石英反应器的反应，在600 ℃以上的主要产物是SiF 4。氧气通过与PFCA和热解产物（即，氟代烯烃和碳氟化合物基团）。铂在低至200摄氏度的温度下改善了PFCAs向COF2的燃烧，而石英在较高温度（>600摄氏度）下促进了PFCAs向SiF4的燃烧，突出了表面反应的重要性，这些反应通常不被纳入计算方法。
The thermal decomposition products and mechanisms of per-and polyfluoroalkyl substances (PFASs) are poorly understood despite the use of thermal treatment to remediate PFAS-contaminated media. To identify the thermal decomposition products and mechanisms of perfluorocarboxylic acids (PFCAs), gaseous perfluoropropionic acid (PFPrA) and perfluorobutyric acid (PFBA) were decomposed in nitrogen and oxygen at temperatures from 200 to 780 degrees C. In nitrogen (i.e., pyrolysis), the primary products of PFPrA were CF2=CF2, CF3CF2H, and CF3COF. CF3CF=CF2 was the dominant product of PFBA. These products are produced by HF elimination (detected as low as 200 degrees C). CF4 and C2F6 were observed from both PFCAs, suggesting formation of perfluorocarbon radical intermediates. Pyrolysis products were highly thermally stable, resulting in poor defluorination. In oxygen (i.e., combustion), the primary product of both PFPrA and PFBA below 400 degrees C was COF2, but the primary product was SiF4 above 600 degrees C due to reactions with the quartz reactor. Oxygen facilitated thermal defluorination by reacting with PFCAs and with pyrolysis products (i.e., fluoroolefins and fluorocarbon radicals). Platinum improved combustion of PFCAs to COF2 at temperatures as low as 200 degrees C, while quartz promoted the combustion of PFCAs into SiF4 at higher temperatures (>600 degrees C), highlighting the importance of surface reactions that are not typically incorporated into computational approaches.