Catalytic Degradation of Hexafluoropropylene Oxide Trimeric Acid during the Hydrothermal Regeneration of Spent Activated Carbon,ACS ES&T Engineering

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Catalytic Degradation of Hexafluoropropylene Oxide Trimeric Acid during the Hydrothermal Regeneration of Spent Activated Carbon
ACS ES&T Engineering ( IF 7.4 ) Pub Date : 2024-05-29 , DOI: 10.1021/acsestengg.4c00004
Qianxin Zhang ₁ , Md Manik Mian ₁ , Aimin Zhang _{1,

2} , Liang Zhou ₁ , Roujia Du ₁ , Wenya Ao ₁ , Gang Yu ₁ , Shubo Deng _{1,

3}

Affiliation

Regeneration of granular activated carbon (GAC) after adsorption of perfluoroalkyl and polyfluoroalkyl substances is an emerging challenge. This study reports a successful regeneration of spent GAC with hexafluoropropylene oxide trimer acid (HFPO–TA) at 120 °C. For the first time, we observed that GAC significantly catalyzed the degradation and defluorination of adsorbed HFPO–TA. The new catalytic degradation mechanism of HFPO–TA on GAC was proposed. Reaction intermediates’ analysis confirmed that the ether group of HFPO–TA near the carboxyl group was first split into hexafluoropropylene oxide dimer acid (HFPO–DA) and trifluoroacetic acid (TFA). Subsequently, HFPO–DA was further broken down to produce PFPrA and TFA. These intermediates were detected only when HFPO–TA was adsorbed on GAC and were not found when HFPO–TA was dissolved in water without GAC. Bond dissociation energy calculations revealed that the ether group close to the carboxylic acid had a smaller dissociation energy and was more susceptible to ether group breakage compared to the decarboxylation reaction of HFPO–TA. The gas-phase products contained significant amounts of 1H-substituted HFPO–TA and 1H-substituted HFPO–DA, indicating the decarboxylation of HFPO–TA. Furthermore, density functional theory calculations indicated that the ether group in the HFPO–TA breakage site carried a more positive charge on GAC, facilitating the breakage through nucleophilic reaction. Finally, the regeneration efficiency of GAC remained at 81% at the fifth adsorption–degradation cycle. This study offers a novel and cost-effective strategy for the degradative regeneration of HFPO–TA-adsorbed GAC.

中文翻译：

废活性炭水热再生过程中六氟环氧丙烷三聚酸的催化降解

吸附全氟烷基和多氟烷基物质后颗粒活性炭（GAC）的再生是一个新的挑战。这项研究报告了在 120 °C 下用六氟环氧丙烷三聚酸 (HFPO-TA) 成功再生废活性炭的情况。我们首次观察到 GAC 显着催化吸附的 HFPO-TA 的降解和脱氟。提出了HFPO-TA在GAC上催化降解的新机制。反应中间体分析证实HFPO-TA靠近羧基的醚基首先分裂成六氟环氧丙烷二聚酸（HFPO-DA）和三氟乙酸（TFA）。随后，HFPO-DA 进一步分解产生 PFPrA 和 TFA。仅当 HFPO-TA 吸附在 GAC 上时才检测到这些中间体，而当 HFPO-TA 溶解在不含 GAC 的水中时则未检测到这些中间体。键解离能计算表明，与HFPO-TA的脱羧反应相比，靠近羧酸的醚基解离能较小，更容易发生醚基断裂。气相产物含有大量的1H-取代的HFPO-TA和1H-取代的HFPO-DA，表明HFPO-TA发生脱羧。此外，密度泛函理论计算表明，HFPO-TA断裂位点的醚基在GAC上带有更多的正电荷，有利于通过亲核反应进行断裂。最终，在第五次吸附-降解循环时，GAC的再生效率仍保持在81%。这项研究为 HFPO-TA 吸附的 GAC 的降解再生提供了一种新颖且具有成本效益的策略。

更新日期：2024-05-29

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