以微波活化過硫酸鹽破壞去除水中全氟辛酸之研究

Decomposition of the Perfluorocarboxylic Acids in Water by Microwaves-induced Persulfate

李育輯(Yu-Chi Lee)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.10244

摘要

全氟化合物特別是全氟辛酸與全氟辛磺酸由於其在環境中包含水體、生物體內普遍性存在的污染，而引起全球性的關注。這些化合物因為特殊的表面特性與化學穩定性而大量的被使用為高分子添加劑於抗污劑、消防藥劑、殺蟲劑與界面活性劑，然而全氟化合物具有極高的化學與熱穩定性導致在環境中被視為無任何可以天然降解的途徑，因此研發一個可以在溫和的條件下有效降解全氟化合物的方法以解決其污染問題，便成為一個十分重要且具有實際經濟價值的技術。
本研究以微波水熱法添加過硫酸鹽在27, 60, 90,與130°C下試驗破壞去除水中的PFOA污染物，發展出一有效的處理方法。結果顯示既使在室溫(27°C) 下，過硫酸鹽對PFOA的降解去除仍有一定的去除率，表示過硫酸鹽對PFOA為極有效的氧化劑，而反應溫度的提升明顯加速PFOA破壞去除的反應，但是過高的反應溫度(130°C)，雖然會加快反應速率，但反而會釋出過量的過硫酸自由基消耗硫酸鹽，而最終得到較低的PFOA降解礦化比例。另外，溶液系統pH是此處理方法中很重要的操作參數，在鹼性的溶液環境中，PFOA幾乎完全不會被降解，而的酸性環境 (pH=6.6與pH=2.5) 下的反應速率為鹼性環境(pH=8.8與pH=10.5)下的反應速率的5至74倍，故反應系統pH對過硫酸鹽降解PFOA具有十分決定性的影響。若改以中間產物C7∼C2等短鍊全氟化合物為目標污染物的實驗中顯示，全氟化合物的碳鍊長度越長者，穩定性越高且越不容易去除，而碳鍊長度越短者相對生成氟離子濃度與礦化比例也越高。
加入零價鐵並以微波活化過硫酸鹽的實驗，在25, 60與90°C下試驗破壞去除水中的PFOA污染物，結果顯示添加過硫酸鹽與零價鐵的PFOA溶液具有最高的去除率，在90℃反應八小時後有73.1%的PFOA被破壞降解並形成短鍊的全氟化合物，而最終的去氟率為23.5%。在PFOA反應實驗中，零價鐵具有協同效應可以加速反應進行，其不只自身可以破壞去除PFOA，而且會釋出二價鐵降低生成過硫酸自由基的活化能而加速硫酸根自由基的生成，因此可以降低反應的溫度。故結合零價鐵與過硫酸鹽的應用可以有效的加速反應，提升PFOA的去除效率，並降低所需的操作溫度與反應時間。

關鍵字

全氟化合物 ； 全氟辛酸 ； 微波 ； 過硫酸鹽 ； 零價鐵 ； 水熱法

並列摘要

Perfluorinated acids, especially perfluorooctanoic acid (PFOA) have recently received much attention and concern worldwide because they are recognized as ubiquitous contaminants in water, wildlife, and humans. These compounds have been widely used as polymer additives, fire retardants, suppressants, pesticides, and surfactants because of their high surface-active effect and good thermal and chemical stability. Moreover, PFCAs, which are extremely stable to chemical and thermal destruction, are considered un-degradable in nature. Therefore, developing a method that is effective in degrading PFCAs to harmless end products under mild conditions will provide a cost-effective solution to the PFCAs pollution problem.
The microwave-hydrothermal decomposition of persistent and bioaccumulative PFOA in water with persulfate (S2O82－) at 27, 60, 90, and 130°C was examined to develop an effective technology for treating PFOA pollution. S2O82－ is an efficient oxidant for degrading PFOA even at the room temperature of 27 °C. Higher temperature accelerates the PFOA decomposition rate, but an extremely high temperature (130 °C) will lead to the formation of significant amount of radical oxidants that are released rapidly to consume most remaining persulfate thus causing a lower mineralization efficiency. The solution pH value is another important factor to influence the degradation rate; there is nearly no PFOA decomposition reaction under alkaline condition. The decomposition rate in acidic condition (pH=6.6 and pH=2.5) was 5–74 times faster than in alkaline condition (pH=8.8 and pH=10.5). Additionally, the proposed method was also effective in decomposing other PFCA species such as the C2–C7 perfluoroalkyl groups. The short-chain PFCAs species are easier to be degraded and mineralized.
The zerovalent iron (ZVI) activated persulfate (PS) oxidation was examined at 25, 60 and 90℃. The results of laboratory study revealed that when treated with 5 mM PS and ZVI solution at 90℃ for 8 hours, 73.1% of PFOA was decomposed to form shorter-chain PFCAs and fluoride ions with 23.5% defluorination efficiency. The introduction of ZVI into the PFOA solution with PS addition will lead to synergetic effect in accelerating the PFOA decomposition rate and reducing the reaction time. ZVI not only decomposes PFOA by itself, but also releases ferrous ions to reduce the activation energy of PS to form sulfate free radical at a lower reaction temperature. The combining use of ZVI and PS enhances the decomposition efficiency of PFOA at lower operating temperature and reduces reaction time.

並列關鍵字

Microwave ； perfluorooctanoic acid ； PFOA ； persulfate ； hydrothermal decomposition ； zerovalent iron..

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