以UV/亞硫酸鹽光催化還原全氟丁烷磺酸之研究

The Study of UV/Sulfite Photo-reduction of Perfluorobutanesulfonic Acid

劉元涵(Yuan-Han Liu)

指導教授 ： 駱尚廉

國立臺灣大學/工學院/環境工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101658

摘要

全氟化物為良好的介面活性劑，具有熱穩定性和化學穩定性之化學特性，並常被用於工業產品中，許多文獻證實長碳鏈全氟化物全氟辛酸 (Perfluorooctanoic acid, PFOA) 與全氟辛烷磺酸 (Perfluorooctanesulfonic acid, PFOS)對環境與人體具有危害性，已被許多國家限制使用，故轉而使用短碳鏈全氟丁烷磺酸(Perfluorobutanesulfonic Acid, PFBS)，作為長碳鏈全氟化物的替代化學品，現今許多環境水體中已測出PFBS，因此開發有效的PFBS處理方法勢在必行。
本研究利用UV/亞硫酸鹽系統光催化誘發水合電子，以還原降解PFBS，並探討不同實驗參數對UV/亞硫酸鹽系統降解PFBS之影響。由結果顯示，濃度20.0 mg/L PFBS溶液之最佳降解參數為亞硫酸鹽濃度0.02M，初始pH值為11，系統溫度45℃，攪拌速率300rpm，於系統反應360分鐘後，可達到去除率79.2 %、脫氟率58.3 %，且生成短鏈全氟羧酸和氟離子，而PFBS去除之反應速率常數為0.33 hr-1，脫氟之反應速率常數為0.21 hr-1。PFBS處理效能與初始pH值和反應溫度呈正相關，曝氮氣呈負相關，而系統中亞硫酸鹽濃度過高，會抑制PFBS之處理效能。由中間產物分析結果表明，水合電子還原降解PFBS主要有三種降解途徑分別為脫磺酸反應、H/F交換反應以及C–C的斷鍵反應。
本研究以最佳參數降解PFOA與PFOS，利用反應動力學比較PFBS、PFOA與PFOS三者，其結果顯示擬一階降解的反應速率常數PFOA > PFOS > PFBS，而降解之反應活化能(Ea)分別為90.2 kJ/mole、319.4 kJ/mole與364.6 kJ/mole。PFBS、PFOA與PFOS三者之去除與脫氟的反應速率會與官能基、氟烷基鏈長度與C–F鍵低鍵離解能的位置和數量有關。同時本研究開發二階反應模型，可準確預測UV/亞硫酸鹽系統在15℃ ~ 45℃之溫度範圍下，PFBS、PFOA與PFOS於各反應時間下之去除率與脫氟率。

關鍵字

全氟丁烷磺酸 ； 全氟辛烷磺酸 ； 全氟辛酸 ； UV/亞硫酸鹽 ； 水合電子

並列摘要

Perfluorinated compounds (PFCs) have been used in many industrial applications as surfactants due to their excellent thermal and chemical stability. Because of the environmental and health hazards, use of long-chain perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) have been restricted in many countries. Short-chain perfluorobutanesulfonic acid (PFBS) is being used as substitutes of PFOA and PFOS. However, PFBS has been detected in many natural water bodies. Development of an effective treatment method to remove PFBS from water is of importance.
This study utilized a UV/sulfite reduction system to generate hydrated electrons for degradation of PFBS. The effects of different experimental parameters of the UV/sulfite system on PFBS degradation were investigated. The experimental results revealed that with 20.0 mg/L PFBS, 0.02 M sulfite solution and initial pH11, 79.2% of PFBS was decomposed to form shorter-chain perfluorinated carboxylic acids (PFCAs) and fluoride ions with 58.3% defluorination efficiency at 45℃ after 6 hours. The PFBS decomposition reaction rate constant is 0.33 hr-1, and the defluorination reaction rate constant is 0.21 hr-1. The decomposition efficiencies of PFBS increased with the initial pH and temperature, and decreased with the nitrogen exposure. The degradation efficiency of PFBS increased initially and then decreased with the increase in sulfite concentration. Based on the analytical results of intermediate products, three reaction pathways were proposed to explain the reductive destruction of PFBS with hydrated electron, including desulfonation, H/F exchange, and chain shortening via direct C–C cleavage.
This study illustrates the optimal parameters for degrading PFOA and PFOS in the UV/sulfite system. The results of reaction kinetics reveal that the reaction rate constants of first-order degradation are PFOA > PFOS > PFBS, and the reaction activation energy (Ea) are 90.2, 319.4, and 364.6 kJ/mole, respectively. The degradation and defluorination reaction rates of PFBS, PFOA, and PFOS are related to the head functional groups, fluoroalkyl chain length, and the position and number of C–F bonds with low bond dissociation energy. In addition, a second-order kinetic model was developed that could successfully predict the PFBS, PFOA, and PFOS decay over the relatively low temperature range from 15°C to 45°C.

並列關鍵字

Perfluorobutanesulfonic acid (PFBS) ； Perfluorooctane sulfonate (PFOS) ； Perfluorooctanoic acid (PFOA) ； UV/sulfite ； hydrated electron

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