Study on the Mineralization of Organofluorine by Photochemical Oxidation Methods

• Main Authors: Meng-TsoTsai, 蔡孟佐
• Other Authors: Yao-Hui Huang
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/58168898479678744599

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 101 === In last decades, organofluorines are widely applied due to human activities. Their bioaccumulation and toxicological properties have caused great concern in environmental issues. This study adopted two photochemical oxidation processes, H2O2 / UV and Na2S2O8 / UV, for the mineralization of the target organofluorines, including difluoroacetic acid (DFA), trifluoroacetic acid (TFA), trifluoroethanol (TFE), 3,3,3-trifluoro-1-propanol, 2,2,3,3-tetrafluoro-1-propanol (TFP), 2,2,3,3,3-pentafluoro-1-propanol (PFP), and perfluoro-octanoic acid (PFOA). Aeration, UV irradiation, and oxidant dosage are the critical parameters to optimize the photochemical experiments. The results of photochemical mineralization of TFP indicated that air purging was more efficient than was nitrogen. In addition, UV 254 nm lamp proved to be more effective than UV 365 nm using a specific amount of oxidant. H2O2 / UV system reduced more than 90% TOC of DFA and TFP solutions, but was incapable of mineralizing TFA, TFE, and 3,3,3-trifluoro-1-propanol, PFP and PFOA (TOC removal lower than 40 %). However, high mineralization level for all target organofluorines (TOC removal all above 90%) could be obtained by Na2S2O8 / UV system as a sufficient amount of oxidant was used, most notably DFA and TFP were completely mineralized in 10 min. The ion chromatographic analyses revealed that TFA was an intermediate commonly recorded in the mineralization of TFE, 3,3,3-trifluoro-1-propanol, and PFP. Moreover, DFA was found during TFP decomposition. Hence, a general reaction pathway for the photochemical treatment of organofluorines was proposed: the mineralization of perfluoroalkyl compounds is initiated by de-hydroxyl of alcohol groups, and then oxidized into carboxylic acid by freeing fluorine atoms; the fluorinated carboxylic acid would release CO2 by radical attacks, and was hydrolyzed into a smaller fluorinated alcohol again. The loop of pathway took place until all remaining TOC turned into CO2, H2O, and fluoride ions.