| Summary: | 碩士 === 國立中山大學 === 環境工程研究所 === 86 === The purpose of this study was to investigate the products converted from the heterogeneous photocatalysis of perchloroethylene(PCE) using near UV/TiO2 and explore the reaction pathways. The experiments were conducted by varying PCE concentration(7.7~45.3 ppmv), relative humidity(R.H.=0~65.2 %), oxygen concentration(0~21 %), and retention time(0.5~2.0 sec). Glass beds coated with Degussa P-25 anatase TiO2 were filled in a Pyrex glass reactor. TiO2 was illuminated by four ultraviolet(UV) lamps of 10 watts. Results from QA/QC experiments indicated that PCE could not be photocatalytically degradated by near UV of wavelength 365 nm. It can be, however, decomposed quickly through heterogeneous photocatalysis. The higher concentration of inlet PCE, the higher conversion ratio of PCE can be achieved. Mass transfer was throught as the controlling step for the heterogeneous photocatalytic reaction. The conversion ratio of PCE can be inhibited at higher relative humidities. PCE was decomposed as oxygen and retention time increased. A higher concentration of oxygen was not efficient on the increase of PCE conversion. The end products observed from UV/TiO2 heterogeneous photocatalytic reactions included CHCl3, CCl4, C2HCl5, C2Cl6, COCl2, CCl3CClO, Cl2, HCl, CO, and CO2. The major chlorinated compound was Cl2 when the photocatalytic reactions proceed at higher oxygen concentration and less humid conditions. As water vapor existed, the major chlorinated compound became HCl. The major product was CO2 during the entire experimental process of heterogeneous photocatalytic reactions. The distribution of products varied with operating parameters, which controlled the competition between chlorine free radicals and oxygen atoms. The competition of chlorine free radicals and oxygen atoms impacted the reaction pathways. Reaction pathways can be significantly affected while oxygen concentration was lower than 1%. Water vapor influenced the conversion ratio of PCE and, however, did not affect the reaction pathways. This study also proposed the reaction pathways of PCE heterogeneous photocatalytic reactions according to the experimental results. The photocatalytic reactions had a tendency to produce CCl4, C2Cl6, and CO2 when oxygen and water vapor were absent. In addition, the photocatalytic reactions had a tendency to produce Cl2 and CO2 when water vapor was absent and oxygen existed.
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