Mechanism and kinetic study for the hydroxyl free radicals mediated photoxidation of organic-contaminated-aqueous solutions /
Recently, advanced oxidation processes (AOPs) involving hydroxyl radicals generation by UV radiation combined with a chemical oxidant such as ozone or hydrogen peroxide have been shown to effectively degrade organic contaminants that resist biological oxidation processes. In this investigation, we s...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1999.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=731685741&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Recently, advanced oxidation processes (AOPs) involving hydroxyl radicals generation by UV radiation combined with a chemical oxidant such as ozone or hydrogen peroxide have been shown to effectively degrade organic contaminants that resist biological oxidation processes. In this investigation, we studied the repudiation of water contaminated with three high explosives (TNT, RDX, and HMX) with UV radiation combined with hydrogen peroxide. Also, the study was extended to repudiating aqueous phenol solution by UV/H₂O₂ AOP. The photochemical oxidation was performed in a completely mixed batch photolytic reactor. The UV irradiation source was a low-pressure mercury vapor lamp that was axially centered and immersed in the contaminated solution. The effects of hydrogen peroxide dosage, initial phenol concentration, H₂O₂/phenol molar ratio, pH, and temperature have been investigated. The experimental results indicate that there is an optimum H₂O₂/phenol molar ratio in the range 100 to 250. Sufficient hydrogen peroxide supply is needed, but a very high H₂O₂ concentration inhibits the photoxidation rate. The initial phenol concentration was inversely proportional to the second-order reaction rate constants. No pH effect was observed in the range of 4-10. In addition, this study aims to understand the phenol degradation mechanism. High performance liquid chromatography (HPLC) has been used to identify the oxidation products and determine their concentrations. A detailed reaction mechanism is proposed. The reaction products include hydroquinones, benzoquinones, and aliphatic acids with up to six carbon atoms. Phenol is oxidized first by the hydrogenation of the aromatic ring to yield hydroquinones. The cleavage of the benzoquinone aromatic ring formed acid. Further hydroxyl radical attacks on bucolic acid produce maleic acid, fumaric acid, and oxalic acid, then formic acid and CO₂. A kinetic model for phenol oxidation in water by UV/H₂O₂ AOP is developed. The model employs the pseudo-steady state assumption to estimate hydroxyl radical concentration and assumes constant pH. Although we experimented with a specific UV lamp intensity, the model can accommodate for other intensities. The model includes all known elementary photochemical reactions. The model is used to determine the reaction rate parameters and it accurately predicts concentrations of phenol, intermediate ring compounds, as well as final products. |
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| Item Description: | Vita. "Major Subject: Chemical Engineering". |
| Physical Description: | xiii, 147 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilm Inc. |
| Bibliography: | Includes bibliographical references (leaves 125-131). |