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Degradation of para-cresol using advanced oxidation technologies
Author
Choo, Wei Kai
Supervisor
Teo, Khay Chuan
Abstract
The petrochemical industry is a key sector for the Singapore economy. However, effluents from petroleum refineries contain a myriad variety of organic and inorganic contaminants that require careful treatment before their discharge into the sea. One such organic pollutant is cresol, which causes respiratory problems in humans, and accumulates in water bodies of low dissolved oxygen content.
The study was conducted to investigate on the viability of Advanced Oxidation Technologies (AOTs) to degrade and mineralize para-cresol into innocuous products, such as carbon dioxide and water. This was accomplished by using powerful oxidants such as hydrogen peroxide, ozone and/or catalysts under two different activation modes: W photolysis or ultrasonolysis.
For a detailed study, collected samples were subjected to Total Organic Carbon (TOC) analyses to determine the degree of mineralization and the associated kinetic profiles. High Performance Liquid Chromatography P L C ) was used to study the degradation kinetics of the pm-cresol under the various advanced oxidation processes (AOPs), as well as the formation of intermediates and their time-profiles. Lastly, samples that revealed the presence of some key intermediates were isolated and concentrated from the sample matrix via Solid Phase Extraction (SPE) and subjected to subsequent Gas Chromatography-Mass Spectrometry (GCMS) analysis.
TOC results have shown that W photolysis with hydrogen peroxide provides the most efficient mineralization of para-cresol. However, a delicate stoichiometric balance at the start between para-cresol and hydrogen peroxide is essential for optimum results as it is well known that the active hydroxyl radicals (HO*) can self-destruct at high concentrations via radical coupling. It was also observed that the mineralization kinetics under power ultrasonic conditions was largely independent of the hydrogen peroxide concentrations. This suggests that the pyrolysis of paracresol vapour within the cavitating bubble is the major degradation pathway, instead of being attacked by the HO* radical around the bubble vicinity. Lastly, it was discovered that sonocatalysis using homogeneous catalyst, such as Fenton's Reagent (Fe2+ or Fe3+ ions) could greatly enhance the mineralization process, and negates the use of excessive quantities of hydrogen peroxide. Such a finding may potentially translate into saving of operating cost on an industrial scale given the cheaper cost of ferrous salts.
Several stable dimeric species were found as the dominant reaction intermediates, possibly via de-alkylation, aromatic ring oxidation, ring-opening and radical coupling mechanisms. Such a finding was in agreement with previous works by other researchers with other phenolic compounds, such as sonication of para-nitrophenol in which intermediates of higher molecular weights other than the original molecule were detected (Kotronarou et. al., 1991).
The study was conducted to investigate on the viability of Advanced Oxidation Technologies (AOTs) to degrade and mineralize para-cresol into innocuous products, such as carbon dioxide and water. This was accomplished by using powerful oxidants such as hydrogen peroxide, ozone and/or catalysts under two different activation modes: W photolysis or ultrasonolysis.
For a detailed study, collected samples were subjected to Total Organic Carbon (TOC) analyses to determine the degree of mineralization and the associated kinetic profiles. High Performance Liquid Chromatography P L C ) was used to study the degradation kinetics of the pm-cresol under the various advanced oxidation processes (AOPs), as well as the formation of intermediates and their time-profiles. Lastly, samples that revealed the presence of some key intermediates were isolated and concentrated from the sample matrix via Solid Phase Extraction (SPE) and subjected to subsequent Gas Chromatography-Mass Spectrometry (GCMS) analysis.
TOC results have shown that W photolysis with hydrogen peroxide provides the most efficient mineralization of para-cresol. However, a delicate stoichiometric balance at the start between para-cresol and hydrogen peroxide is essential for optimum results as it is well known that the active hydroxyl radicals (HO*) can self-destruct at high concentrations via radical coupling. It was also observed that the mineralization kinetics under power ultrasonic conditions was largely independent of the hydrogen peroxide concentrations. This suggests that the pyrolysis of paracresol vapour within the cavitating bubble is the major degradation pathway, instead of being attacked by the HO* radical around the bubble vicinity. Lastly, it was discovered that sonocatalysis using homogeneous catalyst, such as Fenton's Reagent (Fe2+ or Fe3+ ions) could greatly enhance the mineralization process, and negates the use of excessive quantities of hydrogen peroxide. Such a finding may potentially translate into saving of operating cost on an industrial scale given the cheaper cost of ferrous salts.
Several stable dimeric species were found as the dominant reaction intermediates, possibly via de-alkylation, aromatic ring oxidation, ring-opening and radical coupling mechanisms. Such a finding was in agreement with previous works by other researchers with other phenolic compounds, such as sonication of para-nitrophenol in which intermediates of higher molecular weights other than the original molecule were detected (Kotronarou et. al., 1991).
Date Issued
2004
Call Number
QD341.P5 Cho
Date Submitted
2004