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Sonochemical degradation for toxic halogenated organic compounds
Author
Xu, Yanrong
Supervisor
Teo, Khay Chuan
Abstract
Growing international concern for worsening environmental situation has alerted for more effective and economical waste treatment technologies as well as for energy efficiency. Recently, the application of ultrasound in environmental treatment has received a great deal of attention from the academic sector and waste treatment technological organisations. This study has undertaken in order to establish the potential application of ultrasonic method for the treatment of environmental organic contaminants.
Effective acoustic power for sonochemical reaction was measured for three kinds of ultrasonic devices including probe system, cup-horn system and beakertype system. Their efficiencies were investigated in terms of the initial reaction rate. The probe ultrasonic system was found to be the most effective due to its direct ultrasonic irradiation into the immediate reaction media. However, in order to conduct investigation on the intermediates and the associated reaction mechanism, the beaker-type ultrasonic system was selected due to its moderate sonication characteristic. The energy output of the beaker ultrasonic device varies with the position where the reactor was placed, and it was found that center of the beaker is the most favorable position which received the greater irradiation.
The ultrasonic degradation of p-chlorophenol in water was significantly affected by the physical design of the ultrasonic device such as the frequency and power, made and geometry, and subjected to external operating variables such as ambient pressure, temperature and the type of dissolved gas, viscosity of the media. The combination of sonolysis and other agents such as Fenton's reagent can benefit in achieving effective degradation of p-chlorophenol in water.
According to the solvent dependence of sonochemical reaction, it is known that sonolysis of water can generate reactive hydroxyl radicals (OH●) for the participation in many organic reactions. It was proposed that ultrasonic reaction induced by OH● results in the formation of intermediates which were tentatively identified to be 4-chlororesorcinol, 4-chlorocatechol, 1,4-benzoquinone, hydroquinone, and some other unidentified materials. Further sonolysis of these species could lead to complete mineralized products, carbon dioxide, water and hydrochloric acid. Moreover, nitrate was detected as a by-product from the ultrasonic reaction of dissolved nitrogen and oxygen. Under the given conditions, the ultrasonic decomposition of p-chlorophenol generally proceeds quickly, but the presence of other oxidants is often essential to achieve complete mineralization of organic carbon in the reaction matrix.
The overall ultrasonic degradation reaction follows a first order rate law for p-chlorophenol and for each major individual intermediates. With respect to the effect of external conditions on the kinetic, the addition of hydrogen peroxide and Fenton's reagent in certain range of concentration can accelerate the degradation. It was observed that the introduction of gas might not necessary lead to a higher initial reaction rate and is depending on the gas type and the flow rate.
Accurate and convenient analytical methods were developed and established for this work in order to facilitate the collection of analytical data for the sonochemical experiments. High performance liquid chromatography (HPLCLJVIMS) and total organic carbon (TOC) analyzer w&e used to determine the analytes concentration and to evaluate the mineralization of related organic compounds.
Effective acoustic power for sonochemical reaction was measured for three kinds of ultrasonic devices including probe system, cup-horn system and beakertype system. Their efficiencies were investigated in terms of the initial reaction rate. The probe ultrasonic system was found to be the most effective due to its direct ultrasonic irradiation into the immediate reaction media. However, in order to conduct investigation on the intermediates and the associated reaction mechanism, the beaker-type ultrasonic system was selected due to its moderate sonication characteristic. The energy output of the beaker ultrasonic device varies with the position where the reactor was placed, and it was found that center of the beaker is the most favorable position which received the greater irradiation.
The ultrasonic degradation of p-chlorophenol in water was significantly affected by the physical design of the ultrasonic device such as the frequency and power, made and geometry, and subjected to external operating variables such as ambient pressure, temperature and the type of dissolved gas, viscosity of the media. The combination of sonolysis and other agents such as Fenton's reagent can benefit in achieving effective degradation of p-chlorophenol in water.
According to the solvent dependence of sonochemical reaction, it is known that sonolysis of water can generate reactive hydroxyl radicals (OH●) for the participation in many organic reactions. It was proposed that ultrasonic reaction induced by OH● results in the formation of intermediates which were tentatively identified to be 4-chlororesorcinol, 4-chlorocatechol, 1,4-benzoquinone, hydroquinone, and some other unidentified materials. Further sonolysis of these species could lead to complete mineralized products, carbon dioxide, water and hydrochloric acid. Moreover, nitrate was detected as a by-product from the ultrasonic reaction of dissolved nitrogen and oxygen. Under the given conditions, the ultrasonic decomposition of p-chlorophenol generally proceeds quickly, but the presence of other oxidants is often essential to achieve complete mineralization of organic carbon in the reaction matrix.
The overall ultrasonic degradation reaction follows a first order rate law for p-chlorophenol and for each major individual intermediates. With respect to the effect of external conditions on the kinetic, the addition of hydrogen peroxide and Fenton's reagent in certain range of concentration can accelerate the degradation. It was observed that the introduction of gas might not necessary lead to a higher initial reaction rate and is depending on the gas type and the flow rate.
Accurate and convenient analytical methods were developed and established for this work in order to facilitate the collection of analytical data for the sonochemical experiments. High performance liquid chromatography (HPLCLJVIMS) and total organic carbon (TOC) analyzer w&e used to determine the analytes concentration and to evaluate the mineralization of related organic compounds.
Date Issued
2001
Call Number
QD801 Xu
Date Submitted
2001