Study On The Degradation Of Polychlorinated Biphenyls By Microwave Radiation

In the light of rapid developments in industry, plenty of industrial and living wastewater is polluting our water environment seriously with the increasing improvement of the people's living standard and urbanization. Contamination of Persistent Organic Pollutants (POPs) is paid close attention as one of the eight most serious global environment problems. Polychlorinated biphenyls (PCBs) as endocrine disrupter have caused serious damage to the peole and the ecological environment when they entered into the natural water. Based on the analysis and evaluation the status quo that PCBs have been degraded in water by each kind of physical and chemical method and the outfield auxiliary technology in the domestic and foreign, microwave as a new water treatment technology is proposed and it is fast, efficient, pollution-free and so on. Researching the rule of PCBs degradation by microwave and exploring the degradation mechanism and the reaction kinetics provide the basis and reference for application and the further fundamental research in reality.Using the AFC ring automatic coupling of single-model microwave system to analyze factors that affect PCBs degradation on the experimental design analysis, discover the best technological conditions. Through researching reaction mechanism of Fenton reagent and NaHSO₃, explicate the process and the mechanism of PCBs degradation. Through researching the theory of determinating dynamic equation parameters and a series of chemical experiments, determine this reacting system's dynamic parameters and dynamics equation. Through the adsorption as well as desorption of activated carbon's theory research, discuss influence of PCBs degradation rate by activated carbon adsorption technology microwave auxiliary. Around using the ultraviolet, infrared, HPLC (High Performance Liquid Chromatography) technologies, carry on qualitative and the quantitative analysis of PCBs and definite the product.The factors such as microwave power, the reaction time, pH value of water sample and reducing agent amount which effect PCBs degradation were comprehensively surveied by microwave and the union of microwave and reducing agent, as well as the union of microwave and activated charcoal adsorption. Then discovered the best technological conditions. PCB29 was degraded to biphenyl in microwave power 480W, reaction time 3min and the weak acid environment by microwave, and the degeneration rate was 70%. While PCB29 was degraded to biphenyl and xenol in microwave power 200W, reaction time 2min and the reducing agent amount 3g by the union of microwave and reducing agent NaHSO₃, and the degeneration rate was 90%.In the process that PCB29 was degraded into xenol by microwave, the mechanism of free group and the mechanism of nucleophilic substitution (fragrant) may possibly occur. Mechanism of free group is that H₂O is ionized into H and OH, OH and NaHSO₃ together can generate NaHSO₄ and H₂O. PCB29 generates 4,5 - dichloro-2 - biphenyl acetylene by microwave. Biphenyl acetylene is an unstable intermediate and can generate stable 3,4- dichloro-diphenyl with H₂O immediately. Thus a chlorine atom is taken off and finally biphenyl can be got. If the benzyne intermediate and H₂O have an addition reaction, the xenol will be produced. Mechanism of nucleophilic substitution (fragrant) is that PCB29 has the nucleophilic substitution with·OH in water, obtains the intermediate, and the intermediate dechlorinates further into xenol.Through analysis of the reaction kinetics, PCB29 electronation reaction by microwave-assisted NaHSO₃ was approximate in the first-level reaction and the reaction rate constant (k) was 0.6631. Under the traditional heating methods, PCB29 electronation reaction by NaHSO₃ without microwave was also similar to the first-level reaction but the reaction rate constant (k) was 0.0408. With the microwave function, the reaction demonstrates not only "thermal effect" but also "non-thermal effect". "Thermal effect" can maintain the same reaction temperature as the traditional heating way, and "non-thermal effect" makes the reaction rate increase. This reaction system has reflected the molecular orientation movement because of sur-electromagnetic field and the molecular heat movement.Using granular activated carbon adsorption, the adsorption rate of PCB29 may reach 80%. Through the union of double-model microwave and activated carbon adsorption, the effect on PCB29 degeneration was not obvious, while through the union of single-model microwave and activated carbon adsorption, PCB29 could be degraded into biphenyl. In alcohol-water (volume ratio is 3 : 2) system, though the solubility of PCB29 increases, the effect on PCB29 degeneration was not obvious by microwave. In the same system, the degradation products contained dioxin by the union of microwave and Fenton reagent. Contrasting the effect on degradation through single-model microwave with that through double-model microwave, it was found that the single-model microwave is far superior to double-model microwave in reproducibility, consistency and accuracy of reaction. It is the ring single-model resonant cavity which is formation of unique directional coupling system and the directional helical waveguide and whose coupling hole number can be adjusted that provides precise continual pulse and the non-pulse single model coupling microwave to control the decomposition process.