【作者】 王占华；

【导师】 许德玄；

【作者基本信息】 东北师范大学 ， 环境科学， 2009， 博士

【摘要】 高压放电低温等离子体技术是一种全新的高级氧化技术,逐渐被应用于水处理领域的研究。本论文重点研究了新型放电反应器对染料脱色过程的影响因素、处理效果、反应机理及其动力学过程。本文的主要内容和取得的研究成果及结论如下:(1)设计了新型放电低温等离子体反应器,其结构包含介质阻挡放电系统和电晕放电系统。此反应器的优点在电压达到放电电压时,雾化状态水溶液开始放电,由于介质层的存在,电荷在介质表面积累,形成感应电场与外加电场的叠加,雾化放电空间内电场场强得到增强,在雾化区域内形成许多小细丝状流注放电通道,通道内部形成大量的低温等离子体活性物质,低温等离子体活性物质能紧密与染料分子接触,形成低温等离子体向被处理染料分子的最佳传质形式,全部低温等离子区均被包括在处理水雾化区之中,低温等离子活性物种最浓处也是处理水雾最密处,达到最佳的能量利用率。(2)实验测试并优化了反应器参数。结果表明,在介质阻挡放电系统电极间距为30mm、电晕放电系统电极间距为25mm、电源电压为25kV时,反应器体系中两个放电系统雾化均很充分,按质量计算,大部分液滴的粒径在100-500μm之间。放电状态较好,甚至有些雾化液滴可达到100μm以下。雾化液滴较小,其比表面积则较大,具有强大的表面能,液滴表面的染料分子能充分和放电过程中生成的活性基团物质接触、氧化、分解。(3)分析测定了反应器工艺参数和染料溶液性质对其脱色的影响。随电压的升高和处理时间的延长,实验染料溶液的脱色效率不断增大,且电压越高,溶液短时间脱色效率提高越迅速,但当脱色效率达到较高水平后,脱色效率的提高变得缓慢。随染料浓度的增大而脱色率减小。但绝对去除率随染料浓度的增加而增加。酸性条件下,直接大红染料溶液的脱色率最低;中性条件下,脱色率开始前1个小时高于碱性和酸性条件,而随着实验的延长,超过一小时以后,初始pH较高(≈12)的脱色率升高。(4)分析测定了反应器工艺参数对能量效率的影响。较低电压的能量水平较高,随着电压的升高,能量效率水平反而下降。介质阻挡放电系统的电极间距较小时,反应器的能量效率水平较高,而随着电极间距的增大,在低电压阶段能量效率迅速下降,而电压升高时,不同电极间距的能量效率差异缩小。电晕放电系统电极间距对能量效率水平的影响差距不大,随着电压的升高这种差距变得越来越小。在电压为20kV、25kV时,不同电极间距的能量效率水平几乎相等。(5)确定了反应器最佳工作状态。结合电极间距、电源电压对染料溶液脱色率和能量效率的影响,确定本实验反应器最佳工作状态是介质阻挡放电系统的电极间距为30mm、电晕放电系统电极间距为25mm、电源电压20kV。(6)测定分析了直接大红染料脱色过程。通过测定直接大红染料脱色过程中的溶液pH、TOC、紫外可见光谱图和高效液相色谱图可知,在脱色处理时间(6h)范围内,染料溶液的COD值增大, pH值持续下降,TOC值逐渐降低,结合紫外可见光谱图和高效液相色谱图,说明染料分子虽然已经遭到破坏,染料分子内强生色基团偶氮双键确实遭到攻击,大的共轭体系被破坏,染料分子被脱色,却没有完全被彻底矿化成二氧化碳等无机物,出现了芳环和萘环结构的累积现象,可见完全破坏芳环比破坏偶氮双键发色团更困难。(7)分析了等离子体对染料脱色的机理。在反应器放电极加入高电压后,空气中的电子在电场力的作用下,发生气体放电产生大量活性物质,接触到雾化液滴表面时,氧化染料分子、溶解在液滴内部与染料分子反应;同时,由喷嘴喷出的液体在交流高压电场的作用下,液滴发生畸变并产生液滴尖的微放电,产生了大量的活性物质与液滴表面和内部的染料发生反应,使其脱色;当荷电雾化液滴流至尖端,产生尖端电晕放电,又产生大量活性物质,它与在电晕电场内雾化下落的液滴接触,继续发生表面氧化,同时H2O2和O3可溶解在液滴内的活性物质溶解在液滴内部,随液滴一起落入下贮水箱时,氧化反应仍在继续。(8)分析建立了动力学方程。结果表明,在不同初始浓度、pH和电源电压的实验条件下,溶液中直接大红染料的质量浓度随反应时间的增加呈现指数性降低。等离子体对染料脱色的动力学过程受实验条件限制。在染料脱色效率较高的实验条件下,脱色过程符合一级反应动力学。此时脱色速率常数随染料初始浓度的增大而减小;随电压升高而增大,随pH的增大而增大。更多还原

【Abstract】 The high voltage discharge non-thermal plasma technology is one of brand-new advanced oxidized technologies and being applied gradually in the water treatment researches. The study on the influencing factors, treatment effects, reaction mechanisms and kinetics of the process was emphasized for the decolorization process of refractory organic dye with a novel discharge non-thermal plasma reactor in this paper.The research contents, results and conclusions are as follows:(1) A new discharge non-thermal plasma reactor was designed. It consists of the dielectric barrier discharge system and the corona discharge system. The advantages of this reactor are that as soon as the voltages reach the discharge voltage, the atomized water starts to discharge, and many filamentary streamer discharge channels are formed in the atomizing region, in witch the active species are produced and contact closely with the dye molecules to form a better mass transfer pattern. All of the non-thermal plasma is included in the atomizing region of treated water. Therefore the densest regions of both the non-thermal plasma active species and the water atomizing droplets situate in the same one, in order to achieve the better energy efficiency.(2) The reactor parameters were tested and optimized. The results shown when electrode spacing of the dielectric barrier discharge system and the corona discharge system is respectively 30 mm and 25 mm and the power voltage is 25 kV, the full atomization occur in both the two discharge systems and the sizes of most droplets are 100-500μm, even the sizes of some atomizing droplets reach below 100μm. The atomization droplets possess formidable surface energy because of the smaller size and the bigger specific surface area. The surface dye molecules can contact completely with the active species, in order to be oxidized and decomposed in the discharge process.(3) The reactor craft parameters and the influence of dye solution nature on the decolorization were determined. The decolorizing efficiency of the experiment dye solution was increased as the voltage was rising and the process time was extended, and the higher the voltage was, the more rapidly the decolorizing efficiency increased during a short time. But after the decolorizing efficiency achieved a high level the enhancement became slow. The decolorizing efficiency reduced as the dye concentration was increasing, and the absolutely decolorizing efficiency increased along with the dye concentration. Under the acidic condition, the decolorization rate of Erie Congo Dye solution is the lowest. Under the neutral condition, decolorization rate during the first 1 hour was higher than the alkalinity and the acidic condition, but the decolorization rate increased for the solution of a initial high pH value (≈12) after the first 1 hour.(4) The analysis has determined the influence of the reactor craft parameters on the energy efficiency. The energy efficiency of the low voltage was high, and along with the voltages increased the energy efficiency was dropping. When electrode spacing of the dielectric barrier discharge system was small, the reactor energy efficiency was high. However the reactor energy efficiency dropped rapidly along with electrode spacing enlarged and the differences of energy efficiency for different electrode spacing reduced as the voltages were rising. The differences of influences for corona discharge spacing on energy efficiency were smaller and reduced along with rising voltages. When the voltage was 20 kV or 25 kV, the energy efficiencies of different electrode spacing almost were the same.(5)The best working status of this reactor was fixed. According to the effect of electrode spacing and the voltage on decolorization rate of dye solution as well energy efficiency, The best working status areas follow: dielectric barrier discharge system of the electrode spacing is 30 mm, corona discharge system for electrode spacing is 25 mm, voltage is 20 kV, and the best working status of this reactor is defined.(6) The degrading process of Direct Scarlet Dye was determined and analyzed. Through taken the measurements of pH, TOC, UV-Vis spectra and high-performance liquid chromatograph in the degrading process of solution ,it was found that the COD of dye solution increased, pH continuing declined and TOC reduced gradually. The UV-Vis spectra and high-performance shown that though dye molecules had been destroyed, Strong Chromophore Azo Double Bond of dye was certainly under attack, the big conjugated system was vandalized and dye molecules were decolorized degradation, but they were not completely changed into carbon dioxide and other inorganic matter by mineralization, it appeared accumulation of aromatic ring and double benzene nucleus, so it is thus evident that complete destruction of aromatic ring is more difficult than the double benzene.(7)The degradation mechanism of dye was analyzed. After the high voltage applied on the discharge electrode in reactor, the electrons in the air produce gas discharge under the affection of electric force and yield a lot of active species. When the active species touch the surface of atomized droplets, they oxidize the dye molecules, dissolved into the droplets and react with dye molecules. At the same time, by the action of communication high voltage electric field, droplets ejected from the nozzle take distortion and produce the micro-discharges in the pointed ends of droplets, then produce a lot of active species and they react with the dye of inter and the surface of the droplets and dye is degraded. When charged droplets flow down to the points of the dielectric plate, the point corona discharges occur and again produce lots of active species, which are in touch with the droplets and continue to take surface oxidation. At the same time the H2O2 and O3 are dissolved in the droplets and the active species fall into storage water tank so that the oxidation reaction continues. (8) The kinetic equation has been set up and analyzed. The result shows that at the experimental conditions of the different initial concentrations, pH and the supplying voltages,the mass concentration of the direct red dye in solution decreases exponentially with the lengthening reaction time. The kinetic process of the plasma degradation of dyes is limited by the experimental conditions. At decolorizing efficient experimental conditions, the degradation process accords with the first order reaction kinetics. At this moment, the degradation rate constant decreases with the increase of initial dye concentration and increases with the rise of voltage and pH.更多还原