【作者】 张轶；

【导师】 雷乐成；

【作者基本信息】 浙江大学 ， 环境工程， 2008， 博士

【摘要】 高压脉冲气液混合放电利用气相和液相共同放电产生臭氧、双氧水、羟基自由基等活性物质,提高污染物去除效率和电源能量利用率。本文以对氯苯酚（4-CP）为目标污染物,对该体系下反应器设计和比较、电源参数及工艺参数优化、有机污染物降解机理探讨以及降解动力学模型建立等方面进行较为系统的研究。首先,为了研究液相与气相放电的协同作用,比较了三种气液混合放电反应器形式:高压电极和地极均浸没在溶液中（HDBW）;高压电极浸没在水中,地极置于液面上（HDAW）;高压电极置于液面上,地极浸没在水中（GD）。通过比较4-CP降解效率、中间产物变化、TOC矿化、能量利用率、放电形式、臭氧和双氧水产生等方面,认为HDAW反应器能结合气相和液相共同放电促进4-CP降解,是一种高效新型的气液混合放电反应器。同时对该反应器各种操作参数进行优化,其中火花放电7min后4-CP去除效率能达到100%。通过研究不同的放电形式、活性物质在放电过程中的作用,认为4-CP的降解主要以^*OH氧化为主。其次,设计了一种新型的连续流气液混合放电反应器,并研究脉冲输入电压、脉冲频率、初始浓度、氧气流速以及串联个数对4-CP降解和能量利用率的影响,当脉冲电压为16 kV,脉冲频率为100 Hz,液体流速为40 ml/min,氧气流量为0.4 m³/h时,能量利用率维持在一个较高的值(5.39×10^-9mol/J),同时4-CP降解效果也较高（88.3%）。该反应器所产生的臭氧和双氧水也能用于4-CP去除。根据基本化学工程原理建立动力学模型来预测4-CP降解以及中间产物变化情况。在此基础上,探讨了O₂、N₂、Air条件下4-CP降解机理。O₂和N₂条件下,均产生双氧水,O₂条件下产生臭氧O₃,N₂条件下产生硝酸根、亚硝酸根。4-CP在O₂和N₂条件下产生苯环类产物,如氯代邻苯二酚、对苯酚、2,4-二氯酚、对苯醌,以及有机酸等。在N₂条件下还检测到含氮化合物5-氯-3-硝基邻苯二酚、4-氯-2-硝基酚。Air条件下4-CP降解产物与N₂条件相近。O₂条件下,4-CP主要是通过羟基自由基攻击苯环以及臭氧氧化降解;N₂条件下,主要是通过羟基自由基以及N等离子体攻击苯环进行降解;Air条件下,主要是羟基自由基、N等离子体、臭氧共同作用。最后,建立了完善的气液混合放电体系下4-CP降解动力学模型。确定了脉冲电压、脉冲频率、溶液电导率和氧气流量条件下活性物质(H₂O₂、O₃、^*OH、e_aq^-)的初始速率常数。利用相关系数r和方差分析ANOVA（F,p）体系检验模型的有效性。根据模型计算得到^*OH氧化在4-CP降解中占主要作用,为88.9%。该模型能很好地模拟4-CP在间歇流以及连续流反应器中的降解过程,为今后大规模工业化应用提供理论指导。更多还原

【Abstract】 Pulsed high voltage gas-liquid hybrid discharge could combine gas phase and liquid phase discharge to produce plenty of active species,such as ozone,hydrogen peroxide,hydroxyl radical etc.,which enhanced the removal efficiency of pollutant and energy yield of electric source.In this paper,4-chlorophenol（4-CP）is selected as a typical organic pollutant for degradation.During this study,three discharge reactors were designed and compared with each other;the electric parameters and operation parameters were optimized;the degradation mechanisms of 4-CP were deduced;and the kinetic model was also established.Firstly,in order to investigate the synthetic effect of liquid phase and gas phase discharge,three gas-liquid hybrid discharge reactors:HDBW reactor with both electrodes submerged into liquid phase,HDAW reactor with high voltage hollow electrodes immersed in water whereas the ground electrode placed over water,and GD reactor with pulsed high voltage electrodes in the gas phase above water level and the ground electrode submerged into liquid,were compared with each other.In this study,degradation of 4-CP,mineralization of TOC,energy yield,discharge mode,and the change of ozone and hydrogen peroxide in these three reactors were investigated. During the comparison,it is considered that HDAW reactor could combine discharge in both liquid phase and gas phase to enhance 4-CP removal.It appears that HDAW reactor is promising as a high-performance gas-liquid hybrid discharge reactor.In addition,special attention was given to some important operation parameters affecting 4-CP removal and energy yield.At the pulsed voltage of 16 kV,pulse repetition frequency of 100 Hz,electrode distance of 20 mm,oxygen flow rate of 0.3 m³/h,and initial concentration of 50 mg/L,the 4-CP removal efficiency was 100%after 7 min spark discharge.The effects of discharge modes and active species on 4-CP removal were also investigated to obtain that the hydroxyl radical oxidation played a main role in 4-CP degradation.Second,a novel continuous gas-liquid hybrid discharge reactor was designed.The effects of pulsed high voltage,repetition frequency,initial concentration of 4-CP,gas flow rate of oxygen and discharge unit on 4-CP removal and energy yield were investigated.At the pulsed voltage of 16 kV,pulse repetition frequency of 100 Hz, liquid flow rate of 40 ml/min,oxygen flow rate of 0.4 m³/h,the 4-CP removal efficiency was 100%and energy yield was 5.39×10^-9mol/J.Ozone and hydrogen peroxide was produced in this reactor and was utilized for 4-CP removal.An improved model was estimated by classical basic chemical engineering principles to predict 4-CP degradation and intermediates formations.In addition,the reaction mechanisms of 4-CP with oxygen,nitrogen,or air bubbling were explored.In the both case of oxygen bubbling and nitrogen bubbling, plenty of hydrogen peroxide was produced,while only ozone was formed in oxygen atmosphere and nitrate and nitrite ions were formed in nitrogen atmosphere.Except for the main similar intermediates,such as 4-chlorocatechol,hydroquinone, 1,4-benzoquinone,2,4-dichlorophenol,formic acid,acetic acid,oxalic acid,etc., produced in the both cases of oxygen and nitrogen bubbling,special intermediates （5-chloro-3-nitropyrocatechol and 4-chloro-2-nitrophenol）were produced in nitrogen atmosphere.The intermediates of 4-CP degradation with air bubbling were similar with that nitrogen bubbling.The reaction pathway of 4-CP in the case of oxygen bubbling was oxygen/ozone attack on the radical hydroxylated derivatives of 4-CP.In the case of nitrogen bubbling,hydroxylation was the main reaction pathway with effect of N atom on degradation of 4-CP.In the case of air bubbling,the reaction pathway was hydroxylation,ozone oxidation and N atom attack.Finally,the kinetic model for 4-CP degradation in gas-liquid hybrid discharge system was established.The effect of pulsed voltage,repetition frequency,liquid conductivity and oxygen flow rate on the reaction rate constants of active species (H₂O₂、O₃、OH、e_aq^-)was investigated.The correlation coefficient（r）and ANOVA system（F,p）between the experimental and predicted model was evaluated.During the model calculation,it was validated that the effect of hydroxylation on 4-CP removal was more than 88.9%,which played the main role in 4-CP degradation.The model could acceptably predict the 4-CP degradation in both batch reactor and continuous reactor for further large-scale applications.更多还原