【作者】 刘永军；

【导师】 姜玄珍；

【作者基本信息】 浙江大学 ， 物理化学， 2007， 博士

【摘要】 放电等离子体水处理技术是近20年来发展的具有工艺灵活，无二次污染的新型水处理高级氧化技术。和其他等离子体技术相比，辉光放电等离子体具有电压低，适合处理高含盐量的废水和工艺简单等优点，但是常规的辉光放电等离子体有较强的电极腐蚀。我们通过对各种放电形式的分析，结合等离子体产生的基本规律，对常规的辉光放电水处理装置进行彻底改进，应用隔膜产生辉光放电等离子体，使等离子体可以与水溶液更大地接触，并使放电可以在没有电极的参与下进行，探索以前国内外没有报道的新技术，使之具有能量效率高，不需要特殊电极和没有电磁辐射等特点。放电中的有机合成是令人振奋的研究工作，可以合成常规热反应难得到的产物。但是目前该技术的缺点在于产物的选择性和收率低。我们利用水溶液中辉光放电等离子体与催化相结合的方法由苯一步合成苯酚，提高了苯酚的收率和选择性，为等离子体和催化相结合的研究开拓新领域。论文分为两部分共五章：第一章介绍了高级氧化技术的概念，讨论了应用等离子体降解水中有机污染物的原理，并将典型的等离子体水处理工艺及其原理和发展趋势作了介绍；讨论了放电中的有机合成的现状和未来的发展趋势。第二章以硝基苯为模拟废水，采用辉光放电等离子体对其降解进行了研究。考察了污染物浓度、电流、催化剂等外界条件对降解速率的影响，比较了高压脉冲放电和辉光放电在硝基苯的去除和过氧化氢的生成过程中的能量效率，并探讨了硝基苯的降解机理。结果表明硝基苯降解遵守一级反应动力学规律，降解速率随着放电电流的增大而增大，pH值对降解没有明显的影响。反应过程生成了硝基苯酚，苯酚，1，3-二硝基苯、羧酸、硝酸根和亚硝酸根。其中硝基苯酚的分布规律是：邻＞对＞间硝基苯酚。主要的羧酸为甲酸，乙酸和醋酸，最终的降解产物是硝酸根离子、水和二氧化碳。反应过程中有大量的过氧化氢生成，加入三价铁离子比二价铁离子的催化效果好。实验证明降解过程中三价铁离子被反应中间体还原为二价铁离子，然后二价铁离子与溶液中生成的过氧化氢发生Fenton反应，从而加速硝基苯的降解。50mg／L的硝基苯在最佳条件下10分钟内可以完全被去除。第三章以4-氯苯酚为模拟废水，采用辉光放电等离子体对其降解进行了研究。考察了电压、pH、催化剂等外界条件对4-氯苯酚降解和过氧化氢生成速率的影响，比较了有和没有催化剂存在的条件下4-氯苯酚降解的中间产物。结果表明在有催化剂存在下，4-氯苯酚的降解中间产物与没有催化剂时不同，在催化剂存在下主要的中间产物为对4-氯儿茶酚、对苯醌和对苯二酚。实验证明降解过程中铁离子的良好催化作用是因为其被中间体还原为亚铁离子，然后亚铁离子与溶液中生成的过氧化氢发生Fenton反应，从而加速4-氯苯酚的降解。第四章对传统的辉光放电等离子体装置进行了改进，开发了隔膜型辉光放电等离子体水处理装置。以苯酚为模拟废水，从放电电压、自由基清除剂、pH等多个方面评价了实验效果，并研究了降解机理。结果表明提高电压、降低pH和加入一定量的铁盐对降解有利；而正丁醇和碳酸根离子会降低苯酚的去除速率。苯酚的降解的主要中间产物为儿茶酚、对苯醌、对苯二酚和羧酸。随着放电的进行，溶液的pH逐渐降低，苯酚的去除速率加快。和其他放电水处理技术比，本技术没有电极损耗、没有电磁辐射和实验装置简单等特点。本章结果已被著名杂志EST发表。第五章运用辉光放电等离子体和催化相结合的方法对苯一步合成苯酚进行了初步的研究，考察了催化剂和pH值对苯酚收率和选择性的影响，对机理进行了初步的解释，证实了催化与等离子体相结合用于有机合成是可行的。结果发现在铜铁混合型催化剂存在下苯酚的收率和选择性可达8.3％和81％。降低pH对苯酚合成有利。更多还原

【Abstract】 Water treatment by electrical discharges is a novel kind of advanced oxidation processes that is developed in recent 20 years. Many types of discharges have been or are being developed, such as pulsed corona, gliding are or glow discharge. Compared with other electrical processes, the glow discharge plasma has the advantage of lower voltage needed and being able to operate at high conducting liquids. At the same time, it has the problem of electrode erosion. Based on the analysis of the principles of plasma generation, a new diaphragm glow discharge reactor for water treatment is developed for the first time in this thesis, where the issue of electrode erosion has been completely resolved.The organic synthesis in electrical discharges is an interesting topic for many researchers, because many organic compounds that are difficult to synthesize by conventional thermal reactions can be easily implemented by plasma. However, at present this technology has the disadvantages of poor yield and selectivity. We first utilize the glow discharge plasma in combination with catalysts to direct synthesize phenol from benzene, a very important industrial raw material, where the phenol yield and selectivity of as high as 8.3% and 81% have been reached.The present paper includes 5 chapters:Chapter 1 reviews the advanced oxidation processes especially the application of low temperature plasma technology in the treatment of wastewater and the organic syntheses in electrical discharges.Chapter 2 describes the degradation of nitrobenzene in a normal glow discharge plasma reactor. It is found that the nitrobenzene degradation follows a first order reaction kinetics. The degradation products were detected by high performance liquid chromatography and ionic chromatography, respectively. The major aromatic intermediates were nitrophenols, phenol and 1, 3-dinitrobenzene. The distribution of nitrophenols follows the order o-＞p-＞m-nitrophenol. Oxalic acid, formic acid and acetic acid were found to be major carboxylic intermediates. The eventual products were shown to be nitrate ion and carbon dioxide. During the degradation, a large amount of hydrogen peroxide was produced. Addition of ferrous or ferric ion into the system greatly enhanced the degradation rate due to Fenton’s reaction. The energy efficiency of NB degradation and simultaneous hydrogen peroxide formation were compared with pulsed corona discharges. Based on the intermediate analysis, a possible reaction pathway was proposed.In Chapter 3, various influencing factors for 4-chlorophenol removal and simultaneous hydrogen peroxide production in a normal glow discharge reactor are examined. It is found that enhancing pH and applied voltage favors the 4-chlorophenol removal and hydrogen peroxide production. In addition, the major intermediate products in the presence of catalysts are found to be different from that observed in the absence of the catalysts. The major aromatic intermediate products were 4-chlorocatechol, benzoquinone and hydroquinone in the presence of iron ions.In Chapter 4, a non-pulsed DC diaphragm glow discharge process was first developed for phenol degradation in aqueous solution. The discharge was generated by a small hole in a dielectric diaphragm interposed between two submersed graphite electrodes. The experimental results revealed that the supplied voltage, initial pH, iron salts and radical scavengers impact the phenol degradation significantly. Enhancing the applied voltage, lowering the solution pH and adding appropriate amounts of Fe²⁺ or Fe³⁺ to the solution have shown to be favorable for phenol degradation. Carbonate ions or n-butanol in the solution can decelerate the phenol removal. With increasing time, the pH value of the solution decreased, leading to a synergistic effect on phenol elimination. The main intermediates such as hydroquinone, pyrocatechol, p-benzoquinone and organic acids produced during the treatment process were determined by HPLC and IC analysis. Compared with the high-voltage corona discharge plasma in distilled water, this process bears the advantages of experimental simplification, higher energy efficiency, easier scale-up and applicability to salt-containing wastewater with no electrode erosion and electrical radiation. The results of this chapter have been published by EST. salt-containing wastewater with no electrode erosion and electrical radiation. The results of this chapter have been published in EST.In Chapter 5, direct phenol synthesis from benzene in aqueous solution where water was used as the oxidant through glow discharge plasma process is described for the first time. The effec of pH, ferrous and cupric ions on the phenol yield and selectivity was examined. Phenol yield of 8.3% and selectivity of 81% has been achieved. The results of this chapter are to be published in Plasma Chem. Plasma process.更多还原