【作者】 李新杰；

【导师】 赵宝昌； 张跃军；

【作者基本信息】 南京理工大学 ， 材料学， 2013， 博士

【摘要】 采用氯酸钠与盐酸反应制备ClO2的单级R5法ClO2发生器由于设备简单、易于操控、安全性好和性价比高等特点而使其成为国内自来水行业替代氯的主要消毒设备之一。针对国内单级R5法ClO2发生器效率低的现状和ClO2在消毒应用过程存在的急待解决的一些问题,本文对单级R5法ClO2制备工艺的优化与反应动力学、ClO2发生液的组成与毒性、ClO2投加过程的影响因素、ClO2在水中的衰变规律以及PAC和AsA去除ClO2-的特性等方面进行了研究,以期为单级R5法ClO2发生器的工艺改进、ClO2投加和消毒工艺可靠性与安全性的提高以及消毒副产物ClO2-的有效去除等工作提供参考依据和或理论指导。主要内容如下：(1)单级R5法ClO2制备工艺优化研究本着对单级R5法ClO2制备工艺整体优化的思路,根据ClO3-/Cl-反应体系各物质相互作用的机理和条件,通过间歇式ClO2制备实验,研究了NaClO3/HCl的配比、反应温度、反应时间和催化剂等因素对NaClO3转化率、ClO2得率及纯度的影响规律,得到的最佳反应条件是：NaClO3与HCl的摩尔比为0.25、温度为50℃、时间为50min及催化剂MnCl2的用量为0.01mol·L-1。进而,利用间歇式ClO2制备实验获得的最佳反应条件,实验分析连续式制备装置的效率,发现连续反应器其效率低的主要原因是：物料混合不均、升温滞后和返混。采用预热预混的原料预处理方式和基于推流式反应器原理设计较大轴径比的反应器,改善了物料在反应器中混合与受热的均匀性,减小了物料的返混作用。结果表明：NaCl3转化率、ClO2得率及其纯度分别可达95%、82%和61%以上比目前文献报道的同类总体最好指标,分别可提高14、11和10个百分点以上。(2)单级R5法ClO2制备反应动力学研究根据ClO3-/Cl-体系的一般反应机理和NaClO3/HCl体系高酸度反应的特点,用ClO3-和Cl2变化的等量关系对Hong-Lenzi的理论速率方程进行了简化,对动力学参数进行了测定,得到了单级R5法ClO2制备反应的经验速率方程。该速率方程对ClO3-浓度近似为一级和二级的组合；该方程参数较少且易于测定,故便于工程应用。(3)ClO2发生液的组成、毒性及其对饮用水消毒的安全性研究对ClO2发生液的组成、毒性及其浓度的衰变趋势进行了考察,对ClO2发生液用于饮用水消毒时ClO3-、ClO2-残留量的安全性进行了评价。结果显示：在常规ClO投加量(0.5～2mg·L-1)下,ClO2发生液引入饮用水后的ClO3-和ClO2-的剂量是安全的,但会降低水的pH值；ClO2发生液对小鼠骨髓嗜多染红细胞无致微核作用,对小鼠的急性经口毒性为低毒级；将ClO2发生液稀释1倍以上时,其对小鼠急性经口毒性降为实际无毒级。该研究结果对ClO2发生液投加过程的安全投加量、安全稀释倍数及安全防护等级的设计具有一定指导作用。(4)ClO2投加过程影响投加量及消毒效果的因素研究通过单级R5法ClO2发生器在常规自来水厂的制水工艺消毒工段的现场实验,研究并得到了进料流量、反应温度和反应停留时间等发生器额定运行参数波动对消毒效果及出厂水水质的影响规律,获得了其运行参数的安全波动范围。通过发生器在模拟管道供水条件下的加药实验,研究了管道水压力对ClO2投加量的影响规律,进而,通过对该规律在实际供水管道中验证实验,考察了ClO2在管道中分散特性及消毒效果,获得了ClO2发生器用于管道带压加药可供参考的工艺参数。(5)水中ClO2自身衰变动力学研究通过对ClO2在纯水中自身衰变机理的分析和实际产物的测定,建立了ClO2在纯水中自身衰变的速率方程模型,通过研究水温和pH对ClO2衰变速率的影响规律,初步确定了以常温和中性水为基础的速率方程的参数。结果显示,ClO2在纯水中衰变的主要产物是Cl2(或HClO)和ClO3-等,而ClO2-的量较少,不同于在碱性强化条件下的水解产物；ClO2的衰变对ClO2为1级,对H+为-0.155级。可见,ClO在常温、中性或偏酸性的水中比在高温或碱性水中更稳定。(6)PAC和AsA对水中ClO2-去除特性研究在常规水处理的pH及温度下,通过烧杯搅拌实验对ClO2-在粉末活性炭(PAC)上的等温吸附特性及吸附机理进行研究。用Langmuir和Freundlich模型对等温吸附实验结果进行拟合,考察了吸附的性质及热力学行为；用伪一级、伪二级动力学模型以及颗粒内扩散、液膜扩散模型对吸附动力学实验数据进行分析,探讨了吸附过程的机理及速率控制机制。结果显示：在常规水处理条件下,PAC对ClO2-的吸附是自发、吸热的化学吸附过程,适于吸附的最佳pH为6；吸附等温线更符合Freundlich等温吸附规律,吸附动力学更符合伪二级动力学规律。可见,化学吸附反应是PAC吸附ClO2-速率的主要控制机制。另一方面,在常规水处理条件下,考察了抗坏血酸(AsA)对ClO2-的去除作用以及pH.AsA投加量、反应温度和作用时间等工艺因素对ClO2-去除率的影响规律,得到了AsA去除水中ClO2-的最佳工艺条件为：pH为5.0、温度为30℃.AsA与ClO2-的质量比为5.5和作用时间为25min在此条件下,AsA对水中含量为2～10mg·L-1ClO2-的去除率大于98%,处理后水中ClO2-的含量低于0.02mg-L-1,符合GB5749-2006标准的要求。可见,在上述最佳条件下,AsA对水中的Cl02-具有很好的还原去除效果。更多还原

【Abstract】 The ClO2generator, using the single-stage-R5-technology based on the reaction of sodium chlorate and hydrochloric acid, has become one of the primary substitutes for chlorine disinfection equipments of drinking water, as being easy to control and with simple structure, high security, and high performance-to-price ratio.In view of the low efficiency actualities of domestic ClO2generators based on single-stage-R5-technology and some problems existing in tapwater-disinfection process for ClO2, the following aspects were researched in this paper:optimization of ClO2preparation technics based on single-stage-R5-technology; reaction kinetics of ClO2preparation; composition and toxicity of ClO2solution produced; influences of various factors on dosage, disinfection effect and water quality in ClO2dosing process; self decay law of ClO2in water; and chlorite removal by powdered activated carbon (PAC) and ascorbic acid (AsA) from water. These studies can provide reference methods or theoretical guidance for the works such as:the process modification of ClO2generator based on the single-stage-R5-technology, the perfection of the ClO2dosing and disinfecting technics, and the effective removal of ClO2-from water, and so on.The researches of the dissertation are mainly focused on:(1) The optimization of ClO2preparation technics based on single-stage-R5-technologyAccording to a design of systemic optimization of the ClO2preparation process using single-stage-R5-technology, and based on the mechanism and the interaction conditions of various substances in ClO3-/Cl-reaction system, the batch preparation experiments of ClO2were conduced to explore the effects of such parameters as mole ratio of NaC103to HCl, temperature, reaction time, and catalysts on the NaClO3conversion rate, ClO2yield, and ClO2purity. The optimum conditions obtained are that:the mole ratio of NaClO3to HCl is0.25, the temperature is50℃, the reaction time is50min, and catalyst amount of MnCl2is0.01mol·L-1. Then the continuous preparation experiments of ClO2were performed under the optimum reaction conditions. Based on the analysis of experimental results and flow conditions of the continuous reactor, it was discovered that the low efficiency of continuous reactor mainly resulted from the uneven-mixing of raw materials, the hysteresis of heating up and the back-mixing of raw materials. Finally, by means of the preheating-and-premixing treatment of raw materials and using the larger-axis-diameter-ratio reactor designed according to principle of plug flow reactor, the mixing degree of raw materials and the temperature uniformity in reactor were improved, and the back-mixing of materials was reduced as well. The results show that NaClO3conversion and ClO2yield increase significantly, and NaClO3conversion rate, C102yield and ClO2purity can be up to95%,82%and61%and above, respectively. The values increase14,11and10percentage points respectively than the best results of present literatures.(2) Reaction kinetics of the ClO2preparation based on single-stage-R5-technologyBased on the general reaction mechanism of ClO3-/Cl-system and the characteristics of high acidity reaction system of NaClO3/HCl, the theoretical reaction rate equation derived by Hong-Lenzi was simplified utilizing equivalent substitution of ClO3-for Cl2, then the rate constants were determined by means of kinetic experiments, and the empirical rate equation of this reaction was finally deduced as the formula with mixed-order (combination of the first order and the second order with respect to ClO3-). This formula is convenient for engineering use as the parameters are fewer and easy to measure.(3) The composition, toxicity and security for tapwater disinfection of ClO2solution producedThe composition, toxicity, and concentration decay trends of the produced ClO2solution were determined. The security of the residual amounts of ClO3-and ClO2-contained in this ClO2solution used for drinking water disinfection was evaluated subsequently. The results show that the quantitiies of ClO3-and ClO2-introduced in drinking water accompanying with the disinfection process of produced ClO2solution are safe within the conventional ClO2dosages range of0.5to2mg·L-1, but the pH of treated water would decrease. The produced ClO2solution has no inducing effect on the mice bone marrow polychromatic erythrocytes micronucleus, its acute oral toxicity to mice is low-toxic class, but it is non-toxic class to mice when diluted more than one times. These results have certain instruction significance for the designs of the safe ClO2dosage, safe dilution ratio of ClO2solution produced, and the secure protection class of dosing process.(4) Influences of various factors on dosage, disinfection effect and water quality in ClO2dosing processBy means of the disinfection experiments of the ClO2generator using single-stage-R5-techology in conventional water plant, the effects of such operating parameters of generator as feed flow, reaction temperature and reaction time on sterilizing efficacy and finished water quality were investigated. The corresponding safty-operating parameters with certain range for drinking water disinfection were also obtained. Meanwhile, the influence of pipeline water pressure on ClO2dosage, its distribution characteristics in pipeline water, and disinfection effect of it were investigated as well through an experiment in imitating pipeline, and then these regulations were further verified in practical pipeline water. The referential tephnics-parameters were obtained finally available for ClO2generator dosing with pressure in pipeline water (5) Kinetic study of ClO2self-decay in waterThe decay rate equation of ClO2in pure water was established by measuring decay products and analyzing decay mechanism. The rate equation parameters were determined by testing the effects of temperature and pH on the decay rate. The results show that the products of ClO2decay in pure water are mainly as: Cl2(HC10), ClO3-, and few ClO2-, somewhat different from that of ClO2decay in alkaline water. The reaction order of ClO2decay in pure water is1with respect to ClO2, and-0.155with respect to H+. Obviously, ClO2is more stable in acidic or lower temperature water than in neutral, alkalescent, or higher temperature water.(6) Chlorite removal performance by powdered activated carbon (PAC) and ascorbic acid (AsA) from waterFirstly, the isotherms and mechanism of the sorption of ClO2-on PAC from water were studied by using the beaker-stirring experiments under the pH and temperature of conventional water treatment. The sorption Characteristics and thermodynamics were investigated by using Langmuir and Freundlich models to fit and discuss the isotherms. The sorption kinetics data were analyzed by using the models of pseudo first order, pseudo second order, intraparticle diffusion, and film diffusion to recognize the mechanism and rate control steps of the sorption. The results show that the sorption process of chlorite on PAC from water is spontaneous and endothermic with the mechanism of chemisorption. The sorption of chlorite on PAC is most favorable at pH=6. The sorption isotherms are well described by Freundlich model, and the sorption kinetics fits well the pseudo-second-order model. Therefore, the experimental results prove that the chemisorption reaction is the main rate-control mechanism of chlorite sorption by PAC.Secondly, the chlorite removal performance by AsA from water and its influencing factors were studied under the conditions of conventional water treatment. The effects of pH, temperature, AsA dosage, and action time on chlorite removal were investigated. The optimal conditions of treatment were obtained as that:pH=5.0, temperature was30℃, reaction time was25min, and mass ratio of AsA to chlorite was5.5. Under the optimal conditions and within the chlorite concentrations of2-10mg·L-1in water, the chlorite removal rates were more than98%. Therefore, the contents of residual ClO2-in treated water can be limited below0.02mg·L-1, in line with the requirement of GB5749-2006.更多还原