溶液初始pH值对2,4-D臭氧直接反应动力学的影响

引言 目前,农药被大量研制及施用,由此带来的农药污染越来越受到人们的重视.含氯苯氧梭酸类除草剂2,4-D(2,4-二氯苯氧乙酸)是一种使用较广、应用较早的除草剂.2,4-D自然降解较慢,由于具有非挥发性和可溶性,易导致地下水或地表水污染,水体中已经可以检测到2,4-D的存在.     

Rate Constants for Herbicide Degradation by Ozone

Rate constants for the degradation of five herbicides (Mecoprop, MCPA, 2,4-D, Simazine and Atrazine) by ozone were determined in the laboratory under controlled conditions at both acidic and neutral pH using a competition kinetic method. The order of herbicide degradation rate was found to be as follows: Mecoprop > MCPA > 2,4-D > Simazine > Atrazine, both at pH 2 and pH 7.5. The half-life times for herbicide removal at pH 7.5 and in the presence of bicarbonate ions are, respectively, 25.9; 27.5; 39.5; 66.6 and 94.2 minutes for Mecoprop, MCPA, 2,4-D, Simazine and Atrazine at a dissolved ozone concentration of 10 μM. The kinetics of ozone consumption for the three phenoxyalkyl acid derivatives were investigated at pH 2. The study has demonstrated that at neutral pH the initial concentration ratio of two herbicides in solution together did not affect their relative degradation rate.     

臭氧与2，4-二氯苯氧乙酸的直接反应动力学

随着现代农业的发展,农药大量研制及施用,农药污染日益严重,对农药污染的控制成为环境研究领域努力探索的课题．2,4-D（2,4-二氯苯氧乙酸）是使用较广的除草剂,具有非挥发性和可溶性,自然降解较慢,施用后易淋溶迁移导致地下水或地表水污染．2,4-D及其代谢产物如2,4-二氯苯酚等不仅有生物毒性,还能导致基因伤害,已对人类健康和自然环境构成了明显威胁．     

Influence parameters in the ozonation of phenol wastewater treatment using bubble column reactor under continuous circulation

The ozonation of phenol wastewater treatment system has been investigated with effective mass transfer between gas and liquid phase in a bubble column reactor. The designed bubble column reactor was investigated for increasing the rate of mass transfer of ozone, the rate of oxidation of phenol in the solution, the solubility and decomposition rate of ozone in the distilled water were also studied at different flow rates. The decomposition rate constants were calculated based on pseudo first order kinetics. The oxidation of phenol was investigated in order to provide the overall reaction rate constant for the reaction between ozone and phenol at 25 °C. The influence of the operating parameters like initial phenol concentration, ozone flow rate and pH for the destruction of phenol by ozonation were studied. The pseudo first order rate constant was depending on the initial concentration of phenol solution. A comparison of TOC removal percentage between bubble column reactor and bubble diffuser using ozonation were reported.     

异丙醇的O3/H2O2复合氧化动力学研究

采用停流光谱仪研究了异丙醇在T=298K和pH=3～11范围内O3 / H2O2复合氧化的反应动力学.结果表明异丙醇的O3 / H2O2复合氧化反应动力学随反应体系的pH值不同而不同.在酸性和中性条件下,反应相对于O3浓度、异丙醇浓度都为1级;在碱性条件下,异丙醇较容易被O3/H2O2复合氧化降解,总反应级数为2级,相对于O3浓度、异丙醇浓度和H2O2浓度分别为1级、0级和1级,可见异丙醇的降解速率与它的浓度无关.在T=298K,当pH值从9增大到11, 反应速率常数从3486.1(mol·L-1)-1·s-1增大到38239.2(mol·L-1)-1·s-1. 表明在酸性条件下,异丙醇的O3/H2O2复合氧化是O3分子直接攻击异丙醇的反应占主导;在碱性条件下,自由基型反应占主导.     

臭氧氧化双酚A的性能及机理

采用臭氧氧化法在动态条件下降解双酚A，考察了臭氧浓度、水样进水流速、pH、双酚A初始浓度及温度对氧化降解双酚A效果的影响，探究了臭氧氧化双酚A的反应机理。结果表明，臭氧对溶于水中的双酚A具有良好的去除效果，在反应条件(臭氧浓度11.04 mg/L、水样进水流速2 mL/min、原水pH=6.83、双酚A初始浓度10 mg/L、温度40℃)下，去除率达86.12%。增加臭氧浓度或适当升高温度可增加臭氧氧化双酚A去除率。pH和进水流速的提高会降低双酚A去除率。偏酸性条件下，臭氧降解双酚A的效果更好。臭氧氧化双酚A反应活化能较低，属于快速反应。臭氧浓度不变，增加双酚A初始浓度会使其去除率减小。臭氧氧化双酚A以臭氧直接氧化为主，同时也存在羟基自由基间接氧化。     

苯酚的O_3/H_2O_2化学氧化反应动力学研究

应用 Stopped- flow光谱仪研究苯酚在 2 88～ 30 8K和 p H=3.2～ 9.8的 O3 / H2 O2 氧化反应动力学。通过实验及分析认为 :在不同酸度的实验条件下苯酚 O3 / H2 O2 氧化降解的途径及动力学不同。在酸性及弱酸性(p H=6 .5 )下苯酚 O3 / H2 O2 氧化反应机理是苯酚直接为 O3 氧化 ,在碱性 (p H=9.8)时为自由基机理     

Photodecomposition of 2,4-dichlorophenoxyacetic acid

Three types of reactor operation, flow-differential, flow-integral, and batch-recycle were employed to study the kinetics of the photolysis and oxidation of 2,4-dichlorophenoxyacetic acid (2,4-D). The flow-through annular reactor was irradiated with a polychromatic lamp located at the axis of the annulus. Using aqueous solutions of pollutant-level concentrations (5-50 ppm), the initial rate was found proportional to the light abosrbed and otherwise independent of 2,4-D and dissolved oxygen concentrations.Using thin-layer chromatographic and spectroscopic analytical methods, 2,4-dichlorophenol (2,4-DCP) was identified as one of the photolysis products. Measurements were also made of the initial rate and rate at finite conversions for 2,4-DCP. The results were consistent with a rate equation based upon a photo-activation process followed by formation of peroxides.Of particular significance was the autocatalytic effect of intermediates on the rate of disappearance of 2,4-D. One such catalytic agent was 2,4-DCP.Carbon dioxide was produced as the final oxidation product when either 2,4-D or 2,4-DCP was the reactant. The amount of CO₂ formed proved that the aromatic ring was ruptured. This suggests the possibility of employing photochemical oxidation for reducing refractory, aromatic pollutants into fragments more susceptible to biological oxidation.     

活性炭负载Fe~(3+)催化臭氧氧化水中双酚A

采用浸渍法在活性炭上负载铁制备催化剂Fe/AC,用于催化臭氧氧化水中内分泌干扰物双酚A(BPA),研究了Fe/AC/O3体系的协同效应,探讨了Fe/AC投加浓度、臭氧浓度和BPA初始浓度等工艺参数的作用规律,并分析了Fe/AC/O3体系在不同pH值下的催化反应机制。结果表明,在Fe/AC/O3体系下,反应60 min后,BPA和COD的去除率分别为97.44%和69.47%,效果明显优于臭氧体系的70.15%、30.89%和活性炭体系的14.69%、7.53%之和,具有明显的协同作用;Fe/AC/O3体系降解BPA符合一级反应动力学,当Fe/AC的投加浓度为5.0 g/L,臭氧浓度为15.0 mg/L,BPA初始浓度为50.0 mg/L时,Fe/AC/O3体系降解BPA的反应速率常数为0.05972 min-1;其反应机制受溶液pH值的影响,在酸性条件下是吸附和臭氧直接氧化共同作用,而在碱性条件下以·OH间接氧化为主,活性炭上负载的Fe3+促进了·OH的生成,大大提高了BPA的反应效率和矿化率。     

臭氧降解土壤2，4-D污染物的动力学分析

为了控制土壤有机物污染,对负载污染物2,4-D（2,4-二氯苯氧乙酸）的模拟土壤柱进行臭氧化修复研究,通过考察羟基自由基抑制剂的加入、土壤粒径的影响以及混合气体中臭氧产生量的影响,分析了2,4-D污染土 壤的臭氧修复动力学,研究了土壤含水量对动力学的影响。研究结果表明,液膜内羟基自由基、气液相臭氧、 土壤颗粒表面的活性位均对降解2,4-D发挥作用。经过合理简化和假设,推导可知2,4-D降解符合拟一级动 力学,对实验数据采用拟一级动力学进行拟合,相关系数均大于0.9。基于土壤含水量,提出动力学模型。实际的实验数据指出在土壤质量含水量低于9.38%范围内,拟一级动力学速率常数和水分含量之间基本符合二次多项式关系。     

Treatment of Water Contaminated with Chlorinated Organic Herbicide 2,4-D by an Ozone/Gamma Process

Radiation-induced degradation of 50 ppm 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated in different ozonation times. Co-60 gamma-source was used as a gamma-source with a dose rate of 0.07 kGy/h. Ozonized samples were irradiated for the 0.2 kGy dose. It is observed that irradiation enhances the degradation of 2,4-D with ozone. The amount of passed ozone from samples is between 0.0695 g/L and 8.33 g/L with a flow rate of ozone at 0.078 L/min (10 g/h), from 10 s to 1200 s with the ozone generator. Aliphatic acids and chloride were determined with ion chromatography. Formaldehyde, dissolved oxygen, pH and total acidity were also measured. Both species and amounts of radiolytic intermediates were determined. 2,4-dichloro phenol (2,4-DCP) is one of the toxic intermediates of 2,4-D observed with GC/MS and it decomposes at further ozonation times. It is observed that combination of ozone/gamma irradiation is more effective for degradation of 2,4-D and its intermediate 2,4-DCP. Chloride ions are observed as completely released with combined processes at lower ozonation times although nearly 98% are released with 20 min' ozonation. Intermediate 2,4-DCP decomposes at earlier ozonation times than 2,4-D.     

DECOMPOSITION OF 4-NITROPHENOL BY OZONATION IN A HOLLOW FIBER MEMBRANE REACTOR

The effect of initial pH, liquid flow rate, gas flow rate, and gaseous ozone concentration on the ozonation of 4-nitrophenol in a membrane reactor was investigated. The results showed that the disappearance of 4-nitrophenol increased with the increase of liquid flow rate, gas flow rate, and gaseous ozone concentration. The rise of the initial pH value led to an increase in 4-nitrophenol removal rate, but the increase became negligible after initial pH exceeded 9.5. The highest removal efficiency of 4-nitrophenol achieved was 94% after 100 min reaction when gaseous ozone concentration was 0.51 mmol L^?1, gas flow rate was 57 mL min^?1, liquid recirculation rate was 72 mL min^?1, and initial pH was 10.3. The membrane reaction system could be modeled based on the lumped kinetics of 4-nitrophenol removal, and the corresponding rate constant of 4-nitrophenol removal was determined from the model.     

臭氧纳米气泡对水中三价砷的氧化效果

砷污染防治技术,将三价砷[As(Ⅲ)]先氧化成五价砷[As(Ⅴ)]是保证治理效果的必要手段。文中为了提高臭氧氧化效果,将臭氧以纳米气泡(NBs)的形式通入水中。在不同As(Ⅲ)初始浓度、不同pH下,NBs系统对As(Ⅲ)氧化率均远远高于臭氧大气泡系统,最高可达96.5%[对应As(Ⅲ)初始浓度为0.2mg/L],比大气泡系统提高了44.47%。NBs系统对As(Ⅲ)的氧化率随初始浓度的增大而有略微提高。溶液初始pH值为3、9时,NBs系统对As(Ⅲ)的最高氧化率达95.1%、94.2%,高于pH值为7时的氧化率;碳酸根离子对臭氧大气泡和NBs系统均具有一定的促进作用,添加了碳酸钠的NBs系统对As(Ⅲ)的氧化率达97.8%,比未添加药剂的系统提高了1.8%。     

臭氧氧化处理苯胺废水

采用臭氧氧化法处理苯胺溶液，考察了反应时间、苯胺浓度、溶液pH、臭氧流量等因素对苯胺降解率的影响。研究结果表明：初始浓度200mg／L时，pH值9．0、臭氧流量为300mg／h，经10min后苯胺去除率达到99％以上。苯胺降解反应符合一级反应动力学。TOC降解速率低于苯胺分子降解速率，反应30min后，TOC去除率比苯胺去除率低40％左右，表明伴随着苯胺的分解，生成一系列中间产物。     

KINETICS AND MECHANISM OF THE REACTION BETWEEN OZONE AND O-CRESOL IN AQUEOUS SOLUTIONS

The stopped-flow spectrophotomctric method was applied to study the kinetics of the ozonation of o-cresol in aqueous solutions of pH values varying from 2 to 9 at 10 to 40°C. The fast reaction between o-cresol and ozone is second order overall with first order in each reactant. The ozonation rale increases with the temperature and pH value of the solution. In neutral solutions, the overall rate constant increases from 422,000 M^-1S^-1 at 10°C to 1,549,000 M^-1 S^-1 at 40°C. The activation energy is about 30 KJ/mol in the neutral solutions; it increases slightly with the acidity of the solution.

A mechanism based on the initial attack of ozone moleculesat the ortho and para positions of o-cresol is proposed for the ozonation reaction. According to this mechanism, three moles of ozone are required to react with each mole of o-cresol resulting in the rupture of the aromatic ring and production of various acids. The oxidation products were identified by these and other investigators. The proposed mechanism yields a second order kinetics for the overall reaction, as confirmed by the kinetic experiments.     

臭氧氧化法处理硝基苯废水实验研究

采用臭氧氧化法处理硝基苯溶液,考察了反应时间、硝基苯浓度、溶液pH、臭氧流量等因素对硝基苯降解率的影响。研究结果表明：初始浓度200 mg/L时,pH 9.5、臭氧流量为300 mg/h,经30 min后硝基苯去除率达到95.3%以上。硝基苯降解反应符合一级反应动力学。TOC降解速率低于硝基苯分子降解速率,反应30 min后,TOC去除率比硝基苯去除率低45%左右,表明伴随着硝基苯的分解,由？OH或臭氧和硝基苯分子作用生成一系列中间产物。     

Advanced oxidation with ozone of 1,3,6‐naphthalenetrisulfonic acid in aqueous solution

The kinetics of oxidation with ozone of 1,3,6‐naphthalenetrisulfonic acid was analysed by studying the influence of different experimental parameters such as the concentration of tert‐butyl alcohol (2‐methyl‐2‐propanol), initial concentration of the acid, pH, and temperature. The rate constant of the direct reaction at 25 °C was calculated (k_D = 6.72 M ^?1s^?1). The constant of the free radical reaction was determined with the competitive kinetics method, using sodium 4‐chlorobenzoate as reference compound, obtaining a value of k_OH = 3.7 × 10⁹ M ^?1s^?1. It was demonstrated that even at very acid pH values, 80% of the 1,3,6‐naphthalenetrisulfonic acid was degraded by free radical reactions, so that the ozonation of this acid may be considered an advanced oxidation process. © 2002 Society of Chemical Industry     

OZONE TREATMENT OF METHYLENE BLUE IN AQUEOUS SOLUTIONS

The kinetics of ozonation of the sulfur dye Methylene Blue in aqueous solution is studied. The experiments have been carried out in a bubble column, using a single nozzle as gas sparger. The influence of the operating variables (initial concentration of Methylene Blue, ozone partial pressure, temperature and pH) on the oxidation process is established. A stoichiometric ratio of 3 moles of ozone consumed per mol of dye reacted is deduced. A reaction scheme based on the direct ozone attack to the dye is suggested, and it agrees with the found stoichiometry. The overall reaction orders and rate constants as a function of pH and temperature are determined following the film theory which is applied to the experimental data. The process develops in the fast pseudo mth order kinetic regime of absorption.     

新型铁铈复合氧化物催化臭氧氧化工艺去除对硝基苯酚

对硝基苯酚(4-NP)作为一种难降解的有机污染物,在自然环境中半衰期较长,对水生生物及水体环境均有不利影响。采用水热法制备新型铁铈复合氧化物,将其作为臭氧催化剂用于去除水中的4-NP。采用单因素试验,探究铁铈摩尔比、臭氧浓度、催化剂投加量、初始p H等因素对4-NP去除效果的影响。结果表明:在铁铈摩尔比为10∶1、水中臭氧浓度为7.0 mg/L、催化剂投加量为1.0 g/L、初始p H值为7时,催化臭氧法去除4-NP的速率最快,其反应假一级动力学常数为0.054 min-1,是单独臭氧氧化的4.2倍。添加Na HCO3可显著降低催化臭氧工艺的效率,间接证明了羟基自由基可能在有机物氧化过程中起到主要作用。     

Ultraviolet-Enhanced Ozonation of Organic Compounds: 1,2-Dichloroethane and Trichloroethylene as Model Substrates

1,2–Dichloroethane (DCE) and trichloroethylene (TCE) were used as model compounds to study the oxidation of organic chemicals by ozone/ultraviolet radiation, ozone, and hydrogen peroxide/ultraviolet radiation. It was found that ozone/ultraviolet radiation oxidized both 1,2–dichloroethane and trichloroethylene in batch systems, at pH = 2 (phosphate buffer). At ozone concentrations in the 1 to 5 mg/L range, the reaction was first order in both ozone and substrate. At pH = 2 and initial ozone concentration 2.2–2.6 mg/L, rate constants (k)Q = 25 and 130 M^-1sec^-1 were observed for the ozone/ultraviolet radiation oxidation of DCE and TCE, respectively. The rat e constants for ozone oxidation of DCE and TCE without ultraviolet radiation were 4.3 and 47 M^-1sec^-1, respectively.

The higher rate of TCE oxidation implies that direct reaction occurs with the double bond. Finite reaction rate of DCE with ozone, and substantial increases in rate at higher pH imply the participatation of hydroxyl radicals in the oxidation of both compounds. For example, at pH = 7, initial ozone concentration of 2.3 mg/L, the k_o for TCE oxidation by ozone/ultraviolet radiation is approximately 500 M^?1 sec^?1 almost too fast to measure in a batch system.The rate also is increased by increased ultraviolet radiation intensity, and by the presence of hydrogen peroxide, which acts as a catalyst.