Kinetics of Burning Side Reaction in the Liquid-phase Oxidation of p-Xylene

During the liquid-phase oxidation of p-xylene,over-oxidation of reactant,intermediates and solvent to carbon dioxide and carbon monoxide is generally known as the burning side reaction.Batch and semi-continuous experiments were carried out,and the experimental data of the burning side reaction were analyzed and reported in this paper.The results showed that the rates of burning side reactions were proportional to the rates of the main reaction,but decreased with the increasing concentrations of reactant and intermediates.The inter-stimulative and competitive relationship between the burning side reaction and the main reaction was confirmed,and the rates of the burning side reaction could be described with some key indexes of the main reaction.According to the mechanism of the side reactions and the kinetics model of main reaction which were proposed and tested in the previous papers,a kinetic model of the burning side reactions involving some key indexes of the main reaction was developed,and the parameters were determined by data fitting of the COx rate curves.The obtained kinetic model could describe the burning side reactions adequately.

Kinetics and Mechanism of Oxidation Induced Contraction of MgAl2O4 Spinel Carbon Composites Reinforced by Al4C3 in situ Reaction

Kinetics and mechanism of oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction were researched in air using vertical high temperature thermal dilatometer from 25℃to 1400℃.It is shown that oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced Al4C3 in situ reaction is the common logarithm of oxidation time t and the oxygen partial pressure P inside MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction in air at 1400℃is as follows:P=F(-2.75×10^-4A+2.13×10^-3)lnt.The nonsteady diffusion kinetic equation of O2 at 1400℃inside the composites is as follows:J=De lnt.Acceleration of the total diffusional?flux of oxygen inside the composites at 1400℃is in inverse proportion to the oxidation time.The nonsteady state effective diffusion coefficient De of O2(g)inside the composites decreases in direct proportional to the increase of the amount of metallic aluminium.The method of preventing the oxidation induced contraction of MgAl2O4 spinel carbon composites reinforced by Al4C3 in situ reaction is to increase the amount of Al.The slag erosion index of MgO-Al2O3 spinel carbon composite reinforced by Al4C3 in situ reaction is 0.47 times that of MgO-CaO brick used in the lining above slag line area of a VOD stainless steel-making vessel.HMOR of MgO-Al2O3 spinel carbon composite reinforced by Al4C3 in situ reaction is 26.7 MPa,HMOR of the composite is 3.6 times the same as that of MgO-CaO brick used in the lining above slag line area of a VOD vessel.Its service life is two times as many as that of MgO-CaO brick.

Extracting reaction mechanism analysis of Zn and Si from zinc oxide ore by NaOH roasting method

The orthogonal test was used to optimize the reaction conditions of roasting zinc oxide ore with NaOH aiming to comprehensively utilize zinc oxide ore.The optimized reaction conditions were molar ratio of NaOH to zinc oxide ore 6:1,roasting temperature 450°C,holding time 150 min.The molar ratio of NaOH to zinc oxide ore was the most predominant factor affecting the extraction ratios of zinc oxide and silica.The mineral phase transformations were investigated by testing the phases of specimens obtained at different temperatures.The process was that silica reacted with molten NaOH to form Na_2SiO_3 at first,then transformed into Na_4SiO_4 with temperature rising.ZnCO_3 and its decomposing product ZnO reacted with NaOH to form Na_2ZnO_2.Na_2ZnSiO_4was also obtained.The reaction rate was investigated using unreacted shrinking core model.Two models used were chemical reaction at the particle surface and diffusion through the product layer.The results indicated that the reaction rate was combine-controlled by two models.The activation energy and frequency factor were obtained as 24.12 k J/mol and 0.0682,respectively.

Structure, characterization, and dynamic performance of a wet air oxidation catalyst Cu–Fe–La/γ-Al_2O_3

A Cu–Fe–La/γ-Al_2O_3(CFLA) catalyst was prepared by the excessive impregnation method and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that the catalyst contained mostly Cu^(2+), Fe^(3+), and La^(3+)and a small amount of Cu^+, Fe^(2+), and La. The active components were uniformly distributed in the catalyst, and the particle size of the components was approximately 7.5 nm. The CFLA catalyst was used for the treatment of methyl orange(MO) solution by catalytic wet air oxidation(CWAO), and it exhibited a high catalytic activity. The catalytic reaction involved variable valence states of metals and free-radical reaction mechanism. The CWAO reaction of MO solution was fitted by a segmented first-order dynamic model, and the rapid reaction apparent activation energy was 13.9 k J·mol^(-1).

Kinetic simulation of oxidative coupling of methane over perovskite catalyst by genetic algorithm:Mechanistic aspects

The reaction kinetics of oxidative coupling of methane catalyzed by perovskite was studied in a fixed bed flow reactor.At atmospheric pressure,the reactions were carried out at 725,750 and 775℃,inlet methane to oxygen ratios of 2 to 4.5 and gas hourly space velocity （GHSV） of 100 min^-1.Correlation of the kinetic data has been performed with the proposed mechanisms.The selected equations have been regressed with experimental data accompanied by genetic algorithm （GA） in order to obtain optimized parameters.After investigation the Langmuir-Hinshelwood mechanism was selected as the best mechanism,and Arrhenius and adsorption parameters of this model were obtained by linear regression.In this research the Marquardt algorithm was also used and its results were compared with those of genetic algorithm.It should be noted that the Marquardt algorithm is sensitive to the selection of initial values and there is possibility to trap in a local minimum.

Product identification and toxicity change during oxidation of methotrexate by ferrate and permanganate in water

Accompanying an annual increase in cancer incidence,the global use of anticancer drugs has remarkably increased with their worldwide environmental prevalence and ecological risks.In this study,the oxidation of methotrexate(MTX),a typical anticancer drug with ubiquitous occurrence and multi-endpoint toxicity,by ferrate(VI)(Fe(VI))and permanganate(Mn(VII)))was investigated in water.Fe(VI)exhibited a higher reactivity with MTX(93.34 M^(−1) s^(−1))than Mn(VII)(3.01 M^(−1) s^(−1)) at pH 8.0.The introduction of Cu(II)and Fe(III)at 1.0 mM improved the removal efficiency of 5.0μM MTX by 100.0μM Fe(VI)from 80%to 95%and 100%after 4 min,respectively.Seven oxidized products(OPs)were identified during oxidative treatments,while OP-191 and OP-205 were characterized as specific products for Fe(VI)oxidation.Initial ketonization of the L-glutamic acid moiety and cleavage of the peptide bond of MTX were proposed.Additionally,a multi-endpoint toxicity evaluation indicated no genotoxicity,neurotoxicity,or endocrine-disrupting effects of MTX and its OPs.Particularly,serious developmental toxicity in zebrafish larvae was observed in the treated MTX solutions.Based on the acute and chronic aquatic toxicity prediction,OP-190,OP-192,OP-206,and OP-208 were deemed toxic or very toxic compared to harmful MTX.Furthermore,the reduced biodegradability index from 0.15(MTX)to−0.5 to−0.2(OP-192,OP-206,and OP-468)indicated the formation of lower biodegradable OPs.Overall,this study suggests that Fe(VI)and Mn(VII)oxidation are promising treatments for remediating anticancer drug-contaminated water.However,the environmental risks associated with these treatments should be considered in the evaluation of water safety.

Recent progress in production and usage of hydrogen peroxide

Hydrogen peroxide has attracted increasing interest as an environmentally benign and green oxidant that can also be used as a solar fuel in fuel cells.This review focuses on recent progress in production of hydrogen peroxide by solar-light-driven oxidation of water by dioxygen and its usage as a green oxidant and fuel.The photocatalytic production of hydrogen peroxide is made possible by combining the e^(-)and 4e-oxidation of water with the e^(-)reduction of dioxygen using solar energy.The catalytic control of the selectivity of the e^(-)vs.4e-oxidation of water is discussed together with the selectivity of the e^(-)vs.4e-reduction of dioxygen.The combination of the photocatalytic e^(-)oxidation of water and the e^(-)reduction of dioxygen provides the best efficiency because both processes afford hydrogen peroxide.The solar-light-driven hydrogen peroxide production by oxidation of water and by reduction of dioxygen is combined with the catalytic oxidation of substrates with hydrogen peroxides,in which dioxygen is used as the greenest oxidant.

The role of proton dynamics on the catalyst-electrolyte interface in the oxygen evolution reaction

The development of non‐precious metal catalysts that facilitate the oxygen evolution reaction(OER)is important for the widespread application of hydrogen production by water splitting.Various perovskite oxides have been employed as active OER catalysts,however,the underlying mechanism that occurs at the catalyst‐electrolyte interface is still not well understood,prohibiting the design and preparation of advanced OER catalysts.Here,we report a systematic investigation into the effect of proton dynamics on the catalyst‐electrolyte interfaces of four perovskite catalysts:La_(0.5)Sr_(0.5)CoO_(3‐δ)(LSCO),LaCoO_(3),LaFeO_(3),and LaNiO_(3).The pH‐dependent OER activities,H/D kinetic isotope effect,and surface functionalization with phosphate anion groups were investigated to elucidate the role of proton dynamics in the rate‐limiting steps of the OER.For oxides with small charge‐transfer energies,such as LSCO and LaNiO_(3),non‐concerted proton‐coupled electron transfer steps are involved in the OER,and the activity is strongly controlled by the proton dynamics on the catalyst surface.The results demonstrate the important role of interfacial proton transfer in the OER mechanism,and suggest that proton dynamics at the interface should carefully be considered in the design of future high‐performance catalysts.

Numerical study of novel OME_(1-6) combustion mechanism and spray combustion at changed ambient environments

For a climate-neutral future mobility,the socalled e-fuels can play an essential part.Especially,oxygenated e-fuels containing oxygen in their chemical formula have the additional potential to burn with significantly lower soot levels.In particular,polyoxymethylene dimethyl ethers or oxymethylene ethers(PODEs or OMEs)do not contain carbon-carbon bonds,prohibiting the production of soot precursors like acetylene(C_(2)H_(2)).These properties make OMEs a highly interesting candidate for future climate-neutral compression-ignition engines.However,to fully leverage their potential,the auto-ignition process,flame propagation,and mixing regimes of the combustion need to be understood.To achieve this,efficient oxidation mechanisms suitable for computational fluid dynamics(CFD)calculations must be developed and validated.The present work aims to highlight the improvements made by developing an adapted oxidation mechanism for OME1-6 and introducing it into a validated spray combustion CFD model for OMEs.The simulations were conducted for single-and multi-injection patterns,changing ambient temperatures,and oxygen contents.The results were validated against high-pressure and high-temperature constantpressure chamber experiments.OH*-chemiluminescence measurements accomplished the characterization of the auto-ignition process.Both experiments and simulations were conducted for two different injectors.Significant improvements concerning the prediction of the ignition delay time were accomplished while also retaining an excellent agreement for the flame lift-off length.The spatial zones of high-temperature reaction activity were also affected by the adaption of the reaction kinetics.They showed a greater tendency to form OH^(*) radicals within the center of the spray in accordance with the experiments.

由乙烯焦油制备锂离子电池负极材料用碳质前驱体的氧化反应机理与反应动力学

为了得到优质的碳质前驱体,研究了乙烯焦油在空气中的氧化反应机理及其反应动力学,并制备出高软化点沥青应用于锂离子电池负极石墨材料的包覆改性。根据热重曲线将乙烯焦油的氧化过程分成350−550、550−700和700−900 K三个阶段,并采用质谱和红外技术对不同反应温度下的尾气成份进行在线分析以揭示乙烯焦油在空气中的氧化反应机理。根据不同反应温度下乙烯焦油与氧气的热失重曲线,整个反应过程被分为4个阶段,进一步利用Coats-Redfern等转化率法分析17种常用反应动力学模型与实验数据的拟合度,筛选出最适宜表达乙烯焦油与氧气的反应动力学模型。结果表明:(1)在乙烯焦油的氧化过程中,芳香化合物的支链先与氧气反应生成醇类、醛类小分子化合物和含有过氧自由基的芳香化合物,然后含有过氧自由基的芳香化合物进行热缩聚反应形成分子量更大的芳香族化合物;(2)可采用四级反应模型描述乙烯焦油的前3阶段反应动力学,活化能分别为47.33、18.69和9.00 kJ·mol^(−1);可采用三维扩散模型描述第4阶段的反应动力学,其活化能为88.37 kJ·mol^(−1)。(3)经所制沥青包覆改性后,石墨负极循环300圈后的容量保持率由51.54%增长为79.07%。

ZnO超微粒子光催化氧化SO_2的研究

利用ZnO光催化技术对SO2 氧化进行了研究 .结果表明 ,在一定的反应条件下 ,ZnO超微粒子光催化SO2 氧化的转化率较高 ,32 0℃下焙烧的ZnO超微粒子上SO2 氧化的转化率高达 99% .考察了氧和水蒸气分压等因素对SO2 氧化反应的影响 .用化学法对气态和凝聚态产物SO3 进行了定性分析 ,并对SO2

对二甲苯液相催化氧化动力学(Ⅰ)反应机理和动力学模型

针对PX高温液相催化氧化过程的特点开发了一套气液固三相反应实验技术 ,进行了氧化过程的动力学实验研究 .根据自由基反应机理和Co Mn Br三元催化体系的作用机制对PX氧化过程进行了深入的剖析 ,分析了芳烃中甲基和醛基的各步氧化机理及其与催化剂循环之间的耦合作用 .在此基础上推导出关于反应物浓度的动力学模型 ,并根据实验数据计算出各动力学参数 .

含油废水的超临界水氧化反应机理及动力学特性

针对传统的处理方法不能有效地去除油田开采废水中化学需氧量(COD)的缺点,引入超临界水氧化法作为含油废水的深度处理技术,研究了含油废水在超临界水中的氧化降解过程,并用自由基反应机理解释了超临界水氧化反应的机理.实验结果表明:超临界水氧化法是一种高效快速的有机废物处理技术,COD的去除率近90%;反应温度、停留时间是影响废水COD去除率的主要因素,随着反应温度、停留时间的增加,废水COD去除率显著增大;氧化反应对废水的反应级数为1.62,对氧为0.22,反应活化能和频率因子分别为(92.2±9.9)kJ.mol-1和(3.53±3.33)×103,所建立的反应动力学模型与实验结果的偏差在±10%之内.此外,在分析综述基础上指出了超临界水氧化处理过程存在的问题及可能的解决方法.

催化湿式氧化法处理废水的研究进展

介绍了催化湿式氧化(CWAO)法废水处理技术在催化剂开发、反应机理探讨和反应动力学研究等方面取得的进展;提出研制高效稳定的催化剂、探讨反应机理和研究反应动力学模型对于CWAO法的推广起着非常重要的作用。

高铁酸盐氧化降解水中苯酚的动力学及机理研究

以自制高铁酸钾（K2FeO4）为原料，探讨了影响高铁酸盐氧化降解苯酚的主要因素，并研究了苯酚降解的动力学特征和反应机理。结果表明，高铁酸盐加入量、pH值、持续搅拌、反应温度、反应时间都影响苯酚去除效果。其中高铁酸盐加入量是影响苯酚去除效果的关键因素，高铁酸盐氧化降解苯酚的最佳pH值范围为9～10，持续搅拌和提高反应温度只影响苯酚降解速率而不影响苯酚降解率。苯酚的降解过程遵循一级反应动力学模型。苯酚被高铁酸盐氧化生成CO2、H2O以及一部分难矿化的有机物。

肾上腺素氧化反应的研究——氧化反应动力学和机理以及自由基中间体

用紫外吸收光谱法结合计算机模拟研究了肾上腺素(Adjn)在Cu(Ⅱ)离子催化下,用H_2O_2氧化产生肾上腺素红(Adom)的反应动力学,考查了反应的速率随体系中肾上腺素的初始浓度,Cu(Ⅱ)离子浓度和H_2O_2浓度的变化情况。在流动法或添加自由基稳定剂的条件下,利用顺磁共振法检测丁肾上腺素自氧化,光氧化和Cu(Ⅱ)离子催化H_2O_2氧化产生的半醌自由基。考查了Cu(Ⅱ)离子催化下自由基的相对浓度随反应条件的变化情况。在反应动力学和顺磁共振实验的基础上所提出的可能的反应机理,半定量地解释此反应动力学实验结果和顺磁共振实验中的自由基行为。

V_2O_5催化甲烷液相部分氧化工艺过程研究

以V2O5为催化剂,在发烟硫酸中进行了甲烷液相选择性氧化的研究工作,考察了V2O5催化剂用量、反应温度、反应时间、发烟硫酸浓度等工艺条件对反应收率的影响,进行了甲烷液相选择性氧化的催化机理探讨和宏观动力学推导。甲烷在部分氧化反应中首先转化为硫酸甲酯,后者进一步水解得到甲醇。甲烷转化率可达54.5%,选择性45.5%,相应的工艺条件为催化剂用量0.0175mol、反应温度180℃、发烟硫酸中SO3含量50%(wt)、反应时间2h。V2O5催化甲烷液相部分氧化反应遵循亲代取代机理,甲烷液相部分氧化反应为一级反应。

二甲醚气相氧化反应机理及动力学研究进展

综述了近年来二甲醚（CH3OCH3）在不同条件下气相氧化反应机理和动力学的研究情况。在高温（800-1300K）条件下，CH3OCH3氧化反应时主要产物有CO，C02，HCHO，CH4，C2H6，H2O等。在低温（室温～800K）条件下，CH3OCH3氧化反应分为两种情况：低压（低于100kPa）氧化反应，主要产物为HCHO；高压（100kPa以上）氧化反应。主要产物为HCOOH，同时生成CH3OCHO。在低温（不高于800K）条件下，CH3OCH3氧化反应的反应速率常数的测定值为（1～50）×10^-12cm^3／（mol·s）。

基于自由基反应机理的芳烃液相氧化动力学模型

基于自由基链式反应机理,概括性地提出了芳烃液相氧化的基元反应步骤。针对芳烃氧化的特点对动力学模型进行了简化处理,减少了模型参数。运用提出的建模方法,建立了3个氧化实例的动力学模型,包括对二甲苯(PX)氧化生产对苯二甲酸(TPA)、对甲基苯甲酸(p-TA)氧化生产TPA、乙苯(EB)氧化生产乙苯氢过氧化物(EBHP)。拟合回归结果表明,上述动力学模型对实验数据的拟合效果均较好,最大拟合偏差不大于10%;并且涉及链传递和链终止反应步骤的共用参数不随反应条件而改变。

SiC涂层/三维碳纤维编织体的氧化动力学和机理研究

采用原位反应法在三维碳纤维编织体(简称:RB)的纤维表面制得SiC涂层,通过 XRD、SEM、等温氧化失重和非等温热重分析等测试手段研究了制备方法对SiC涂层均匀性 的影响,并对SiC涂层／碳纤维编织体(简称:CB)材料在等温和非等温条件下,氧化反应的 动力学和反应机理进行了研究.结果表明:SiC涂层均匀、完整地涂覆于编织体内外各纤维表 面;材料等温氧化反应的机理为第一阶段反应控制,第二阶段扩散和反应共同控制;材料的非 等温氧化过程呈现自催化特征,氧化机理为随机成核,氧化动力学参数为:lgA=9.615min-1; Ea=201.73kJ·mol-1.