Partial oxidation of methane to formaldehyde over halogen modified catalyst

The partial oxidation of methane to formaldehyde over Pd-supported on Al₂O₃ in the presence of small amounts of halogen modifiers was investigated in an isothermal integral flow reactor at atmospheric pressure between 300 and 510°C. The effects of several variables, feed ratio of air to methane, reaction temperature, reciprocal of space velocity, and the type and amount of halogen modifiers on the conversion and product distribution, were determined by gas chromatography. Though 13 different mechanisms were postulated the rate of reaction was most satisfactorily correlated by a mechanism which assumes the rate controlling step to be the surface reaction between charged, adsorbed methane and oxygen.     

甲基丙烯磺酸钠合成方法的改进

以焦亚硫酸钠和3-氯-2-甲基丙烯为原料合成了甲基丙烯磺酸钠,研究了反应温度、反应物摩尔比、反应时间等因素对结果的影响.确定了合成目标产物的最佳反应条件为:3-氯-2-甲基丙烯1.0mol,焦亚硫酸钠与3-氯-2-甲基丙烯的摩尔比为0.6∶1,3-氯-2-甲基丙烯滴加到焦亚硫酸钠溶液中,65℃下反应120 min,在此...     

甲苯液相氧化反应过程的模拟

甲苯液相空气氧化是环境友好的苯甲酸和苯甲醛生产工艺。根据在模拟工业条件下测定的动力学数据和观察到的实验现象,提出了该反应的反应机理和反应网络,建立了相应的动力学模型。根据该动力学方程,对现有工业生产过程进行了模拟,发现现有工业过程处于严重供氧不足的情况。提出了3种强化方案并分别对其进行了模拟计算和比较。模拟结果表明,通过增大空气供给量和采用富氧空气氧化均可有效强化现有工业生产过程。采用富氧空气氧化,其甲苯转化率可提高到22.24%,甲苯反应量可增大57%。采用增大空气量的方法,可提高甲苯反应量31%,甲苯转化率可提高到18.61%。若同时增大甲苯和空气负荷,甲苯反应量可提高71%。     

Role of steam in partial oxidation of propylene over a Pd/SDB catalyst

Step-response studies of propylene partial oxidation with oxygen over a hydrophobic Pd/SDB catalyst were conducted at 1000 kPa and 185°C in a fixed-bed reactor. CO₂ was found to be the only oxidation product when the feed contained only propylene and oxygen. CO₂ formation was significantly suppressed by addition of steam to the feed, and this addition leads to the formation of partial oxidation products: acrolein and acrylic acid. A competitive reaction mechanism involving water molecules is proposed to explain the significant influence of steam concentration on the rate of propylene oxidation and product selectivity.     

Kinetics of cupric oxide catalysed oxidation of propylene in a stirred reactor

The catalytic air oxidation of propylene to acrolein over a supported copper oxide catalyst was investigated in a continuous stirred vessel reactor between 375° and 450°C at atmospheric pressure. The effect of temperature, ratio of oxygen to propylene in feed and total feed rate (or contact time) on the conversion of propylene and the yield of acrolein were determined. It was found that with an increase in temperature, ratio of oxygen to propylene and contact time, the yield drops considerably though conversion increases. A study of the mixing characteristics of the stirred vessel reactor was carried out by following the conversion at various stirrer speeds. The kinetic data obtained were tested to determine the most probable model by the Hougen-Watson method. The model that satisfactorily correlated the data describes the rate-controlling step as the surface reaction occurring between adsorbed propylene, a vacant site and oxygen in the gas phase. The following Hougen-Watson type rate equation has been proposed The constants in the rate equation have been expressed as a function of temperature.     

进气氧浓度对PX氧化反应器的影响

以对二甲苯（PX）液相催化氧化反应器的连续鼓泡釜模型，对尾氧浓度保持3．5％时不同进气氧浓度下的反应器进行了模拟。模拟计算发现反应温度随着进气氧浓度的增加而升高，可以通过减少塔顶抽出水量或降低反应压力维持反应釜温度不变。较高的氧浓度进气对反应器操作的影响主要表现在温度效应和浓度效应上，温度效应使得主反应的速率增加，浓度效应却降低主反应的速率。随着进气氧浓度的增加，温度效应和浓度效应共同作用的结果是氧化反应器的生产能力先增大后减小，因此存在一个适宜的进气氧浓度，由计算得到为26.6％。     

柴油氧化脱硫技术的研究

通过H2O2/HCOOH体系对柴油选择性氧化脱硫技术的研究。考察了H2O2/HCOOH体系反应温度、反应时间、剂油比等因素对氧化脱硫效果的影响。实验结果表明,温度为60℃,反应时间为30min,剂油比为1：15,在反应进行到25min时加入相转移催化剂脱硫率达最大,油脱硫率可达90.0%。     

流化床串联多段冷激式绝热固定床HCl氧化反应模拟优化

提出了由流化床与多段冷激式绝热固定床串联的新型HCl氧化制氯反应工艺. 通过物料、能量、动量衡算建立了绝热反应器一维数学模型,对绝热固定床反应器段间冷激气种类、流率、流化床反应器进口处HCl与O2摩尔配比及催化剂用量等工艺参数进行了优化计算. 结果表明,液态氧为较适宜的冷激气,流化床反应器入口处最佳HCl与O2摩尔配比为1:0.7,流化床和绝热床中最佳催化剂用量分别为4.3与8.6 t,在该条件下,HCl转化率可达85%.     

Kinetics and reaction mechanism of catalytic oxidation of low concentrations of hydrogen sulfide in natural gas over activated carbon

The kinetics of the hydrogen sulfide oxidation process, producing mostly sulfur and water, was studied using 0.25 to 1.0 g Hydrodarco activated carbon catalyst and varying the O₂/H₂S ratio (molar basis) in the feed gas between 0.5 to 0.6 in the temperature, and pressure ranges from 125 to 200°C and 225 to 780 kPa. SO₂ was obtained as an undesirable by-product during H₂S oxidation reaction or as a product during regeneration of the catalyst. The feed gas contained 0.9 — 1.3 mol% H₂S with approximately 80 mol% CH_4. In this paper, the factors affecting the H₂S conversion and SO₂ formation are presented. The rate expressions for (a) H₂S conversion and (b) SO₂ formation were developed from the Langmuir-Hinshelwood surface control reaction model. The experimental data were well correlated by the rate equations. Also, the rate parameters were evaluated and correlated with temperature. The activation energies for H₂S oxidation and SO₂ production reactions were calculated to be 34.2 and 62.5 kJ/mol, respectively. Partial pressures of oxygen and H₂S were found to influence H₂S conversion whereas, the presence of water in the feed gas up to 10.5 mol% did not affect H₂S conversion significantly. Heats of adsorption for various species on the active sites were calculated. SO₂ production was, as expected, enhanced at higher temperature, and its rate was much smaller than the oxidation rate of H₂S under the reaction conditions used.     

铬铁矿无钙焙烧过程中氧含量对氧化率的影响

在不同的氧含量下,通过改变焙烧温度、焙烧时间、填料（废渣）添加量及配碱率等实验条件,分析各因素对铬氧化率的影响趋势。实验结果表明,高氧含量可以提高铬氧化率,是重要的影响因素。氧含量为40%（体积分数）左右较为合理;合理的焙烧温度和时间分别为1 100 ℃和60 min;应结合铬铁矿中的铬的最大氧化率和炉料阈值来确定填料的用量;配碱率的增加在提高了铬氧化率的同时,也降低了碱利用率,配碱率低于1.4时对铬氧化率影响较大。     

含乙醇废水的超临界水氧化反应动力学及反应机理

研究了等温平推流反应器中乙醇的超临界水氧化反应（SCWO）,反应温度475～550 ℃、压力22～30 MPa、停留时间0.6～63.7 s、氧气与乙醇摩尔浓度比4.56～9.09.一氧化碳和二氧化碳分别是反应中间产物和最终产物.随停留时间增大、温度升高,乙醇去除率增大,压力和氧气浓度变化对过程无显著影响.以幂指数方程描述乙醇SCWO动力学,乙醇和氧气的反应级数分别为1和0,计算值和实验值相差基本在10%以内.超临界条件下分别以过氧化氢和氧气为氧化剂时乙醇的氧化反应无明显差别,亚临界条件下过氧化氢氧化速率大于氧气.基于对此现象的分析,作者推测：无论以过氧化氢或氧气作为氧化剂,在超临界水中,它们之间可以通过一系列自由基反应迅速达到平衡,且各物种的平衡分布与初始分布无关,体系的主要氧化过程在平衡分布下进行.     

工艺参数对硫化碱转化及二氧化硫释放的影响研究

基于煤粉还原芒硝法生产硫化碱的碱回收锅炉技术,研究了不同工艺参数对硫化碱转化率及二氧化硫释放率的影响。结果表明,反应温度为1 200 ℃、煤粉粒径为550~830 μm、停留时间为8~10 min为较优参数,在此条件下硫化碱转化率可达93.67%,继续提高反应温度或增加停留时间对提升硫化碱转化率效果有限;芒硝与煤粉质量比应控制在1∶（1.05~1.15）,可达到较高的硫化碱转化率和较低煤耗;在有氧气氛下,二氧化硫主要由硫化碱氧化生成,由硫化碱氧化生成的二氧化硫量远大于煤的热解和氧化生成的二氧化硫量,因此可通过控制反应区的氧浓度来降低二氧化硫生成量;随着反应温度升高,二氧化硫释放时间提前,但过高的反应温度会加剧硫化碱氧化,从而增加二氧化硫生成量。     

Effects of Oxygen Transfer Limitation and Kinetic Control on Biomimetic Catalytic Oxidation of Toluene

Under oxygen transfer limitation and kinetic control, liquid-phase catalytic oxidation of toluene over metalloporphyrin was studied. An improved technique of measuring dissolved oxygen levels for gas-liquid reaction at the elevated temperature and pressure was used to take the sequential data in the oxidation of toluene catalyzed by metalloporphyrin. By this technique the corresponding control step of toluene oxidation could be obtained by varying reaction conditions. When the partial pressure of oxygen in the feed is lower than or equal to 0.070 MPa at 463 K, the oxidation of toluene would be controlled by oxygen transfer, otherwise the reaction would be controlled by kinetics. The effects of both oxygen transfer and kinetic control on the toluene conversion and the selectivity of benzaldehyde and benzyl alcohol in biomimetic catalytic oxidation of toluene were systematically investigated. Three conclusions have been made from the experimental results. Firstly, under the oxygen transfer limitation the toluene conversion is lower than that under kinetic control at the same oxidation conditions. Secondly, under the oxygen transfer limitation the total selectivity of benzaldehyde and benzyl alcohol is lower than that under kinetic control with the same conversion of toluene. Finally, under the kinetics control the oxidation rate of toluene is zero-order with respect to oxygen. The experimental results are identical with the biomimetic catalytic mechanism of toluene oxidation over metalloporphyrins.     

在VPO催化剂上丁烷选择氧化的质谱研究

The selective oxidation of n-butane to maleic anhydride(MA) on a vanadium-phosphorus oxide (VPO) catalyst was studied using on-line gas-chromatography combined with mass spectrometry(GC-MS) and transient response technique.The reaction intermediates,butene and furan,were found in the reaction effuent under near industrial feed condition (3% butane 15% O2),while dihydrofuran was detected at high butane concentration (12% butane,5%O2).Some intermediates of MA decomposition were also identified.Detection of these intermediates shows that the vanadium phosphorus oxides are able to dehydrogenate butane to butene,and butene further to form MA.Based on these observations,a modified scheme of reaction network is proposed.The transient experiments show that butane in the gas phase may directly react with oxygen both on the surface and from the metal oxide lattice,without a proceeding adsorption step.Gas phase oxygen can be adsorbed and transformed to surface lattice oxygen but it can not participate in selective oxidation.Adsorbed oxygen leads to deep oxidation,while lattice oxygen leads to selective oxidation.     

Kinetics of the oxidative dehydrogenation (ODH) of methanol to formaldehyde by supported vanadium-based nanocatalysts

The aim of the present contribution was to develop a detailed kinetic analysis of the oxidative dehydrogenation (ODH) reaction of methanol to formaldehyde on a nano-structured supported vanadium oxide catalyst, selected in a preliminary screening. The chosen vanadium catalyst, supported on TiO₂/SiO₂, has been prepared by grafting vanadyl alkoxide, dissolved in dioxane, and characterized by BET, XRD, Raman, XPS and SEM. An exhaustive set of experimental runs has been conducted in an isothermal packed bed tubular reactor by investigating several operative conditions, such as: temperature, contact time, methanol/oxygen feed molar ratio and water feed concentration. Depending on the operative conditions adopted, the main products observed were formaldehyde and dimethoxymethane while lower amounts of methyl formate and CO₂ were also found. At low contact time, the main reaction product was dimethoxymethane which was then converted into formaldehyde through the reverse equilibrium reaction with water. As a confirmation of this observation, a peculiar behaviour was detected consisting in an increase of selectivity to formaldehyde by increasing methanol conversion. The obtained experimental data of methanol conversion and selectivity towards products were modelled by means of an integral reactor model and the related kinetic parameters were determined by non-linear regression analysis. The adopted reaction rate expressions were of the Mars van Krevelen–Langmuir Hinshelwood type and a good agreement was found between the model theoretical prediction and the experimental data. A reaction mechanism and a detailed reaction scheme (rake-type) were proposed for methanol ODH on a nano-structured catalyst that were able to interpret correctly the collected experimental observations.     

THE ROLE OF LATTICE OXYGEN IN THE DYNAMIC BEHAVIOR OF OXIDE CATALYSTS

The lattice of an oxide catalyst used for oxidation reactions can act as a reservoir for oxygen, storing and releasing it for reactions at the catalyst surface under appropriate conditions. The implication of this oxygen storage property of an oxide catalyst on its dynamic response characteristics has been investigated through an experimental study of 2-butene oxidation over vanadium oxide as a model reaction. Isothermal reaction rate measurements in a differential reactor and nonisothermal studies in a single pellet reactor have been carried out. Following a step increase in the feed butene concentration, isothermal reaction rate overshoot and pellet temperature overshoot were observed. These observations could be modelled in a qualitatively correct way by a very simple model accounting for the participation of lattice oxygen in the catalytic reactions under dynamic conditions. It is demonstrated through model simulations that the ignition characteristics of a catalyst pellet are significantly affected by the participation of the lattice oxygen, when steady state multiplicity is present.     

Development of a transient kinetic model for the CO oxidation by O2 over a Pt/Rh/CeO2/γ-Al2O3 three-way catalyst

A transient kinetic model was developed for the CO oxidation by O₂ over a Pt/Rh/CeO₂/γ-Al₂O₃ three-way catalyst. The experiments which were modelled consisted of periodically switching between a feed stream containing 0.5 mol% CO in helium and a feed stream containing 0.5 mol% O₂ in helium, with a frequency from 0.1 to 0.25 Hz, in the temperature range 393–433 K. These temperatures are representative for cold start conditions. The transient experiments yield information about the reaction mechanism. A transient kinetic model based on elementary reaction steps was developed which describes the experimental data in the above mentioned range of experimental conditions adequately. The kinetic model consists of two monofunctional and one bifunctional contribution. The first monofunctional reaction path comprises competitive adsorption of CO and O₂ on the noble metal surface followed by a surface reaction. The second monofunctional reaction path consists of CO adsorption on an oxygen atom adsorbed on the noble metal surface, followed by a reaction to CO₂. The bifunctional reaction path involves a reaction between CO adsorbed on the noble metal surface and oxygen from ceria at the noble metal/ceria interface. Also, reversible adsorption of carbon dioxide on the support is taken into account. The kinetic parameters, i.e. preexponential factors and activation energies for the different elementary reaction steps, and the oxygen storage capacity were estimated using multi-response non-linear regression analysis of the oxygen, carbon monoxide and carbon dioxide outlet concentrations.     

Oxidation of sunflower oil during storage

Effects of temperature and oxygen concentration on oxidative deterioration during storage of crude sunflower oils, obtained by pressing and solvent extraction, were studied. Oxidation was monitored through several analytical and chromatographic methods that determine chemical and physical changes or analyze specific oxidation compounds at different stages of the process: peroxide value, p-anisidine value, free fatty acids, weight gain, total content and distribution of polar compounds, and composition of fatty acids. Extracted oil showed a higher oxidative stability than pressed oil. Oxidative deterioration was strongly dependent on temperature, oxygen availability, and the ratio of exposed surface to sample volume. A kinetic model of two series reactions was developed to represent oxidation rate in terms of peroxide value, the reaction rate constants and their temperature dependence being evaluated by nonlinear regression. Finally, good correlations between the percentage of polar compounds or oxidized triglyceride monomers and the peroxide value were found.     

Effect of Water on Methane and Ethane Oxidation in the Conditions of Oxidative Coupling of Methane Over Model Catalysts

The effect of water onto the rate and selectivity of methane and ethane oxidation in the conditions of oxidative coupling of methane (OCM) is studied. The effect of water strongly depends on the OCM catalyst composition: whereas PbO_X/Al₂O₃ undergoes an irreversible deactivation, no effect of water is observed on both reaction rate and OCM selectivity over La/MgO. Over NaWMn/SiO₂ catalyst both rate of reaction and selectivity are enhanced by water addition to the feed at low conversions during methane oxidation. In the case of ethane oxidation, the rate of reaction is strongly affected by water addition, whereas selectivity to ethylene does not change at equal conversions. At increasing concentration of water in the feed gas its relative effect onto the methane oxidation substantially decreases, so the increasing concentration of water above ~8 vol% does not further enhance the rate of methane oxidation. The observed effects are explained by the participation of water in the active site turnover, namely in its re-oxidation by shifting the prevailing re-oxidation route from filling surface oxygen vacancies to oxidative dehydrogenation of surface hydroxy-groups.     

用混凝-微电解-催化氧化工艺预处理含拉开粉的丁腈橡胶废水

采用混凝-微电解-催化氧化工艺预处理含拉开粉的丁腈橡胶废水,通过静态和动态放大试验探讨了微电解时的pH值、反应时间、铁炭比、气水比以及催化氧化时的pH值、反应时间、氧化剂和催化剂用量等对化学需氧量、悬浮物及拉开粉去除率的影响。结果表明,在微电解反应时pH值为3～4、铁炭比为2/1(质量比)、反应时间为30min、气水比为12/1(体积比),以及催化氧化反应时pH值为5左右、催化剂质量浓度为0.75g/L、氧化剂质量浓度为5g/L、反应时间4h的条件下,处理后废水的悬浮物去除率可达到90%以上,化学需氧量去除率达到45%以上,拉开粉的去除率达到90%以上。生物化学需氧量与化学需氧量比值由0.08提高到0.16,废水可生化性得到提高,水中悬浮物得以大幅度降低,水质得到改善,为后续处理奠定了基础。