Mass transfer and kinetics study on the sulfite forced oxidation with manganese ion catalyst

Wet limestone scrubbing is the most common flue gas desulfurization process (FGD) for control of sulfur dioxide emissions from the combustion of fossil fuels. Forced oxidation, which controls the overall reaction of the sulfur dioxide absorption, is the key path of the process. Manganese which comes from the coal is one of the catalysts during the forced oxidation process. In the present work, the two-film theory was used to analyze the sulfite forced oxidation reaction with an image boundary recognition technique, and the oxidation rate was experimentally studied by contacting pure oxygen with a sodium sulfite solution. There was a critical sulfite concentration 0.328 mol/L without catalyst or at a constant catalyst concentration value. The kinetics study focused on the active energy of the reaction and the reaction constant k; furthermore, we obtained the order with respect to the sulfite and Mn²⁺ concentrations. When the Mn²⁺ catalyst concentration was kept unchanged, the sulfite oxidation reaction rate was controlled by dual film and the reaction kinetics was first order with respect to sulfite while SO₃²⁻ concentration was below 0.328 mol/L; the sulfite oxidation reaction rate was controlled by gas film only and the reaction kinetics was zero order with respect to sulfite while SO₃²⁻ concentration over 0.328 mol/L. When SO₃²⁻ concentration was kept unchanged, the sulfite oxidation reaction rate depended on gas-liquid mass transfer and the reaction kinetics was different in various stages with respect to Mn²⁺ concentrations. This work was presented at the 6 ^th Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006.     

亚硫酸盐强制氧化传递与化学反应动力学

在湿法烟气脱硫的过程中,吸收塔底部发生的反应主要是亚硫酸钙和空气或氧气之间的气液传递与化学反应过程,根据双膜理论模型,分析了该反应的吸收机理,用一种图像边界识别的方法分析亚硫酸盐强制氧化气液反应.在没有催化剂或固定钴离子催化剂浓度时,SO^2-₃存在临界浓度0.328 mol•L^-1.当SO^2-₃的浓度低于0.328 mol•L^-1时,过程为双膜控制,SO^2-₃的反应级数为1;当SO^2-₃的浓度大于0.328 mol•L^-1时,过程逐渐变为气膜控制,SO^2-₃反应级数为0.当固定SO^2-₃浓度时,催化剂钴离子的反应级数则受到气液传质的影响,分为几个阶段,且反应级数不同.     

Kinetics of oxidation of ammonium sulfite by rapid-mixing method

The kinetics of the reaction of oxygen with ammonium sulfite in aqueous solution have been studied by the rapid-mixing method of Hartridge and Roughton at 30°C. The rate of oxidation of ammonium sulfite was found to be approximately twice as low as that of sodium sulfite.The experimental findings showed that the reaction rate was zero order with respect to oxygen and three-halves order with respect to sulfite, and the promoting effect of cobalt ions was proportional to the square root of the total concentration of cobalt added to the reacting solution. The apparent activation energy for the overall oxidation was calculated to be 21·5 kcal per gmole.A reaction mechanism has been proposed and a rate expression derived is in good agreement with the experimental data.     

对二甲苯氧化过程控制步骤分析

实验测定了对二甲苯高温氧化各步反应动力学数据。结合反应器中的气液传质数据以及有关的混合时间数据,比较了反应、传质和混合速率的相对大小。结果表明,工业反应器中的混合速率远大于反应速率,反应器可以作为理想混合反应器考虑。在典型的工业条件下,对二甲苯氧化过程为液相化学反应控制,控制步骤为对甲基苯甲酸生成对羧基苯甲醛的反应步骤。     

邻二甲苯液相氧化动力学的研究

在搅拌釜（φ107×350mm）中进行邻二甲苯液相氧化动力学的研究,其结果表明,在本试验条件下（搅拌釜转速为1200rpm空釜线速≥1.5cm/s,氧化温度在130℃以下）可以消除传质影响。 本研究建立了邻二甲苯（OX）氧化的动力学方程式（在 OX的转化率<50％时适用）,为气液反应器放大提供计算氧化速度的动力学 模型。 本工作还对邻二甲苯氧化七组分的主副反应动力学进行研究,测定了不同温度下各反应的速率常数和活化能。其数值与采用鼓泡塔氧化的结果相一致,再次表明邻二甲苯氧化为串、并联一级反应。     

Mass Transfer Reaction Kinetics of β‐Isophorone Oxidation by Air in an Agitator Bubbling Reactor

The mass transfer reaction kinetics of β‐isophorone (β‐IP) oxidation reaction by air was investigated in a lab‐scale agitator bubbling reactor. This reaction can be regarded as instantaneous and there exists a critical concentration of β‐IP. When the catalyst concentration is kept unchanged, the reaction rate is only controlled by the gas film and the reaction kinetics is of zero order with respect to β‐IP when the β‐IP concentration lies over the critical concentration. The reaction rate is controlled by the dual film and the kinetics is of first order with respect to β‐IP when its concentration is below the critical concentration. Under the gas film‐controlling condition, the effect of temperature, agitator speed, and aeration on the reaction rate is evaluated. A correlation equation of gas phase volumetric mass transfer coefficients combining superficial gas velocity and agitator speed is defined.     

搅拌反应器中氧气 - 正癸烷 - 水溶液体系的气液传质实验

用亚硫酸钠氧化法测定了机械搅拌高压釜中氧气-亚硫酸钠溶液体系、氧气-正癸烷-亚硫酸钠溶液体系和氧气-正癸烷-亚硫酸钠溶液+表面活性剂体系的气液体积传质系数(k La).研究了搅拌转速、搅拌桨高度、有机相与水相体积比和表面活性剂浓度对k La的影响,得到了经验关联式.k La随有机相体积分率和表面活性剂浓度的增大而降低,随搅拌转速、搅拌桨高度与液相高度比的增大而增大.     

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.     

微细颗粒强化氧气吸收实验

引言目前,石灰石-石膏湿法烟气脱硫工艺是在燃煤电厂应用最广的烟气脱硫技术,脱硫的副产品是脱硫石膏(CaSO4.2H2O)。但在实际运行过程中由于氧化率未达到要求值,从而使得产生的石膏晶体不足,形成了亚硫酸钙和硫酸钙的混合晶体[1];另外,燃煤锅炉产生的烟气虽经除尘,但进入脱硫装置时仍含有大量粉尘颗粒[2-3]。因此,在电厂实际的脱硫过程中,发生的并不是单纯的两相     

HYDRODYNAMICS AND MASS TRANSFER IN BUBBLE COLUMNS: EFFECT OF SOLIDS

The hydrodynamics and mass transfer in a large diameter bubble column (D_c 0.305 m), specifically, the effects of gas velocity and the presence of solids on the gas holdup structure, gas-liquid interfacial area, and volumetric mass transfer coefficients in viscous as well as low viscosity solutions are studied. The sulfite oxidation technique was employed to measure the gas-liquid interfacial area. Volumetric mass transfer coefficients were measured using a chemical method (sulfite oxidation) as well as physical absorption of oxygen from air, and the overall gas holdups were measured using the hydrostatic head technique. The effect of solids on the gas holdup structure was examined using the dynamic gas disengagement method. With the addition of polystyrene particles, the gas-liquid interfacial area decreased for low viscosity systems, whereas it increased for viscous systems. This was shown to be due to the effect of solids on bubble coalescence. The wettability characteristics of solid surfaces in the presence of different liquids have been suggested as the reason for the effect of solids on coalescence. Oil shale slurries presented a special case because of the mineral dissolution effect.     

亚硫酸铵的氧化反应动力学研究

利用鼓泡反应装置,对亚硫酸铵氧化过程各影响因素进行了研究。通过改变pH、亚硫酸铵浓度、空气流量及温度,研究了亚硫酸铵的氧化反应动力学。实验结果表明,空气流量低于380 L/h时,反应速率随流量的增大而增加;pH为5.5左右时,氧化速度最快;高浓度(≥3 mol/L)的亚硫酸铵不能被迅速完全地直接氧化成硫酸铵。     

Study on the characteristics of micro-interface intensified oxidation of ammonium sulfite

The process intensification of interfacial area and reaction conditions in multi-phase systems are important issues in industrially scaled reactors. In order to investigate the intensifying effect of micro-interface system on gas-liquid mass transfer and reaction rate, the ammonium sulfite oxidation was selected as the research object. A systematic air forced oxidation experiment was carried out through the micro-interface intensification reactor (MIR) and the traditional bubble column reactor (BCR) under the same experiment platform and operating conditions. The bubble size distribution and overall gas holdup were measured by high-speed camera technology and differential pressure measurement, respectively. The experimental results showed that MIR obtained higher gas holdup because of the micro-interface structure, the interfacial area was increased by more than 10 times, the reaction rate increased by 56.8% averagely compared with BCR. The experimental conclusions provide certain data support for the industrial application of the multiphase reaction system of the micro-interface intensification reactor.     

亚硫酸铵微界面强化氧化特性研究

以亚硫酸铵水溶液的空气氧化为研究对象，考察了微界面强化对该体系传质与氧化过程的影响。在同一实验平台和操作工况下，对微界面强化与传统鼓泡塔氧化过程的传质和反应性能进行了实验研究。利用高速摄像与压差测量技术，分别对反应过程的空气气泡分布与气含率变化进行了测定。结果表明，相较于传统鼓泡塔空气氧化反应器，微界面强化氧化反应器以微界面体系取代了传统毫-厘米级宏界面，在不同盐离子浓度与氧化气量工况下均表现出了良好的强化效能。在微界面体系强化下，亚硫酸铵氧化过程气含率大幅提升，相界面积增加十余倍，反应速率平均提升56.8%，实验结论为微界面强化反应器的多相反应体系工业应用提供了一定的数据支撑。     

HYDRODYNAMICS AND MASS TRANSFER IN BUBBLE COLUMNS: EFFECT OF SOLIDS

The hydrodynamics and mass transfer in a large diameter bubble column (D_c 0.305 m), specifically, the effects of gas velocity and the presence of solids on the gas holdup structure, gas-liquid interfacial area, and volumetric mass transfer coefficients in viscous as well as low viscosity solutions are studied. The sulfite oxidation technique was employed to measure the gas-liquid interfacial area. Volumetric mass transfer coefficients were measured using a chemical method (sulfite oxidation) as well as physical absorption of oxygen from air, and the overall gas holdups were measured using the hydrostatic head technique. The effect of solids on the gas holdup structure was examined using the dynamic gas disengagement method. With the addition of polystyrene particles, the gas-liquid interfacial area decreased for low viscosity systems, whereas it increased for viscous systems. This was shown to be due to the effect of solids on bubble coalescence. The wettability characteristics of solid surfaces in the presence of different liquids have been suggested as the reason for the effect of solids on coalescence. Oil shale slurries presented a special case because of the mineral dissolution effect.     

OXIDATION OF SULFUR DIOXIDE IN DIFFERENT TYPES OF THREE PHASE REACTORS

Five different types of three-phase reactors are compared with each other by using oxidation of sulfur dioxide on activated carbon. The kinetic measurements were carried out by changing concentrations of sulfur dioxide from 0.04 to 0.17% (volume) and those of oxygen from 2 to 21%. The reaction rate was 0.2 order with respect to sulfur dioxide and 0.5 order with respect to oxygen. The catalytic effectiveness factor and intraparticle diffusivity were evaluated by changing particle sizes of activated carbon from 0.03 to 1.6 mm. Resistances of gas-liquid, liquid-solid mass transfer and intraparticle diffusion were estimated for individual reactors. The optimum reactor was dependent on operating conditions such as gas flow rates, rotating speeds and particle sizes.     

Microinterface intensification in hydrogenation and air oxidation processes

Hydrogenations and air oxidations usually have low apparent reaction rate, generally controlled by mass transfer rate, and widely exist in the modern chemical manufacturing process. The key to increase the mass transfer rate is the reduction of the liquid film resistance 1/k_La. In this work, the original concept of microinterface intensification for mass transfer and then for these reactions has been proposed. We derived the regulation model and set up the mathematical calculation method of micron-scale gas-liquid interface structure on mass transfer and reaction, designed the mechanical energy exchange device that can produce gas-liquid microinterface system on a large scale, and established the OMIS system which is able on line to measure the diameter and distribution of millions of microbubbles, interface area a and mass transfer film thickness δ_M, as well as developed a series of microinterface intensified reactor systems (MIRs) for the applications of hydrogenation and air oxidation processes. It is believed that this research will provide an up-to-date development for the intensification of hydrogenation and air oxidation reactions.     

己二酸氨化制己二腈的宏观动力学

己二酸氨化法是工业上生产己二腈的重要方法之一,其中和反应步骤受气液相传质影响很大。采用体积为1 L的半间歇式反应釜,对己二酸中和反应的宏观动力学进行了研究。在磷酸质量分数为0.2%、搅拌速率为1800 r·min^-1、氨气流量为600 L·h^-1的条件下,实验考察了210～260℃范围内温度对己二酸浓度随时间变化的影响。由实验数据拟合结果表明:在250℃己二酸浓度大于0.1 mol·L^-1时为传质控制阶段,中和反应对于己二酸为一级,反应活化能为42.9 kJ·mol^-1;在250℃己二酸浓度小于0.1 mol·L^-1时为反应控制阶段,中和反应对于己二酸为二级,反应活化能为52.7 kJ·mol^-1。模型计算值与实验值相吻合,并结合理论模型得出对己二酸的本征反应级数为二级。保持总压(略大于常压)、温度260℃、搅拌速率1800 r·min^-1和磷酸质量分数0.2%保持不变,在氨气流量为200～600 L·h^-1的范围内考察了氨气分压对己二酸浓度随时间变化的影响,动力学拟合结果表明对氨气分压的本征反应级数为一级。     

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions: A kinetic study

The oxidation of Cu(I) by oxygen gas in concentrated NaCl solutions was studied in a standard stirred reactor. Each test was carried out at constant pH and under stable hydrodynamic conditions. The effect of stirring speed, solution volume, temperature, pH, oxygen partial pressure, chloride and copper ion concentration of the solution were evaluated.The oxidation of Cu(I) followed linear kinetics up to 85% of the copper ions in the cupric state. The experimental results were interpreted by using the film theory of mass transfer with chemical reaction. In the linear range, the chemical reaction was found to be first order with respect to oxygen concentration. The kinetic constant is given. The flux equation was specific of a fast reaction regime and the overall reaction rate was independent of the mass transfer coefficient k_L up to a k_L-value of about 10^?2 cm/sec. A parallel study of the oxidation of SO₃^2? by oxygen gas was carried out in the same reactor. The effects of stirring speed and solution volume were similar for both systems.     

上流式反应器气液相间传质特性的实验研究

上流式反应器设置在固定床渣油加氢反应器前有利于提高渣油原料适用性,延长装置运行时间。实验研究了上流式反应器气液相间传质,采用五齿柱形氧化铝催化剂模拟工业催化剂颗粒,水溶液模拟渣油,空气模拟氢气,采用无氧水物理吸收和亚硫酸钠化学吸收的方法,测定了在高气液比的条件下上流式反应器床层气液相间传质特性实验。考察了表观气速、表观液速、填料粒径、内构件、催化剂级配和床层高径比对液相体积传质系数和气液相界比表面积的影响规律。实验数据表明,液相体积传质系数随着气、液速的增大而增大;随填料颗粒增大而减小;在床层内安装合适的内构件或增大反应器高径比,能够促进气液相间传质。基于实验数据拟合了适合上流式反应器液相体积传质系数和气液相界比表面积的经验关联式,拟合误差最大分别为12%和24%;表明所建气液相间传质的经验关联式能更好地预测上流式反应器中的气液相间传质特性。     

西南稀土矿黑色风化矿泥还原浸锰的动力学

对西南稀土矿黑色风化矿泥进行了亚硫酸钠还原浸锰动力学研究,考察了浸出反应温度、矿石粒度对浸出速率的影响,求出了表观活化能为11．0kJ／mol．其浸出过程可用缩核模型描述,属于内扩散控制,其动力学方程为：