A study of oxygen absorption kinetics in ionic Cu(I) aqueous solutions

We developed the oxidation reaction of Cu(I) ion in aqueous hydrochloric solution by oxygen in a gas-lift capillary bubble column. The method of gas-liquid absorption with chemical reaction was used. Test data confirmed that the rate constant of the reaction is strongly affected by solution compositions, and that chloride ions induce an inhibition effect. The kinetical orders found are equal to 1 and 2 for oxygen and Cu(I) respectively. The influence of temperature on reaction rate constant showed the existence of a maximum value between 303 and 313K. The effect of gas-liquid of gas-liquid system on the liquid-side mass transfer coefficient k_L was also investigated.     

An indirect electrochemical process for the removal of NOx from industrial waste gases

The development of a new electrochemical process for the absorption of NOx from industrial waste gases is described. Conversion of NO was performed by an indirect outer cell process using dithionite as the redox mediator and Fe(II)EDTA as the complexing agent. The absorption process, involving complex formation with Fe(II)EDTA in the absence and presence of dithionite, was investigated using a packed bubble column. In semibatch experiments the dependence of different system parameters on the degree of NO conversion was studied: concentration of dithionite and Fe(II)EDTA, gas flow rate, oxygen content, and temperature. The reaction products in the gas phase and in the liquid phase were analyzed using gas chromatography and ion chromatography, respectively. This analysis proved that, instead of N2 or N2O, ammonia and amidosulfonic acid are the main reaction products in the solution. The kinetics and the conditions for the regeneration of dithionite by electrochemical reduction of sulfite were studied on RDE and by experiments in a divided cell. For the dithionite production a current efficiency of about 80% was found in 0.2 m Na2SO4 at pH 5.6. By combining the chemical NO absorption in a gas/liquid contactor with the electrochemical regeneration of dithionite in a divided plate and frame cell a degree of NO conversion better than 90% under continuous operation can be obtained.     

The kinetics of dissolved oxygen reaction in aqueous sodium dithionite solutions

The kinetics of the reaction between dissolved oxygen and sodium dithionite in alkaline aqueous solution was investigated in a stirred cell. For dithionite concentrations below 0.08 kmol/m³ and sodium hydroxide concentrations from 0.044 to 0.27 kmol/m³, the results show the reaction to be first order in dithionite and zero order in oxygen. The Arrhenius activation energy was determined to be 76.2 MJ/kmol in the temperature range 15 to 34°C. Addition of other electrolytes (sodium sulphate or potassium chloride) had no effect on the kinetics.     

Intensification of nitrous acid oxidation

An alternative solution to the reduction of a discharge of residual nitric oxide and nitrogen dioxide into atmosphere has been proposed. Instead of using methane or ammonia for SCR or gas absorption into alkali solutions, which are the most popular treatment methods of tail gases, now the use of powerful oxidant—ozone capable of transforming nitrous acid and nitric oxides into nitrogen of the highest oxidation level—could be employed for this purpose. As the intensive oxidation and ozonation of nitrous acid is the heterogeneous gas-liquid process, the solubility of oxygen and ozone in HNO₂/HNO₃ aqueous solution was necessary to be determined. Variations of reaction rates depending on temperature, ozone dose and nitrous and nitric acid concentrations were studied experimentally. The kinetic model of the reactions, 2HNO₂+O₂→2HNO₃ and HNO₂+O₃→O₂+HNO₃, were proposed and the kinetic parameters (rate constants and activation energies) were estimated on the basis of experimental data in semi-batch laboratory gas-liquid contactor with the liquid phase drawn from an absorption column in the nitric acid plant. The determined kinetic parameters were then used in designing and modeling of the oxidation of nitrous acid using ozone-oxygen mixture in a continuous bubble column. The model consists of mass transfer kinetic equations and material balance equations for the gas and liquid phases. The co-current flow of gas and liquid phases and the complex kinetics of chemical reaction in the liquid phase were taken into account. The variation of the following process conditions, flow rate, compositions of the gas and liquid phases, temperature, and pressure in the bubble column of different diameters and heights, were studied in numerical solutions of the proposed model.     

Oxidation kinetics of Fe(II)NTA to Fe(III)NTA by oxygen

The oxidation of aqueous solutions of Fe(II)NTA was investigated in a bubble column reactor. The rate of the oxidation reaction was found to be proportional to the partial pressure of oxygen and to have an order of 0.5 with respect to the Fe(II)NTA concentration. The overall transfer of oxygen appears to be predominantly reaction controlled for Fe(II)NTA concentrations in the order of 1 mmol l⁻¹, whereas for high concentrations (100 mmol l⁻¹) mass transfer becomes the controlling factor. Overall mass transfer coefficients and reaction rate constants were determined in the range between 25 and 60°C and for a wide range of Fe(II)NTA concentrations (5-250 mmol l⁻¹).     

Modelling Industrial Wastewater Ozonation In Bubble Contactors. 2. Scale-up From Bench To Pilot Plant

A kinetic model constituted by ozone mol balance equations both in the gas and in the water phases and a total mole balance equation has been applied to predict concentrations of dissolved ozone, C_o3, ozone partial pressure at the reactor outlet, P_(o3)0, and remaining chemical oxygen demand, COD, for the ozonation of two industrial wastewaters released from distillery and tomato processing plants.

Kinetic equations for ozone absorption rate present in the model were derived from the application of film theory to an irreversible gas-liquid reaction. Parameters involved in the model, reaction rate and mass transfer coefficients, Henry's law constant, etc., were estimated from bench-scale experiments. The model was applied to ozonation in bubble contactors of height/diameter ratio equal to that of the bench scale contactor and to a pilot plant bubble column of a height/diameter ratio about 3.6 times higher.     

Analysis of dispersion coefficient of bubble motion and velocity characteristic factor in down and upflow bubble column reactor

Dispersion coefficient of bubble motion based on velocity distribution theory has been analyzed in up and downward gas-liquid two-phase contactor. The intensity of dispersion of phase depends on motion of the dispersed phase and the characteristics of velocity distribution. In this paper the effects of operating and geometric variables on the dispersion coefficient of bubble motion and the characteristic factor of velocity distribution have been analyzed within the range of column diameter 0.10-2.5 m, superficial liquid velocity, 0.04-0.21 m/s and superficial gas velocity 0.41-3.16 mm/s. From the different developed model of longitudinal dispersion coefficient of liquid, comparison of dispersion coefficient of bubble motion and characteristic feature of velocity distribution in down and upflow two-phase contactor has been reported. Also the functionalities of dispersion coefficient of bubble motion and velocity characteristic factor have been developed with operating variables. The condition for dispersion based on velocity pattern has also been discussed in the present work. The present analysis on the dispersion coefficient of bubble motion and velocity distribution factor associated with the knowledge of the liquid phase dispersion in two-phase contactor can give insight into a further understanding and modeling of multiphase reactor in industrial applications.     

Absorption of oxygen by n-butyraldehyde

The kinetics of absorption of oxygen by n-butyraldehyde dissolved in n-butyric acid, in the range of concentrations up to 3·1 × 10^?3 gmole/cm³ (25 wt.-%), in the presence of manganese acetate, was studied in stirred cells and a bubble column. It was found that diffusion of oxygen is important. The reaction was found to be first-order in oxygen and second-order with respect to the aldehyde. The overall third-order reaction rate constant was found to be about 4 × 10⁶ (cm³/gmole)² sec^?1 at 20°. The effect of the catalysts, cobaltous acetate and (cobaltous + 4 cupric) acetates, on the specific rates of absorption of oxygen was also studied. Manganese acetate was found to be the best catalyst.     

气泡大小对反应器内氧传递系数的影响

在气液反应过程中,气泡的大小对结果往往起了决定性的作用。通过减小气泡的尺寸,可以促进气液传递,加快反应的进程。在气液搅拌式反应器上安装了一种特殊的气体分布器,通过搅拌产生离心场,从而诱导生成泰勒涡柱,使大量进入反应器的空气气泡保持在泰勒涡柱的内部。由于减少了气泡间的凝并作用,气泡尺寸减小,与对照组相比,反应器中最小的气泡尺寸减小了近50%,气泡的比表面积增加近80%。通过对不同通气流量和搅拌速度下气液反应器内氧传递系数的测量,与对照实验比较,使用特殊气体分布器的反应器中,氧的传递系数增加了10%~40%,证明这种气体分布器确实可以增加气液间氧的传递。     

高温高压浆态鼓泡床反应器中的气-液传质

The gas-liquid mass transfer of H2 and CO in a high temperature and high-pressure three-phase slurry bubble column reactor is studied. The gas-liquid volumetric mass transfer coefficients kLa are obtained by measuring the dissolution rate of H2 and CO. The influences of the main operation conditions, such as temperature, pressure,superficial gas velocity and solid concentration, are studied systematically. Two empirical correlations are proposed to predict kLa values for H2 and CO in liquid paraffln/solid particles slurry bubble column reactors.     

Study on the reaction rate of sulfite oxidation with cobalt ion catalyst

Wet limestone scrubbing is the most common flue gas desulfurization process for control of sulfur dioxide emissions from the combustion of fossil fuels, and forced oxidation is a key past of the reaction. In the present work the oxidation rate was experimentally studied by contacting pure oxygen with a sodium sulfite solution. The sulfite oxidation reaction rate was then measured photographically for various sodium sulfite and Co²⁺ concentrations. The sulfite oxidation reaction rate was affected by the mass transfer characteristics of the gas-liquid absorbers with the cobalt ion catalyst as well as the reaction kinetics. The sulfite oxidation reaction rate controlled by the reaction kinetics was first order with respect to the sulfite. When the sulfite oxidation reaction rate was controlled by the gas-liquid rate of mass transfer characteristics, the reaction was zeroth order with respect to the sulfite.     

Multistage bubble suspended-bed column reactor for hydrocarbon oxidation processes

The results of testing a bubble column reactor in the oxidation of cyclododecane by air oxygen in the presence of boric acid at a temperature of 160–165°C and atmospheric pressure are given. A characteristic feature of the multistage column reactor is a number of flow circuits organized via gas-lift pipes arranged above each other. The solid phase (catalyst) is fed at the top into the upper flow circuit and further distributed among all the flow circuits over the liquid volume. The reactor may find applications in catalytic reactions and continuous processes of dissolution, flotation, contact crystallization, and hydraulic classification.     

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.     

Determination of rate constants for the reaction between diglycolamine and carbonyl sulphide

The kinetics of the reaction between carbonyl sulphide (COS) and aqueous 2-(2-aminoethoxy) ethanol (diglycolamine or DGA) were investigated over a temperature range of 307 to 322 K and pressure range of 345–414 kPa. A gas-liquid contactor was designed to simulate a single tray in an absorption column. The contactor was operated isothermally with both the gas and liquid feeds continuous, the liquid being perfectly mixed. In the contactor, the gas was sparged through the aqueous DGA solution using a fritted plate and the froth spilled over a weir where the gas disengaged from the amine solution. Good material balance closure verified that the reactor could be used to obtain absorption rate data. The carbonyl sulphide and other components in the amine solution were analysed with a gas chromatographic (GC) technique developed as a part of this work. The GC analysis could be performed in less than 10 min and comparison of the results from the GC technique with material balance closure showed excellent agreement. The experimental data were correlated by assuming the reaction to be kinetically controlled. The observed reaction rates were significantly larger than those for the COS/H₂O system. Therefore, it was concluded that DGA had a catalytic effect on the COS hydrolysis reaction. The analysis indicated that the reaction followed a second-order rate equation: first-order in COS and first-order in DGA. Justification for assuming kinetic control of the absorption was demonstrated by doubling and tripling the stirring speed which produced no significant change in the absorption rate (mol s⁻¹). Another series of tests were carried out which showed that the absorption rate (mol s⁻¹) was proportional to the reactor volume. In addition, the activation energy was out of the range of ordinary mass transfer control.     

Kinetics of nitrous oxide decomposition over Cu-ZSM-5

The kinetics of nitrous oxide decomposition on an overexchanged Cu-ZSM-5 catalyst were measured using a gradientless reactor. Isothermal oscillations of nitrous oxide and oxygen concentrations can be observed in a broad range of experimental conditions. A transition of the catalytic activity during oscillations is accompanied by a change in the oxygen content of the catalyst and by the formation of traces of nitric oxide. The presence of excess oxygen does not significantly alter the behaviour of the catalyst whereas NO concentrations as low as 10 ppm quench the oscillations in the whole temperature range studied (375 to 450°C), maintaining steady-state operation at maximum catalytic activity. Reaction rates in this ‘ignited’ state are first order with respect to nitrous oxide concentration and not affected by either oxygen or nitric oxide. At temperatures above 400°C, the observed reaction rates are influenced by pore diffusion effects. In the region of intrinsic kinetics, the temperature dependence of the first order rate constant can be described by an activation energy of ca. 100 kJ/mol.     

Modeling of bubble column slurry reactor for reductive alkylation of p-phenylenediamine

A bubble column slurry reactor (BCSR) model has been developed for the reductive alkylation of p-phenylenediamine (PPDA) with methyl ethyl ketone (MEK) to N,N^′-di-secondary-alkyl-p-phenylenediamine (Di-amine). This particular reaction system is commercially relevant and involves a combination of parallel and consecutive reactions comprising equilibrium non-catalytic (homogeneous) and catalytic (heterogeneous) steps. The proposed model is based on the ‘mixing cell approach’. In this work the mixing cell approach has been extended by including a liquid backflow stream from all but the bottommost mixing cell. The model incorporates the contributions of gas-liquid and liquid-solid mass transfer, heat effects, and complex multistep reaction kinetics. CFD model is used to estimate the extent of backflow among mixing cells and its dependence on operating parameters. The effect of gas and liquid velocities, catalyst loading, inlet PPDA concentration, and temperature on the conversion, selectivity, global rate of hydrogenation, and temperature rise is discussed. The comparison of the current approach with the traditional mixing cell model is discussed. The BCSR model presented here will be useful to provide guidelines for designing and improving overall performance of bubble column reactors.     

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.     

Formation of fine magnetite particles by oxidation of aqueous suspensions of ferrous hydroxide

Fine magnetite particles were prepared by oxidation of aqueous ferrous hydroxide suspensions in a bubble column equipped with an internal concentric draft tube. The oxidation reaction rate could be expressed apparently as zero-order with respect to the concentration of total ferrous species and first-order with respect to the concentration of dissolved oxygen. The final particle size generally decreased with increasing reaction rate. The geometric Standard deviation of size-distribution ranged from 1.20 to 1.35 under the present experimental conditions, and increased with an increase in reaction rate.     

The Effect of Ozone Gas-Liquid Contacting Conditions in a Static Mixer on Microorganism Reduction

The effect of gas-liquid contacting conditions in a static mixer on ozone transfer efficiency and reduction of Bacillus subtilis spores was studied in an experimental ozone contactor. An empirical mathematical model was developed that related the transfer efficiency in the experimental system to the superficial liquid velocity in the mixer, the gas-liquid flow rate ratio and the height of the down-stream bubble column. Spore reduction was determined primarily by the dissolved ozone concentration-time (C_avgt_m) product in the reactive flow segment and was independent of the gas-liquid contacting conditions in the static mixer. In an integrated ozone contacting system, the static mixer should be designed to maximize ozone mass transfer while the reactive flow segment should be designed for efficient microorganism reduction.     

浆态鼓泡床反应器气液传质特性的研究进展

本文总结了有关浆态鼓泡床反应器气液传质特性的研究成果。详细地阐述了主要影响因素如系统压力、温度、气体表观气速、液体性质,固体浓度及其物性等对传质特性的影响,并对浆态鼓泡床传质模型进行了归纳介绍,最后对反应器未来的研究方向进行了预测。