Catalytic oxidation of sulphite in diluted aqueous solutions

The rate of reaction of dissolved oxygen and sulphite ions in diluted aqueous solutions, which has industrial importance in abatement of air pollution by sulphur dioxide, was investigated in homogeneous and in heterogeneous systems. Cobaltous sulphate was used as a catalyst.The rate of sulphite oxidation was found to be zero order with respect to oxygen and three-halves order with respect to sulphite. The influence of the catalyst concentration was found to follow a square root dependence. The reaction rate constant increased with pH. The heterogeneous conditions resulted in a reaction rate that was about one order of magnitude lower than that under homogeneous conditions. This difference indicates an induction period of the sulphite oxidation.     

Absorption of oxygen by aqueous sodium sulphite solutions

New data have been reported on the absorption of oxygen by aqueous sodium sulphite solutions with cobalt sulphate as catalyst at 30°C. It is observed that the absorption rate increases up to a critical sulphite concentration beyond which the absorption rate becomes constant and this critical concentration varies with the catalyst concentration. The order of reaction with respect to sulphite and oxygen in the constant absorption rate regime was found to be zero and two respectively. The absorption rate is affected by the total ionic strength (sulphite and sulphate) in addition to the effect of pH and catalyst concentraion. The reported data were also analysed to ascertain the effect of temperature and a relationship has been proposed for prediction of the second order reaction rate constant.     

The kinetics of oxidation of sodium sulphite

The kinetics of the reaction of oxygen with sodium sulphite in aqueous solution without and with a catalyst of cobaltous sulphate have been studied by a flow thermal method. The rate of reaction of oxygen and sodium sulphite was found to be first-order with respect to oxygen and variable order with respect to sulphite, and the promoting effect of cobaltous catalyst was proportional to its concentration. A reaction mechanism has been proposed and a rate expression derived which is in good agreement with the experimental data.     

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.     

Efficient mineralization of sugar industry wastewater by catalytic wet air oxidation as an eco-friendly method and its kinetic modelling

In this study, catalytic wet air oxidation using lanthanum cobalt oxide (LaCoO₃) as catalyst was employed for the efficient treatment of synthetic sugar industry wastewater in a single process. A parametric study was performed to determine the optimum conditions. The results showed that reaction temperature and theoretical air percentage were the most effective parameters. Sugar derivatives were almost completely destroyed at the optimum conditions and total organic carbon (TOC) and chemical oxygen demand (COD) removals were determined as 91% and 87%, respectively, indicating a high mineralization degree, which was the main goal of advanced oxidation. The reaction kinetics were investigated by pseudo-homogeneous and heterogeneous models based on two different parameters: sucrose and TOC concentration. The degree of fit showed that the reaction order was determined as two for the pseudo-homogeneous approach. According to the surface concentration calculations for heterogeneous models, the presence of mass transfer limitations was only observed for oxygen as gas reactant. All heterogeneous models also fitted the reaction rate data accurately, but the Mars–van Krevelen was the selected model for sucrose and TOC oxidation with the best fit.     

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.     

Phase Transfer Catalysis:Oxidation of 2-Methyl-1-butanol

abstract In liquid-liquid systems, the substrates in the liquids are inaccessible to each other for the reaction. By adding a smal quantity of phase transfer catalyst, the reaction can be made accessib...     

The oxidation of aqueous sodium sulphite solutions

In this paper new experimental work on the kinetics of the absorption of oxygen in an aqueous solution of sodium sulphite with cobaltous sulphate as a catalyst, has been presented and compared with already published data. It is shown that the reaction of oxygen with sodium sulphite is zero order in sulphite, first order in cobalt and second order in oxygen for 2 × 10⁴ N/m² <p_O2 < 10⁵ N/m², 150°C <T < 60°C, 3 × 10^?6 kmol/m³ <c_Co⁺⁺ < 3 × 10^?3 kmol/m 7.50 < pH < 8.50 and 0.4 kmol/m² <c_SO2-- < 0.8 kmol/m³. The reaction rate constant can be varied by more than two decades by changing the cobalt concentration, pH and temperature.The specific interfacial areas, a, and mass transfer coefficients, k_L, measured by DeWaal and Beek [14, 15] using an incorrect kinetic model of this reaction, are reinterpreted with the results of the present kinetic investigation. It is shown that their values of a and k_L are a factor 2.2 too low and too high, respectively, but that their values of k_La are correct.     

乙醇在Pt/ZSM-5上催化氧化动力学

在内径为4 mm的石英管燃烧器中进行了富氧条件下乙醇在Pt/ZSM-5上的催化深度氧化动力学实验,反应温度控制在428 K以下,建立了Power-rate law模型和Langmuir-Hinshelwood模型来表征乙醇的低温深度氧化反应,Power-rate law模型和Langmuir-Hinshelwood模型的活化能分别为95.96和103.72 kJ·mol^-1,乙醇和氧气的反应级数分别为0.38和1.38。Langmuir-Hinshelwood模型中,乙醇的吸附常数比氧气的吸附常数大,说明乙醇在催化剂表面的吸附能力比氧气强,提高氧气的浓度比提高乙醇的浓度更有利于提高反应速率,这一点同样反映在氧气的反应级数比乙醇的反应级数大。     

Oxidative dehydrogenation of n-butane on V/MgO catalysts—kinetic study in anaerobic conditions

The kinetics of the oxidative dehydrogenation of butane on a V/MgO catalyst has been studied under anaerobic conditions. In these conditions the oxygen from the catalyst lattice is consumed by the reaction, and the oxidation degree of the catalyst changes during the experiment. A kinetic model is proposed in which each reaction rate is related with the oxidation degree of the catalyst. The whole kinetic model is useful for the modelling of reactors where the catalyst operates in non-steady state, i.e. where the oxidation degree of the catalyst changes with time. It has also been found that whereas the main contribution to the oxidative dehydrogenation reaction comes from the lattice oxygen, there is also a non-selective contribution from weakly adsorbed oxygen.     

环己烯分子氧氧化多相催化剂研究进展

根据催化剂主组分的不同,综述了国内外环己烯分子氧氧化多相催化剂的研究进展;主要介绍了钴系、锰系、铁系及镍系催化剂在环己烯分子氧氧化中的应用及其优缺点.指出负载型纳米金催化剂与传统的钴、锰催化剂相结合制备双活性中心催化剂在环己烯分子氧氧化中有较好的应用前景.     

Aerobic Oxidation of Alcohols under Mild Conditions Catalyzed by Novel Polymer‐Incarcerated,Carbon‐Stabilized Gold Nanoclusters

Polymer‐incarcerated, carbon‐stabilized gold nanoclusters were found to be highly active in heterogeneous catalysis for the oxidation of secondary alcohols using molecular oxygen in aqueous medium. After optimization of catalyst preparation methods, highly loaded and highly effective catalysts were obtained, and a broad range of secondary alcohols could be oxidized by using these catalysts under mild conditions. The catalysts could be recovered and reused several times without significant loss of activity. Moreover, kinetics of the oxidation reaction with (±)‐1‐phenylethanol was investigated.     

KINETIC MODELS FOR LIQUID-PHASE CATALYTIC OXIDATION OF TOLUENE TO BENZOIC ACID WITH PURE OXYGEN

The liquid phase oxidation of toluene to benzoic acid by pure oxygen has been performed in a bubble reactor by using cobalt acetate tetrahydrate as catalyst. The influence of the oxygen partial pressures on the reaction kinetics were first investigated, and the results showed that the influence was neglectable in the high oxygen pressure range (>0.5 MPa) under 155°C. Thereby, the reaction rates in the oxidation using pure oxygen are independent of the oxygen partial pressure and expressed as the first order to liquid reactants. Based on a kinetic scheme that involves both benzyl alcohol and benzaldehyde, the kinetic models can well describe the reaction process. Furthermore, the results indicated that the production of benzyl alcohol is much slower than its consumption to form benzaldehyde and the scheme can be further simplified to a kinetic equation, which involves only benzaldehyde as intermediate. The simplified reaction scheme also well describes the reaction, and, thus, the derived kinetic models agree well with the experimental data. The reaction constants follow the Arrhenius law. The estimated activation energies are in the range from 92.63 kJ·mol^?1 to 67.81 kJ·mol^?1.     

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.     

Investigation of the Reduction/Oxidation Behavior of Cobalt Supported on Nano-ceria

The oxidation and reduction behavior of cobalt catalysts supported on nano-ceria (5–8 nm) was investigated under hydrogen, oxygen and water atmospheres. A novel quantitative isothermal reduction (QIR) technique was introduced to analyze the kinetics and activation barrier of Co reduction. CoO to Co reduction was found to be of first order in the 250–350 °C temperature range. Temperature programmed reduction and oxidation experiments were conducted and the Kissinger method was used to obtain apparent activation energies for reduction and oxidation with O₂. The apparent activation energy for CoO reduction was found to agree with that obtained from the QIR technique. Re-oxidation of Co metal was found to have a slightly lower activation energy barrier than the reduction. The reduction and oxidation behavior was further investigated with in situ XANES where the reaction order for reduction was observed to change at 450 °C. The pre-reduced samples were seen to re-oxidize under a water atmosphere, where the oxidation followed first order kinetics. Re-oxidation by water yielded a higher activation energy when compared to re-oxidation under oxygen.     

Factors affecting the kinetics of the heterogeneous oxidation of ammonium sulfite

Absorption of oxygen into 0.09 – 0.7 M solutions of ammonium sulfite was measured by utilizing a stirred cell. The concentration ranges of the cobalt sulfate catalyst was 5.5 × 10^?5 – 4.7 × 10^?3 M and that of oxygen in the gas phase 21 – 100%. The theory of absorption with fast pseudo-nth order reaction was used to find the order of intrinsic rate of reaction with respect to reactants and the catalyst. Above a critical sulfite concentration the order in sulfite is zero, in O₂ is 0.4 – 1, and in CoSO₄ is 1. Under those conditions a proposed reaction mechanism yields orders of zero, 1, and 1, respectively. Below the critical point the order in sulfite is 2, indicating that another reaction mechanism is applicable. Although an increase of the ionic strength enhances the reaction rate slightly, an increase of pH from 7.6 to 8.5 causes a 1.4 fold increase. Under oxidative conditions deactivation of the catalyst and insoluble precipitate formation is observed.     

Kinetics of absorption of oxygen in aqueous solutions: (1) acidic chromous chloride, (2) acidic titanous chloride and (3) ammoniacal cuprous chloride

The kinetics of absorption of oxygen in aqueous solutions of acidic chromous chloride and ammoniacal cuprous chloride were studied in a stirred cell. Both these reactions were found to be very fast and the theory of gas absorption accompanied by fast pseudo-m^th order reaction was used to analyse the results. The kinetics of absorption of oxygen in aqueous acidic solutions of titanous chloride were investigated in a bubble column where the reaction was found to be free from diffusional resistance.The reaction between oxygen and chromous chloride was found to be first order with respect to oxygen and second order with respect to chromous ion. The value of the third order rate constant for 2·0 M HCl solution was found to be 2·7 × 10¹² (cm³/g mole)² sec^?1 at 30°C.The oxidation of titanous chloride was observed to be zero order with respect to titanous ion and first order with respect to oxygen. The value of the first order rate constant was found to be 8·6 × 10^?3 sec^?1. It has been suggested that in this case hydrolysis precedes the oxidation and it is likely that the reaction of oxygen with the hydrolysed product is the rate controlling step.The absorption of oxygen in aqueous ammoniacal cuprous chloride was found to be third order; first order with respect to each species, namely Cu⁺, oxygen and free ammonia. The value of the third order rate constant was found to be 7·5 × 10¹⁰ (cm³/g mole)² sec^?1. The higher value of the rate constant compared to that for oxidation of acidic solutions of curpous chloride indicates that the presence of a complexing agent such as ammonia increases the rate of absorption of oxygen substantially.     

Some kinetic aspects of unsteady-state partial oxidation reactions. Dynamic processes on metal oxide surfaces

It is shown that steady-state kinetic data do not allow the discrimination between the redox and associated mechanisms of the partial oxidation reactions. A discrimination between these mechanisms was performed using transient experiments. The obtained rate expressions are in agreement with experimental kinetic data for catalytic partial oxidation of o-xylene.

An influence of the conjugate oxidation of a catalyst surface on dynamics and kinetics of the heterogeneous catalytic oxidative reactions is considered. Computing simulation of methane oxidative coupling of methane reaction at lowered temperature and elevated pressure has been performed. It showed that the reaction order with respect to oxygen exceeding unity is consistent with the chain branching mechanism of the reaction in the presence of TiSi₂ and TiB₂ and showed the important role of the branching chain cycles in the low-temperature OCM reaction at elevated pressure.     

A Mechanistic Study on Alcohol Oxidations with Oxygen Catalysed by TPAP‐Doped Ormosils in Supercritical Carbon Dioxide

The heterogeneous oxidation of various alcohols with oxygen catalysed by TPAP‐doped ormosils in scCO₂ at 75 °C and 22.0 MPa has been studied in detail. Sol‐gel segregation of TPAP into the inner porosity of an organically modified silica (ormosil) xerogel along with the use of a reaction medium which does not dissolve the catalyst, prevents aggregation of oxidation‐inactive ruthenium derivatives without the need of chemical tethering. Thus, at least 140 TONs may be obtained in the oxidation of primary alcohols with the formation of aldehydes as sole reaction products. Investigation of the oxidation mechanism shows that the catalytic process exhibits a first‐order dependence on the amount of catalyst, a fractional order on the alcohol concentration and a negative order for oxygen pressures higher than 0.2 bar. Evidence is presented for an associative oxidation mechanism simultaneously involving TPAP, organic substrate and oxygen.