Kinetics of heterogeneous oxidation of ammonium sulphite

The heterogeneous oxidation of ammonium sulphite was investigated with cobalt sulphate catalyst at 30°C. For a wide range of concentrations the reaction was found to be nearly first order in oxygen and zero order in sulphite. These kinetics contrast with the results of homogeneous experiments which indicate that the reaction is zero order in oxygen and three-halves order in sulphite. The catalytic effect of cobalt ions was found to be proportional to the square root of the total concentration of cobalt. The apparent activation energy for the overall oxidation was calculated to be 13 kcal/g mol. It is concluded that the kinetics in the heterogeneous system are determined by the catalyst regeneration reaction which is diffusion controlled.     

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.     

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.     

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...     

Hydration of propylene oxide using ion-exchange resin catalyst in a slurry reactor

Kinetics of hydration of propylene oxide using an ion-exchange resin catalyst in a slurry reactor was studied. The kinetics of homogeneous, uncatalyzed reaction was studied separately and used to obtain heterogeneous reaction kinetics. The homogeneous reaction was found to be 0.43 order with respect to propylene oxide concentration. The heterogeneous reaction was found to have intraparticle diffusional resistance under certain conditions. The intrinsic kinetic parameters and effective diffusivity were obtained from these data. The heterogeneous reaction was found to be 0.55 order with respect to propylene oxide concentration. The activation energies obtained for homogeneous and heterogeneous reactions were 51.5 and 53.4 kJ/mol, respectively. A theoretical model incorporating all the mass transfer resistances has been proposed.     

Catalytic wet oxidation of p-coumaric acid: Partial oxidation intermediates, reaction pathways and catalyst leaching

The catalytic oxidation of p-coumaric acid, a compound representative of the polyphenolic fraction typically found in olive processing and wine-distillery wastewaters, has been investigated using various homogeneous and heterogeneous catalysts. Experiments have been performed with homogeneous Fe²⁺, Cu²⁺, Zn²⁺ and Co²⁺ ions at pH = 1, and with metal oxide catalysts in suspension at pH 3.5, 7 and 12. Additional uncatalyzed experiments have been performed and the results are compared to those of the catalyzed runs. The temperature was 403 K and the oxygen partial pressure was 2.8 MPa in all runs. The distribution of the reaction intermediates was determined, using HPLC and GCMS as the main analytical techniques, and reaction pathways are speculated. It was found that the use of catalysts could increase the rate of destruction of p-coumaric acid compared to the uncatalyzed reaction, while the distribution of the intermediate compounds was strongly dependent on the pH of the solution. A CuO·ZnOAl₂O₃ heterogeneous catalyst was found to be effective for the oxidation of p-coumaric acid although leaching of dissolved metals to the solution was found to occur. The stability of the heterogeneous catalysts was investigated by measuring the extent of metal leaching into the solution. The results are discussed with respect to the impact of various conditions (catalyst, pH) on the oxidation of p-coumaric acid and compared to those of the uncatalyzed reaction, studied in previous work.     

OXIDATION OF GLUCOSE ON SUSPENDED PT/C: REACTION KINETICS AND ABSORPTION STUDIES

In search of a suitable model reaction system for studying hydrodynamic properties of slurry reactors under reactive conditions, the oxidation of glucose on a suspended Pt/C catalyst was investigated. In addition to homogeneous kinetic measurements, gas absorption experiments in a stirred cell with a plane interface were also carried out at 25 to 45^°C using finely powdered catalyst particles. It was found that the oxygen consumption rale followed first order kinetics only at the very beginning of the reaction. If the total amount of reacted oxygen was considerably more than that of the initial saturation value (i.e. kinetic runs repeated after some time of aeration under vigorous stirring or lengthy gas absorption experiments), the order with respect to oxygen was ½ Furthermore, the half order rate constant dropped to about ½ to ¼ of its initial value and was constant only after an amount of about 1.5 x 10^?2mol O₂/g catalyst was reacted. A new plot is also proposed which permits the simultaneous determination of the volumetric mass transfer coefficients and the rate constants for a half order reaction from gas absorption experiments at various catalyst concentrations. The rate constants and the k_La values which were obtained from completely different methods were in reasonable agreement.     

环己烷绿色氧化合成环己醇/环己酮(KA油)催化剂及机理研究进展

环己烷绿色氧化合成环己醇/酮(KA油)一直是饱和C—H氧化领域的研究热点。本文综述了近十年来过氧化氢环己烷氧化和分子氧液相环己烷氧化的催化研究情况,指出过氧化氢环己烷氧化反应虽然条件温和、环己烷转化率和KA油选择性高,但活性较高的反应体系一般为包含昂贵配合物、酸、溶剂和氧化剂的复杂均相体系,不利于产物和催化剂分离,同时过氧化氢利用率较低,氧化剂成本高。液相分子氧环己烷氧化采用多相催化剂,操作简单,其中金和纳米氧化物有望成为潜在的工业催化剂。对环己烷氧化机理成果进行分析,指出除了金属卟啉的氧异裂非自由基机理,环己烷氧化按自由基机理进行,为自催化反应,但催化剂可促进活性自由基产生,活化C—H键,提高反应速率。最后指出开发有潜力的环己烷氧化多相催化剂和探索反应机理是今后的研究方向。     

Liquid phase synthesis of methyl tert-butyl ether catalyzed by ion exchange resin

Synthesis of methyl tertiary butyl ether (MTBE) from methanol and isobutene was studied using macroporous cation exchange resin, Amberlyst 15 in the hydrogen form, as a catalyst in the temperature range of 313-328 K. The reaction was carried out in a batch reactor at a pressure of one atmosphere in the liquid phase. A high degree of agitation was maintained in order to eliminate film diffusion resistance. The effect of catalyst loading, catalyst particle size and reaction temperature on reaction rate were studied. The reaction rate increased with increase in catalyst concentration and reaction temperature. Resin particle size had virtually no effect on the rate under the experimental conditions. The reaction rate data were analysed using homogeneous kinetics and heterogeneous models based upon Langmuir-Hinshelwood rate expressions. The apparent activation energies using homogeneous and heterogeneous models were determined and found as 79.0 kJ/mol and 76.7 kJ/mol respectively.     

Heterogeneous kinetics of oxidation of alcohols: PTC techniques

2‐ethyl‐1‐hexanol, n‐heptanol, and n‐hexanol oxidation by potassium permanganate was carried out in a baffled stirred reactor under heterogeneous conditions using phase transfer techniques. Tricaprylylmethylammonium chloride (Aliquat 336) was employed as the phase transfer catalyst. Kinetics of the oxidation was investigated. The rate constants were determined by varying the concentration of the catalyst, the concentration of alcohols and temperature. The rate constants agree well with those obtained under homogeneous conditions for all the three alcohols. The variation in the values under heterogeneous conditions were found to be less than 6 %.     

Partial oxidation of methane catalyzed by YBa2Cu3Ox in a solid state electrochemical reactor

The catalytic oxidation of methane was studied between 840 and 1110 K on a YBa₂Cu₃O* mixed-conducting electrode deposited on an yttria stabilized zirconia solid electrolyte. The lattice oxygen supplied electrochermically to the catalyst surface actively participated in the oxidation reaction, with CO as the major product, and CO₂, CH₃OH and HCHO as the minor products. The reaction rate was found to be of first order with respect to methane. The rate constant depended strongly on the electrochemically imposed bias. Under DC bias condition, the reaction rate was enhanced by as much as two orders of magnitude over that observed under open-circuit conditions. An Eley-Rideal mechanism for the interaction of CH₄ with surface oxygen is proposed as the rate-determining step.     

Catalytic Liquid Phase Oxidation of Toluene to Benzoic Acid

The production of benzoic acid from toluene in the liquid phase with pure oxygen was studied. Investigations have been carried out with a view to determining the most suitable reaction conditions with respect to operating variables including oxygen flow rate, reaction temperature, batch time and catalyst loading. In a series of batch experiments carried out at 4 atm, the optimum values of mole ratio of oxygen to toluene, temperature, reaction time, and catalyst loading were found to be 2, 157 °C, 2 h and 0.57 g/L, respectively. In addition, a kinetic study was carried out by taking into consideration the optimum reaction conditions. The model dependent on the formation of benzyl radical was found to be feasible for describing the catalytic oxidation of toluene to benzoic acid in the liquid phase. The activation energy was determined as 40 kJ/mol.     

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.     

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.     

The contribution of homogeneous and non-oxidative side reactions in the performance of vanadyl pyrophosphate,catalyst for the oxidation of n-butane to maleic anhydride,under hydrocarbon-rich conditions

The reactivity of vanadyl pyrophosphate, catalyst for the selective oxidation of n-butane to maleic anhydride, was examined under n-butane-rich conditions, simulating a feed in which oxygen is the limiting reactant, and a process in which the unconverted n-butane is recycled. A lower selectivity to maleic anhydride was found with respect to the hydrocarbon-lean conditions, due to the higher selectivity to carbon oxides and to the formation of C₈ by-products: tetrahydrophthalic and phthalic anhydrides. The latter compounds formed by a consecutive reaction of maleic anhydride with the unsaturated C₄ intermediates. This occurred under conditions of total oxygen conversion, due to the decreased catalyst oxidizing property. A relevant contribution of radicalic, homogeneous reactions was also observed, which mainly led to the formation of carbon oxides and olefins. This contribution decreased in the presence of the catalyst, which acted as a radical scavenger, but nevertheless remained important at temperatures higher than 400 °C. When conditions were used under which the conversion of oxygen was not total, olefins generated in the gas phase reacted at the catalyst surface yielding maleic anhydride. This homogeneously initiated heterogeneous process led to an unusual effect, of a relevant increase of maleic anhydride yield over 400 °C.     

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.     

Regeneration of silica-alumina catalyst particles

The oxidation of carbon on a silica-alumina catalyst has been investigated in the temperature range 420–544°c under differential reactor conditions. The reaction was first order in oxygen but the order with respect to the deposited carbon could be interpreted as either a first-order or surface reaction process. However, a statistical analysis and mechanistic considerations suggest that the surface reaction mechanism is more probable.     

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.     

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。     

Kinetics of fish meal oxidation

A mathematical model has been developed for the oxidation kinetics of fish meal, based on assumptions of the theory of gas liquid reactions and the kinetics of homogeneous oxidation reactions. This foresees that if diffusional control exists for the oxygen, the observed reaction will be of the first order with respect to this component. The specific rate constant for the reaction will be a function of the interfacial area. The performance of the model was tested experimentally.