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.     

Full transition from metal to ceramic by direct oxidation of metallic cobalt powder

The study deals with the direct oxidation kinetics of micronic cobalt metal particles and its simulation for the complete transition from metal to ceramic. The simulation was also experimentally verified. All the three possible interfaces, Co/CoO, CoO/Co₃O₄ and Co₃O₄/O₂ (air), have been taken into consideration for the simulation. The complete oxidation kinetics has been investigated from the thermogravimetric studies under isothermal conditions in the temperatures 973–1173 K. A quantitative interpretation based on the diffusion of Co or oxygen ions through the grown oxide layer has been proposed. The activation energy for the oxidation kinetics calculated from the Arrhenius law was 161 ± 20 kJ mol⁻¹.     

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.     

Investigation of CO Oxidation Transient Kinetics on an Oxygen Pre-covered Au(211) Stepped Surface

The desire to explain the origin(s) of the unexpected catalytic activity of oxide-supported Au nanoparticles for CO oxidation discovered by Haruta and coworkers has stimulated numerous experimental and theoretical studies of Au nanoclusters in the gas phase and on metal oxide supports, and on Au single-crystal surfaces. In order to explore further the reactivity of low-coordination Au step sites, we have performed transient kinetics studies of CO oxidation on an O-precovered, stepped Au(211) single crystal surface. We found behavior similar to that observed previously on flat Au(111) and (110) surfaces; i.e., there is no evidence in these transient kinetics for any special reactivity associated with this stepped Au surface. The CO oxidation reaction rate was highly dependent on the initial oxygen coverage, and we determined an apparent activation energy for CO oxidation of ?7.0 kJ mol^?1 for θ _O ^init  = 0.9 ML. Within the Langmuir-Hinschelwood (LH) reaction scheme, we estimate an activation energy of E _LH = 20–43 kJ mol^?1 on this surface for CO oxidation via this pathway. This is somewhat below the value of 67 kJ mol^?1 predicted by recent theoretical calculations.     

Analysis of the crosslinking process of a phenolic resin by thermal scanning rheometry

The curing reaction of a phenolic resin (resole type) carried out in the absence of an initiator was studied by thermal scanning rheometry under isothermal conditions at temperatures from 70 to 105°C. The same curing reaction was studied in the presence of an acid as a catalyst in the temperature range of 50–80°C. The gel time, which was defined by several criteria, was found to be a good parameter to determine the apparent activation energy of this process. An empirical model was used to predict the change in complex viscosity with time until the gel time was reached. If first‐order kinetics were assumed, the apparent kinetic constant of the curing reaction could be obtained. Furthermore, the effect that the addition of water and free phenol had on the curing process of this type of resin was studied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 57–65, 2002     

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.     

Oxidation reaction kinetics of Athabasca bitumen

The oxidation reaction kinetics of bitumen from Athabasca oil sands have been investigated in a flow-through fixed bed reactor using gas mixtures of various compositions. The system was modelled as an isothermal integral plug-flow reactor. The oxidation of bitumen was found to be first order with respect to oxygen concentration. Two models were examined to describe the kinetics of bitumen oxidation. In the first, the Athabasca bitumen is considered to be a single reactant and the oxidation reaction a single irreversible reaction. The activation energy for the overall reaction was found to be 80 kJ mol^?1. This model is limited to calculating the overall conversion of oxygen. Because the fraction of oxygen reacting to form carbon monoxide and carbon dioxide increases with temperature, a more sophisticated model was proposed to take this into account. The second model assumes that the bitumen is a single reactant and that the oxidation of bitumen may be described by two simultaneous, parallel reactions, one producing oxygenated hydrocarbons and water, the other producing CO and CO₂. The activation energy for the first reaction was found to be 67 kJ mol^?1, and for the second, 145 kJ mol^?1. This more sophisticated model explains the result that at higher temperatures more oxygen is consumed in the oxidation of carbon, because this reaction has a higher activation energy than the reaction leading to the production of oxygenated hydrocarbons and water. This model can also predict the composition of the product gases at various reaction conditions.     

LOW TEMPERATURE OXIDATION OF LOW RANK COALS

The low temperature oxidation of a Montana subbituminous coal was investigated using round bottom 100 ml flasks in constant temperature baths. The experiments were carried out in normal and oxygen enriched air at 30°C, 45°C and 70°C with particle sizes ranging from 4 mesh to 100 mesh. Periodic analysis of gas samples from the flasks provided the rate data. The reactivity of the as received coal was compared with that of the same coal dried (i) in high pressure steam and (ii) in hot water

A rate equation has been proposed incorporating the effects of oxygen diffusion and surface reaction. For higher oxygen concentration and smaller particle sizes, the zero order surface reaction was found to be controlling. The temperature dependency of the reaction rate was found to be well represented by the Arrhenius equation. The activation energy varied slightly under various conditions between 15 to 20 kca)/g mole

The reactivity of the hot water dried coal was found to be similar to that of the as received coal. Steam dried coal however, was found to be much less reactive.     

Kinetic modeling of CO oxidation on Pt/CeO2 in a gradientless reactor

Cerium oxide is a major additive in three-way catalysts used in emission control of automobile exhaust. Pt/CeO₂ was studied in order to better understand the role of ceria in promoting CO oxidation reaction. The kinetics of carbon monoxide oxidation on Pt/cerium oxide catalyst, was studied over the temperature range 100–170°C. Steady state kinetic measurements of CO oxidation were obtained in a computer controlled micro-CSTR reactor. Activation energies were reported to vary between 39·5 and 51·2 kJ mol⁻¹. At low concentrations of either reactant (CO, O₂) and total conversion, the catalyst exhibited multiple steady states, similar to the multiplicity behavior of Pt/Al₂O₃. The total conversion was reached at 120°C. In comparison, the total conversion at low reactant concentrations was reached at a temperature of 148°C for the alumina-supported catalyst. Langmuir–Hinshelwood mechanisms gave a good fit to the data. However, no single rate expression could effectively describe the CO oxidation data over the whole concentration in the product of the CSTR reactor. The facts gathered indicate that oxygen adsorbed on interfacial Pt/Ce sites and ceria lattice oxygen provides oxygen for CO oxidation. Cerium oxide has been found to lower CO oxidation activation energy, enhance reaction activity and tends to suppress the usual CO inhibition effect.     

Kinetics of wet oxidation of nylon 66

The kinetics of the aqueous phase oxidation of nylon 66 was studied at temperatures up to 190°C. The nylon 66, in the form of a cylindrical disc, was attached to the shaft of a variable-speed drive inside the reactor. With a rotating disc geometry, the chemical kinetics of the surface reaction can be separated from the mass transfer effects. By measuring the reaction rates at different temperatures, pressures, and disc rotational speeds, a kinetic rate expression was developed relating nylon degradation to dissolved oxygen concentration and temperature. The order of reaction with respect to dissolved oxygen concentration was 0.6, and the activation energy was 42 kcal/g-mole.     

Influence of heating rate on the pyrolysis of oil shale

The decomposition of oil shale from the Kvarntorp deposit in Sweden has been investigated using isothermal and non-isothermal methods. It was found that the heating rate during the initial non-isothermal period in the isothermal experiments had a considerable effect on the rate of devolatilization. At heating rates in the order of 10⁵°C/s the total weight loss exceeded the weight loss predicted from the volatile matter according to a proximate analysis.The effect of particle and sample size on the rate of decomposition (weight loss) was studied and found to have a significant influence at heating rates of the order of 10⁵°C/s while no effect was detected at heating rates around 200 °C/s (isothermal) or below 50°C/min (non-isothermal). The decomposition at low heating rates was completed at temperatures below 600°C and about 50 percent of the devolatilization could be described by first order kinetics with an apparent activation energy of 130 KJ/mole.At heating rates of 200°C/s (isothermal) the decomposition could also be described by simple first order kinetics but with an activation energy of 67 KJ/mole, thus indicating a different rate-determining mechanism.     

Influence of boron treatment on oxidation of carbon fiber in air

An investigation is performed to study the influence of boron treatment on carbon fiber: its oxidation behaviors, kinetics, and structure and properties at a high-temperature atmosphere in air. PAN-based carbon fiber is treated with either liquid organoborate or inorganic borate, which elevates the decomposing point above 260°C and doubles the average oxidation activation energy from about 100 kJ/mol of the untreated fiber to above 200 kJ/mol of the treated fiber, with the first order of the fiber oxidation reaction under nonisothermal conditions. The boron coating formed on the fiber surface after the treatment may cap off the specific surface active sites to function as a diffusion barrier that inhibits the oxidation, and its main structure is identified as boron oxide by means of X-ray diffraction and XPS analyses. During the process, the mechanical properties develop slightly; however, the morphology structure observed by SEM changes greatly. © 1996 John Wiley & Sons, Inc.     

Analysis of the crosslinking process of epoxy–phenolic mixtures by thermal scanning rheometry

The curing reaction of different mixtures of an epoxy resin (diglycidyl ether of bisphenol A type) and a phenolic resin (resole type) cured with different amine concentrations (triethylene tetramine) was studied with thermal scanning rheometry under isothermal conditions from 30 to 95°C. The gel time, defined by several criteria, was used to determine the apparent activation energy of the process. Moreover, with an empirical model used to predict the change in the complex viscosity versus time until the gel time was reached, and under the assumption of first‐order kinetics, the apparent rate constant and the apparent activation energy for the curing process were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 818–824, 2005     

Antioxidant Stability in Vegetable Oils Monitored by the ASTM D7545 Method

The PetroOXY method was used to evaluate the kinetics of oxidation of two edible vegetable oils, extracted from moringa and passion fruit. This method, which uses pure oxygen at 700 kPa is effective and fast and our experiments were carried out at temperatures 110–140 °C with BHA antioxidant additive concentration ranging from 0 to 500 ppm. Moringa and passion fruit oils followed first-order kinetics although, in the case of passion fruit oil, mathematical approximations in the first-order kinetic expression resulted in a final equation that could also be interpreted as deriving from zero-order kinetics. The higher stability of moringa oil was characterized by an activation enthalpy ca. 50 % higher than the one related to passion fruit oil.     

The Effect of Cobalt on the Degradation of Methyl β-D-Gluco-Pyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Abstract

The effect of Co(II) (0 to 0.25 mW CoSO₄) on the degradation of methyl β-D-glucopyranoside (MBG) at 120°C in 1.25M NaOH with 0.68 MPa oxygen pressure was studied. When the Co(II) was increased from 0.00 to 0.01 to 0.05 mM the MBG half-life decreased from 12 to 6 to 1.5 hours, reflecting approximately a 0.5 order kinetic dependence on cobalt. An oxidation-reduction cycle between Co(II) and Co(III) involving oxidation of Co(II) by oxygen and oxidation of the glucoside by Co(III), hydroxyl radical, or superoxide is proposed for the degradation. At the 0.25 mM Co(II) addition level highly adsorptive Co(OH)₂ formed prior to reaction initiation with oxygen and removed otherwise soluble cobalt from solution. This resulted in lower rates of MBG degradation than obtained even at 0.01 mM Co(II) addition. However, Co(II) solubility could be enhanced if silicate anions or polyols (including MBG) were added to the alklaine medium prior to the Co(II) addition. In reactions initially containing 0.25 mM soluble Co(II), an adsorptive precipitate, presumably CoO(OH), gradually formed after reaction initiation with oxygen. Precipitation of the Co(III) solid coincided with a rapid decline in the rate of MBG degradation. Cobalt had little effect on the products of MBG degradation.     

Oxidation Behavior of SiC Whiskers at 600–1400°C in Air

The oxidation behavior of SiC whiskers (SiC_W) with a diameter size of 50–200 nm has been investigated at 600°C–1400°C in air. Experimental results reveal that SiC_W exhibit a low oxidation rate below 1100°C while a significant larger oxidation rate after that. This can be attributed to the small diameter size of SiC_W, which determines that it is hard to form a protective SiO₂ layer thick enough to hamper the diffusion of oxygen effectively. Both nonisothermal and isothermal oxidation kinetics were studied and the apparent oxidation energy was calculated to further understand the oxidation behavior of the SiC_W.     

The Role of Mass Transfer in the Kinetics of Chemical Oxidation of Anthracine Slurry to Anthraquinone in a Batch Stirred Tank Reactor

The kinetics of chemical oxidation of anthracine powder by acidified dichromate in a batch agitated vessel stirred by a 45° four pitched blade turbine impeller was studied under different conditions. Variables studied were impeller rotation speed, solution physical properties and temperature. The rate of anthracine oxidation was found to increase with temperature according to the Arrhenius equation with an activation energy of 3.98 cal/mole. The rate of anthracine oxidation was found to increase with 0.56 power of impeller rotation speed. The value of the activation energy and the sensitivity of the rate of oxidation to stirring lend support to the diffusion‐controlled nature of the reaction. The data were correlated by the equation: Sh = 0.5 · 10^–3 Sc^0.33 · Fr^0.33 Implication of the above equation for the operation of industrial reactors was noted.     

Wet oxidation of active carbon

As a preliminary step to studies on the regeneration of active carbon, its wet oxidation has been followed in order to obtain information about the different parameters involved: agitation, temperature and pressure. The oxidation reaction takes place in the liquid phase and it does not proceed at significant rates below 200°C, even with high initial oxygen pressures. The oxidation proceeds rapidly beyond 275°C at pressures as low as 30 atm. The only detectable reaction product is carbon dioxide. Although mass transfer effects are minimized at stirring speeds higher than 400 rpm, a visible abrasion of the carbon was apparent beyond 300 rpm. Consequently, the study was carried out at around 200 rpm. Mass transfer effects had to he considered then. Estimation of the different transfer coefficients was done from the experiments and through existing correlations. In this way the kinetics could be obtained. The rate of reaction can be represented by a first order kinetic expression. Comparison of the rates has been done at fixed conversions. The intrinsic rate constant has a surprisingly low activation energy of 8.4 Kcal/mole suggesting that the oxidation reaction proceeds via a free radical mechanism. The overall rates show a maximum at conversions varying between 0.10 and 0.40. The specific surface area decreases regularly with reaction time, indicating that the reaction takes place throughout the particle.     

Temperature dependence of morphology and oxygen reduction reaction activity for carbon-supported Pd–Co electrocatalysts

In this study, we investigated the heat treatment temperature effect on the morphology and oxygen reduction reaction activity of carbon-supported Pd–Co alloy electrocatalysts. As prepared Pd–Co bimetallic nanoparticles showed a single-phase face-centered cubic disordered structure, and the mean particle size decreased with a Co content. In order to improve activity and stability, the catalysts were heat-treated in a temperature range of 300 to 700 °C. From the results of oxygen reduction reaction activity tests, the optimal heat treatment temperature was found to be 700 °C for the low Co content samples, while 300 °C was the best condition for the high Co content samples.     

Wet oxidation of glucose

Wet oxidation is used to oxidize organic substances at a controlled rate in an aqueous medium at elevated temperatures and pressures. Aqueous glucose solutions were oxidized with pure oxygen at four different temperatures in the range 176.7°C to 260.0°C, and at an oxygen pressure of 2.3 MPa. Three distinct stages of wet oxidation were found — induction, rapid oxidation, and slow oxidation. During the rapid oxidation period the reaction was assumed to be confined to a thin liquid layer next to the gas-liquid interface. The activation energy for the rapid oxidation period was estimated to be 130 ± 20 kJ/mol. Acetic acid was found to accelerate the rate of wet oxidation of glucose only slightly.