An oxyluminescence investigation of the auto-oxidation of nylon 66

The kinetics of the thermal oxidation of stabilised and unstabilised nylon 66 fibres and films have been studied by photon counting oxyluminescence methods from 50°C to 150°C. The activation energies for initiation (E₁), propagation (E₃) and termination (E₅) over this temperature range are: E₁ = 16 kcal mol^?1, E₃ = 17·5 kcal mol^?1 and E₅ ≈ 12 kcal mol^?1. The extent of orientation of the polymer does not change the nature of the oxyluminescence curve or E₃ and E₅ above 110°C.Significant losses of critical mechanical properties of the fibres occur in the induction period at 100°C and non-stationary kinetics are described to enable this region to be studied by oxyluminescence. The oxidation rate in the induction period and the limiting rate region in air is one-third the rate in oxygen at atmospheric pressure. Non-stationary methods show that alkyl radical reactions are competitive with alkyl peroxy radical formation in air over the temperature range 100°C to 140°C. This affects the course of the oxidation reaction and the stabiliser efficiency and explains the observation of unsaturated oxidation products by phosphorescence spectroscopy.     

Study on dynamics characteristics of wet air oxidation of non-ionic surfactants

Wet air oxidation is an effective method to deal with highly concentrated nondegradable emulsification wastewater which contains non-ionic surfactants. This article illustrates our investigation on dynamic characteristics of wet air oxidation of typical non-ionic surfactants like polyether, phenol ether and widely used alcohol ether. The experimental results indicated that the oxidation rate of polyether, phenol ether and alcohol ether obviously ascended as the temperature rose. A good oxidation effect was available at 240℃. The TOC removal rate could reach 88.0%, 94% and 91.5%, after 125 min reaction. Alcohol ether was prone to an easier oxidation compared with polyether and phenol ether when the temperature was 220℃ or below. The oxidation rate of alcohol ether was higher than that of polyether at 160℃, while the oxidation rate of polyether was higher than that of phenol ether between 180℃ and 220℃. During the later period of the reaction at 240℃, the rate of phenol ether was higher than that of alcohol ether, which was still higher than that of polyether. Partitioned first order kinetics model analy-sis showed that the apparent activation energy of alcohol ether was lower than that of both polyether and phenol ether in the leading stage and lagging stage, and it was easy to acquire a higher oxidation rate for alcohol ether at low temperature. Three parameter general dynamics model analyses showed that the reason why the oxidation rate of polyether was lower than that of alcohol ether was that the oxidation of polyether was more apt to be converted to intermediate production than that of alcohol ether, whereas between 200℃ and 220℃, the direct oxidation rate of polyether and the oxidation rate of intermediate product were obviously lower than that of alcohol ether. The apparent activation energy of direct and indirect oxidation of polyether was 43.37 and 60.45 kJ?mol?1, respectively, while the corre-sponding apparent activation energy of alcohol was 38.74 and 58.09 kJ·mol?1, respectively.     

Kinetics of crude oil combustion

In this research, thermal characterization and kinetics of Karakus crude oil in the presence of limestone matrix is investigated. Thermogravimetry (TG/DTG) is used to characterize the crude oil in the temperature range of 20-900°C, at 10°C min ^-1 heating rate using air flow rate of 20 mL min ^-1. In combustion with air, three distinct reaction regions were identified known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). Five different kinetic methods used to analyze the TG/DTG data to identify reaction parameters as activation energy and Arrhenius constant. On the other hand different f(α) models from literature were also applied to make comparison. It was observed that high temperature oxidation temperature (HTO) activation energy of Karakus crude oil is varied between 54.1 and 86.1 kJ mol ^-1, while low temperature oxidation temperature (LTO) is varied between 6.9 and 8.9 kJ mol ^-1.     

Kinetics of Ir (III)-catalyzed Oxidation of D-glucose by Potassium Iodate in Aqueous Alkaline Medium

The kinetics of Ir (III) chloride-catalyzed oxidation of D-glucose by iodate in aqueous alkaline medium was investigated at 45°C. The reaction follows first-order kinetics with respect to potassium iodate in its low concentration range but tends to zero order at its higher concentration. Zero-order kinetics with respect to [D-glucose] was observed. In the lower concentration range of Ir (III) chloride, the reaction follows first kinetics, while the order shifts from first to zero at its higher concentration range. The reaction follows first-order kinetics with respect to [OH^?] at its low concentration but tends towards zero order at higher concentration. Variation in [Cl^?] and ionic strength of the medium did not bring about any significant change in the rate of reaction. The first-order rate constant increased with a decrease in the dielectric constant of the medium. The values of rate constants observed at four different temperatures were utilized to calculate the activation parameters. Sodium salt of formic acid and arabinonic acid have been identified as the main oxidation products of the reaction. A plausible mechanism from the results of kinetic studies, reaction stoichiometry, and product analysis has been proposed.     

Non-isothermal kinetic analysis and feasibilty study of medium grade crude oil field

In this research, non-isothermal kinetics and feasibility study of medium grade crude oil is studied in the presence of a limestone matrix. Experiments were performed at a heating rate of 10°C min⁻¹, whereas the air flow rate was kept constant at 50 mL min⁻¹ in the temperature range of 20 to 600°C (DSC) and 20 to 900°C (TG). In combustion with air, three distinct reaction regions were identified in all crude oil/limestone mixtures, known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The activation energy values were in the order of 5–9 kJ mol⁻¹ in LTO region and 189–229 kJ mol⁻¹ in HTO region. It was concluded that the medium grade crude oil field was not feasible for a self-sustained combustion process.     

Kinetic Studies of Chromic Acid Oxidation of Glyoxal

The kinetics of chromic acid oxidation of glyoxal is reported. The reaction is first-order in glyoxal and indicates a gradual change from a first-order to a zero-order dependence on acidity. The kinetic nature of this reaction has been studied and the rate law is consistent with a proposed mechanism as follows; rate = kK_b, K[Cr⁺⁶][Gx][H⁺]/(l+0.238[H⁺]) at 25°C. The product analysis indicates that formic acid is the oxidation product under similar kinetic condition.     

Kinetics and mechanism of aqueous oxidation of H2S by Fe+3

The reaction kinetics of aqueous oxidation of H₂S by Fe⁺³ is investigated at 25°C by spectrophotometric method. The study conducted at various reactant concentrations and pH revealed that the reaction proceeds according to complex‐series reactions involving polysulfides as intermediates. The reaction of each step is first order with respect to Fe⁺³ and hydrogen sulfide or polysulfide. A mechanism is proposed, involving sulfido and polysulfido radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 331–335, 1999     

The Oxidation of Phenylhydrazine by Tyrosinase

Tyrosinase was found to catalyze the oxidation of phenylhydrazine to phenol in a reaction that did not resemble those typically performed by tyrosinase. The kinetics of this reaction was investigated by measuring the initial velocity of the formation of phenol (25 °C). The values of k _cat and K _M for the oxidation of phenylhydrazine were obtained as 11.0 s^?1 and 0.30 mM, respectively. The generation of superoxides during the oxidation of phenylhydrazine by tyrosinase was monitored by nitroblue tetrazolium (NBT) assay. In the phenylhydrazine-tyrosinase reaction, 1 mol O₂ was required for the production of 1 mol phenol and 1/6 mol superoxide. The decomposition of superoxide by superoxide dismutase enhanced the rate constant of the oxidation of phenylhydrazine. Phenol formed in the oxidation of phenylhydrazine by tyrosinase was further oxidized by tyrosinase to an o-quinone, after the oxidation of phenylhydrazine by tyrosinase was almost completed.     

Combustion characteristics of lignite and oil shale samples by thermal analysis techniques

In this research thermal analysis and kinetics of ten lignite's and two oil shale samples of different origin were performed using a TA 2960 thermal analysis system with thermogravimetry (TG/DTG) and differential al analysis (DTA) modules. Experiments were performed with a sample size of ~10 mg, heating rate of 10°C min^-1. Flow rate was kept constant (10 L h^-1) in the temperature range of 20-900°C. Mainly three different reaction regions were observed in most of the samples studied. The first region was due to the evaporation of moisture in the sample. The second region was due to the release of volatile matter and burning of carbon and called as primary reaction region. Third region was due to the decomposition of mineral matter in samples studied. In kinetic calculations, oxidation of lignite and oil shale is described by first-order kinetics. Depending on the characteristics of the samples, the activation energy values are varied and the results are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Aerobic oxidation of cumene to cumene hydroperoxide catalyzed by metalloporphyrins

A protocol for the aerobic oxidation of cumene to cumene hydroperoxide (CHP) catalyzed by metalloporphyrins is reported herein. Typically, the reaction was performed in an intermittent mode under an atmospheric pressure of air and below 130°C. Several important reaction parameters, such as the structure and concentration of metalloporphyrin, the air flow rate, and the temperature, were carefully studied. Analysis of the data obtained showed that the reaction was remarkably improved by the addition of metalloporphyrins, in terms of both the yield and formation rate of CHP while high selectivity was maintained. It was discovered that 4 or 5 h was the optimal reaction time when the reaction was catalyzed by monomanganese-porphyrin ((p-Cl)TPPMnCl) (7.20 × 10^?5 mol/l) at 120°C with the air flow rate being 600 ml/min. From the results, we also found that higher concentration of (p-Cl)TPPMnCl, longer reaction time and higher reaction temperature were all detrimental to the production of CHP from cumene. Studies of the reaction kinetics revealed that the activation energy of the reaction (E) is around 38.9 × 10⁴ kJ mol^?1. The low apparent activation energy of the reaction could explain why the rate of cumene oxidation to CHP in the presence of metalloporphyrins was much faster than that of the non-catalyzed oxidation.     

High temperature oxidation of Cr–Mo–V tool steel in carbon dioxide

This study aims to examine the oxidation resistance and kinetics of Cr, Mo, and V containing tool steel (Calmax) when exposed in CO₂ high temperature environment by thermogravimetric measurements, X-ray diffraction analysis, and microscopic observation. The tool steel samples begin to oxidize at 480 °C while over 600 °C, the oxidation rate increases significantly. Finally, at 900 °C, the oxidation rate is significantly high. The activation energy of the oxidation was calculated as 160.1 kJ mol^?1. Microscopically, the thickness of the scale was found to increase with the exposure temperature, and the as formed scales consisted of two distinguishable oxide layers.     

Kinetics and mechanism of oxidation of glycine,alanine, and threonine by fluoride coordinated bismuth(V) in aqueous HClO4–HF medium

The kinetics of oxidation of amino acids viz. glycine, alanine, and threonine with bismuth(V) in HClO₄–HF medium have been studied. The kinetics of the oxidation of all these amino acids exhibit similar rate laws. The second-order rate constants were calculated to be 2.04 × 10^?2 dm³ mol^?1 and 2.72 × 10^?2 dm³ mol^?1 s^?1 for glycine and alanine, respectively, at 35°C and 5.9 × 10^?2 dm³ mol^?1 s^?1 for threonine at 25°C. All the possible reactive species of both bismuth(V) and amino acids have been discussed and a most probable kinetic model in each reaction has been envisaged. © 1994 John Wiley & Sons, Inc.     

In vitro Inhibition Effect of Transition Metal Ions on Succinate‐Fumarate System in ATP Cycle

Oxidation of sodium succinate in aqueous solution by potassium ferricyanide was investigated. The effects of different reaction parameters such as initial concentration of succinate, concentration of ferricyanide, and influence of metal ions (Zn⁺², Ni⁺², Cu⁺², Cd⁺²) on the oxidation of succinate were investigated at 25 ± 0.05 °C. Large rate enhancements were observed in the redox reaction between succinate and ferricyanide with increasing concentrations of both oxidant and reductant. The kinetics results indicated that the succinate oxidation was significantly inhibited in the presence of metal ions. Pseudo first order rate constants values were found decreased with increase in concentrations of metal ions which reflected that inhibition rate was directly influenced with the metal ions concentration.     

Oxidative degradation of levofloxacin by water-soluble manganese dioxide in aqueous acidic medium: a kinetic study

Pharmaceuticals, especially fluoroquinolone antibiotics, have received increasing global concern, due to their intensive use in the environment and potential harm to ecological system as well as human health. Degradation of antibiotics, such as oxidative degradation by metal oxides, often plays an important role in the elimination of antibiotics from the environment. The kinetics of oxidation of levofloxacin by water-soluble manganese dioxide has been studied in aqueous acidic medium at 25 °C temperature. The stoichiometry for the reaction indicates that the oxidation of 1 mol of levofloxacin requires 1 mol of manganese dioxide. The reaction is second order, that is first order with respect to manganese dioxide and levofloxacin. The rate of reaction increases with the increasing [H⁺] ion concentration. A probable reaction mechanism, in agreement with the observed kinetic results, has been proposed and discussed. The energy and enthalpy of activation have been calculated to be 30.54 and 28.07 kJ mol^?1, respectively.     

Kinetics and mechanism of oxidation of <Emphasis Type="SmallCaps">l</Emphasis>-cystine by manganese(III) in sulfuric acid medium

The kinetics of oxidation of l-cystine by Mn^III have been studied in sulfuric acid medium at 30 °C. The reaction was followed spectrophotometrically at λmax = 500 nm. The reaction shows first order dependence on both [Mn^III] and [cystine]. It was found that the rate of the reaction decreases with increase of [H⁺] up to a certain point and then remains unchanged. The oxidation product of the reaction was found to be cysteic acid. A plausible mechanism has been proposed to account for the experimental results.     

Thermal oxidation of polyacetylene

The thermal oxidation of undoped trans-polyacetylene powder in dry air has been studied and the principal features of the mechanism have been developed. Thermogravimetric and differential thermal analysis reveal an exothermic process that first leads to a weight increase, followed by precipitous weight loss above 240°C due to formation of volatile oxidation products. Isothermal weight gain studies between 25 and 142°C show first-order kinetics below 90°C with a rate constant of 3.10^?7 s^?1 at 25°C and an apparent activation energy of 16 kcal/mol. A weight gain of more than 40% has been observed at 25°C after 2000 h of exposure to air. A change in first-order kinetics occurs at temperatures above 90°C. Identification of solid oxidation products with photoacoustic infrared spectroscopy reveals that oxygen intercalates into the polymer structure in large concentrations, similar to other electron acceptors. However, oxidative attack on the polymer backbone occurs simultaneously. At elevated temperatures or for long-term oxygen exposure, the concentration of dopant oxygen decreases, probably by intramolecular regrouping of hydrogen atoms, resulting in the formation of hydroxyl groups and enhanced polymer degradation. This mechanism is consistent with the finding of others that the conductivity of polyacetylene upon oxygen exposure increases initially before decreasing significantly with continued exposure, especially at elevated temperatures.     

The oxidation of thiosulphate ions by octacyanotungstate(V) in weak acidic medium

The kinetics of the oxidation of thiosulphate ions by octacyanotungstate(V) ions has been studied in the pH range 3.9–5.0. The reaction showed zero-order kinetics with respect to [W(CN)₈^3?] and is consistent with the rate law R = k[H⁺][S₂O₃^2?]². A reaction mechanism is proposed for the reaction with a third-order rate constant of 0.26 M^?2 s^?1 at 25°C.     

Kinetics and mechanism of the formation of poly[(1,1,3,3-tetramethyldisiloxanyl)ethylene] and poly(methyldecylsiloxane) by hydrosilylation

The kinetics of the formation of poly(carbosiloxane), as well as of alkyl-substituted poly(siloxane), by Karstedt's catalyst catalyzed hydrosilylation were investigated. Linear poly(carbosiloxane), poly[(1,1,3,3-tetramethyldisiloxanyl)ethylene], (PTMDSE), was obtained by hydrosilylation of 1,3-divinyltetramethyldisiloxane (DVTMDS) and 1,1,3,3-tetramethyldisiloxane (TMDS), while alkyl-substituted poly(siloxane), poly(methyldecylsiloxane), (PMDS), was synthesized by hydrosilylation of poly(methylhydrosiloxane) (PMHS) and 1-decene. To investigate the kinetics of PTMDSE formation, two series of experiments were performed at reaction temperatures ranging from 25 to 56 °C and with catalyst concentrations ranging from 7.0 × 10⁻⁶ to 3.1 × 10⁻⁵ mol Pt/mol CHCH₂. A series of experiments was performed at reaction temperatures ranging from 28 to 48 °C, with catalyst concentrations of 7.0 ×10⁻⁶ mol of Pt per mol of CHCH₂, when kinetics of PMDS formation was investigated. All reactions were carried out in bulk, with equimolar amounts of the reacting Si H and CHCH₂ groups. The course of the reactions was monitored by following the disappearance of the Si H bands using quantitative infrared spectroscopy. The results obtained showed typical first order kinetics for the PTMDSE formation, consistent with the proposed reaction mechanism. In the case of PMDS an induction period occurred at lower reaction temperatures, but disappeared at 44 °C and the rate of Si H conversion also started to follow the first-order kinetics. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2246–2258, 2007     

Evaluation of antioxidants using oxidation reaction rate constants

An evaluation method for the capacity of antioxidants to protect drugs against oxidation is presented. As a new viewpoint, to determine the priority of the competitive oxidations between the antioxidant and the protected drug, and to compare the drug-protection capacity of antioxidants, it is important to determine their oxidation rate constants using chemical kinetics instead of standard oxidation (or reduction) potentials. Sodium sulfite, sodium bisulfite and sodium pyrosulfite were used as models for the determination of oxidation reaction rate constants in aqueous solutions. In the experiments, sufficient air was continually infused into the solution to keep the concentration of dissolved oxygen constant. The residual concentrations of the antioxidants were determined by iodimetry, and the concentration of dissolved oxygen by oxygen electrode. The data were fitted by linear regressions to obtain the reaction rate constants. It was found that the degradation of sodium sulfite, sodium bisulfite or sodium pyrosulfite obeyed pseudo zero-order kinetics in the buffer solutions. Because of the ionization equilibrium, these three antioxidants have the same ion form in solutions at a definite pH value and therefore their apparent rate constants were essentially the same. The average apparent rate constants of the three antioxidants at 25°C are (1.34 ± 0.03) × 10⁻³ at pH 6.8, (1.20 ± 0.02) × 10⁻³ at pH 4.0 and (6.58 ± 0.02) × 10⁻³ mol·L⁻¹·h⁻¹ at pH 9.2, respectively. Translated from Acta Chimica Sinica, 2006, 64(6): 496–500 (in Chinese)     

Oxidation of sodium (2-14C) acetate with alkaline permanganate

The mechanism and kinetics of the oxidation of sodium acetate with permanganate in alkaline and neutral media, has been investigated using (2-¹⁴C) acetate. The reaction is first order both with respect to permanganate and acetate ions. The initial second order rate constants depend linearly on the square of the hydroxide ion concentration. Arrhenius acitvation energy of the oxidation reaction carried out in 12M NaOH is 24.0 kcal/mole in the temperature interval 50–100°C. The mechanism of the principal path leading to the oxalate formation and the mechanism of the side reaction resulting in the carbon dioxide production has been proposed and discussed.