Rate Of Peroxide Decomposition Research Articles

The effects of iron species and mineral particles on advanced oxidation processes for the removal of humic acids

Influence of iron species and mineral particles added on the advanced oxidation processes (AOP) for the humic acids (HA) removal was elucidated. It was observed that decomposition rate of hydrogen peroxide increased when the modified ferrous ion (M-Fe, of which main species are pre-hydrolyzed ferrous species as FeOH +) was added. Addition of bentonite in the iron-catalyzed oxidation process adversely affected H 2O 2 degradation. Iron salts, were adsorbed onto the surface of bentonite, suppressed the reaction between iron and H 2O 2. In contrast, adding glass powder slightly increased the H 2O 2 degradation rate. In addition, changes in the molecular and structural characteristics of HA and the hydrophobic and hydrophilic fractions of trihalomethanes (THMs) precursors after the Fenton and photo-Fenton oxidation were evaluated by GPC, NMR spectra and Py-GC/MSD.

Soil organic matter–hydrogen peroxide dynamics in the treatment of contaminated soils and groundwater using catalyzed H 2O 2 propagations (modified Fenton's reagent)

The interactions between catalyzed H 2O 2 propagations (CHP—i.e. modified Fenton's reagent) and soil organic matter (SOM) during the treatment of contaminated soils and groundwater was studied in a well-characterized surface soil. The fate of two fractions of SOM, particulate organic matter (POM) and nonparticulate organic matter (NPOM), during CHP reactions was evaluated using concentrations of hydrogen peroxide from 0.5 to 3 M catalyzed by soluble iron (III), an iron (III)-ethylenediamine tetraacetic acid (EDTA) chelate, or naturally-occurring soil minerals. The destruction of total SOM in CHP systems was directly proportional to the hydrogen peroxide dosage, and was significantly greater at pH 3 than at neutral pH; furthermore, SOM destruction occurred predominantly in the NPOM fraction. At pH 3, SOM did not affect hydrogen peroxide decomposition rates or hydroxyl radical activity in CHP reactions. However, at neutral pH, increasing the mass of SOM decreased the hydrogen peroxide decomposition rate and increased the rate of hydroxyl radical generation in CHP systems. These results show that, while CHP reactions destroy some of the organic carbon pools, SOM does not have a significant effect on the CHP treatment of soils and groundwater.

Oxidation kinetics of soybean oil in the presence of monoolein, stearic acid and iron

The oxidation kinetics of soybean oil containing 1% (w/w) monoolein, 1% (w/w) stearic acid and 0.005% (w/w) iron was evaluated at 55 °C under light. The oxidation rates were determined by oxygen consumption and peroxide formation. Addition of monoolein, stearic acid or iron to the soybean oil accelerated the rate of lipid oxidation during the storage. Monoolein increased the rate of oxygen consumption whereas iron increased the rate of peroxide decomposition. The reaction order of soybean oil was found to fit first-order kinetics and was not affected by the addition of monoolein, stearic acid or iron. The rate constants were 2.55 × 10 −2, 2.94 × 10 −2, 2.91 × 10 −2, 3.02 × 10 −2 h −1, and the half-lives were 27.18, 23.58, 23.82, 22.95 h for the soybean oil, monoolein, stearic acid and iron samples, respectively.

Hydrogen peroxide at the Bermuda Atlantic Time Series Station: Temporal variability of seawater hydrogen peroxide

Hydrogen peroxide concentrations, production rates and decomposition rates were measured during each of two 3-week cruises in August 1999 and March 2000 at the Bermuda Atlantic Time Series Station. Patterns of variation in the concentrations of hydrogen peroxide in surface seawater at BATS were drastically different in August of 1999 compared with March of 2000. In August, hydrogen peroxide concentrations were primarily controlled by input from rain, whereas in March, they were controlled by photochemical processes and showed diurnal variations. The highest concentrations in surface water in August followed rain events, whereas in March, they occurred at approximately 1400 after rapid photochemical production. This production in March was followed by an equally rapid loss of H 2O 2, probably driven by a secondary photochemical process, then by much slower decline at night. The combination of photochemical production and consumption processes resulted in a steady-state system over a 24-h period in March but not August. The dark decomposition of surface water hydrogen peroxide incubated in storage experiments was the same during both August and March and followed first order kinetics with a rate constant of 0.009 h − 1. This was in remarkably good agreement with the decay of the atmospheric hydrogen peroxide signal in surface seawater observed in August. The comparable rate constant for deep water from 200 m was about one-third of that for BATS surface seawater in March. Because filtered seawater had lower production rates than unfiltered seawater from the same depth, biological production may contribute to surface seawater hydrogen peroxide at BATS during the March spring plankton bloom, but it is not the dominant source.

Barrier and Copper Seedlayer Wet Etching

This paper summarizes the process development of TiN barrier etching in presence of copper, for a thick copper level in BICMOS technology. In an industrial context, we have chosen to use a SC1 chemistry in a spin etch single wafer tool. The SC1 composition and therefore the pH level allows - the barrier to be etched with no metallic residues, ( if not clear this can be a source for shorts) - control of the selectivity between copper and TiN - control of lateral etching under copper lines, the possible source of open chains by W attack during TiN etch. The electrical results show a robust process according to current specifications, in terms of leakage and via resistance with a fresh chemistry approach. In fact, the recirculation of SC1 is not possible due to substantial concentration changes during processing, high evaporation rate of Ammonia and high decomposition rate of Peroxide in the presence of copper on surface wafer.

The role and rate of hydrogen peroxide decomposition during hydrocarbon two-stage autoignition

The role of hydrogen peroxide during the development of two-stage ignition of alkanes is discussed in propane combustion using a reduced kinetic model comprising 58 species in 344 irreversible reactions. Numerical simulations of two-stage and multiple-stage ignitions of propane + oxygen in a closed vessel, and two-stage ignition in a rapid compression machine are made. The model is validated by a construction of the closed vessel p– T a ignition diagram and comparing it with published experimental results. A detailed analysis, using temperature/composition versus time and phase-plane [H 2O 2]– T plots, is made to show regions of kinetic sensitivity leading to ignition. Rate of production and sensitivity analyses are used to determine the most important reactions contributing to the formation of hydrogen peroxide as an intermediate, and to the heat release rate eventually culminating in the second stage of two-stage ignition. The most important (but not exclusive) sequence of reactions leading to HO 2 formation is identified to be through formaldehyde as a molecular intermediate, it being formed predominantly from methyl radical oxidation. This seems not to have been previously recognized. The relationship to other sources of HO 2 is investigated, and the effect of change in temperature, pressure, and composition on the kinetics is discussed.

Effect of acetonitrile on the catalytic decomposition of hydrogen peroxide by vanadium ions and conjugated oxidation of alkanes

The rate of hydrogen peroxide decomposition in acetonitrile in the presence of a vanadate anion and pyrazine-2-carboxylic acid decreases remarkably when alkane (cyclohexane, n-heptane, isooctane) is added to the reaction solution. The alkane added is oxidized by this system to alkyl hydroperoxide. This is explained by the fact that much more hydrogen peroxide molecules are consumed to acetonitrile oxidation with formation of the final products, which is suppressed considerably by additives of necessary amounts of alkane, than those consumed to the oxidation of cyclohexane to form cyclohexyl hydroperoxide. In an organic solvent, H2O2 decomposes in a non-chain radical process.

NADPH dependent activation of microsomal glutathione transferase 1

Microsomal glutathione transferase 1 (MGST1) can become activated up to 30-fold by several mechanisms in vitro (e.g. covalent modification by reactive electrophiles such as N-ethylmaleimide (NEM)). Activation has also been observed in vivo during oxidative stress. It has been noted that an NADPH generating system (g.s.) can activate MGST1 (up to 2-fold) in microsomal incubations [Y. Aniya, M.W. Anders, J. Biol. Chem. 264 (1989) 1998–2002], but the mechanism was unclear. We show here that NADPH g.s treatment impaired N-ethylmaleimide activation, indicating a shared target (identified as cysteine-49 in the latter case). Furthermore, NADPH activation was prevented by sulfhydryl compounds (glutathione and dithiothreitol). A well established candidate for activation would be oxidative stress, however we could exclude that oxidation mediated by cytochrome P450 2E1 (or flavine monooxygenase) was responsible for activation under a defined set of experimental conditions since superoxide or hydrogen peroxide alone did not activate the enzyme (in microsomes prepared by our routine procedure). Actually, the ability of MGST1 to become activated by hydrogen peroxide is critically dependent on the microsome preparation method (which influences hydrogen peroxide decomposition rate as shown here), explaining variable results in the literature. NADPH g.s. dependent activation of MGST1 could instead be explained, at least partly, by a direct effect observed also with purified enzyme (up to 1.4-fold activation). This activation was inhibited by sulfhydryl compounds and thus displays the same characteristics as that of the microsomal system. Whereas NADPH, and also ATP, activated purified MGST1, several nucleotide analogues did not, demonstrating specificity. It is thus an intriguing possibility that MGST1 function could be modulated by ligands (as well as reactive oxygen species) during oxidative stress when sulfhydryls are depleted.

The Effect of Magnesium Ions and Chelants on Peroxide Bleaching

Summary We recently reported that during peroxide bleaching, magnesium is substantially more effective when in a complex form with either pulp or a chelant. We also speculated that different magnesium forms affected the catalytic activity of transition metals towards peroxide decomposition to different degrees. As oxygen-delignified pulps still containing lignin were used, it was impossible to separate the catalytic peroxide decomposition by transition metals from the peroxide reaction with lignin, and thus to determine where in the pulp-liquor system magnesium or chelants, or both, were deactivating transition metals. In this paper, we studied the peroxide decomposition kinetics with different modes of addition of the P-stage chemicals in the presence of fully-bleached kraft pulps which are virtually lignin-free, in alkaline filtrates, in P-stage filtrate and in water. We found that most of the peroxide decomposition occurring during a P-stage applied to chemical pulps takes place through interaction with transition metals in the pulp rather than with transition metals in the soluble bulk phase. We also concluded that in any component of a peroxide bleaching system, magnesium is extremely efficient at reducing the rate of peroxide decomposition, while a chelant becomes more valuable when complexing magnesium.

Pressure and Temperature Dependence of the Decomposition Rate of Aliphatic tert-Amyl Peroxyesters

Abstract Thermal decomposition of several aliphatic tert-amyl (TA, 1,1-dimethylpropyl) peroxyesters, RC(O)OOTA, has been studied in dilute solution of n-heptane at pressures up to 2500bar and temperatures up to 195°C. The peroxides under investigation were: tert-amyl peroxyacetate (TAPA), tert-amyl peroxy-n-butanoate (TAPnB), tert-amyl peroxy-iso-butanoate (TAPiB, TA peroxy-2-methyl propionate), tert-amyl peroxy-2-ethylhexanoate (TAPO), and tert-amyl peroxypivalate (TAPP, TA peroxy-2,2-dimethyl propionate). The experiments were carried out in a tubular reactor at residence times up to 140s. Peroxide concentration was monitored under continuous flow conditions via quantitative FT-IR spectroscopic analysis in an optical high-pressure cell positioned behind the tubular reactor. First-order decomposition kinetics over several half-lives were observed. For each TA peroxyester, rate equations for the first-order rate coefficient, k obs(p,T), are presented. k obs values for TA peroxyester decomposition are by 23 ± 9 per cent above the corresponding numbers reported for associated tert-butyl (TB) peroxyesters, with the same R group and at identical p, T, and solvent environment. The carbon atom of the R moiety that is in α-position to the carbonyl group controls decomposition kinetics. k obs is smallest in cases where this particular C-atom is a “primary” one and is largest when it is “tertiary”. The “primary” TA peroxyesters are associated with activation energies around 140 kJ mol-1 whereas the E A′s of the “secondary” and “tertiary” TA peroxyesters are around 130 und 120 kJ mol-1, respectively. The activation volumes, ΔV ‡ obs, of the “secondary” and “tertiary” TA peroxyesters are in the narrow range of ΔV ‡ obs = 3.0 ± 1.5cm3mol-1. The ΔV ‡ obs′s of the “primary” TA peroxyesters are above 8cm3mol-1. Within the limits of experimental accuracy, the activation parameters of TA peroxyester decomposition are identical to the corresponding quantities reported for the associated TB peroxyesters. The activation parameters suggest that “primary” aliphatic peroxyesters decompose via single-bond scission whereas the “secondary” and “tertiary” TA peroxyesters undergo concerted two-bond scission or extremely fast successive scission of the two bonds which latter two processes can not be distinguished on the timescale of the experiments. The mode of primary bond dissociation, via single-bond or via concerted two-bond scission, largely affects initiator efficiency in free-radical polymerization. The peroxide decomposition rate data measured in dilute solution of compressed n-heptane are useful for simulation and optimization of technical high-pressure ethene polymerizations.

Kinetics of Hydrogen Peroxide Decomposition in Guaiacol Solution, Catalyzed by Hexacyanoferrate(II)

The kinetics of hydrogen peroxide decomposition in a guaiacol solution, catalyzed by potassium hexacyanoferrate(II), were studied. The reaction mainly follows the pathway of guaiacol hydroxylation. The reaction order is 1 with respect to H2O2, 0.5 with respect to hexacyanoferrate, and from 0.4 to 0 with respect to guaiacol (the latter parameter decreases with increasing guaiacol concentration). The apparent activation energy is 105 kJ mol- 1. A kinetic scheme of the process was proposed. An expression consistent with the experiment was obtained for the rate of hydrogen peroxide decomposition in the presence of guaiacol, catalyzed by hexacyanoferrate(II).

Nitrite-catalase interaction as an important element of nitrite toxicity.

It was established that nitrite in the presence of chloride, bromide, and thiocyanate decreases the rate of hydrogen peroxide decomposition by catalase. The decrease was recorded by the permanganatometric method and by a method of dynamic calorimetry. Nitrite was not destroyed in the course of the reaction and the total value of heat produced in the process was not changed by its presence. These facts suggest that nitrite induces inhibition of catalase with no change in the essence of the enzymatic process. Even micromolar nitrite concentrations induced a considerable decrease in catalase activity. However, in the absence of chloride, bromide, and thiocyanate inhibition was not observed. In contrast, fluoride protected catalase from nitrite inhibition in the presence of the above-mentioned halides and pseudohalide. As hydrogen peroxide is a necessary factor for triggering a number of important toxic effects of nitrite, the latter increases its toxicity by inhibiting catalase. This was shown by the example of nitrite-induced hemoglobin oxidation. The naturally existing gradient of chloride and other anion concentrations between intra- and extracellular media appears to be the most important mechanism of cell protection from inhibition of intracellular catalase by nitrite. Possible mechanisms of this inhibition are discussed.

Selectivity of peroxide‐initiated graft modification of ethylene copolymers

AbstractExperimental data on the kinetics and selectivity of peroxide‐initiated graft modification of ethylene copolymers with vinyltriethoxysilane (VTEOS) and maleic anhydride (MAn) are presented. Rate data for the VTEOS modification and crosslinking of poly(ethylene‐co‐vinyl acetate) demonstrate the controlling influence of peroxide decomposition rates. Analysis of the selectivity for grafting versus crosslinking showed considerable scope for optimization of VTEOS modifications through variation of monomer and peroxide loadings. However, the MAn system was found to be less amenable to optimization, most likely because of differences in the graft propagation cycle and radical termination preferences.

Kinetic study of hydrogen peroxide decomposition by catalase in a flow-mix microcalorimetric system

The kinetics of hydrogen peroxide decomposition by the enzyme catalase was studied at pH 7.4 in the temperature range 10–30 °C. Experiments were performed by the LKB-2277 Thermal Activity Monitor equipped with a flow-mix cylinder. The calorimetric reaction unit was schematised as a tubular reactor operating under plug-flow conditions. A first-order kinetic expression, with respect to both the substrate and the enzyme, was used to describe the rate of hydrogen peroxide decomposition. Regression analysis of calorimetric data provided a molar reaction enthalpy of −87.55 kJ mol −1 and an activation energy of 11 kJ mol −1. Analysis of model residuals and the normal probability plot indicated that the results obtained were statistically significant.

Changes in the Surface Chemistry and Adsorptive Properties of Active Carbon Previously Oxidised and Heat-Treated at Various Temperatures. I. Physicochemical Properties of the Modified Carbon Surface

Several active carbon samples with different quantities of surface oxides were obtained by annealing previously oxidised material under vacuum at various temperatures (ranging from 180°C to 900°C). Concentrated HNO3 was used as the oxidiser. The oxygen content, the pH of the aqueous slurry and the concentration of surface functional groups were determined for all the carbons. Spectral studies (FT-IR, XPS) were performed for selected samples. The heterogeneous decomposition of hydrogen peroxide was also studied. The catalytic activity for H2O2 decomposition correlated well with the acid consumption on the carbon materials. A linear relationship was derived between the oxygen reduction potentials and the logarithm of the peroxide decomposition rate constants.

Alkene epoxidation with peroxide in a catalytic membrane reactor: a theoretical study

Catalytic membrane reactor (CMR) is an emerging novel technology. In the present work, a mathematical model has been developed for the oxidation of alkenes to epoxides in a CMR. Effects of various parameters such as peroxide and alkene concentration in liquid phase, sorption coefficient of the membrane for peroxide and alkene, membrane–catalyst distribution coefficient for peroxide and alkene and catalyst loading have been studied. The model predictions show that in CMR with an organophillic membrane phase, peroxide concentration remains low at catalyst active site, reducing the rate of peroxide decomposition. By proper selection of the parameters mentioned above, high peroxide efficiency and significant rate of generation of the epoxide can be obtained in CMR.

Long‐term behavior of oil‐based varnishes and paints. Fate of hydroperoxides in drying oils

AbstractThe thermal stability of linseed oil and poppyseed oil hydroperoxides in a temperature range from ambient to 120°C has been investigated on the basis of iodometric titration. The peroxide value (PV) vs. oxidation time curves show similar developments at the six temperatures chosen for the experiments. These curves are characterized by a fast increase in the PV up to a maximal value, followed by a decrease in the PV at a lower rate. The maximal PV is higher when the curing temperature is lowered. This result indicates thermal decomposition of the hydroperoxides. The peroxy crosslink concentration in the dried oil film varies similarly to the hydroperoxide concentration. This indicates that, for dried films, the network is almost totally constituted of ether and C‐C crosslinks. A comparison of the rates of peroxide decomposition under thermolytic and thermooxidative conditions has evidenced that the only homolytic scission of the O‐O bonds cannot justify the decreased of the PV in thermooxidation. Another mechanism accounting for hydroperoxide decomposition, based on an induced decomposition of the hydroperoxides, has been proposed. These results have permitted completing the description of the curing mechanisms of drying oils.

Microwave Heating in the Hydrogen Peroxide Oxidation of Benzene on Zeolite Catalysts

In this paper benzene hydroxylation with hydrogen peroxide (H2O2) in the presence of the titan-silicates-zeolites was studied. The initial catalyst, HZSM-5 zeolite type was treated to obtain both cobalt-and titan-silicates—zeolite. These improved catalysts were also used for oxidation. To obtain reaction temperature heating was made by conventional techniques and by microwave treatment. From this research it was concluded that reaction temperature is a very important parameter to keep a proper equilibrium between the decomposition rate of hydrogen peroxide and the oxidation rate ofaromatic compound. It was also found that microwaves affect the reaction selectivity.

Kinetics of hydrogen peroxide decomposition with complexed and ?free? iron catalysts

The hydrogen peroxide decomposition kinetics were investigated for both “free” iron catalyst [Fe(II) and Fe(III)] and complexed iron catalyst [Fe(II) and Fe(III)] complexed with DTPA, EDTA, EGTA, and NTA as ligands (L). A kinetic model for free iron catalyst was derived assuming the formation of a reversible complex (Fe–HO2), followed by an irreversible decomposition and using the pseudo-steady-state hypothesis (PSSH). This resulted in a first-order rate at low H2O2 concentrations and a zero order rate at high H2O2 concentrations. The rate constants were determined using the method of initial rates of hydrogen peroxide decomposition. Complexed iron catalysts extend the region of significant activity to pH 2–10 vs. 2–4 for Fenton's reagent (free iron catalyst). A rate expression for Fe(III) complexes was derived using a mechanism similar to that of free iron, except that a L–Fe–HO2 complex was reversibly formed, and subsequently decayed irreversibly into products. The pH plays a major role in the decomposition rate and was incorporated into the rate law by considering the metal complex specie, that is, EDTA–Fe–H, EDTA–Fe–(H2O), EDTA–Fe–(OH), or EDTA–Fe–(OH)2, as a separate complex with its unique kinetic coefficients. A model was then developed to describe the decomposition of H2O2 from pH 2–10 (initial rates = 1 × 10−4 to 1 × 10−7 M/s). In the neutral pH range (pH 6–9), the complexed iron catalyzed reactions still exhibited significant rates of reaction. At low pH, the Fe(II) was mostly uncomplexed and in the free form. The rate constants for the Fe(III)–L complexes are strongly dependent on the stability constant, KML, for the Fe(III)–L complex. The rates of reaction were in descending order NTA > EGTA > EDTA > DTPA, which are consistent with the respective log KMLs for the Fe(III) complexes. Because the method of initial rates was used, the mechanism does not include the subsequent reactions, which may occur. For the complexed iron systems, the peroxide also attacks the chelating agent and by-product-complexing reactions occur. Accordingly, the model is valid only in the initial stages of reaction for the complexed system. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 24–35, 2000

Hydrogen peroxide decomposition in model subsurface systems

Rates of hydrogen peroxide decomposition, hydroxyl radical production, and oxygen evolution were investigated in silica sand–goethite slurries using unstabilized and stabilized hydrogen peroxide formulations. The goethite-catalyzed decomposition of unstabilized hydrogen peroxide formulations resulted in more rapid hydrogen peroxide loss and oxygen evolution relative to systems containing a highly stabilized hydrogen peroxide formulation. Systems at neutral pH and those containing higher goethite concentrations were characterized by higher rates of hydrogen peroxide decomposition and by more oxygen evolution. The stabilized hydrogen peroxide formulation showed greater hydroxyl radical production relative to the unstabilized formulations. Furthermore, hydroxyl radical production rates were greater at neutral pH than at the acidic pH regimes. The results suggest that when stabilized hydrogen peroxide is injected into the subsurface during in situ bioremediation, naturally occurring minerals such as goethite may initiate Fenton-like reactions. While these reactions may prove to be toxic to microorganisms, they have the potential to chemically oxidize contaminants in soils and groundwater.