Study on the non-isothermal kinetics of decomposition of 4Na<Subscript>2</Subscript>SO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O<Subscript>2</Subscript>·NaCl

The non-isothermal decomposition kinetics of 4Na₂SO₄·2H₂O₂·NaCl have been investigated by simultaneous TG-DSC in nitrogen atmosphere and in air. The decomposition processes undergo a single step reaction. The multivariate nonlinear regression technique is used to distinguish kinetic model of 4Na₂SO₄·2H₂O₂·NaCl. Results indicate that the reaction type Cn can well describe the decomposition process, the decomposition mechanism is n-dimensional autocatalysis. The kinetic parameters, n, A and E are obtained via multivariate nonlinear regression. The n ^th-order with autocatalysis model is used to simulate the thermal decomposition of 4Na₂SO₄·2H₂O₂·NaCl under isothermal conditions at various temperatures. The flow rate of gas has little effect on the decomposition of 4Na₂SO₄·2H₂O₂·NaCl.     

Kinetics of the thermal decomposition of nitrocellulose after treatment with weak acids

The kinetics of the thermal decomposition of nitrocellulose, treated with weak acids after nitrationin a nitric-sulfuric acid mixture, have been studied in the temperature range 75–110°C. It was found by Chromatographic analysis of the gaseous decomposition products that to an extent of up to 10% the decomposition takes place according to second order autocatalysis kinetics, and the rate of decomposition can vary by a factor of approximately two with the duration of the preliminary treatment and with the nature of the original cellulose. The activation energy in the initial stages of the process, determined from the rate of evolution of N₂O, CO₂, CO, and NO amounted to 24 kcal/mole. It was concluded that thermal decomposition is determined by acid hydrolysis of nitrocellulose residues by sulfuric acid. The rate constant for the hydrolysis of nitrocellulose by sulfuric acid in a nitrate ester medium and the diffusion constant of H₂SO₄ in nitrocellulose have been estimated.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2744–2750, December, 1991.     

Catalytic Pyrolysis of Methane

Methane decomposition over metal oxides/SiO₂ surface was investigated. At 1400 K obtained product distribution of this decomposition varied with metal oxide used. The effectiveness of these catalysts has been discussed in terms of activity and C₂ selectivity. ThO₂/SiO₂ was found to be the most effective catalyst for the catalytic decomposition of methane. Positive catalytic effect of ThO₂/SiO₂ on the pyrolysis has also been confirmed at 1073 K. At low reaction conversions, ethane and ethylene are found as major products. Yields of ethylene and other unsaturated products are sensitively inhibited by NO impurities in the methane. A reaction mechanism has been proposed to account observed experimental results.     

Simultaneous capillary GC of acids and sugars as their silyl(oxime) derivatives: Quantitation of chlorogenic acid,raffinose, and pectin substances

Our GC-MS method for the simultaneous quantitation of sugars and acids as their silyl(oxime) derivatives, from one solution by one injection, has been extended to the reproducible determination of high molecular weight compounds sensitive to decomposition yet requiring a high evaporation temperature (e.g. chlorogenic acid and rffinose) and for the quantitation of the decomposition products of pectin (i.e., for the determination of galacturonic acid at low ng levels in the presence of a 10–100 fold excess of glucose eluting just before the acid). The optimized GC procedure has been used for quantitation of the sugar and acid (including chlorogenic acid) composition of potato samples, and for the determination of the increasing amount of the decomposition products of pectin substances in apple pulp after different storage times.     

Kinetics and mechanism of thermal decomposition of hydroxylammonium nitrate

The kinetics of thermal decomposition of melted hydroxylammonium nitrate have been investigated by the rate of heat production in the temperature range 84.8–120.9°C. The decomposition proceeds with autocatalysis and up to 60 % of conversion the rate of the process increases proportionally to the square of the degree of decomposition. The initial rate is proportional to the square of the concentration of HNO₃ formed due to dissociation of the salt. The activation energy of this process is 15.3±1.8 kcal/mol. It is suggested that the initial stage the process proceeds via interaction between N₂O₃ and NH₃OH⁺, whereas the subsequent acceleration is due to oxidation of NH₃OH⁺ by nitrogen oxides formed as well as by nitrous acid.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1897–1901, November, 1993.     

Kinetics of Thermal Decomposition of Solid Propellant Based on Aluminum and Ammonium Perchlorate

Kinetic regularities of the mass loss and heat and-gas release were studied in the thermal decomposition of a solid propellant composed of aluminum, ammonium perchlorate, and a polymer binder. It was shown that, under heating from 40 to 340°C under permanent vacuum conditions, propellant samples decompose without ignition, with the limiting mass loss in the decomposition being 48%. When experiments were performed in air, the propellant formulation decomposes with sharp ignition, with the inflammation temperature (270–287°C) and amount of volatiles released by this instant of time (10–16 wt %) dependent on the heating rate. The kinetic regularities of the mass loss in the decomposition of a solid propellant were described in terms of the polychromatic kinetics model that assumes that the reaction system has ensembles of particles differing in reactivity. The distribution functions of the mass fractions of the propellant by activation energies of decomposition were calculated. The heat release kinetics in the decomposition of a propellant formulation in the temperature range 153–270°C in a closed evacuated system is described by a sum of equations for two parallel reactions: 1st-order reaction with a heat effect Q₁ = 200 ± 5 kJ kg^–1 and 1st-order autocatalysis with heat effect Q₂ = 1900 ± 50 kJ kg–1. The rate constants and the activation parameters of the process were determined.

     

The gas phase pyrolysis of phenol

Phenol pyrolysis has been studied in a turbulent flow reactor by analyzing concentration-time profiles of three major decomposition products: carbon monoxide, cyclopentadiene, and benzene. Experimental conditions were P = 1 atm, T = 1064 ? 1162 K, and initial phenol concentrations of 500?2016 ppm. The major experimental observations were that the decomposition product profiles were nearly linear as a function of time and that the overall rate of carbon monoxide production was greater than that of cyclopentadiene. The rate difference is explained by a mechanism which includes a radical combination reaction of cyclopentadienyl and phenoxy. With literature and approximate rate coefficient data, the mechanism reproduced the experimental observations very well. The mechanism and data provide estimates of rate coefficients for the phenol decomposition initiation step, abstraction of hydrogen from phenol by cyclopentadienyl, and the phenoxy-cyclopentadienyl combination, all of which have not been available in the literature.     

Kinetics of thermal decomposition of hexanitrohexaazaisowurtzitane

Thermal decomposition of hexanitrohexaazaisowurtzitane (HNIW) in the solid state and in solution was studied by thermogravimetry, manometry, optical microscopy, and IR spectroscopy. The kinetics of the reaction in the solid state is described by the first-order equation of autocatalysis. The rate constants and activation parameters of HNIW thermal decomposition in the solid state and solution were determined. The content of N₂ amounts to approximately half of the gaseous products of HNIW thermolysis. The thermolysis of HNIW and its burning are accompanied by the formation of a condensed residue. During these processes, five of six nitro groups of the HNIW molecule are removed, and one NO₂ group remains in the residue, which contains amino groups and no C−H bonds. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 5, pp. 815–821, May, 2000.     

Role of Bipolar Pulsed DBD on the Growth of <Emphasis Type="Italic">Microcystis aeruginosa</Emphasis> in Three-Phase Discharge Plasma Reactor

Algae in drinking water supplies often bring about impact on the water treatment. In this study, a bipolar pulsed dielectric barrier discharge system in three-phase discharge plasma reactor was constructed for investigating its ability to control excessive growth of cyanobacteria, Microcystis aeruginosa. Experimental results show there was almost no change in optical density immediately after the interruption of electrical discharge, but the decreasing trend of optical density, cell density and chlorophyll-a content was obvious during the incubation period, indicating a significant residual effect of electrical discharge process on the algal growth inhibition. Scanning electron microscopy investigation of algae revealed surface damage, apparent leakage of intracellular contents and pores formed after electrical discharge process, which showed that algal cells had no potential to survive and grow. Compared with the control sample, it was observed that electrical discharge on the algal extracellular products has almost no residual effect and the growth rate of algae slightly decreased before three days storage. Hydrogen peroxide was produced by electrical discharge in the μM level and showed a first-order decay. But at such level, the external addition of hydrogen peroxide alone is not likely to cause the residual effect. These results implicated that the growth inhibition of M. aeruginosa was mainly caused by electrical discharge process, and it made the algal cells lose ability to survive, demonstrating the considerable potential of such an alternative process for efficient water purification.     

Effect of oxygen on the polymerization of vinyl chloride. I. Kinetic features

The effect of oxygen on the liquid-phase polymerization of vinyl chloride at 55°C in the presence of an added initiator, bis(4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox 16), has been studied by the technique of tumbled dilatometry. With this method, at constant initiator concentration, the induction period showed a half-order dependence on the initial oxygen concentration. At a constant initial oxygen concentration, the induction period varied inversely as the square root of the initiator concentration. Under the experimental conditions empolyed, the polyperoxy radicals with chloroalkyl (～CH₂?HCl) endgroups were not wholly scavenged by molecular oxygen but could undergo various decomposition reactions. The degree of conversion of the initial oxygen to peroxidic compounds did not exceed 30% by weight and was dependent on the shape of the reaction vessel empolyed. The existence of other oxidation products has been demonstrated. At 55°C, the average velocity constant for decomposition of the peroxide products from vinyl chloride, measured in dichloromethane solution, was found to be 8 × 10^?5 sec^?1. A kinetic scheme involving a predominant cross-termination reaction is proposed to explain the experimental results.     

Thermal analysis of transition metal salts of carboxylic acids

The thermal decomposition of salts (both normal and acid) of transition metals with carboxylic acids (maleic, ortho-phthalic and terephthalic) was studied in inert atmosphere. The residues after pyrolysis (up to 450°C) are composites including two structural components: an organic polymer matrix and spherical conglomerates from metal grains coated with polymer. Thermal decomposition of solid solutions of metal bimaleates (Co-Ni, Fe-Ni, Zn-Ni) was investigated. Thermogravimetric data (obtained at different rates of linear heating) were processed with 'Netzsch Thermokinetics' computer program. Kinetic parameters were calculated only for the first decomposition step, and the process is described by Prout-Tompkins equation of n ^th order with autocatalysis. Some properties of the resulting composites have been studied qualitatively. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal decomposition of methane: Autocatalysis

The origin of autocatalysis in the pyrolysis of methane has been investigated by kinetic modeling. A mechanism is presented that provides good agreement with experimental data at 1038 K and 433 torr into the autocatalytic region. The main causes of autocatalysis are secondary initiation by hydrocarbon products larger than C₂H₆ and chain radical methylation sequences.     

Kinetics and mechanism of the decomposition of N-bromoalcoholamines in aqueous solution

The decomposition reactions of N-bromodiethanolamine, N-bromoethylethanolamine, and N-bromomethylethanolamine in aqueous solution have been studied kinetically under various experimental conditions. The results support a proposed reaction mechanism in which the rate controlling step is assumed to be the formation of an imine which is then hydrolyzed to the final decomposition products.     

Kinetics of the oxidative degradation of d-xylose in the presence and absence of cationic and anionic surfactants

The oxidative degradation of d-xylose by cerium(IV) has been found to be slow in acidic aqueous solution with the evidence of autocatalysis. The reaction is accelerated in the cetyltrimethylammonium bromide (CTAB) micellar medium but sodium dodecyl sulfate (an anionic surfactant) has no effect. The pseudo first-order rate constants have been determined at different [reductant], [oxidant], [H₂SO₄], temperature, and [CTAB]. The reaction rate increased with increasing [d-xylose] and decreased with increase in [H₂SO₄]. The CTAB-micelle-catalyzed kinetic results can be interpreted by the pseudophase model. The kinetic parameters such as association constant (K _s), micellar medium rate constant (k _m), and activation parameters (E _a, ΔH ^# and ΔS ^#) are evaluated and the reaction mechanism is proposed. The reaction rate is inhibited by electrolytes and the results provide an evidence for the exclusion of the reactive species from the reaction site.     

The thermal decomposition of diimide in the gas phase: Kinetics and stoichiometry

The kinetics and stoiehiometry of the decomposition of N₂H₂ and N₂D₂ have been studied as a function of sample size, pressure, and temperature. The reaction follows a single first order kinetic expression over most of its time course. It is suggested that the rate-determining step in the mechanism is a first-order homogeneous gas-phase isomerization of trans-diimide with rate constants:k = 1.8 exp (-4.2 kcal/mol/RT) sec^?1 and k = 1 exp (-4.4 kcal/mol/RT) sec^?1. The detailed mechanism of this isomerization, however, is not evident. At temperatures above room temperature, self-heating has been observed which leads to an initial fast decay. At room temperature the reaction exhibits autocatalysis with the rate increasing as the reaction proceeds. This has been attributed to enhancement by a surface decay process involving adsorbed hydrazine. The only significant products from the decomposition of N₂H₂ are N₂, H₂, and N₂H₄, and the results are interpreted in terms of two parallel reactions: The decomposition of N₂D₂ occurs almost completely by the single reaction giving N₂ + N₂D₄. No azide formation has been detected from either N₂D₂, or N₂D₂, and limits have been put on the yield of ammonia. Extinction coefficients at 365 nm of 3.9 ± 0.2 for N₂H₂ and 3.3 ± 0.1 for N₂D₂ have been measured. Both the rate of decay and the stoichiometry of products show pressure dependence below 150 torr, and this is suggested to be due to direct decomposition of cis-N₂H₂ on the surface.     

Kinetics and mechanism of ruthenium(III)-catalysed oxidation of allyl alcohol by acid bromate-autocatalysis in catalysis

The kinetics of oxidation of CH₂=CHCH₂OH with KBrO₃ in the presence of Ru^III catalyst in aqueous acid medium has been studied under varying conditions. The active species of oxidant and catalyst were HBrO₃ and [Ru(H₂O)₆]³⁺ respectively. The autocatalysis exhibited by one of the products, i.e., Br^–, was attributed to the formation of a complex between the bromide ion and Ru^III. A composite scheme and rate law were proposed. Reaction constants involved in the mechanism have been evaluated.     

The reactions of atomic hydrogen and active nitrogen with hydrogen azide

Detection of atoms by mass spectrometry has been used to study the reactions of hydrogen azide, HN₃, with H atoms and active nitrogen, in a fast flow reactor at pressures of about 1 torr. Stoichiometry and products of the H + HN₃ reaction have been determined and the rate constant of the initial step, assumed to be H + HN₃ → NH₂ + N₂, was found to be 2.54 × 10^?11 exp (?4600/RT) cm³ molecule^?1 s^?1, in the temperature range of 300–460K. The formation of NH₃ and H₂ products has been discussed from the different secondary steps which may occur in the mechanism. For the reaction of active nitrogen with HN₃, evidence has been found for the participation of excited nitrogen molecules produced by a microwave discharge through molecular nitrogen. The influence of excited nitrogen molecules has been reduced by lowering the gas flow velocity. It was then possible to study the N + HN₃ reaction for which the rate constant of the initial step was found to be 4.9 × 10^?15 cm³ molecule^?1 s^?1 at room temperature. Finally, the occurrence of these elementary reactions has been discussed in the mechanism of the decomposition flame of HN₃.     

Experimental and Computational Study of the Thermal Decomposition of 3‐Methyl‐3‐buten‐1‐ol in m‐Xylene Solution

An experimental study of the thermal decomposition of a β‐hydroxy alkene, 3‐methyl‐3‐buten‐1‐ol, in m‐xylene solution, has been carried out at five different temperatures in the range of 513.15–563.15 K. The temperature dependence of the rate constants for the decomposition of this compound in the corresponding Arrhenius equation is given by ln k (s^?1) = (25.65 ± 1.52) ? (17,944 ± 814) (kJ·mol^?1)·T^?1. A computational study has been carried out at the M05–2X/6–31+G(d,p) level of theory to calculate the rate constants and the activation parameters by the classical transition state theory. There is a good agreement between the experimental and calculated rate constants and activation Gibbs energies. The bonding characteristics of reactant, transition state, and products have been investigated by the natural bond orbital analysis, which provides the natural atomic charges and the Wiberg bond indices. Based on the results obtained, the mechanism proposed is a one‐step process proceeding through a six‐membered cyclic transition state, being a concerted and slightly asynchronous process. The results have been compared with those obtained previously by us (Struct Chem 2013, 24, 1811–1816) for the thermal decomposition of 3‐buten‐1‐ol, in m‐xylene solution. We can conclude that in the compound studied in this work, 3‐methyl‐3‐buten‐1‐ol, the effect of substitution at position 3 by a weakly activating CH₃ group is the stabilization of the transition state formed in the reaction and therefore a small increase in the rate of thermal decomposition.     

Kinetics of vanadium (V) catalyzed oxidation of gallic acid by potassium bromate in acid medium

The kinetics of oxidation of gallic acid with potassium bromate in the presence of vanadium(V) catalyst in aqueous acid medium has been studied under varying conditions. The active species of catalyst and oxidant in the reaction were understood to be HBrO₃ and VO₂⁺. The autocatalysis exhibited by one of the products, i.e. Br⁻, was attributed to complex formation between bromide and vanadium(V). A composite scheme and rate law were possible, some reaction constants involved in the mechanism have been evaluated. © 1996 John Wiley & Sons, Inc.     

Research of thermal decomposition of hydrated methanesulfonates

Hydrated methanesulfonates Ln(CH₃SO₃)₃·nH₂O (Ln=La, Ce, Pr, Nd and Yb) and Zn(CH₃SO₃)₂·nH₂O were synthesized. The effect of atmosphere on thermal decomposition products of these methanesulfonates was investigated. Thermal decomposition products in air atmosphere of these compounds were characterized by infrared spectrometry, the content of metallic ion in thermal decomposition products were determined by complexometric titration. The results show that the thermal decomposition atmosphere has evident effect on decomposition products of hydrated La(III), Pr(III) and Nd(III) methanesulfonates, and no effect on that of hydrated Ce(III), Yb(III) and Zn(II) methanesulfonates. This revised version was published online in August 2006 with corrections to the Cover Date.