Kinetics of thermal decomposition of pyrite in an inert atmosphere

The thermal decomposition of pyrite in an inert atmosphere was studied in order to obtain a detailed knowledge of the kinetics and mechanism of the reaction 2 FeS₂=2FeS+S₂, which is one of the methods of producing elementary sulphur. The process was studied under isothermal conditions at temperatures of 600, 660, 700, 750, 800 and 850 °C in a nitrogen atmosphere, by means of a thermobalance. The rate-controlling processes were determined and their kinetic parameters were calculated. The optimum temperature for the process was found to be 800 °C.

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Zusammenfassung Es wurde die thermische Zersetzung von Pyrit in inerter Atmosphäre bestimmt, um detaillierte Informationen über Kinetik und Mechanismus der Reaktion 2 FeS₂=2FeS+S₂, einer der Darstellungsreaktionen von elementarem Schwefel zu erlangen. Der Vorgang wurde mittels einer Thermowaage unter isothermen Bedingungen bei Temperaturen von 600, 660, 700, 750, 800 und 850 °C untersucht. Es wurden die geschwindigkeitsbestimmenden Schritte bestimmt und deren kinetische Parameter errechnet. Als Optimumtemperatur für diesen Prozeß erwies sich 800 °C.

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- 2FeS₂=2FeS + S₂, . 600, 660, 700, 750, 800 850 ° . , 800°.

     

Thermal decomposition of pyrite

Thermal decomposition of natural pyrite (cubic, FeS₂) has been investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. X-ray diffraction analysis of pyrite ore from different sources showed the presence of associated minerals, such as quartz, szomolnokite, stilbite or stellerite, micas and hematite. Hematite, maghemite and pyrrhotite were detected as thermal decomposition products of natural pyrite. The phase composition of the thermal decomposition products depends on the temperature, time of heating and starting size of pyrite crystals. Hematite is the end product of the thermal decomposition of natural pyrite.     

The thermal decomposition of vermiculite

Vermiculite shows some promising potentials, both as ion-exchange material and thermal insulation. The thermal decomposition of vermiculite from Sokli, Finland, has been studied by various thermoanalytical methods, including high-temperature X-ray diffraction and high-pressure DTA. The major phases occurring during successive heating are: 15Å → 11.8Å → 10.1Å → 9.74Å → 9.3Å (all d₀₀₂ spacings). Reaction enthalpies and activation energies are given for most of the reactions. For the evaluation of kinetic parameters, high-temperature X-ray diffraction is suggested as a powerful tool, superior to most conventional methods.     

The thermal decomposition of n-hexane

The kinetics of the pyrolysis of n-hexane was studied in a conventional static reactor over a temperature range of 650–840 K. The overall reaction is essentially first order with the kinetic parameters A = 10^13.92 s^?1 and E_A = 260.3 kJ/mol. The distributions of the main products were analyzed by gas chromatography. A reaction model involving 240 elementary reactions was developed to describe the experimental rate data. The agreement of the model with experimental data was surprisingly good over a wide range of temperatures and pressures and up to medium extents of conversion. Methods for sensitivity studies based upon the quasi-stationary-state assumption (QSSA) were developed, and for a number of more detailed effects, such as self-inhibition, explanations could be given. It was also shown that the hexyl isomerization reactions influence strongly the product distribution. The outstanding capability of kinetic modeling with computer simulations in handling complex kinetic systems is demonstrated.     

The thermal decomposition of chlorodifluoromethane

The kinetics of pyrolysis of chlorodifluoromethane have been studied in a flow system between 670° and 750° using partial press of CF₂HCl between 17 mm and 200 mm Hg. The reaction obeys first order kinetics at low conversions, but is retarded by hydrogen chloride. The major features of the reaction are explained by the following mechanism:     

The thermal decomposition of water

The reflected shock tube technique with multipass absorption spectrometric detection of OH‐radicals at 308 nm, corresponding to a total path length of 1.749 m, has been used to study the reaction H₂O + M → H + OH + M between 2196 and 2792 K using 0.3, 0.5, and 1% H₂O, diluted in Kr. As a result of the increased sensitivity for OH‐radical detection, the existing database for this reaction could be extended downward by ～500 K. Combining the present work with that of Homer and Hurle, the composite rate expression for water dissociation in either Ar or Kr bath gas is k_{1,Ar(or Kr)} = (2.43 ± 0.57) × 10^?10 exp(?47117 ± 633 K/T) cm³ molecule^?1 s^?1 over the T‐range of 2196–3290 K. Applying the Troe factorization method to data for both forward and reverse reactions, the rate behavior could be expressed to within <±18% over the T‐range, 300–3400 K, by the three‐parameter expression k_1,Ar = 1.007 × 10⁴ T^?3.322 exp(?60782 K/T) cm³ molecule^?1 s^?1 A large enhancement due to H₂O with H₂O collisional activation has been noted previously, and both absolute and relative data have been considered allowing us to suggest k₁, H₂ O = 1.671 × 10² T^?2.440 exp(?60475 K/T) cm³ molecule^?1 s^?1 for the rate constants with H₂O bath gas over the T‐range, 300–3400 K. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 211–219, 2006     

The thermal decomposition of biacetyl

The thermal decomposition of biacetyl has been studied at small percentage conversion over the temperature range 375-417°C. For these conditions, an almost quantitative mass balance was obtained by gas-chromatographic analysis. The following equation was obtained for the overall reaction Between 240° and 277°C, the decomposition of biacetyl initiated by methyl radicals has also been studied. As source of radicals, the thermolysis of azomethane was used. Moreover, the Arrhenius parameters of the following reactions were determined: where A is in sec^?1 for reaction (1) and in cm³mole^?1 sec^?1 for reactions (3) and (4); E is in kcal/mole. Evidence is provided that the displacement reaction (4) proceeds by a two step mechanism.     

The thermal decomposition of zinc hydroxocarbonate

Institute of Catalysis, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 5, pp. 8–13, September–October, 1990.     

The thermal decomposition of phosphorus iodides

The thermal decomposition of crystalline PI₃ and P₂I₄ in nitrogen and oxygen is reported. The oxidation of PI₃ leads mainly to the formation of phosphorus pentoxide and iodine together with P_xI polymeric species as a minor product. The decomposition of the polymeric species P₃I₂O₆ in oxygen and nitrogen follows a two-stage route which precludes its involvement in the oxidation of P₂I₄.

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Zusammenfassung Es wurde die thermische Zersetzung von kristallinem PI₃ und P₂I₄ in Stickstoff und Sauerstoff untersucht. Die Oxydation von PI₃ führt zur Bildung von Phosphorpentoxyd und Jod mit wenig Polymeren der Zusammensetzung P_xI. Die Zersetzung der Polymeren P₃I₂O₄ in Sauerstoff und Stickstoff erfolgt in zwei Stufen, die eine Beteiligung in der Oxydation von P₂I₄ ausschließen.

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Résumé On décrit la décomposition thermique, dans l'azote et dans l'oxygène, de PI₃ et de P₂I₂ cristallins. L'oxydation de PI₃ conduit principalement à la formation d'iode et de pentoxyde de phosphore, avec de petites quantités de P_xI de type polymère. La décomposition de l'espèce polymère P₃I₂O₆, dans l'oxygène et dans l'azote, s'effectue suivant un processus en deux étapes excluant sa participation à l'oxydation de P₂I₄.

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I₃ P₂I₄ . I₃, , , — — _xI . ₃I₂₆ , ₂I₄.

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The author is indebted to Mrs. I. M. Walker for practical assistance with the thermoanalysis studies.     

The thermal decomposition of azomethane-d6

The thermal decomposition of azomethane-d₆ has been studied. There is a short chain reaction, and measurements have been made of the rate of production of N₂, CD₄, and C₂D₆. A mechanism is suggested which accounts for these results fairly well. A comparison is made with some similar results of Forst for azomethane. Measurements have also been made of the reaction inhibited by NO. It is believed that the N₂ production, extrapolated to zero NO pressure, measures the rate of the initial step CD₃N₂CD₃ → 2 CD₃ + N₂. This has an activation energy at high pressures of 50.7 kcal per mole and an Arrhenius A·factor of 10^15.49 sec^?1. This is to be compared to values of 55.5 and 10^17.3 found by Forst and Rice for CH₃N₂CH₃ → 2 CH₃ + N₂. The pressure fall-off behavior for CD₃N₂CD₃ → 2 CD₃ + N₂ has also been investigated and compared to the theoretical curves, which seem to fit satisfactorily except at the lowest pressure, where experimental errors may be large. Unexpectedly, the fall-off curve crosses that for CH₃N₂CH₃ → 2 CH₃ + N₂. It is suggested that the extrapolation to zero NO pressure may not be entirely correct in the CH₃N₂CH₃ case where the chain is longer than with CD₃N₂CD₃. It is believed that the decomposition of azomethane-d₆ is a better example for unimolecular-rate theory than is that of azomethane.     

The thermal decomposition of ammonium heptamolybdate

The thermal decomposition of ammonium heptamolybdate has been investigated by TG. The decomposition is discussed, making use of additional information obtained from isothermal studies, X-ray and IR measurements. The formation of two new compounds, namely (NH₄)₂O · 14 MoO₃ and (NH₄)₂O · 22 MoO₃, prior to the formation of MoO₃ is detected, as well as the main intermediate compounds (NH₄)₂O · 2.5 MoO₃ or (NH₄)₂O · 3 MoO₃ (according to the water content of the starting material) and (NH₄)₂O · 4 MoO₃.     

The thermal decomposition of zirconium oxyhydroxide

The thermal decomposition of zirconium oxyhydroxides prepared by the mixture of aqueous zirconium oxychloride solutions and aqueous solutions of sodium hydroxide or ammonium hydroxide under various conditions has been examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectrophotometry. As a result, it is seen that the thermal decomposition of zirconium oxyhydroxide, in which the composition is ZrO_2-x(OH)_2xyH₂O where x2 and 1y<2, proceeds according to the following process:

The thermal decomposition of palladium acetate

The nature, products, and enthalpy of the thermal decomposition of [Pd(CH₃CO₂)₂]₃ were determined in air, nitrogen and vacuum. Thermogravimetry, differential thermal analysis, evolved gas analysis, differential scanning calorimetry, and infrared spectroscopy were used to characterize the process and products. In vacuum the trimer volatilizes completely below 200 °C. The IR spectrum of the gas phase species is reported. At atmospheric pressure the material decomposed to Pd between 200 and 300 °C depending upon the rate of heating. The apparent activation energy for this process is about 115 ± 5 kJ mol^–1 and the enthalpy is 440 ± 20 kJ mol^–1. In the presence of oxygen, however, oxidation of the ligands leads to an overall exothermic process. The resulting the Pd then slowly oxidizes to PdO₂ up to the decomposition temperature of the oxide near 800 °C. There is the slight loss of a Pd containing species, presumably due to sublimation or gas entrainment, during the decomposition below 300 °C. The extent of this loss increases with increasing heating rate, approaching 10% of the total Pd at heating rates of 64 °C min^–1.

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Zusammenfassung Natur, Produkte und Enthalpie der thermischen Zersetzung von [Pd(CH₃CO₂)₂]₃ in Luft, Stickstoff und Vakuum wurden untersucht. Zur Charakterisierung des Prozesses und der Produkte wurden TG, DTA, EGA, DSC und IR-Spektroskopie herangezogen. Im Vakuum verflüchtigt sich das Trimere vollständig unterhalb 200°. Das IR-Spectrum der gasförmigen Species ist angegeben. Bei Atmosphärendruck zersetzt sich das Material, abhängig von der Aufheizgeschwindigkeit, zwischen 200 und 300° zu Pd. Die scheinbare Aktivierungsenergie für diesen Prozeß beträgt 115 ± 5 kJ · mol^{– 1}, die Enthalpie beläuft sich auf 440 ± 20 kj · mol^–1. In Gegenwart von Sauerstoff werden die gasförmigen Produkte sofort oxydiert, was ein exothermen Bruttoeffekt zur Folge hat. In Gegenwart von Sauerstoff wird Pd langsam bis zur Zersetzung des Oxids bei nahe 800° oxydiert. Es wird ein geringer Verlust einer Pd enthaltenden Species beobachtet, der vermutlich auf Sublimation oder auf Mitreißen im Gasstrom während der Zersetzung unterhalb 300° zurückzüfuhren ist. Dieser Verlust wird mit der Erhöhung der Aufheizgeschwindigkeit größer und erreicht bei einer Aufheizgeschwindigkeit von 64° · min^–1 10% des Gesamt-Pd.

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, [Pd(CH₃CO₂)₂]₃, . , , , . 200°. . 200 300° . 155±5 · ^–1, –440±20 · ^–1. , , . 800°. 300° , , , . 10% 64° .

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Presented in part at the 14th Annual NATAS Conference, San Francisco, CA, Sept. 1985.     

The thermal decomposition of aluminium sulfate

The mechanism of thermal decomposition of aluminum sulfate has been investigated in the 500–700°C temperature range using a flow reactor system with the emitted gaseous sulfur oxides collected in a Goksøyr—Ross coil and a hydrogen peroxide impinger. Sulfur trioxide (SO₃) was found to be the primary sulfur oxide released during thermal decomposition (1).

Less than 3% of the released sulfur oxides were sulfur dioxide (SO₂), indicating that the SO₃ dissociation reaction (2) is slow relative to the residence time of the SO₃ in the reactor (～ 1 sec).

The experimental technique should be readily adaptable to the study of the thermal decomposition of other metal sulfates.     

The thermal decomposition of ammonium metavanadate

On heating, ammonium metavanadate (AMV) decomposes in several atmospheredependent stages. An important decomposition intermediate, ammonium hexavanadate (AHV), may also be prepared by wet-chemical methods and the kinetic parameters for the thermal decomposition of AMV and of the AHV preparation have been obtained. The kinetic study has been supplemented by surface-area measurements and by electron microscopic examination of the surfaces of reactant, intermediate and product crystallites. On the basis of the type of decomposition curve, the measured activation energies, and the effects of oxygen and water vapour on the decomposition rate, it has been concluded that in vacuum and in inert atmospheres the evolution of ammonia is the rate-determining step, while in oxidizing atmospheres evolution of water is rate determining. Comparison of the kinetic parameters with thermodynamic data for the decomposi. tion has led to suggestions as to the nature of the activated complexes involved.     

The thermal decomposition of NaHCO3

New EGA findings revealed that the small endothermal event preceding that of the main decomposition of commercial NaHCO₃ involves the simultaneous evolution of water and CO₂. At very high sensitivity, EGA experiments evidenced that the above (limited) evolution of gases also took place from the recrystallized material for which thermal methods gave no indication of endotherms.Careful reexamination of previous DSC results indicated that for one kind of recrystallized material a very small endotherm had been neglected. Renewed experiments revealed that this endotherm can be enhanced if the samples are prepared by crushing and sieving in a wet atmosphere. Parallel FT-IR experiments on commercial and recrystallized materials demonstrated the presence of carbonate in samples that had previously been taken just beyond the first small endotherm; this confirmed the EGA results. SEM experiments showed that surface texture changes take place when samples are heated to temperatures just above that of the preliminary endotherm. On the basis of these new findings, the interpretation previously given to the small endotherm is revised and detailed knowledge is gained on the mechanism of decomposition of NaHCO₃.The authors express their gratitude to Dr. Stephen B. Warrington (Thermal Analysis Consultancy Service, Leeds Metropolitan University) for having communicated the EGA results that led to the present report. The authors also feel indebted to Dr. Mario Paolieri of the Centro Interdipartimentale per la Microscopia Elettronica e la Microanalisi (M.E.M.A.) for his help in performing and interpreting the SEM experiments, and to Mr. Paolo Parri for his careful preparation of the illustrative material. Financial support from the University of Florence (ex 60% MURST) is greatly appreciated.     

邻苯二甲酸钙的热分解反应研究

用热重和示差扫描量热分析法研究了-水合邻苯二甲酸钙的热分解过程。其热分解过程分为三个阶段: 在160~260℃脱水生成无水盐; 在460~780℃分解生成CaCO~3.C; 在780~900℃生成CaO和CO。用粉未X射线衍射、红外光谱和色-质联用分析法表征了各阶段热分解产物的组成和结构。讨论了热分解产物的自由基反应机理。