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°.

     

Maximally inhibited gas phase elimination kinetics of methyl 3-bromopropionate

The gas phase elimination of methyl 3-bromopropionate has been studied in a static system and in vessels seasoned with allyl bromide. The reaction is autocatalyzed by HBr. However, under maximum inhibition with propene, the reaction obeys first order kinetics and is a homogeneous unimolecular elimination. The products are methyl acrylate and hydrogen bromide. The observed rate coefficients are represented by the Arrhenius equation: log k₁ (s^–1)=(12.94±0.46)–(214.5±6.0) kJ/mol/2.303 RT in the temperature range 400.1–449.9 °C and pressure range 49–98 Torr. The pyrolysis of methyl 3-bromopropionate is 3.5 times faster than that of ethyl bromide. This significant difference may be attributed to the greater acidity of the -hydrogen in 3-bromopropionate compared to that in ethyl bromide.

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3- , . HBr . . . , , : log k₁ (^–1)=(12,94±0,46)–(214,5±6,0) ·^–1/2,303 RT 400,1–449,9°C 49–98 . - 3,5 , . - - .

     

Acid-base and catalytic properties of binary oxides in the oxidative dehydrodimerization of toluene

Acidity and basicity of binary oxide catalysts measured by the CO₂ and NH₃ thermodesorption method are compared with their catalytic activity in oxidative conversion of toluene. The rate of toluene dehydrodimerization is shown to increase with the catalyst basicity.

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CO₂ NH₃ . , .

     

A Thermal study of the precipitates formed in ammonia neutralization of acidic solutions of dissolved phlogopite

The precipitates containing mainly iron, aluminium and magnesium hydroxides, obtained from phlogopite dissolved in nitric acid by means of the neutralization procedure with ammonia, have been investigated by thermal analysis (TG, DTG and DTA). According to the present study, which is part of a larger investigation into the chemical utilization of Finnish mica minerals, the formation of solid solutions between iron and aluminium hydroxides in silt increases with an increasing neutralization temperature. Nitrogen exists mainly in the form of nitrate in silts, and magnesium forms mixed hydroxides with aluminium, which causes a separation between the iron hydroxide and magnesium aluminium hydroxide phases.

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Zusammenfassung Die von in Salpetersäure gelöstem Phlogopit durch Neutralisierung mit Ammoniak erhaltenen, hauptsächlich Eisen-, Aluminium- und Magnesiumhydroxid enthaltenden Niederschläge wurden thermoanalytisch (TG, DTG und DTA) untersucht. In der vorliegenden Arbeit, die Teil einer grossangelegten Untersuchung zur chemischen Nutzung finnischer Glimmermineralien ist, wird gezeigt, dass die Bildung fester Lösungen von Eisen- und Aluminiumhydroxiden in Schluff mit zunehmender Neutralisationstemperatur ansteigt. Stickstoff kommt in Schluff hauptsächlich in Form von Nitraten vor, und Magnesium bildet Mischhydroxide mit Aluminium, was eine Trennung der Eisenhydroxidphase von der Magnesium-Aluminium-Hydroxidphase bewirkt.

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, , , . . , , . , , , , .

     

A surface potential study of adsorbed oxygen species on a Bi2Mo3O12 catalyst

Bi₂Mo₃O₁₂ is a selective oxidation catalyst of propylene into acrolein. Surface potential measurements proved the presence of an equilibrium between gaseous oxygen and the O^2– species adsorbed on the surface of the catalyst, under oxygen atmosphere, in the range 538K–673K. This is in accordance with the fact that O^2– is a selective oxidation species. An oxygen adsorption mechanism is also discussed.

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Bi₂Mo₃O₁₂ . O^–2, , 538–613 . , O^–2 . .

     

Potential for coal calorific value corrections,dependent on the carbonate mineral type present

In addition to calcite, other carbonate minerals in coal all undergo endothermic reactions on heating, i.e. dolomite, ankerite, siderite, aragonite, magnesite, rhodochrosite, witherite and strontianite. Of these, when determined in air, siderite and rhodochrosite give small exothermic resultants, while the amount of Fe in ankerites affects the actual endothermic values obtained. The magnitude of these carbonate decomposition reactions can be shown by DTA to be different and will need to be allowed for individually in calorific value corrections of coals containing them.

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Zusammenfassung Nicht nur Kalkspat, sondern auch andere in Kohle vorkommende Karbonatmineralien wie z. B. Dolomit, Ankerit, Spateisenstein, Aragonit, Magnesit, roter Braunstein, Witherit und Strontionit gehen bei Erhitzen endothermische Reaktionen ein. Von diesen zeigen Spateisenstein und roter Braunstein exotherme Ergebnisse kleinen Wertes, während der Betrag an Eisengehalt in Ankeriten den jeweils gemessenen endothermischen Wert beeinflußt. Das Ausmaß dieser Karbonatzersetzungsreaktionen kann durch DTA-Messungen als unterschiedlich nachgewiesen werden und muß bei den Kaloriewertkorrektionen für Kohlen, die diese Mineralien enthalten, berücksichtigt werden.

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, , , , , , , , . , , . , , .

     

Studies of copper-modified V?Mo oxide catalyst for acrolein oxidation to acrylic acid

Modification of a V–Mo oxide catalyst by copper improves its catalytic properties due to the formation of a variable composition V–Cu–Mo–O phase with varying the ratio Mo/Me (Me=V+Cu).

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T–Cu–Mo–O, Mo/Me, Me=V+Cu.

     

Bromine hydrolysis control and two consecutive oscillatory domains in closed, cerium-catalyzed glyoxylic acid Belousov-Zhabotinsky systems

In closed, cerium-catalyzed glyoxylic acid Belousov-Zhabotinsky systems we found a new dynamic behavior, viz. the observation of two oscillatory regimes separated by a nonoscillatory region. Mechanisms for this intermediate nonoscillatory domain are discussed.

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- , , , . .

     

Kinetics of Fe3+ and Cu2+ sorption by fibrous polyampholite

The kinetics of Fe³⁺ and Cu²⁺ sorption from sulfate salt solutions by fibrous polyampholite have been studied.

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Fe³⁺ Cu²⁺ , .

     

On the structure of surface active centers on CuO

It has been established that surface active centers on CuO can be associated with its surface defects, i.e. surface exits of twinning and screw dislocations where highly reactive oxygen and CO can be coordinated.

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, , CO.

     

Temperature programmed desorption (TPD) of carbon monoxide from cobalt surfaces

Three different binding states of CO on cobalt surfaces have been identified by TPD studies. The energetics of these adsorption states and their relevance in Fischer-Tropsch synthesis are considered.

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CO - . -.

     

Temperature-programmed hydrogen desorption from water on bimetallic catalysts Ir?Fe/Al2O3

Desorption of hydrogen liberated in the process of water decomposition on bimetallic catalysts (3% Ir–Fe/Al₂O₃) at linear temperature growth was observed. In the case of iridium the amounts of desorbing hydrogen are relatively small, whereas for iron they are many times greater.

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, 3% Ir–Fe/Al₂O₃ . , , .

     

Thermoanalytical investigations of some industrial wastes produced in steel works

The experiments involves three types of industrial wastes produced by iron works, which create serious hazards to the natural environment: (1) paint-shop sludge, (2) oil-polluted diatomite, and (3) oil-polluted scale. The choice of an appropriate and safe storage method should be based on extensive physicochemical examination.DTA, in combination with other data, allows characterization of the combustible properties of wastes. Thermoanalytical measurements were carried out in a dynamic air atmosphere. Enthalpy values were calculated from peak areas of DTA curves. Thermoanalytical data were compared with calorimetric results obtained with an oxygen bomb.

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Zusammenfassung Drei Arten industrieller Abtälle eines Stahlwerks, die schwere Umweltbelastungen darstellen, wurden untersucht: (1) Lackiererei-Schlamm, (2) ölhaltiger Diatomit, (3) ölhaltiger Kesselstein. Geeignete sichere Deponien setzen ausführliche physikalisch-chemische Untersuchungen voraus. DTA in Kombination mit anderen Untersuchungen erlaubt die Charakterisierung der Verbrennungseigenschaften der Abfälle. Die thermoanalytischen Untersuchungen erfolgten im Luftstrom, die Verbrennungswärmen wurden aus den DTA-peak-Flächen berechnet. Die Ergebnisse werden mit denen kalorimetrischer Messungen in einer Sauerstoffbombe verglichen.

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- , . , . , - . . . . , .

     

Thermoanalytical assessment of the quality of edible and technical oils

An investigation of the thermal decomposition of fish oils and motor lubricating oils resulted in the elaboration of a new method, which, by utilizing the relationship between the temperatures of mass losses and the changes in the cnemical composition due to the oxidative and hydrolytic decomposition of fish oils and to the processes occuring in lubricating oils in the course of their service in the oils system of combustion engines, allows estimations of the physicochemical properties of these oils.

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Zusammenfassung In Zusammenhang mit der Ausarbeitung einer neuen Methode, die die Abschätzung der physikalisch-chemischen Eigenschaften von Fischölen und Motorschmierölen ermöglicht, wurde eine Untersuchung über die thermische Zersetzung dieser Öle durchgeführt. Als Grundlage dafür diente der Zusammenhang zwischen der Masseverlusttemperatur und der mit der oxidativen bzw. hydrolytischen Zersetzung von Fischölen und den Alterungsprozessen von Motorschmierölen in Verbrennungsmotoren in Verbindung stehenden Veränderung der chemischen Zusammensetzung.

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, - , , , , .

     

Influence of SO 4 2− doping and Y-irradiation on the thermal decomposition of barium bromate

The effects of SO ₄ ^2– doping and Y-irradiation on the isothermal (563 K) decomposition of barium bromate have been investigated gasometrically with a vacuum apparatus. Plots of the fraction decomposed avs. timet for pure, doped and irradiated crystals exhibited characteristic stages: initial gas evolution (initial puff), an induction period, linear reaction, an acceleratory period and decay. The data are considered in the light of various kinetic models, e.g. linear rate equation, Prout-Tompkins and Avrami-Erofeev. The plausible mechanism of the reaction and the effects on this of anion vacancies and Y-irradiation are discussed briefly.

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Zusammenfassung Die Wirkung von Versetzen mit SO ₄ ^2} - und -Bestrahlung auf die isotherme (563 K) Zersetzung von Bariumbromat wurde gasometrisch untersucht. Es zeigte sich, daß die Zeitcharakteristiken für die reinen, die versetzten und bestrahlten Kristalle verschiedene Stufen durchlaufen, nämlich anfängliche Gasentwicklung (Aufblähen), Induktionsperiode, lineare Reaktion, Beschleunigung und Abklingen. Die Daten wurden unter dem Gesichtspunkt verschiedener kinetischer Modelle betrachtet, z. B. lineare Geschwindigkeitsgleichung, das Modell von Prout-Tompkins und Avrami-Erofeev. Es werden kurz ein einleuchtender Reaktionsmechanismus und der Einfluß von Anionengitterlücken und -Bestrahlung darauf diskutiert.

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- (563 ) . , ,-, «t» , , , , , . , - -. .

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The authors thank the Department of Atomic Energy, Government of India, for financial support. M.K.S. also gratefully acknowledges the award of a Research Fellowship by the same agency, which made the work possible.     

Solid aluminiumalkyl-based isomerization catalysts. Surface acidity and catalytic activity

Isomerization catalysts with high activity and selectivity were prepared by chemical anchoring of aluminiumethyldichloride on the surface of inorganic oxides. Surface acidity was studied by calorimetric and IR spectroscopy methods, and was found to correspond well with catalytic activity for m-xylene isomerization.

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. . , -.

     

Thermal stabilities of new complexes of magnesium nitrate,acetate and phosphate with amide ligands

The thermal decompositions of complex compounds of magnesium nitrate, acetate and phosphate with urea, acetamide and formamide ligands were investigated by means of simultaneous TG-DTA. The thermal stabilities of the complexes depend on the natures of the anions and the amide ligands.

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Zusammenfassung Die thermische Zersetzung der Komplexverbindungen von Magnesiumnitrat-,acetat und -phosphat mit Harnstoff, Acetamid und Formamid wurden durch simultane TG-DTA untersucht. Die thermische Stabilität der Komplexe hängt von den Anionen des Salzes und den Amidliganden ab.

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-,- , . , .

     

Stoichiometry as canonical transformation of chemical kinetics

Applying the apparatus of differential manifolds and that of classical conservative point mechanics, it is shown that stoichiometry plays the role of canonical transformations in chemical reaction kinetics.

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, , .

     

Effect of medium composition on the monooxygenase activity of immobilized hemin in aniline oxidation

The effect of the composition of the reaction medium on the rate of aniline oxidation to p-aminophenol by hydrogen peroxide on hemin immobilized on -propylimidazole-modified silica has been studied. Organic solvent additives (alcohols, esters and nitriles) are shown to increase the reaction rate. The observed effect is attributed to the decrease of the medium dielectric constant.

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- , , --. , (, , ) . .

     

Calculation of the energy spectrum of surface oxygen on CuO by the interacting bonds method

Using the interacting bonds model a calculation has been made for the energy spectrum of oxygen on the CuO surface. Dissociative adsorption of oxygen can be realized in one and two-center forms with 9.2 and 60.4 kcal/mol, respectively. Intermediate values of the adsorption heats are attributed to oxygen adsorption on induced and biographic defects. The theoretically calculated energy spectrum of adsorbed oxygen is in reasonable agreement with that obtained experimentally from the dependence of isosteric heats of oxygen adsorption on the surface coverage.

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CuO. - 9,2 60,4 / . . .