Recent progress in numerical methods for the determination of thermokinetics

The results of a multinational concerted programme on the determination of thermokinetics are presented. The purpose of the programme was to compare different numerical methods which have been independently proposed for the determination of thermokinetics from experimental calorimetric data. To achieve this end, the same experimental data, obtained from two heat-flow calorimeters, were distributed and successively analyzed by the different methods. Numerical methods based on the state function theory, on Fourier transform analysis, on dynamic optimization and on a simple differentiation of the data were thus critically tested.

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Zusammenfassung Es wurden die Ergebnisse der gemeinsamen Arbeiten über die Bestimmung der Thermokinetik mit 4 numerischen Methoden (dynamische Optimalisierung, Methode der Zustandfunktionen, harmonische Analyse und umgekehrte Korrektion) vorgestellt. Die experimentellen Daten wurden mit Hilfe von 2 Kalorimetern mit einer konstanten Temperatur des Isoliermantels ermittelt. Die Durchführung der Versuche ermöglichte ein Vergleich der angewandten Methoden.

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Résumé Les résultats d'un programme de recherches concerté multinational sur la détermination des données thermocinétiques sont présentés. Le but du programme était de comparer différentes méthodes numériques proposées indépendamment pour la détermination des données thermocinétiques à partir des mesures calorimétriques expérimentales. Pour celà, les mêmes données expérimentales fournies par deux calorimètres à flux de chaleur ont été distribué es et analysées successivement par 4 méthodes: utilisation des variables d'état, analyse de la transformée de Fourier, optimalisation dynamique et simple différentiation des données.

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. , . , , . , , , .

     

Investigation of the self-heating phenomenon in the bulk polymerization of acrylonitrile

The temperature of the polymerizing system was measured with a thermistor during the bulk polymerization of acrylonitrile initiated by azoisobutyronitrile. The temperature of self-heating suddenly rises at a conversion of about 2%. This jump of temperature is presumably caused by the formation of a gel structure and, consequently, the outfall of thermal convection within the system.

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, -- . , - . - , .

     

Generation of model reactions leading to limit cycle behavior

The system of differential equations by Feistel and Ebeling has been generalized. Some new formal kinetic reactions with two internal components, which may exhibit limit cycle behavior have been studied. Based upon the numerical integration of the deterministic models of these reactions the oscillatory character of the systems has been confirmed.

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. , . .

     

Zeolite content determination in kaolinic clays via thermal effects

For application in catalysis and adsorption processes, zeolites are synthesized on the surface of spray-dried kaolin microspheres. Various thermal effects are used for the rapid characterization of the zeolite type and content. From DTA measurements, the exothermic lattice break-down peak gives information on the zeolite type and the thermal stability of the sample. Measurements of the heats of immersion by a very simple and quick method allow conclusions about the type and the sorption properties of the zeolite part of the clay. The most precise method to estimate the zeolite content was a standardized technique of desorption and readsorption of water or organic compounds by means of a thermobalance.

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Zusammenfassung Zur Anwendung in der Katalyse und bei Adsorptinsprozessen werden Zeolithe auf der Oberfläche sprüh-getrockneter Kaolin-Mikrokugeln eingesetzt. Verschiedene thermische Effekte werden zur schnellen Charakterisierung des Zeolith-Typs und -Gehalts genutzt. Der exotherme DTA-peak beim Gitterzusammenbruch liefert Informationen über Zeolith-Typ und thermische Stabilität der Probe. Eine sehr einfache Schnellmethode zur Messung der Immersionswärmen erlaubt Schlussfolgerungen über Typ und Sorptionseigenschaften des zeolithischen Anteils des Tons. Die genaueste Methode zur Bewertung des Zeolithgehalts war eine standardisierte thermogravimetrische Desorptions- und Readsorptions-Methode mit Wasser oder organiscen Verbindungen.

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

     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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, H⁺. . , , , .

     

Structural changes of NaX zeolite during the H2S+O2 reaction

Infrared spectra in the 600, 700, and 1000 cm^–1 regions and X-ray investigations indicate that during H₂S+O₂ reaction in the temperature region of 293–473 K partial dealumination of the NaX zeolite crystal structure occurs. The dealumination increases with reaction temperature.

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- 600, 700 7000 ^–1 , H₂S+O₂ 293–473 NaX. .

     

Chemiluminescent method to measure generation rates of active centers in reaction of hydrogen peroxide with hemin and pyridinehemichrome

A chemiluminescent method was used to measure generation rates of active intermediates in the interaction of hemin with hydrogen peroxide with and without pyridine at pH=8–9. The effect of various inhibitors in these two cases has been examined.

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pH=8+9. .

     

Kinetic study of the thermal decomposition of heterocyclic thiol complexes under non-isothermal conditions

The thermal decomposition in the solid-phase has been studied by thermogravimetric (TG) and differential thermal analysis (DTA) techniques for a number of heterocyclic thiol complexes. The method of Coats and Redfern was used to study the kinetics of the thermal decomposition process. The enthalpy changes and activation energies for the decomposition have been calculated.

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Zusammenfassung Die thermische Zersetzung in fester Phase wurde an einigen heterozyklischen Thiolkomplexen mit den Methoden der dynamischen Thermogravimetrie (TG) und der Differentialthermoanalyse (DTA) untersucht. Die Methode von Coats und Redfern wurde zum Studium der Kinetik des thermischen Zersetzungsvorganges eingesetzt. Die Enthalpie-Änderungen und Aktivierungsenergien der Zersetzung wurden berechnet.

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Résumé Etude de la décomposition thermique en phase solide de plusieurs complexes thiols hétérocycliques par thermogravimétrie (TG) et par analyse thermique différentielle (ATD). La méthode de Coats et Redfern a été appliquée pour déterminer la cinétique du processus de la décomposition thermique. Les variations d'enthalpie et les énergies d'activation de la décomposition ont été calculées.

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(TG) (DTA) . . .

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We are grateful to Prof. K. C. Joshi, Head of the Chemistry Department and Dr. A. K. Rai of Rajasthan University, Jaipur for permitting the generous use of the thermorecording balance at the University and to Dr. E. R. Saxena, Assistant Director, Mineral Products and Inorganic Chemicals Division and Mr. P. Narayanachar of Regional Research Laboratory, Hyderabad for their valuable assistance in taking DTA trace. Thanks are also due to Prof. V. V. S. Murti, Head of the Chemistry Department, University of Delhi for his interest in the work. The author (K. A. V.) thanks the University Grants Commission, New Delhi for the award of the fellowship under which these investigations have been carried out.     

DTA investigation of the solid-liquid equilibrium for methyl derivatives of naphthalene with some nitroaromatics

The two-component solid—liquid phase eqilibria systems of some methyl derivatives of naphthalene with 2,4,6-trinitrophenol and 2,4,6-trinitrotoluene have been examined by DTA. All systems contain molecular complexes with 11 compositions.

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Zusammenfassung Zweikomponentige Fest-Flüssig-Phasengleichgewichtssysteme von einigen Methylderivaten von Naphthalen mit 2,4,6-Trinitrophenol und 2,4,6-Trinitrotoluol wurden mittels DTA untersucht. Alle Systeme enthalten Molekülkomplexe der Zusammenserzung 11.

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2,4,6- 2,4,6-. 11.

     

Formation and thermal decomposition of silicon oxynitride compounds. Part III

The formation of a previously unknown compound with stoichiometry Li₆SiN₂O₂ was found during studies on the reactivity of Li₂SiN₂ with Li₂O, of SiO₂ with Li₃N and of Li₃SiNO₂ with Li₃N.

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Zusammenfassung Die Bildung einer bisher unbekannten Verbindung der Stöchiometrie Li₆SiN₂O₂ wurde bei Untersuchungen der Reaktivität von Li₂SiN₂ mit LiO, von SiO₂ mit Li₃N und von Li₃SiNO₂ mit Li₃N beobachtet.

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Li₆SiN₂O₂ Li₂SiN₂ , , Li₃SiNO₂ .

     

Kinetics and mechanism of elimination of methoxyphenethyl chlorides in the gas phase

The kinetics for the gas phase elimination of o-and m-methoxy-2-phenylethyl chlorides have been investigated over the temperature range of 390-464°C and pressure range of 38–119 Torr. The reactions in seasoned vessels and in the presence of the free radical inhibitor propene, are homogeneous and unimolecular and follow a first-order rate law. The o-anisyl and p-anisyl substituents at the -position of ethyl chloride assist anchimerically the elimination processes. The formation of a cyclic product, benzodihydrofuran, from o-methoxy-2-phenylethyl chloride suggests an intimate ion pair mechanism operating in this reaction.

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- --2- 390–464°C 38–119 . - , , , . - - - . , , --2- , .

     

Determination of diffusion coefficients of radicals by photochemical space intermittence method. Temperature effect on the diffusivity of CCl

Diffusion coefficients of CCl ₃ ^. radicals at T=298–343 K have been measured using the photochemical space intermittence method. The estimated activation energy of CCl ₃ ^. diffusion in CCl₃Br solutions amounts to 24 kJ/mol.

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298–343 . CCl ₃ ^. 24 /.

     

Influence of mechanical activation on decomposition of a chalcopyrite-pyrite mixture in an oxidizing atmosphere

The influence of the addition of pyrite and mechanical activation on an oxidative decomposition of chalcopyrite was studied. The course of the thermoanalytical curves and X-ray identification of the products showed that addition of pyrite affects mainly the endothermic processes taking place in region of low temperatures but does not significantly influence the temperature of CuSO₄ formation and its content in the products of decomposition. Changes in fine and superfine structure of chalcopyrite brought about by mechanical activation at grinding cause the complex of exothermic oxidative reactions to proceed at temperatures as much as 180 deg lower than for a non activated sample. The endothermic effect of these oxidation reactions become more marked and the proportion of CuSO₄ in the products of the oxidative decomposition increases significantly.

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Zusammenfassung Am oxidativen Zerfall von Chalkopyrit wurde der Einfluss der Zugabe von Pyrit sowie der mechanischen Aktivierung untersucht. Der Verlauf der thermoanalytischen Kurven und Röntgendiffraktionsanalyse der Produkte zeigten, dass die Zugabe von Pyrit hauptsächlich die sich bei niedrigeren Temperaturen abspielenden endothermen Prozesse beeinflusst, nicht aber die Bildungstemperatur von CuSO₄ sowie dessen Gehalt in den Zersetzungsprodukten. Durch mechanisches Aktivieren mittels Feinmahlen hervorgerufene Veränderungen in der Fein- und Superfeinstruktur lassen die Gesamtheit der exothermen oxidativen Reaktionen bei Temperaturen ablaufen, die etwa 180 Grad unterhalb derer für unaktivierte Proben liegen. Die endotherme Färbung dieser Oxidation wird eindeutiger und der Anteil von CuSO₄ in den Produkten des oxidativen Zerfalles nimmt eindeutig zu.

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. , . , , - , 180° , . - .

     

Mechanism of the liquid-phase oxidation of diethyl sulfide catalyzed by heteropoly acids

It has been established that in the oxidation of diethyl sulfide by¹⁸O₂ in CH₃C¹⁶O₂H–H₂ ¹⁶O solution at 369 K catalyzed by heteropoly acids, sulfoxide and sulfone with 44–54%¹⁸O enrichment are formed. The process is accompanied by isotope exchange of molecular oxygen.

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, ¹⁸O₂ CH₃C¹⁶O₂H–H₂ ¹⁶O 369 ¹⁸O 44–54%, .

     

The concentrations of radicals in hexane pyrolysis

The concentrations of the radicals CH₃, C₂H₅ and H have been determined by a kinetic method at 973–1088 K using additives of D₂. The values obtained are compared with results of the analysis of the kinetic model for n-alkane pyrolysis. The rate constants of the reactions of CH₃ and C₂H₅ with hexane have been determined.

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D₂ CH₃, C₂H₅ H 973–1088 K. -. CH₃ C₂H₅ .

     

Modification of catalytic properties of silica-supported rhodium

A sharp change in the catalytic properties of rhodium in benzene hydrogenation, propane hydrogenolysis and n-hexane conversion has been found for catalysts prepared via interaction between Rh(CO)₂Cl₂ and silica modified by Sn, Pb, Mo and W ions.

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, Rh(CO)₂Cl₂ , Sn, Pb, Mo W, , , -.

     

IR characterization of surface hydroxy groups on haematite

The OH stretching absorptions (3670, 3640 and 3460 cm^–1) detected on haematite samples obtained by thermal decomposition of goethite, are assigned to monocoordinated and bridged free surface OH's and to hydrogen bonded OH's in surface micropores, respectively, on the basis of their behavior to successive adsorption of methanol, pyridine and D₂O and surface structural models.

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OH (3670, 3640 3460 ^–1) , . OH, OH, , , , D₂O, .

     

Selective oxidation and ammoxidation of isobutene over mixed oxides of tin and antimony

The oxidation and ammoxidation of isobutene were studied over mixed oxides SnO₂/Sb₂O₄ as catalysts, in a pulse reactor between 598 and 698 K. From the point of view of methacrylonitrile production the catalysts of compositions SnSb=4–51 behaved most appropriately at the optimum reaction temperature of 673 K. Below this temperature the production of methacrolein was preferred, even in the presence of ammonia, whereas at higher temperatures total oxidation prevailed.

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SnO₂/Sb₂O₄, 598 698 . SnSb=4–51 , 673 . , , .