Analogies between point mechanics and chemical reaction kinetics

A few rather interesting analogies are shown between classical point mechanics and chemical reaction kinetics. The approach used is that of the differential geometry.

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Traitement mecanique des materiaux III

Résumé Les auteurs ont recherché l'effet du broyage sur la réactivité ultérieure des hydrates K₂C₂O₄ · H₂O; CaC₂O₄· H₂O et BaC₂O₄ ·nH₂O avecn=0, 1/2, 1 et 2. La thermolyse de ces hydrates préalablement broyés montre que le traitement mécanique provoque dans la plupart des cas un abaissement de la température de déshydratation mais aussi, dans certains cas, une modification des étapes de cette réaction. Ces effets se manifestent surtout lorsque le broyage préalable est de courte durée et ils peuvent être modifiés par les conditions de pression et de température imposées pendant le traitement mécanique. La comparaison des variations, en fonction du temps de broyage, de la température de déshydratation commençante et des autres caractéristiques physico-chimiques de l'hydrate broyé a permis de montrer que la tension superficielle des grains du matériau broyé est un facteur d'action prépondérant.

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The authors studied the effects of prior grinding on the reactivity of the hydrates K₂C₂O₄ · H₂O, CaC₂O₄ · H₂O and BaC₂O₄ ·nH₂O, withn= 0, 1/2, 1 and 2. The thermal decomposition of these previously ground hydrates showed that in most cases the mechanical treatment brings about a decrease in the thermal dehydration temperature, but also change in the reaction steps in some cases. These effects are mainly notable after short-time grinding, and they may be modified by changes in the grinding temperature and vapour pressure conditions. Comparison of the variations with time of the beginning dehydration temperature and the other physico-chemical characteristics of the ground hydrates showed the prevailing influence of the surface tension of the ground material.

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Zusammenfassung Es wurde der Einfluß eines vorhergehenden Mahlens auf die Reaktivität der Hydrate: K₂C₂O₄ · H₂O; CaC₂O₄ · H₂O; BaC₂O₄ ·n H₂O mitn=0. 1/2, 1 und 2 untersucht. Die Thermoanalyse dieser vorher gemahlenen Hydrate zeigt, daß die mechanische Behandlung in den meisten Fällen eine Abnahme der Dehydratisierungstemperatur zur Folge hat, in einigen Fällen jedoch auch eine änderung in den Reaktionsschritten. Diese Effekte werden hauptsächlich bei dem Kurzzeit-Mahlen sichtbar und müssen durch änderung de Mahltemperatur und der Dampfdruckbedingungen modifiziert werden. Der Vergleich der änderungen der anfänglichen Dehydratisierungstemperatur und der anderen physikalisch-chemischen Charakteristika des gemahlenen Hydrats mit der Zeit zeigt den dominierenden Einfluß der Oberfläche auf das Mahlgut.

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K₂C₂O₄· H₂O; CaC₂O₄· H₂O; BaC₂O₄·nH₂O cn=0, 1/2, 1 2 . , , — . . - , .

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Les auteurs remercient tout particulièrement Madame le Professeur G.Watelle pour l'aide précieuse qu'elle leur a apporté dans la discussion et la présentation de ce travail.     

Two mechanisms of the interaction between atoms and solids

The chemical action of atoms on solids can be due to both direct reactions with the structural units of solids and heterogeneous recombination energy transfer to the crystal lattice.

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Measurement of the thermal capacity of solids by DSC

The methods for determining the thermal capacity of solids using a SETARAM DSC-III calorimeter have been studied. Two methods can be employed: periodic heating and continuous heating. The method using periodic heating is characterized by an accuracy of 0.6%,'while the method with continuous heating has an accuracy of 5%. Thermal capacity measurements on corundum, copper oxide and magnetite are reported.

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Zusammenfassung Methoden zur Bestimmung der Wärmekapazität von Festkörpern wurden mittels des Kalorimeters SETARAM DSC-III untersucht. Zwei Methoden können angewandt werden, nämlich periodisches und kontinuierliches Aufheizen. Bei periodischem Heizen beträgt die Genauigkeit 0,6%, bei kontinuierlichem 5%. Über Messungen der Wärmekapazität von Korund, Kupferoxid und Magnetit wird berichtet.

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-III «CETAPAM». - . 0,6%, 5%. , .

     

Kinetic investigation of CO oxidation in the presence of SO2

The kinetics of CO oxidation on a mixed, Pd-containing catalyst have been studied by the gradientless method. The reaction rates were measured as a function of the temperature and the CO and SO₂ concentrations. A break has been found on the kinetic curves, showing the influence of CO concentration on the reaction rate.

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CO . — , CO .

     

Reaction of alkali and ammonium bifluorides with aluminium and silicon

The reactions of alkali and ammonium bifluorides with aluminium and silicon were studied by DTA. Reaction temperatures were determined and reaction products identified. The reaction mechanism of the fluorinating reaction was established. Hydrofluorides appear very promising fluorinating agents.

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Zusammenfassung Die Reaktionen von Alkali- und Ammoniumbifluoriden mit Aluminium und Silicium wurden mittels DTA studiert. Die Reaktionstemperaturen wurden bestimmt und die Reaktionsprodukte identifiziert. Der Reaktionsmechamismus der Fluoridierungsreaktion wurde ermittelt. Die Hydrofluoride erwiesen sich als vielverheißende Fluoridierungsreagenzien.

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Résumé On a étudié par ATD les réactions données par les hydrogénofluorures alcalins et d'ammonium avec l'aluminium et la silice. On a déterminé les températures des réactions et identifié les produits de réaction. On a établi le mécanisme de la réaction de fluoration. Les hydrogénofluorures semblent être des réactifs de fluoration très prometteurs.

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Some problems of diffusion controlled reactions treated by the Monte Carlo technique

The Monte Carlo technique is used to describe the kinetic behavior of radicals in spurs. The experimentally well established linear relationship between the yields of molecular products and cube root of scavenger concentration is explained by considering spur reactions as random walk with annihilating interactions.

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Temperature dependence of CO insertion on S-, Ag-, and Cu-promoted Rh/SiO2 catalysts

The addition of sulfur and silver to Rh/SiO₂ inhibits hydrogenation of C₂H₄, but promotes CO insertion and extends the linearity of Arrhenius curves for CO insertion above 543 K.

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Rh/SiO₂ C₂H₄, CO CO 543 .

     

Light olefin production from CO/H2 over silica supported Fe/Mn/K catalysts derived from a bimetallic carbonyl anion, [Fe2Mn(CO)12]?

Fe/Mn/K catalysts derived from support of the anionic carbonyl, [Fe₂Mn(CO)₁₂]^– on silica were compared with catalysts prepared by aqueous impregnation methods, and found to be more selective for production of C₂–C₄ olefins. Addition of K had little effect, whereas variations in reaction conditions altered selectivity owing to secondary reactions of the alkene products.

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Fe/Mn/K, , [Fe₂Mn(CO)₁₂]^–, , , , C₂–C₄. , , .

     

Kinetic simulation of oxidative dehydrogenation of n-butenes over SnO2?Sb2O4 catalysts

A previously suggested reaction mechanism was utilized to evaluate a kinetic model for the oxidation of n-butenes over ShSb=31 mixed oxide catalyst. With this model, kinetic curves measured at 673 K were simulated, illustrating the changes of amounts of undetectable surface components, too.

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- SnSb=31 . , 673 K, .

     

Solvent effects on reaction rates in a catalytic slurry reactor

By carrying out static adsorption measurements, it is shown that absolute values of adsorption strength parameters required in an earlier Langmuir type model for liquid phase catalytic hydrogenation in the presence of an adsorbing solvent can be obtained. These can be used to predict the relationship between reaction rate and reactant concentration in the solvent.

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Study of solid-phase reaction of RbNO3 with V2O5

Using DTA, TG and DTG methods, the reaction between RbNO₃ and V₂O₅ in the molar ratio 65 in air atmosphere was studied. The reaction proceeds stepwise. In individual steps of the reaction the formation of RbV₃O₈, RbVO₃ and Rb₃V₅O₁₄ was observed. Rubidium pentavanadate is thermally unstable. At 1000°, RbVO₃ and Rb₂V₄O₁₁ were identified as products of its thermal decomposition. Rubidium tetravanadate was also prepared by the isothermal reaction of RbNO₃ with V₂O₅ in the molar ratio 11.

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Zusammenfassung Unter Anwendung der DTA-, TG- und DTG-Methoden wurde die Reaktion RbNO₃-V₂O₆ bei dem Molverhältnis von 65 in Luft untersucht. Die Reaktion verläuft stufenweise. Bei den einzelnen Stufen der Reaktion wurde die Bildung von RbV₃O₈, RbVO₃ und Rb₃V₅O₁₄ beobachtet. Rubidiumpentavanadat ist thermisch instabil. Bei 1000° wurden RbVO₃ und Rb₂V₄O₁₁ als Produkte seiner thermischen Zersetzung beobachtet. Rubidiumtetravanadat wurde auch durch die isotherme Reaktion von RbNO₃-V₂O₅ bei dem Molverhältnis von 11 hergestellt.

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Résumé On a étudié par ATD, TG et TGD dans l'air, la réaction RbNO₃-V₂O₅ (rapport molaire 65). La réaction s'effectue par étapes, avec formation de RbV₃O₈, RbVO₃ et Rb₃V₅O₁₄. Le pentavanadate de rubidium est thermiquement instable. A 1000°, RbVO₃ et Rb₂V₄O₁₁ ont été identifiés comme produits de la décomposition thermique. Le tétravanadate de rubidium a également été préparé par voie isotherme en faisant réagir RbNO₃-V₂O₅ (rapport molaire 11).

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, , RbNO₃-V₂O₅ 6 5. . RbV₃O₈, RbVO₃ Rb₃V₅O₁₄. 1000° RbVO₃ Rb₂V₄O₁₁, . RbVO₃-V₂O₅ 11.

     

The general applicability of the Kissinger equation in thermal analysis

Computer modelling calculations will be presented which verify the fact that, if a single reaction follows either Arrhenius or transition state kinetic theory over its entire extent, then the maximum rate of reaction data obeys the modified Kissinger equation, irrespective of the applicable kinetic model. The magnitude of the Kissinger parameter correction term is dependent on the model, ranging from about 0.4% for n^th order and random nucleation, Avrami-Erofeev models to 17% for three dimensional diffusion controlled reactions. The consequences of selecting the incorrent kinetic model in interpreting experimental thermoanalytical data will be examined, thereby giving a rational explanation for the wide range of published kinetic parameters for a number of solid state decompositions.

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Zusammenfassung Computer-Modellberechnungen werden dargelegt, die die Tatsache bestätigen, daß die maximale Reaktionsgeschwindigkeit unabhängig vom angewandten Modell von der modifizierten Kissinger-Gleichung beschrieben wird, wenn eine einzelne Reaktion über den gesamten Verlauf hinweg entweder der kinetischen Arrhenius- oder der Übergangszustands-Theorie folgt. Die Größe der Kissinger-Parameter hängt vom Modell ab und liegt zwischen 0,4% für Avrami-Erofeev-Modelle mitn-ter Ordnung und ungeordneter Kristallkeimbildung und 17% für dreidimensionale diffusionskontrollierte Reaktionen. Die bei Wahl eines falschen kinetische Modells für die Interpretierung thermoanalytischer Daten eintretenden Folgen werden untersucht, wobei eine vernünftige Erklärung für die große Streuung von publizierten kinetischen Parametern einer Anzahl von Festkörperzersetzungsreaktionen gegeben wird.

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, , , , . 0,4% n- - 17% — - . , .

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Presented at the 13th North American Thermal Analysis Society Conference, Sept. 1984, Philadelphia, PA, paper 55.This work was conducted as a part of the Kentucky Energy Resource Utilization Program supported by the Commonwealth of Kentucky, Kentucky Energy Cabinet.     

Kinetic investigations on the carbonylation of aromatic nitro compounds to isocyanates in the presence of rhodium carbonyl complexes

The kinetics of carbonylation of aromatic nitro compounds to isocyanates have been studied at 100°C and 1 atm CO in the presence of Rh₂Cl₂(CO)₄ and MoCl₅. The rate is first order in the nitro compounds as well as in MoCl₅ and 1/2 order in Rh₂Cl₂(CO)₄; the rate is independent of the carbon monoxide pressure. Large substituents in position 2 of the nitro compound increase the reaction rate.

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100°C 1 CO Rh₂Cl₂(CO)₄ MoCl₅. MOCl₅, 0,5 Rh₂Cl₂(CO)₄. . 2 .

     

Electrocatalytic oxidation of cyclohexane by molecular oxygen in non-aqueous solvents in the presence of perchloric acid and perchlorates

Several new electrocatalytic systems are described for the oxidation of cyclohexane by molecular oxygen at room temperature. The solvent is acetonitrile. Perchloric acid and perchlorates are used as supporting electrolytes. The maximum electrochemical yield amounts to 9.6% and is observed in the presence of perchloric acid.

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, . , — . 9,6% — .

     

Hydrogenation of CO2 on carbon-supported nickel and cobalt

The hydrogenation of CO₂ has been studied at atmospheric pressure on Co/C and Ni/C catalysts and the results are compared with those obtained on unsupported Co and Ni. Specific activites in the form of turnover frequencies for CO₂ hydrogenation decrease with increasing metal dispersity. Carbon supported Co and Ni present a smaller selectivity for methane than bulk metals. Higher specific activities and smaller activation energies are obtained on Co catalysts, compared with those determined for Ni catalysts.

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CO₂ Co/ Ni/ Co Ni . CO₂ . Co Ni , . .

     

On the mechanism of alcohol insertion into the carbonyl group in the coordination sphere of Fe(III) tris-hexafluoroacetylacetonate

The kinetics of formation of hemiacetals in the Fe(III) coordination sphere resulting from the reaction of Fe(III) tris-hexafluoroacetylacetonate with methanol has been studied by the stopped-flow method. Two molecules of methanol and coordinated hexafluoroacetylacetonate anion (HFA^–) take part in the rate-determining step. The effect of the second molecule of alcohol can be attributed to catalysis of proton transfer from methanol to the HFA^– ligand through the chain of hydrogen bonds in 6-membered cyclic structures.

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stopped-flow Fe(III). , -. , , .

     

Dynamic purity determinations. II. Some additional systems

Menadione and phenacetin systems were each prepared with a series of concentrations of materials of varying similarity to the host. The data indicate that the measured impurity is dependent upon not only the concentration but also the nature of the impurity. The determination of the actual beginning of melting by nuclear magnetic resonance results in more precise purity measurements.

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Zusammenfassung Es wurden Menadion- und Phenacetinsysteme mit je einer Konzentrationsreihe von Zusatzstoffen, der Matrix in verschiedentlichem Ausmaß ähnlich, hergestellt. Die Ergebnisse zeigen an, daß die gemessene Verunreinigung nicht allein von ihrer Konzentration, sondern auch von ihrer Natur abhängig ist. Genauere Reinheitsmessungen erfolgen aus der Bestimmung des wahren Schmelzanfangs mittels kernmagnetischen Resonanzmessungen.

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The data are taken from a dissertation presented in partial fulfillment of the requirements for the Doctor of Philosophy degree.

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This work was supported in part by the U.S. National Science Foundation through Research Grant CHE 76-08765.     

Kinetics of oxidative coupling of thiophene in the presence of Pd(OAc)2

The kinetics of oxidative coupling of thiophene to bithiophene in the presence of Pd(OAc)₂ in acetic acid solution has been studied at 60–80°C. The mechanism of the reaction is discussed.

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Pd (OAc)₂ HOAc 60–80°. .

     

Structural and thermal studies on sisal fibre

Mechanical characteristics of sisal fibre, such as UTS and Young's modulus, have been determined. The thermal degradation of sisal fibre has been observed by running its DSC and TG/DTG.

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Zusammenfassung Die mechanischen Kennwerte (UTS, Young's Modul) von Sisalfasern wurden bestimmt. Der thermische Abbau von Sisalfasern wurde mittels DSC und TG/DTG untersucht.

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The authors wish to thank Dr. R. K. Tiwari, Dr. S. V. Prasad and Dr. M. Patel for their useful suggestions.