Dehydration of lithium triphosphate pentahydrate,Li5P3O10· 5H2O

The kinetics of isothermal-isobaric dehydration of Li₅P₃O₁₀·5H₂O in vacuum (p=10^–1 hPa) and in water vapour atmosphere ( =23·hPa) was investigated by TG in the temperature range 40–140°. It was shown that the initial non-degradation removal of 1/10 of the crystal water, the rate of which is sensitive to , proceeds according to the laws of reversible topochemical reactions. In the next, irreversible degradation stage, where the bulk of the crystal water is removed, the kinetic characteristics of the process and the DSC effects exhibit a low sensitivity to the water vapour pressure. The peculiarities of Li₅P₃O₁₀·5H₂O dehydration were considered in comparison with the thermal behaviour of Na₅P₃O₁₀·6H₂O and K₅P₃O₁₀·4H₂O.

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Zusammenfassung Die Kinetik der isotherm-isobaren Dehydratisierung von Li₅P₃O₁₀·5H₂O in Vakuum (p=10^–4 hPa) und in Wasserdampfatmosphäre ( =23 hPa) wurde durch TG im Temperaturbereich von 40–140° untersucht. Es wurde gezeigt, daß die anfängliche, noch keine Zersetzung zur Folge habende Eliminierung von 1/10 des Kristallwassers, deren Geschwindigkeit von abhängt, nach den Gesetzen der reversiblen topochemischen Reaktionen abläuft. Im nächsten irreversiblen Zersetzungsschritt, in dem die Hauptmenge des Kristallwassers austritt, sind die kinetischen Kennwerte des Prozesses und die DSC-Effekte nur wenig vom Wasserdampfdruck abhängig. Die Besonderheiten der Dehydratisierung von Li₅P₃O₁₀·5H₂O werden im Vergleich mit dem thermischen Verhalten von Na₅P₃O₁₀·6H₂O und K₅P₃O₁₀·4H₂O erörtert.

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40–140° - Li₅P₃O₁₀ · 5₂ (=10^–4 ) (=23 ). , 1/10 , . , - . L₅₃₁₀·5₂ Na₅P₃O₁₀·6H₂O K₅₃₁₀·4₂.

     

Interaction of tribenzyltitanium with butadiene

It has been established that the interaction of (C₆H₅CH₂)₃Ti with butadiene does not change the parameters of ESR spectra. Only the hydrodynamic radius of this complex increases.

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, (C₆H₅CH₂)₃Ti . .

     

Hydrogenation of xylenes over supported Pt catalysts. Influence of different variables on their catalytic activity

In this work we studied and compared the catalytic activity of various supported Pt systems on the gas-phase hydrogenation of o-, m- and p-xylene. We analyzed the influence of different catalyst preparation variables (solvent, precursor, salt, support and catalyst reduction temperature used) on the catalytic activity and selectivity towards the corresponding cis-and trans-dimethylcyclohexanes.

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- o-, m- -. (, , ) - -.

     

Influence of the sample mass and the presence of the reaction products on the thermoanalytical results

It has been known from the very beginning of the thermal analysis that the transport processes can significantly influence the thermoanalytical results. In this paper, three characteristic examples are given to show that this problem is more complex and arises more frequently than it is generally believed. The studied reactions are the carbon monoxide evolution from calcium oxalate, the thermal degradation of polytetrafluoroethylene, and the thermal decomposition of azodicarbonamide. TG and DSC experiments were carried out with sample masses varying between 0.05 and 8 mg. The necessity of the development of new kinetic models is concluded.

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Zusammenfassung Seit den Anfängen der Thermoanalyse ist bekannt, dass Transportprozesse die thermoanalytischen Ergebnisse weitgehend beeinflussen können. Es werden hier drei Beispiele beschrieben, die zeigen, dass dieses Problem weitauf komplizierter ist und häufiger auftritt als allgemein angenommen wird. Die untersuchten Reaktionen sind die Kohlenmonoxidabspaltung aus Calziumoxalat, die thermische Zersetzung von Polytetrafluoräthylen und der thermische Zerfall von Azodicarbonamid. Die TG- und DSC- Untersuchungen wurden mit Probenmassen zwischen 0.05 und 8 mg durchgeführt. Es wird auf die Notwendigkeit der Entwicklung neuer kinetischer Modelle geschlossen.

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, . , , . , . , 0,05 8 . .

     

Hydrocarbon hydrogenolysis on nickel-tin catalysts

Hydrogenolysis of ethane, n-hexane and cyclohexane has been studied on nickel-kieselguhr catalysts modified by organic and inorganic compounds of tin. Tin additives decrease nickel reactivity with respect to C–C dissociation, which is ascribed to the formation of surface intermetallides on the catalyst.

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, - - , . . C–C .

     

Temperature programmed reduction and oxidation of Ir/Al2O3 catalysts

3 % Ir/Al₂O₃ catalysts have been studied by means of temperature programmed reduction and oxidation. With growing degree of metal oxidation (higher T_ox) reducibility of the catalysts at low temperatures decreases.

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3% Ir/Al₂O₃ . ( ) .

     

Thermal and mechanical studies on the cure time optimisation of polysulphide resin

The effect of two commercially available metal oxide curing agents, PbO₂ and MnO₂, on the cure time, kinetic parameters and ultimate tensile strength of the polysulphide polymer was investigated. The kinetic parameters for the thermal decomposition of the two systems were evaluated from their TG data. Both the energy of activation and pre-exponential factor showed a systematic increase with increase in cure and levelled off after the reaction. The cure time was also followed by determining the mechanical properties of the samples at regular intervals. The ultimate tensile strength values and the kinetic parameters follow similar trend with respect to the cure time. The kinetic parameters and the ultimate tensile strength for the PbO₂ cured polysulphide system were on the higher side.

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Zusammenfassung Es wurde der Einfluß von zwei im Handel erhältlichen Metalloxidhärtemitteln. PbO₂ und MnO₂, auf die Aushärtungszeit, die kinetischen Parameter und die Zugfestigkeit von Polysulfidpolymeren untersucht. Die kinetischen Parameter für die thermische Zersetzung der zwei Systeme wurden aus deren TG-Daten ermittelt. Sowohl die Aktivierungsenergie als auch der präexponentielle Faktor wachsen mit fortschreitender Aushärtung ständig an und erreichen nach Verlauf der Reaktion einen konstanten Wert. In gleichmäßigen Zeitabschnitten wurde die Aushärtungszeit auch durch Bestimmen der mechanischen Eigenschaften der Proben verfolgt. In Bezug auf die Aushärtungszeit zeigen die Zugfestigkeit und die kinetischen Parameter einen ähnlichen Verlauf. Die kinetischen Parameter und die Zugfestigkeit von mit PbO₂ gehärteten Polysulfidsystemen zeigen bessere Werte.

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

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We thank Dr. R. Ramaswamy for supplying the resin and Dr. K. V. C. Rao and Director, VSSC for the kind permission to publish this work.     

Dilution effect on catalytic pyrolysis of hydrocarbons

It is shown that unlike thermal pyrolysis, the rate of catalytic pyrolysis is greatly affected by dilution of hydrocarbons with inert gases. The nature of this effect has been analyzed.

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, . .

     

Mechanism of isotope exchange of dihydrogen with liquid water catalyzed by hydroxide ions

In the analysis of the reaction between dissolving hydrogen and aqueous alkali hydroxide solutions the interaction of hydrogen with the molecular ion (H₃O₂)^– should be studied. This interaction is analyzed by the interacting bonds method. The activation energy (E_a) is estimated.

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, (H₃O₂)^–. . (E_a).

     

Oxidative coupling of alkylbenzenes to diaryls catalyzed by the palladium(II)-heteropolyacid system

Oxidative coupling of alkylbenzenes (benzene, toluene, o-xylene, durene) is shown to proceed in the presence of palladium salts and heteropolyacids under the action of oxygen with a high yield of diaryls. The addition of mercury salts and variation of the solvent affect the reaction rate and isomer composition of the products.

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, (, , -, ) . .

     

Catalytic preparation of diacetone alcohol in controlled flow conditions

Catalytic preparation of diacetone alcohol from acetone was studied using strong basic ion exchangers as catalysts. A continuous process was carried out in an enlarged laboratory set-up with controlled flow rate. Experiments were performed with respect to experiment duration, temperature, flow rate, catalyst porosity and catalyst-acetone ratio. The quantity of DAA was determined by gas chromatography. The effects of temperature, catalyst porosity and catalyst-acetone ratio on the reaction course were significant in comparison with other parameters examined. An exponential dependence of C/A ratio on DAA yield was found.

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

     

Le systeme eau-theophylline

The binary system water—theophylline was studied by DTA and radiocrystallography. The slow dehydration of theophylline monohydrate was observed at room temperature at relative humidities lower than 60%, without the formation of any other hydrate. The isochoric phase diagram was established. At 78 °C, a peritectic invariant occurred, owing to decomposition of the monohydrate. The existence of only one binary compound (theophylline H₂O) was confirmed by the.Tammann diagram.

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Zusammenfassung Mittels DTA und Radiokristallographie wurde das binäre System Wasser-Theophyllin untersucht. Bei einer relativen Luftfeuchtigkeit unter 60% wird bei Raumtemperatur eine langsame Dehydratation von Theophyllinemonohydrat ohne Formung anderer Hydrate beobachtet. Es wurde ein isochores Phasendiagramm entwickelt. Wegen der Zersetzung des Monohydrates tritt bei 78 °C eine peritektische Invariantheit auf. Die Existenz nur einer binären Verbindung (Theophyllin, H₂O) wird mittels eines Tammanndiagrammes bekräftigt.

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— . 60% - . . 78° , . -.

     

Effect of iron on the behavior of Fe2O3?MoO3/SiO2 ammoxidation catalysts

Catalytic ammoxidation of propylene was studied using Fe₂O₃–MoO₃/SiO₂ catalysts, which have been prepared following a special method. Interaction of ammonia with the catalysts was studied by means of IR spectroscopy and gravimetrically using a McBain balance. Introduction of iron into MoO₃/SiO₂ catalysts modifies acidic as well as redox properties.

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Fe₂O₃–MoO₃/SiO₂ . . - . MoO₃/SiO₂ , .

     

Catalytic properties of the vanadium-molybdenum oxide system for acrolein oxidation

The catalytic properties and phase composition of the silica-supported vanadium-molybdenum oxide system have been studied in acrolein oxidation. The active component of the catalyst is the compound VMo₃O_11+x, whose maximum content is observed in the compositions range of 10–15 mol.% V₂O₅ –90–95 mol.% MoO₃.

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, SiO₂. VMo₃O_11+x, 10–15 .% V₂O₅÷90–85 .% MoO₃.

     

Novel method for comparative activity testing of catalysts for methane steam reforming

The method suggested permits to achieve considerable acceleration in comparative testing of the activity of catalysts for methane steam reforming and to extend the amount of information obtained as well as to improve its quality.

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, .

     

Partial hydrogenation of benzene over platinum supported catalysts

Partial hydrogenation of benzene to cyclohexene has been studied on Pt/Nylon 66, Pt/MgO and Pt/TiO₂. An effect of the support on the selectivity to cyclohexene was observed, Pt/Nylon showing the highest selectivity, followed by Pt/MgO and Pt/TiO₂. An interaction of platinum with the more basic supports (Nylon, MgO) and a pretreatment under oxidizing conditions, results in a higher selectivity to cyclohexene.

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Pt/ 66, Pt/MgO PtTiO₂. , Pt/, Pt/MgO Pt/T,O₂. (, MgO) .

     

Cracking of n-hexane on Na, H-mordenite: Coke poisoning

n-Hexane cracking was studied on Na, H-mordenites at 400 °C under atmospheric pressure. It was found that the degree of exchange of Na⁺ for H⁺ affected both the initial and the steady state activity of the mordenite. The deactivation by coke also varied with the degree of proton exchange of the zeolite.

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- Na, H- 400°C . , , Na⁺ H⁺. .

     

Dehydrogenation of tetrahydrothiophene on nickel-zeolite catalysts

Application of Y zeolites for the preparation of nickel-containing catalysts makes it possible to increase the yield of thiophene up to 55–65% at a selectivity of 70–73% (450–500°C). The activity of nickel-zeolite samples, deactivated during the reaction, is completely restored by regeneration with air at 550°C.

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Y 55–65% 70–73% (450–500°C). 550°C.

     

Eine Thermowaage für den Unterricht

Zusammenfassung Eine Thermowaage, mit der gleichzeitig die Masse und die Temperatur in einer Probe gemessen werden können, wurde für Lehrzwecke entwickelt. Am Beispiel der Verdunstung von Aceton, der Entwässerung von Kupfersulfat-pentahydrat, der Zersetzung von Magnesiumoxalat-dihydrat und der Pyrolyse von Weichholz werden ihre TG-Kurven diskutiert.

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A thermobalance for teaching purposes was constructed which is able to measure simultaneously mass and temperature in a sample. The effectiveness of the device is discussed by the TGA curves of the evaporation of acetone, the dehydration of copper sulphate pentahydrate, the decomposition of magnesium oxalate dihydrate, and the pyrolysis of wood.

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, . , , .