Thermal desorption analysis:

Experiments on water desorption from silicate glass powders of different chemical compositions were carried out by means of DSC. In order to establish the desorption energy distributions, a model of the heterogeneous surface was applied to the thermoanalytical desorption curves, and the results are discussed together with contact angle measurements on flat polished glass samples.The maxima in the desorption curves shift to lower temperature with increasing hydrophobic character; this is caused by divalent cations such as Pb²⁺, Ca²⁺ and Zn²⁺, while alkali metal ions are responsible for an increase in the hydrophilic behaviour.

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Zusammenfassung Wasserdesorptionsexperimente an Silikatglaspulvern unterschiedlicher Zusammensetzung wurden mittels DSC ausgeführt. Für die Berechnung von Desorptionsenergieverteilungen wurde ein Modell der heterogenen Oberfläche genutzt und zusammen mit Randwinkelmessungen an glatten, polierten Glasoberflächen diskutiert. Das Maximum der Desorptionskurven verschiebt sich mit wachsendem hydrophoben Verhalten nach tieferen Temperaturen, wofür divalente Kationen wie Pb²⁺ Ca²⁺ Zn²⁺ verantwortlich sind, während Alkaliionen das hydrophile Verhalten begünstigen.

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. . , , , .

     

Thermal analysis of phenolic resin based pyropolymers

The formation and thermal behaviour of pyropolymers based on novolak resin synthesized under carefully controlled processing conditions have been studied by various thermoanalytical techniques. A suitable reaction scheme has been proposed for the formation of these pyropolymers. Only a small (3–8%) weight loss has been observed up to 800 °C in static air. DTA curves confirmed multistage exothermic processes predominantly due to two different linkages which control their thermo/thermo-oxidative stability. Hot metal filtration (700 °C) in an inert atmosphere exhibited only negligible weight loss.

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Zusammenfassung Mittels verschiedener thermoanalytischer Verfahren wurde Bildung und thermisches Verhalten von Pyropolymeren auf Novolackbasis unter streng geregelten Reaktionsbedingungen untersucht. Zur Bildung dieser Pyropolymere wurde ein geeignetes Reaktionsschema entwickelt. In unbewegter Luftatmosphäre kann bis 800 °C nur ein geringer (3–8%) Gewichtsverluft beobachtet werden. Die DTA-Kurven zeigen einen exothermen Mehrstufenprozeß, der hauptsächlich auf zwei verschiedene Verkettungen zurückzuführen ist, welche die thermische/thermisch-oxidative Stabilität bestimmen.

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. . 800° (3–8%) . , , / - . (700° .

     

Influence of the entropy factor on the equilibrium and kinetics of chemisorption

A correction to the model of uniform heterogeneous surface has been introduced. This correction extends the limits of application to processes with entropy changes of the adsorbent. On the basis of the model thus corrected a kinetic equation has been deduced, which takes into account the role of the entropy factor. The presence of a compensation effect in chemisorption kinetics is supported theoretically.

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- , , . , . .

     

Reactivity of the carbonaceous surface overlayer on supported platinum catalysts studied by high temperature pyrolysis gas chromatography

The reactivity of the carbonaceous surface overlayer formed on Pt/Al₂O₃ catalysts in n-hexane dehydrocyclization has been studied by high temperature Pyrolysis Gas Chromatography. This method can be used to characterize surface carbon overlayers formed on different catalysts in the course of hydrocarbon reactions.

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, Pt/Al₂O₃ -, . , .

     

Effect of the network structure on the flammability ofcis-1,4-polyisoprene vulcanizates

The combustibilities ofcis-1,4-polyisoprene and its peroxide and sulphur vulcanizates have been investigated by means of the oxygen index method. The temperature distribution in the sample and the molecular weight of the liquid products formed as a result of elastomer destruction in the combustion zone have been measured. It has been found that the combustibility ofcis- 1,4-polyisoprene diminishes as its cross-link density increases. This effect is much stronger for sulphur than for peroxide vulcanizates. The investigations lead to the conclusion that a mechanism of network degradation and volatile sulphur compounds penetrating to the flame are responsible for this difference.

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Zusammenfassung Die Brennbarkeit des unvernetztencis-1,4-Polyisoprens und seiner Peroxid- und Schwefelvulkanisate wurde mit der Sauerstoffindexmethode untersucht. Messungen der Temperaturverteilung im Prüfling wurden ebenfalls ausgeführt und das Molekulargewicht der infolge der Zersetzung der Elastomere in der Verbrennungszone entstehenden flüssigen Produkte mit der Methode der dynamischen Osmometrie bestimmt. Es wurde festgestellt, daß die Brennbarkeit des cis-1,4-Polyisoprens mit zunehmender Vernetzungsdichte abnimmt, und zwar viel ausgeprägter im Falle der Schwefel- als im Falle der Peroxidvulkanisate. Es wurde gefolgert, daß flüchtige, in die Flamme gelangende Schwefelverbindungen als Verbrennungsinhibitoren wirken.

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-1,4- . , . , -1,4- . . , .

     

Role of transition metals during p-xylene oxidation in aqueous system

The role of transition metals in the mechanism of p-xylene oxidation has been studied in aqueous systems at 140°C and 1.0 MPa of oxygen. The reaction proceeds according to second-order kinetics in p-xylene concentration for all metals and of <0.5 order with respect to metal concentration. For the metals studied the apparent activation energies are almost the same. The results support our previous assumption that (i) the rate-determining propagation step of p-xylene oxidation in aqueous systems does not involve metal ions, (ii) direct oxidation of p-xylene by higher valent metals does not play any significant role.

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- 140°C 1,0 . - , 0,5 . . , , 1. , - , ; 2. - - .

     

Differential scanning calorimetry study of reactions of phenyl glycidyl ether with phosphoric acid

The reactions of phenyl glycidyl ether (PGE) with phosphoric acid in three molar ratios have been studied by means of DSC alone. The results obtained from isothermal measurements are as follows:H=–91.0 kJ/mole PGE(1:1 molar ratio);H=–100.5 kj/mole PGE (1:2/3 molar ratio).The DSC curves obtained from dynamic experiments are multipeaked and giveHvalues higher than those obtained from isothermal measurements. These results can be explained by taking into account the acid concentration, the different reactivities of the hydrogens of the phosphoric acid and the possibility that secondary reactions occur.

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Zusammenfassung Die Reaktion von Phenylglycidyläther (PGE) mit Phosphorsäure wurde bei drei verschiedenen molaren Verhältnissen allein mittels DSC untersucht. Isotherme Messungen ergaben folgende Werte:H=–91.0kJ/mol PGE (molares Verhältnis 1:1);H=–100.5 kJ/mol PGE (molares Verhältnis 3:2). Die bei dynamischen Experimenten erhaltenen DSC-Kurven weisen viele Peaks auf und ergebenH-Werte, die größer als die durch isotherme Messungen erhaltenen sind. Diese Ergebnisse können erklärt werden, wenn die Säurekonzentration, die unterschiedliche Reaktivität der Wasserstoffatome der Phosphorsäure und die Möglichkeit des Verlaufs sekundärer Reaktionen in Rechnung gestellt werden.

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() () . 11 12/3, H, –91.0 –100.5 ·^–1. , , H . , , .

     

Catalytic oxidative hydrolysis of H2PO2? anions in the presence of RhCl3

Kinetics of H₂ evolution in the RhCl₃–NaH₂PO₂–HCl–H₂O system has been studied. As found by³¹P NMR, Rh(I) complexes with the Rh–P(OH)₂O^– bond are formed and play the role of catalysts in the subsequent H₂ evolution reaction.

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H₂ RhCl₃–NaH₂PO₂–HCl–H₂O. ³¹P Rh(I) Rh–P(OH)₂O^–, H₂.

     

Differential-thermal and thermogravimetric analysis of some gagates from Bulgaria

The thermal behaviour of three gagates (Bulgaria) was investigated by DTA and TG. The characteristic endo- and exoeffects and the sequence of the thermal stabilities are established.

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Zusammenfassung Das thermochemische Verhalten von drei Gagaten (Bulgarien) wurde mittels DTA und TG untersucht. Die charakteristischen endo- und exothermen Effekte und die Reihenfolge der thermischen Stabilitäten wurden ermittelt.

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(). - .

     

Measurement of the rate constant of hydrogen atoms with carbon monoxide in tubular and jet stirred open reactors

The reaction of hydrogen atoms with carbon monoxide has been studied in discharge flow systems with a new method of detection of atoms. The results obtained with tubular and jet stirred open reactors agree with those of other authors working in transient conditions and with more sophisticated techniques.

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. , , , .

     

Reaction specificity in catalysts reported to exhibit strong metal-support interactions

The specific activities of a 10% Ni/TiO₂ and a 10% Ni/SiO₂ catalyst for the hydrogenolysis of n-hexane and for the methanation reaction have been investigated. Both catalysts have very similar activities and selectivities for hydrogenolysis. However, the titania-supported catalyst exhibits a considerably greater specific activity for methanation. It is concluded that this enhancement of activity is reaction specific, and we propose a mechanism involving the adsorption of CO onto the surface of titania.

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10% Ni/TiO₂ 10% Ni/SiO₂ - . . , TiO₂ . , . , CO .

     

A method for the treatment of experimental data. Kinetic system comprising two irreversible first order consecutive reactions

A method is proposed for the treatment of data from a kinetic system comprising two irreversible first order consecutive reactions (ABC). It is based on the solving of contrary propositions for an ordinary differential equation.

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(ABC). .

     

Shape-selective ester hydrolysis by octadecyl immobilized H-ZSM-5 catalyst in liquid phase

The shape-selective property of octadecyltrichlorosilane treated H-ZSM-5, keeping the original acid strength (–5.6<Ho–3.0) in liquid phase in the hydrolysis of straight chain esters has been observed by comparing the reaction rates with those over octadecyltrichlorosilane treated SiO₂-Al₂O₃. The most pronounced effect was found in the case of ethyl decanoate, viz. ca. 6 times.

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H-ZSM-5, (–5.6<–3.0) , - . SiO₂–Al₂O₃, . , 6.

     

A new method to determine the distance of electron tunneling transfer and its application to recombination of paramagnetic radiation deffects in CaO

A new method to determine the distance of electron tunneling transfer between paramagnetic reagents based on simultaneous analysis of both kinetic and ESR data is suggested. This method has been used to estimate the tunneling distance and the parameters characterizing the rate of tunneling for finely dispersed CaO.

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, - . CaO , .

     

The determination of the oral form of 5-chloro-7-iodo-8-hydroxyquinoline (clioquinol)

For the routine assay of tabletted dosage forms of clioquinol, as in quality control, the reproducibility of tablet manufacture makes it possible to omit any weighing procedure. The advantages of enthalpimetry allow assay without separation of the analyte from the matrix and colorants.The method can be easily automated and gives an acceptable level of accuracy and precision.

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Zusammenfassung Für die Routineuntersuchung von Clioquinol in Tabletten, beispielsweise zur Qualitätskontrolle, ist ein Wägeverfahren infolge der Reproduzierbarkeit der Tablettenherstellung überflüssig. Die Vorteile der Enthalpimetrie erlauben ein Verfahren ohne Trennung der zu bestimmenden Verbindung von der Matrix und den farbgebenden Substanzen. Die Methode kann leicht automatisiert werden und ist ausreichend genau.

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, , . . .

     

Characterization of active species in alumina and silica supported CuCl2 catalysts by EPR

In a recent paper [1] we proposed that a Cu²⁺ species interacting with the support was responsible for maintaining the catalytic activity of CuCl₂ catalysts used in the methane oxyhydrochlorination reaction (CH₄+HCl+O₂ chloromethanes). This species was detected on Al₂O₃ and TiO₂ supports but it did not appear on SiO₂. In this paper we report EPR results which provide a direct characterization of this species and correlate well with the observed trends in activity.

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[1] , Cu²⁺, , CuCl₂, (CH₄+HCl+O₂ ). Al₂O₃ TiO₂, SiO₂. , .

     

Kinetics of methanol synthesis in the presence of low-temperature catalyst

The kinetics of methanol synthesis performed in a flow circulation installation in the presence of low-temperature copperzinc-aluminium catalyst has been investigated. The application of a power kinetic equation describing the surface chemical interaction on an exponentially inhomogeneous surface is established. The effect of the volume rate and the temperature is studied and the presence of a compensation effect is proved. A possibility of determination of the temperature and the volume rate, under which conditions the side-reactions do not affect the main one, is shown on the basis of the kinetic investigations.

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-- - . - - . . , .

     

Direct reading thermometric analysis

According to the direct reading thermometric method the concentration of the component to be determined is established from the temperature variation of the sample solution obtained on adding to it an excess of a reagent which reacts selectively with the respective component. Under suitably chosen experimental conditions the concentration of the respective component is determined from a single measured value. Since the established measurement technique requires little manual work and the respective components may be determined from the sample solution directly without any separations, the method in its present form is chiefly suitable for rapid serial analyses.

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Zusammenfassung Bei der thermometrischen Methode mit Direktablesung wird die Konzentration der gesuchten Komponente aus der Temperaturänderung der Probelösung bestimmt, die nach Zugabe eines Überschusses von einem selektiv reagierenden Reagens wahrnehmbar ist.Unter geeigneten Versuchsbedingungen kann man die Konzentration der gesuchten Komponente aus einem einzigen Meßwert, nämlich der Temperaturänderung der Probelösung bestimmen. Da die ausgearbeitete Meßtechnologie wenig Arbeit erfordert und die gesuchten Komponenten ohne jede Trennung direkt bestimmt werden können, ist die Methode in ihrer jetzigen Ausführungsart hauptsächlich zu betriebsmäßigen Serien-Schnellanalysen geeignet.

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Résumé Selon la méthode thermométrique à lecture directe, on détermine la concentration du constituant cherché d'après la variation de température de la solution échantillon que l'on additionne d'un excès de réactif sélectif de celui-ci. Dans les conditions expérimentales appropriées, une seule mesure suffit pour déterminer la concentration du constituant cherché. Comme la technique de mesure qui a été mise au point demande peu de travail et comme on peut doser sans aucune séparation les constituants étudiés, la méthode dans sa forme actuelle se prête en premier lieu aux dosages en séries industriels.

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, , . . . , . .

     

Kinetics of gas phase hydrochlorination of acetylene over a mercury catalyst

The kinetics of gas phase hydrochlorination of acetylene over a mercury catalyst has been studied. The kinetic equation is in agreement with the experimental data of various authors.

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. .

     

Influence of pore diffusion on the rate of n-heptane conversion on a Pt/Al2O3 catalyst under reforming conditions

Under reforming conditions, the rate of n-heptane conversion on a large Pt/Al₂O₃ catalyst grain, in contrast to that in the kinetic region, depends on the hydrogen to hydrocarbon mole ratio. The rate equation for the reaction on a large grain agrees well with the experimental results obtained by a gradientless method under pressure.

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