Thermal analysis study of the dynamic decomposition of polymers during rapid heating; limiting temperatures of thermolysis

A new technique is presented for study of the thermal behaviour of materials. Experimental and theoretical bases are established for the limiting temperatures of thermal decomposition of different polymers.

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Zusammenfassung Es wird ein neues Verfahren zur Untersuchung des thermischen Verhaltens von Stoffen. vorgestellt. Es wurden experimentelle und theoretische Grundlagen zur Bestimmung von thermischen Zersetzungstemperaturen verschiedener Polymere erstellt.

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. .

     

A novel method for the dealumination of zeolites

A wide range of halogen containing reagents (metal halides, oxyhalides, acid halides, etc.) are found to interact from the gas phase with exchange ions of zeolites and to effect dealumination at elevated temperatures. The incorporation of extraneous ions into the framework by this technique is not impossible theoretically. The importance of the method in the preparation of dealuminated and/or metal containing catalysts is discussed.

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

     

Promotion of the catalytic activity of zeolites by alkyl halides

The promotion of catalytic activity of zeolites by CCl₄ was studied in a pulse reactor using aromatic alkylation as model reaction. The reaction of surface OH groups with CCl₄ produced HCl which increased the catalytic activity. The maximum enhancement of activity occurred when the catalyst was weakly acidic.

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CCl₄ , . OH CCl₄ HCl, . , .

     

Computation in kinetics, III. A new method for kinetic model search based on simultaneous regression estimation of rate constants, stoichiometry and/or reaction order

Modified samples of natural mordenites have been found to catalyze the oxidative condensation of methane to yield ethane and ethylene. The selectivity towards C₂ hydrocarbons increases, whereas the acidity of zeolites falls.

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, . C₂ .

     

Effect of bond energies of a catalyst with reacting atoms on the selectivity of CO hydrogenation over metals

In hydrogenation over metals (M)_j carbon monoxide is adsorbed as a molecule. C–O bond rupture in partially hydrogenated complex, MCHOH, leads to MO and MCH₂ and then to hydrocarbons, while transformation of MCHOH into MCH₂OH gives alcohols and other oxygen-containing compounds. Selectivity towards hydrocarbons increases with increasing energy of M–O bonds.

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(M) . C–O MCHOH MO MCH₂ — ; MCHOH MCH₂OH . M–O.

     

Oxidative dehydrogenation (OXD) of n-butane I. Activity of natural quartz II. Kinetic and catalytic activity of nickel oxides

The oxidative dehydrogenation of n-butane on nickel oxide catalysts and on natural quartz, used as catalysts diluent, were studied. It is assumed that oxygen ions from the oxide lattice participate in the initial step of the reaction.

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- , . , .

     

Application of percolation theory to the analysis of pore structure by capillary condensation measurements

A method for analysis of the desorption branch of capillary condensation hysteresis in adsorption isotherms is suggested. The method takes into account the possible overlap of radius distribution for voids and necks.

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- , .

     

Oxidation of CO on Ag-based composite oxides

Thermal stability of the oxidized state of silver was increased in the Cr, Mn, Fe and Co oxides. However, Ni and Cu oxides did not stabilize Ag, leading to its aggregation to form metallic Ag at 400°C. The Ag in the former group exhibited high catalytic activity in the oxidation of CO due to the formation of composite oxides with these transition metals.

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Cr, Mn, Fe Co. , Ni Cu Ag, 400°C. Ag CO, .

     

Oxidative polymerization of durene and diphenyl oxide in the presence of palladium(II) and heteropolyacids

The possibility of obtaining tetramers from durene or diphenyl oxide in the presence of H₅PMo₁₀V₂O₄₀, a reversible oxidant, and palladium acetate as catalyst is demonstrated.

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— H₅PMo₁₀V₂O₄₀ .

     

Kinetics of the formation of whewellite and weddelite by displacement reactions

The nucleation and crystallization of whewellite and weddelite during displacement reactions has been investigated by means of thermomicroscopy, thermogravimetry, X-ray diffraction, and scanning electron microscopy. Gypsum cleavage plates were immersed at different temperatures in solutions of oxalic acid and alkali oxalates. The reaction product (whewellite and/or weddelite) formed on the gypsum crystal surface. Depending on the concentration of the solution and on the time and temperature, different degrees of reaction, which means varying amounts and crystal forms or Ca-oxalate were found. An evaluation of the growth rate was possible by means of thermogravimetry. Conditions for the preparation of pure weddelite by precipitation from solutions have been established.

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Zusammenfassung Keimbildung und Kristallisation von Whewellit und Weddelit bei Verdrängungsreaktionen wurden durch Thermomikroskopie, Thermogravimetrie, Röntgenbeugung und Rasterelektronenmikroskopie untersucht. Gipsspaltplättchen wurden bei verschiedenen Temperaturen in Oxalsäure- und Natriumoxalatlösungen eingetaucht. Das Reaktionsprodukt (Whewellit oder Weddelit) bildete sich auf der Oberfläche des Gipskristalls. In Abhängigkeit von der Konzentration der Lösung, der Zeit und der Temperatur wurden verschiedene Umsetzungen, d. h. verschiedene Menge und Kristallformen von Calciumoxalat gefunden. Die Wachstumsgeschwindigkeit ließ sich aus thermogravimetrischen Messungen ermitteln. Die Bedingungen zur Herstellung reinen Weddelits durch Fällung aus der Lösung wurden ermittelt.

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

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We are grateful to Mr. R. Wessicken, Laboratorium für Festkörperphysik, ETH Zürich, Zürich-Hönggerberg, for taking the SEM-Photographs. Also, the kind help of Dr. A. Reller, Institute of Inorganic Chemisty, University of Zürich, for running the X-ray heating photographs is acknowledged.     

A metal reactor for the diaphragm method with chambers providing complete mixing

A new metal reactor with two chambers in which complete mixing of gases is achieved has been developed for use in the diaphragm method. This apparatus is suitable for the determination of the effective diffusion coefficient and its temperature dependence. It can also be used to determine the type of transport, the gas permeability coefficient and to investigate the macrokinetics of catalytic processes.

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. : ; ; .

     

Effect of ammonia on toluene ammoxidation over oxide catalysts

The increased activity of the catalyst for ammoxidation of toluene observed in the presence of ammonia is ascribed to its binding with the acidic centers. which leads to the formation of new active basic sites on the catalyst surface.

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, .

     

Activation energies in catalytic oxidation of benzene

The existence of a linear correlation between the apparent activation energy of benzene disappearance and the primary selectivity was demonstrated for a series of vanadia based catalysts. Analysis of this correlation leads to the conclusion that the activation energies of reaction 1 as well as activation energies of reaction 2 in benzene oxidation scheme do not differ significantly over a series of these catalysts.

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. , 1, 2 .

     

Decomposition of dimethyl sulfide in the presence of Al2O3, and catalyst deactivation

The catalytic decomposition of dimethyl sulfide has been studied over the temperature range of 400–500 °C. The main reaction products are methylmercaptane, H₂S and methane. Catalyst deactivation is due to its coking during the reaction. The possibility of oxidative catalyst regeneration at 550 °C has been shown.

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400–500°C. , . , . 550°C.

     

Induction period of the conversion of methanol to hydrocarbons on a nickel loaded faujasite: Evidence for a suppression of the autocatalytic step

The conversion of methanol to hydrocarbons on nickel loaded faujasites can be retarded for many hours time-on-stream. The induction period is interpreted to be due to a suppression of the autocatalytic step of the reaction. An autocatalytic mechanism is proposed based on the -scission of branched carbenium ion intermediates.

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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 .

     

Investigation of the pore structure of Raney nickel catalysts

Ar and N₂ adsorption and capillary condensation studies at 77.4 and 84K on Raney nickel catalysts modified by Ti, V, Cr, Mn, Zr, Mo, Ta, W, Re and on BAU char coal show that at 77.4K, in pores with d_eff>100Å, argon exists in the solid state.

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Ar N₂ 77,4 84°K - , Ti, V, Cr, Mn, Zr, Mo, Ta, W, Re , d>100 Å 77,4 °K .

     

Extension of the diffusional kinetics models involving changes in activation energy

On the basis of previous modifications of the Zhuravlev and Ginstling-Brounshtein models, a generalization of kinetic diffusional models is proposed. With the assumption that the rate of the activation energy change during the reaction is inversely proportional to the reaction time, it has been shown that all diffusional kinetic equations in heterogeneous systems take the formF()=KT ⁿ , whereF() is a function of the degree of conversion andK andn are constants related to the rate constant.

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Zusammenfassung Auf Grund vorangegangener Modifikationen der Modelle von Zhuravlev und Ginstling-Brounshtein wird eine Verallgemeinerung der kinetischen Diffusionsmodelle vorgeschlagen. Mit der Annahme, daß die Geschwindigkeit der Änderung der Aktivierungsenergie während der Reaktion umgekehrt proportional der Reaktionszeit ist, wird gezeigt, daß alle kinetischen Diffusionsgleichungen für heterogene Systeme die FormF()=KT ⁿ haben, woF() eine Funktion des Konversionsgrades undK undn mit der Geschwindigkeitskonstante in Beziehung stehende Konstanten sind.

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- . , , , F()=KT ⁿ , F() — , K n — .

     

Reactivity of alkyl and polychloroalkyl radicals toward 1-hexene

The kinetics of CCl₃ radical addition to 1-hexene in CCl₃Br and CCl₄ media has been studied. The rate constant of CCl₃ addition to the double bond is shown to be independent of the solvent. The ratios between the rate constants of transfer and allyl chain termination for the alkyl and polychloroalkyl radicals have been estimated by competition methods. Activation parameters for the calculated rate constants are given.

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CCl₃- 1- CCCl₃Br CCl₄. , . . .