Kinetic analysis of thermogravimetric data. XI thermal decomposition of some metal dithionates

A thermal analytical study of Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba and Zn dithionates is reported. The decomposition of the dithionate ion is endothermic in the case of the Na, K, Rb, Cs and NH₄ salts, but exothermic with Li, Mg, Sr, Ba and Zn. Kinetic parameters have been derived from the TG curves by means of the Coats-Redfern method. The validity of a linear kinetic compensation law is reported for the loss of crystal water and separately for the decomposition of the dithionate ion.

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Zusammenfassung Es wird über eine thermoanalytische Untersuchung der Dithionate von Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba und Zn berichtet. Die Zersetzung des DithionatIons ist im Falle von Na, K, Rb, Cs und NH₄-Salzen endotherm, im Falle von Li, Mg, Sr, Ba und Zn hingegen exotherm. Die kinetischen Parameter wurden aus den TG-Kurven mittels der Coats-Redfern-Methode abgeleitet. Es wird über die Gültigkeit eines linearen kinetischen Kompensationsgesetzes für den Verlust von Kristallwasser berichtet und gesondert für die Zersetzung des Dithionat-Ions.

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Résumé On présente les résultats d'une étude par analyse thermique des dithionates de Li, Na, K, Rb, Cs, NH₄, Mg, Ca, Sr, Ba et Zn. La décomposition est endothermique dans le cas des sels de Na, K, Rb, Cs et ammonium tandis qu'elle est exothermique dans le cas des sels de Li, Mg, Sr, Ba et Zn. Les paramètres cinétiques sont déduits des courbes TG par la méthode de Coats-Redfern. La validité d'une loi de compensation cinétique linéaire est étudiée pour la perte de l'eau d'hydratation ainsi que pour la décomposition de l'ion dithionate.

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Li, Na, K, Rb, Cs,. NH₄, Mg, Ca, Sr, Ba Zn. [ Na, K, Rb, Cs NH₄ , Li, Mg, Sr, Ba Zn . - . .

     

A study of thermal preparation OF c-Mn2P4O12

With the application of thermogravimetry under quasi-isothermal-isobaric conditions, the reaction course of the calcination of Mn(H₂PO₄ · H₂O to give dimanganese cyclotetraphosphate has been studied. Isothermal calcination was also carried out in an electric furnace at various temperatures (200 min). The reaction products were analyzed by chromatography, IR and NMR spectrocopy, and X-ray diffraction analysis. The compositions of the calcinates were determined through extraction with various inorganic and organic solvents.

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Zusammenfassung Der Verlauf der Dimangan-cyclotetraphosphat ergebenden Kalzinierung von Mn(H₂PO₄)₂ · H₂O wurde thermogravimetrisch unter quasi-isothermen-isobaren Bedingungen untersucht. Isotherme Kalzinierung wurde auch im elektrischen Ofen (200 min) bei verschiedenen Temperaturen ausgeführt. Die Reaktionsprodukte wurden chromatographisch, IR- und NMR-spektroskopisch sowie röntgendiffraktometrisch analysiert. Die Zusammensetzung der kalzinierten Produkte wurde via Extraktion mit verschiedenen anorganischen und organischen Lösungsmitteln bestimmt.

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Mn(H₂PO₄ · H₂O. . . - , - - . .

     

Differential scanning calorimetry of chloroquine sulphate exposed to sun,heat and ultraviolet radiation

Chloroquine sulphate, like the phosphate, is an antimalarial formulation widely used in the tropics. The stability of such formulations is therefore of interest in the combat against malaria. A DSC study has been made of the effects of exposure to the sun, heat and UV radiation on the stability of chloroquine sulphate, similarly as performed earlier for chloroquine phosphate. When freshly recrystallized from a water-acetone mixture, chloroquine sulphate exhibits two endothermic peaks, at 169.4° and 204.7°, for the expulsion of crystal water (one molecule) and for the melting process, respectively. The exposure of chloroquine sulphate to the sun, heat and UV radiation leads to splitting of the peak for melting.

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Zusammenfassung Chloroquine-Sulfat ist ebenso wie das entsprechende Phosphatderivat ein in den Tropen weitverbreitet angewandtes Antimalaria-Präparat. Die Stabilität dieses Präparates hat damit Bedeutung für die Malariabekämpfung. Die vorliegende Arbeit ist eine Erweiterung einer Untersuchung über den Effekt der Einwirkung.von Sonne, Hitze und UV-Strahlen auf die Stabilität von Chloroquine-Phosphat auf Chloroquine-Sulfat. Aus Wasser-Aceton-Mischungen frisch kristallisiertes Chloroquine-Sulfat zeigt zwei endotherme Peaks bei 169,4 und 204,7 °C, die durch Abgabe von Kristallwasser (ein Molekül) bzw. durch den Schmelzvorgang bedingt sind. Wird Chloroquine-Sulfat der Sonne, Wärme oder UV-Licht ausgesetzt, so wird der dem Schmelzvorgang zuzuscheibende Peak aufgespalten.

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, -, , . . , . , , 169,4 204,7°, , , . , .

     

Strong H2 chemisorption on Al2O3 or SiO2 supported group VIII metals

Following hydrogen treatments at high temperature a decrease in hydrogen chemisorption at room temperature is observed in almost all group VIII elements supported on SiO₂ or Al₂O₃. The effect is attributed to self inhibition by strongly chemisorbed hydrogen on the metals.

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VIII , SiO₂ Al₂O₃. .

     

Kinetics and mechanism of the permanganate oxidation of trans-crotonic acid

The kinetics and intermediates of the permanganate oxidation of trans-crotonic acid have been investigated in the pH range of 0.5–5.0 using the stoppedflow technique. The formation of manganese(III) as a short-lived intermediate has been established. The reaction is first order with respect to both MnO ₄ ^– and crotonic acid (crotonate). The resolved rate constants at 25°C are 730 and 410 M^–1 sec^–1 for the acid and the anion, respectively. The reaction mechanism is discussed.

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pH=0,5–5,0, . (III) . MnO ₄ ^– , (). 25°C 730 410 M^{–1 –1} , . .

     

Preparation of catalysts by spray decomposition

Spray decomposition of solutions is an uncommon but very promising technique for the preparation of multicomponent solid systems with welldefined structure. The experimental arrangement is described and a summary of the systems prepared until now is given. These are MgO–ZnO, CaO, CdO, Al₂O₃. Fe₂O₃ solid solutions and CdO. CdSO₄ and Al₂O₃. Al₂(SO₄)₃ systems.

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, , . : MgO·ZnO, CaO·CdO,. Al₂O₃·Fe₂O₃ CdO·CdSO₄ Al₂O₃·Al₂ (SO₄)₃.

     

Hydrogenation of carbon monoxide catalysts prepared by pyrolysis of Co2(CO)8 on various oxide supports

Catalysts prepared by pyrolysis of Co₂(CO)₈ on oxide supports have been studied in the hydrogenation of CO. It is shown that MgO and -Al₂O₃-based catalysts are less active than those supported on SiO₂, TiO₂ and ZrO₂. The application of -Al₂O₃ as a support increases the relative yield of light hydrocarbons.

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, Co₂(CO)₈ , CO. , MgO -Al₂O₃ SiO₂, TiO₂ ZrO₂. -Al₂O₃ .

     

Non-isothermal thermogravimetry of polymer

A Model of polymer decomposition is proposed which formally involves the termination of active centres. It yields reasonable activation energies for the decompositions of polypropylene, polyethylene, polystyrene and polymethyl methacrylate investigated by non-isothermal thermogravimetry. In the value of a formal reaction orders the model reflects the reaction conditions, such as initial sample weight, atmosphere, ventilation conditions, sample holder nature and shape, etc.

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Zusammenfassung Ein Modell für Zersetzungsreaktionen von Polymeren wurde entworfen, das auf dem Abbau von aktiven Zentren basiert. Es liefert richtige Aktivierungsenergien für die Zersetzung von Polypropylen, Polyäthylen, Polystyren und Polymethylmethakrylat (bestimmt durch nichtisotherme Thermogravimetrie) und macht es ausserdem möglich, die äusseren Reaktionsbedingungen, wie Einwaage, Atmosphäre, Ventillationsbedingungen, Art und Form des Probenhalters usw. zu berücksichtigen.

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, . , , , . «» , , , , . .

     

Hydrogenolysis of 3-methylpentane over group VIII metals

Determination of the fragmentation factor in a wide conversion range over Group VIII metals and Re indicated that the single character of the hydrogenolysis of 3-methylpentane is an inherent property of the catalyst and is almost independent of the conversion level. Multiple hydrogenolysis occurs in most cases as rapid subsequent terminal splitting.

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-- VIII Re, , 3- . .

     

Kinetics of isotopic exchange due to one elementary reaction

Kinetic equations of the isotopic exchange in a system with one elementary reaction have been derived. A principle of quasistationarity in the isotopic kinetics has been formulated.

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. .

     

Kinetics of heterogeneous catalytic hydroformylation of propylene on rhodium-cobalt catalysts. Reaction mechanism

Steady-state kinetics of combined heterogeneous catalytic hydrogenation and hydroformylation of propylene on Rh–Co-containing catalysts has been studied at atmospheric pressure and T=140–170 °C. A reaction mechanism is suggested. The kinetic model adequately describes all observations.

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- Rh–Co- 140–170 °C. . , .

     

Properties of highly dispersed supported catalysts in hydrogenation reactions

Pt/sol and Pt/support catalysts with 6–15 Å Pt particles have been established to be low active in the hydrogenation of propargyl alcohol, butyn-l-ol-3 and dimethylethynylcarbinol. The specific catalytic activity significantly rises with increasing d_Pt above 15 Å and after the thermal treatment of highly dispersed catalysts in a hydrogen flow.

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, -30 -- 6–15 Å , -1, -3 . d_Pt>15 Å .

     

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- -. (, , ) - -.

     

CO/H2 and CO2/H2 reactions with amorphous carbon-metal catalysts

By metal impregnation of selected naturally occurring organic materials followed by controlled carbonization, metal semicoke catalysts can be readily prepared. These catalysts have been tested in the synthesis of hydrocarbons and alcohols from CO/H₂ and CO₂/H₂ mixtures. Fe and Co preparations have been used. Relatively high temperatures are required when using these catalysts, which are quite active for synthesis using CO₂ and H₂. The pressure (5150 kPa) is very favorable both for the synthesis of liquid hydrocarbons (C₅–C₃₀) and alcohols (C₁–C₅).

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. CO/H₂ CO₂/H₂. Fe Co. , CO₂ H₂. 5150 ) (C₅–C₃₀) (C₁–C₅).

     

Thermal and thermoxidative decomposition of ternary grafted copolymers of ABS type

The thermal (under high vacuum, 10^–5 mm Hg) and thermoxidative decompositions of ternary grafted copolymers of ABS type were studied, the dependence of the characteristic thermal data on the overall composition being followed over narrow ranges of variation of comonomer content.It was found that the nature of the solid products obtained on thermal decomposition is dependent on the copolymer structure.

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Zusammenfassung Die thermischen (unter Hochvakuum, 10^–5 mm Hg) und thermooxidativen Zersetzungen ternärer Kopolymere der Typen ABS wurden untersucht, wobei die Abhängigkeit der charakteristischen thermischen Daten von der allgemeinen Zusammensetzung über enge Bereiche der Änderung des Komonomergehaltes verfolgt wurde. Es zeigte sich, daß die Beschaffenheit der bei der thermischen Zersetzung erhaltenen festen Produkte von der Kopolymerstruktur abhängig ist.

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( 10^–5 Hg) ABC. , . , , , .

     

Ht-XRD, DSC and X-ray microprobe analysis of Cu and Al promoted Fe/MgO

Promoter effects of Cu were related to the shifts of the temperature of iron reduction, to the changes of iron particles in reaction conditions and to Cu–Fe distribution over the support. Skin effect of Al promoter was checked by the analysis of Al distribution.

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Cu , Cu–Fe . Al Al.

     

Pt?Fe2O3 catalytic system for hydrogenation reactions

The effect of Fe₂O₃ additives on crotonaldehyde hydrogenation over group VIII metals has been studied. Iron oxide added to platinum black exerts a modifying effect on the reduction of the carbonyl group of croton-aldehyde inhibiting hydrogenation of the C=C bond conjugated with a C=O group.

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Fe₂O₃ VIII -. , , - , C=C , C=O-.

     

An addition scheme of heat capacities of linear macromolecules

The prior developed addition scheme of heat capacities is expanded to macromolecules that contain non-C-bonds in the backbone. Tables for 31 groups are given. 713 data points which have been averaged for group contributions for which more than one measurement was available showed a deviation of 0.1±1.5% (internal consistency). Calculated heat capacities of homopolymers and copolymers for which independent measurements have been made showed average errors of 0.60% and a standard deviation of ±2.35% (177 data points).

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Zusammenfassung Das früher entwickelte Additionsschema für Wärmekapazitäten wird auf Makromoleküle erweitert, die Nicht-C-Bindungen im Stützgerüst enthalten. Tabellen für 31 Gruppen sind angegeben. Von 713 Meßdaten wurden für Gruppenbeiträge, für die mehr als ein Meßwert zur Verfügung stand, Mittelwerte berechnet, wobei sich eine Abweichung von 0.1±1.5% (interne Konsistenz) ergab. Berechnete Wärmekapazitäten von Homopolymeren und Kopolymeren, für die unabhängige Messungen ausgeführt wurden, weisen einen mittleren Fehler von 0.60% bei einer Standardabweichung von 2.35% auf (177 Meßwerte).

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, . 31 . 713 , , 0.1±1.58% ( ). , , 0,60% ±2,35% (177 ).

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This work was supported by the National Science Foundation of the US, Polymers Program, Grant # DMR 8317097.     

Heterogeneous reactions of solid nickel(II) complexes

The influence of different modes of preparation on the stoichiometry of thermal decomposition of isothiocyanatonickel(II) complexes with ammonia was studied. It was found that the complex Ni(NCS)₂(NH₃)₄ (I) prepared by heterogeneous reaction undergoes decomposition in two steps (–2 NH₃, –2 NH₃), while for complex II, of the same composition but prepared by homogeneous reaction from solution, the decomposition proceeds in three steps (–1 NH₃, –1 NH₃, –2NH₃). Electronic and infrared absorption spectra were used for the study of the spectral properties of the starting complex. It was found that the different stoichiometries of thermal decompositions of complexes I and II do not cause differences in the bonding strength of the ammonia molecules (chemical factor); this effect is rather brought about by physical factors such as different imperfections of the crystal lattice.

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Zusammenfassung Der Einfluß der Herstellung auf die Stöchiometrie der thermischen Zersetzung von Amin-Komplexen des Isothiocyanatonickels wurde studiert. Der Zerfall des Komplexes Ni(NCS)₂(NH₃)₄ (I), hergestellt durch heterogene Reaktion, verlief in zwei Etappen (–2 NH₃, –2 NH₃). Beim selben Komplex (II), hergestellt durch homogene Reaktion in Lösung, wurden jedoch drei Etappen beobachtet (–1 NH₃, –1 NH₃, –2 NH₃). Die Eigenschaften des Ausgangsproduktes wurden durch Elektronen- und IR-Spektroskopie untersucht. Das unterschiedliche thermische Verhalten ist nicht auf eine verschiedene Bindungsstärke der NH₃ Moleküle, sondern auf physikalische Ursachen, wie z. B. Unregelmässigkeiten im Kristallgitter zurückzuführen.

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Résumé On a étudié l'influence des diverses méthodes de préparation sur la stoechiométrie de la réaction de décomposition thermique des complexes de l'isothiocyanate de nickel(II) avec l'ammoniac. On a établi que le complexe Ni(SCN)₂(NH₃)₄, (I), préparé rar réaction hétérogène, subit une décomposition en deux étapes (–2NH₃, –2NH₃), tandis que le complexe (II), de même composition, mais préparé par réaction homogène, à partir de solutions, se décompose en trois étapes (–1NH₃,–1NH₃, –2NH₃). Les propriétés spectrales du complexe initial ont été étudiées par absorption électronique et infrarouge. On a trouvé que les différences de stoechiométrie des réactions de décomposition thermique des complexes (I) et (II) n'apportaient pas de différences entre les énergies de liaison des molécules d'ammoniac (facteur chimique). C'est plutôt à des facteurs physiques, comme les différentes imperfections du réseau cristallin, que cet effet serait dû.

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(II) . , Ni(NCS)₂(NH₃)₄ (I), , (–2NH₃,–2NH₃). , II , , (–1 NH₃,–1 NH₃ –2NH₃). . , I II ( ), , .

     

Effect of carbon support on the hydrogen sorption of platinum

The hydrogen sorption of carbon-supported platinum catalysts, studied by the potentiodynamic method, differs significantly from that of unsupported platinum. The difference depends on the preparation method and on the nature of the support. Possible explanations are suggested as (i) some kind of interaction between metal and support atoms during impregnation, (ii) high dispersity (amorphous structure) and (iii) hydrogen spillover onto the carbon support.

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Pt/C, . . (I) , (II) ( ), (III) .