Calculation of the mass transfer coefficient with a chemical reaction in a gas-liquid system

A solution of the problem of mass transfer in a turbulent boundary layer has been obtained with a first-order chemical reaction occurring in the liquid phase. The dependence of the enhancement factor for absorption and of the mass transfer coefficient on the model parameters can be used for building up a hierarchic model of the gas-liquid reactor.

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Interaction of V2O5 with oxygen in the gas phase

Sorption/evolution of oxygen from V₂O₅ in the temperature range of 480–520°C is due to a shift in the defect equilibrium 1/2 O₂ (gas)+V_oO_o. A first-order kinetic equation can be derived under the assumption that the activation energy depends on the concentration of defects.

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/ V₂O₅ 480–520°C 1/2 O₂ ()+V_oO_o. , , .

     

On the reduction of NiO forms in magnesia supported catalysts

Reducibility of Ni/MgO catalysts has been studied by the temperature-programmed reduction (TPR) technique in the temperature range of 373–1273 K. The profile of reduction reveals the presence of various forms of NiO. The effects of nickel loading and treatment temperature on catalyst reducibility have been evaluated. The formation of NiO–MgO solid solution controls the whole reduction of Ni/MgO system.

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Ni/MgO 373–1273 . NiO. . Ni/MgO NiO–MgO.

     

On the initial treatment of kinetic data

The kinetic methods usually employed to determine reaction orders involve some sort of mathematical approximation and provide values approximate and very often discrepant. Three methods are reported to determine accurate reaction orders without introducing approximations.

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, , , , . .

     

Kinetics and mechanism of the oxidation of L-ascorbic acid by 2,6-dichlorophenol-indophenol in aqueous solution

The kinetics of oxidation of L-ascorbic acid by 2,6-dichlorophenolindophenol in aqueous solution has been studied. The rate of the reaction decreases with increasing pH since the hydrogen ascorbate ion is less reactive than the unionized L-ascorbic acid. The rate constants for the oxidation of the two species have been evaluated and a plausible mechanism of the reaction is suggested.

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L- 2,6-- . pH, , L- . .

     

Rh and Pt catalysts activated by UHV treatments

The H₂–D₂ exchange activity of Rh powder was enhanced by high-temperature UHV treatment accompanied with an enrichment of the high-index faces of Rh. The thermal decomposition of H₂PtCl₆·6H₂O under UHV condition resulted in an extremely active Pt powder catalyst.

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H₂–D₂ Rh , - Rh - . H₂PtCl₆·6H₂O Pt .

     

Isothermal crystallization measurements on copolyesters by differential scanning calorimetry

Miller's method for isothermal crystallization measurement was used to determine the progress of crystallization of copoly(ethylene terephthalate/isophthalate) and copoly(ethylene terephthalate/5-methoxyisophthalate) by DSC. The evaluation of kinetic parameters is too complicated for higher contents of comonomer and higher values of molecular mass of copolyesters. On the other hand, the experimental results interpreted by the simplified equation well characterized the differences in the rates of crystallization of different copolyesters.

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Zusammenfassung Die Millersche Methode der isothermen Kristallisierung wurde eingesetzt um den Fortschritt der Kristallisierung von Kopoly(Äthylen-Terephthalat/Isophthalat) und Kopoly(Äthylen-terephthalat/5-Metoxyisophthalat) mittels DSC zu untersuchen. Die Auswertung der kinetischen Parameter ist für höhere Ko-Monomergehalte und höhere Molekularmassenwerte der Ko-Polyester zu kompliziert. Andererseits konnten die an Hand der vereinfachten Gleichung gedeuteten Versuchsergebnisse zur Charakterisierung der Unterschiede der Kristallisierungsgeschwindigkeiten der verschiedenen Ko-Polyester mit gutem Erfolg eingesetzt werden.

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Résumé On a appliqué la méthode de détermination de la cristallisation isotherme de Miller à la détermination par analyse calorimétrique différentielle de l'avancement de la cristallisation du copoly(éthylène téréphtalate/isophtalate) ainsi que du copoly(éthylène téré phtalate/5-méthoxy-isophtalate). L'évaluation des paramètres cinétiques est trop compliquée pour les teneurs plus élevées en comonomère et pour les valeurs plus élevées de la masse molaire des copolyesters. D'autre part, les résultats d'expériences interprétés par l'équation simplifiée ont bien caractérisé les différences de vitesses de cristallisation des divers copolyesters.

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. : Ni(NCS)₂(py)₄, (=), CuSO₄ · 5₂ NiSO₄ · 7₂, . , , .

     

Error analysis of surface area determinations by the chromatographic technique

The systematic and random errors in the determination of the surface area of adsorbents and catalysts by argon thermodesorption chromatography are analyzed.

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Steric substituent effect on the resin catalyzed hydrolysis of alkyl acetate esters

The rates of hydrolysis of seven acetate esters substituted in the alkyl group have been studied in the presence of a sulfonated cation exchange resin in 70% aqueous acetone solution. the slower hydrolysis rates with increasing size of substituent are related to increasing steric influence, as determined by decreasing values of the steric substituent parameter, E_s. The efficiency of the resin catalyst is related to the entropy of substituents. Influence caused by steric hindrance on reaction rates accounts satisfactorily for observed variations of the enthalpies and entropies of activation with alkyl group substituents. The entropy, S^x, values increase in the order: n-octyl-

, , 70%- . , , E_S. . , . , S^*, : --<-<, .