Critical discussion of simple adsorption methods used to evaluate the micropore size distribution

The well-known simple adsorption methods used to evaluate the micropore size distribution from low pressure adsorption isotherms were examined by employing model isotherms for slit-like graphite micropores obtained from nonlocal density functional theory. It was shown that in the range of pore sizes from about 0.4 to 0.9 nm, the Horvath Kawazoe (HK) method satisfactorily reproduces the shape of the micropore size distribution, but the pore sizes are underestimated. In the case of micropores wider than 0.9 nm, the method fails as the formation of the monolayer on the pore walls produces a peak corresponding to 0.6 nm micropores on the HK pore size distribution. Therefore, the HK method indicates the presence of microporosity even for nonporous samples. The Dubinin-Astakhov adsorption isotherms were also examined and it was shown that their application to represent local adsorption isotherms for homogeneous pores is questionable. However, the adsorption potential distributions seem to be promising for micropore analysis.Nomenclature A Adsorption potential kJ/mol - C ₁ Constant in Eq. 3 and 4 kJ * nm/mol - C ₂ Constant in Eq. 3 and 4 nm³ - C ₃ Constant in Eq. 3 and 4 nm⁹ - C ₄ Constant in Eq. 3 and 4 - d Adsorbate molecule diameter nm - d _A Adsorbent atom diameter nm - G Change in the Gibbs free energy kJ/mol - J Pore size distribution cm³/(g*nm) - R The universal gas constant = 8.31431 J/(mol * K) - T Absolute temperature K - V Amount adsorbed expressed in cm³ of liquid adsorbate per 1 g of the adsorbent = 0.0015468 * amount adsorbed expressed in cm³ STP/g cm³/g - x Pore width nm - X Differential adsorption potential distribution cm³ * mol/(g*kJ) - Constant defined as nm - p Pressure Pa - p ₀ Saturated pressure = 760 torr = 101325 Pa Pa - P _c Condensation pressure Pa - Degree of pore filling - S _BET BET specific surface area m²/g - S _ex External surface area obtained fromt-plot method m²/g - V _mi Micropore volume obtained fromt-plot method cm³/g - V ₁ Total pore volume cm³/g - E Characteristic energy in the Dubinin-Astakhov equation kJ/mol - n Exponent in the Dubinin-Astakhov equation      

Hydrogenolysis of n-butane on Ni-Pd/SiO2 catalysts

Supported Ni-Pd/SiO₂ catalysts of different Ni and Pd composition were studied in n-butane hydrogenolysis. The reaction rate, selectivity towards methane, ethane and propane were determined. On the basis of these data the relationship between the size and composition of the active center and the possibility of surface segregation of one of the components is discussed.

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Ni-Pd/SiO₂ Ni Pd -. , . .

     

Average electron momenta in many-electron atoms

In many-electron atoms, the average electron momentum p represents the mean momentum of a single electron when all the electron motions are averaged. If any two electrons are considered simultaneously, however, the average momentum p splits into two different momenta, low momentum p_< and high momentum p_>. For the 102 atoms He through Lr in their ground states, the momenta p_< and p_> are systematically examined at the Hartree–Fock limit level. It is also shown that the sum p_>+p_< and the difference p_>–p_< of the two momenta constitute upper and lower bounds to the electron-pair relative momentum p₁₂=|p₁–p₂| and to the electron-pair center-of-mass momentum P=|p₁+p₂|/2. The tightness of the bounds is discussed for the 102 atoms.     

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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, . .

     

Reduction of higher polymethylbenzenes by the rapid cation exchange of H-mordenite in the conversion of methanol to hydrocarbons

The product distribution in methanol conversion on mordenite is changed by potassium ion exchange depending on the method of ion exchange. The rapid exchange method was the most effective to suppress the formation of higher polymethylbenzenes.

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. .

     

Enthalpies de melange du systeme antimoine-tellure a 909,30 K, 911,85 K et 917,95 K

Thermodynamical data on Sb-Te system at 909,30 K, 911,85 K and 917,95 K. The integral molar enthalpies of formation of liquid Sb-Te alloys were measured at three temperatures by drop calorimetry.Partial molar enthalpies of formation of these alloys, referring to the pure liquid constituants, and enthalpie of formation at 298 K of the compound Sb₄₀₅Te₅₉₅ were deduced.

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Zusammenfassung Thermodynamische Daten, des Systemes Sb-Te bei 909,30, 911,85 und 917,95 K. Mittels Drop-Kalorimetrie wurden die integralen molaren Bildungsenthalpien von flüssigen Sb-Te Legierungen bei drei verschiedenen Temperaturen gemessen. Die partiellen molaren Bildungsenthalpien dieser Legierungen, bezogen auf die reinen flüssigen Komponenten sowie die Bildungsenthalpie der Verbindung Sb_0.405Te_0.595 bei 298 K wurden abgeleitet.

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Sb-Te 909,30; 911,85 917,95 . , Sb_0.4050.595 298 .

     

Investigation of kinetics of curing of triglycidyl-p-aminophenol with aromatic diamines by differential scanning calorimetry

The kinetics of curing of triglycidyl-p-aminophenol with four different diamines in stoichiometric amounts were investigated by means of differential scanning calorimetry. The results indicated that the curing reaction follows first-order Arrhenius kinetics with an activation energy in the range 40–70 kJ · mol^–1. The effect of the structure of the curing agent on the curing characteristics is discussed on the basis of the curing characteristics and the kinetic parameters. An epoxy fortifier was observed to lower the curing temperature of an epoxy-amine system when incorporated prior to curing.

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Zusammenfassung Mittels Differential-Scanning-Kalorimetrie wurde die Kinetik der Vernetzung von Triglycidyl-p-aminophenol mit stöchiometrischen Mengen vier verschiedener Amine untersucht. Laut den Ergebnissen verläuft die Vernetzungsreaktion mit einer Arrhenius-Kinetik erster Ordnung, wobei die Aktivierungsenergie im Bereich von 40–70 kJ/mol liegt. Auf Grundlage der Vernetzungscharakteristika und der kinetischen Parameter wird der Einfluss der Struktur des Vernetzungsreagenz auf die Vernetzungskenndaten beschrieben. Mit einem vor der Vernetzung eingebrachten Epoxyfortifyers konnte die Vernetzungstemperatur eines Epoxy-Amin-Systemes heruntergesetzt werden.

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-- , . , 40–70 ·^–1. . , , , .

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One of the authors (R.D.P.) is grateful to the University Grants Commission, New Delhi, for the award of a Research Associateship under the Special Assistance Programme.     

The preparation and thermal analysis studies on some first row transition metal complexes of 2-aminopyrimidine

Complexes of 2-aminopyrimidine with the chlorides, bromides and iodides of cobalt(II), zinc(II) and also with the chlorides and bromides of manganese(II), nickel(II) and copper(II) have been prepared. The chloride complex of iron(II) was also obtained. The stereochemical configurations of the complexes were deduced using spectral and magnetic properties. The decomposition of the complexes was studied by thermogravimetry and differential thermal analysis.

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Zusammenfassung Komplexe von 2-Aminopyrimidinen mit den Chloriden, Bromiden und Jodiden von Kobalt(II), Zink(II) und den Chloriden und Bromiden von Mangan(II), Nickel(II) und Kupfer(II) wurden hergestellt. Der Chloridkomplex von Eisen(II) wurde ebenfalls erhalten. Die stereochemischen Konfigurationen der Komplexe wurden aus spektralen und magnetischen Eigenschaften abgeleitet. Die Zersetzung der Komplexe wurde durch Thermogravimetrie und Differentialthermoanalyse untersucht.

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Résumé Les complexes de l'amino-2 pyrimidine avec les chlorures, bromures et iodures de cobalt(II), zinc(II) ainsi qu'avec les chlorures et bromures de manganèse(II), nickel(II) et cuivre(II) ont été préparés. Le complexe formé avec le chlorure de fer(II) a aussi été obtenu. Les configurations stéréochimiques des complexes ont été déduites des propriétés spectrales et magnétiques. La décomposition thermique des complexes a été étudiée par thermogravimétrie et analyse thermique différentielle.

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2- , (II) (II), (II), (II) (II). (II). . .

     

Differential scanning calorimetry applied to cross-linking of a filled epoxy resin: Accuracy of the Borchardt and Daniels equation for describing the curing process kinetics

From the point of view of the chemical reactions describing the curing process of a mixture epoxy resin-dicarboxylic acid anhydride-tertiary amine-polyol and silica filler, it is difficult to understand the network formation: several different reactions are involved, so that the interaction between the epoxy resin and the other components of the mixture is unquestionably complex. However, a linear plot is obtained when Kissinger's method is applied to dynamic DSC results (four different scanning rates), which confirms the calculation assumptions. In particular, the Borchardt and Daniels equation, where the specific rate constant is assumed to be of Arrhenius form appears to be a good mathematical model for describing the curing process under dynamic DSC conditions. The apparent activation energy determined by means of this analytical method is in good agreement with those obtained by other methods in the literature.

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Zusammenfassung Die bei der Härtung eines Epoxidharz, Dicarboxylsäure-Anhydrid, tertiäres Amin, Polyol und einen SiO₂-Füllstoff enthaltenden Gemisches vor sich gehende Vernetzung ist schwer zu überblicken; es verlaufen mehrere unterschiedliche Reaktionen, so daß die Wechselwirkung zwischen dem Epoxidharz und den anderen Komponenten außerordentlich komplex ist. Eine lineare Abhängigkeit wird jedoch erhalten, wenn dynamische DSC-Ergebnisse erhalten bei 4 verschiedenen Scanning-Geschwindigkeiten nach der Kissinger-Methode aufgearbeitet werden, was die Richtigkeit der für die Berechnung gemachten Annahmen bestätigt. Besonders die Gleichung von Borchardt und Daniel, bei deren Ableitung für die spezifische Geschwindigkeitskonstante eine Arrhenius-Form angenommen wird, scheint ein gutes mathematisches Modell zur Beschreibung des Härteprozesses unter DSC-Bedingungen zu sein. Die nach dieser Methode bestimmte scheinbare Aktivierungsenergie stimmt gut mit den nach anderen in der Literatur beschriebenen Methoden bestimmten Werten überein.

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

     

Sedimentation equilibrium of suspensions of colloidal particles at finite concentrations

Equilibrium concentration profiles of non-dilute colloidal suspensions are calculated by means of the Carnahan-Starling expression for the osmotic compressibility of hard sphere liquids. The profiles depend on the average volume fraction of the suspension, , and on the field interaction parameter, ₀ (reciprocal of the Péclet number at infinite dilution). Profiles are computed for values of and ₀ typical of those encountered in sedimentation field-flow fractionation experiments. It is found that, in most cases, the volume fraction at the depletion wall is negligibly small and that the volume fraction at the accumulation wall ₀, depends on the ratio <>₀/₀ only. An inflexion point is found in the concentration profile if ₀ is larger than 0.13 whatever the value of ₀.     

Application of high resolution ICP-spectrometry to the determination of B,Be, Co,Mo and Sn in soils and similar matrices

The most sensitive emission lines for the elements B, Be, Co and Mo are strongly influenced by disturbing emission lines of Fe using normal optical resolution. The advantages of high resolution, applying the new ICP-spectrometer JY 38 Plus (Jobin-Yvon, France) with the 2400 lines/mm grating measuring in the 1st and 2nd order will be discussed. Beside the concentrations in soils, sediments and sludges, applying aqua regia and HF decomposition methods, the detection limits in these matrices will be given. The possibilities of ICP-spectrometry for the determination of the above-mentioned elements are shown at the examples of SRMs (standard reference materials). The materials used here were three soils and three sludges from the BCR (Community Bureau of Reference, European Communities) and one sediment from NBS (National Bureau of Standards, USA). For example, the most sensitive and normally used line for the determination of boron at 249.7733 nm cannot be used in case of this type of matrix due to normally high Fe-concentrations and due to a strong Fe-interference. Therefore, it is necessary to use the line at 249.6778 nm, where an interference-free measurement can be achieved in case of high optical resolution. The measured B-contents in these samples are in the range of 20 to 60 g/g, for Co in the 10 g/g region, for Be well below 1 g/g, for Sn between 3 and 400 g/g. Mo was only detectable in the sludge samples (limit of determination 0.5 g/g).Presented in part at the 1989 European Winter Conference on Plasma Spectrochemistry, Reutte, Austria     

Excited state wave functions

Wave functions and energies were calculated for the 2s, 3p ₀, and 4d ₀ states of the hydrogen atom using the Messmer and Rayleigh-Ritz variational methods with minimization of the second eigenvalue. The wave functions were linear expansions of Gaussian functions and both linear and exponential parameters were varied. Except for the two term expansions, calculated values of the energies and expectation values, r ^–1, r and r ² were within two percent of the true values for both methods.     

Study of interaction between nitrogenous gases and ruthenic catalysts

The effect of temperature on the interaction of nitrogenous gases with Ru-black has been studied by the method of temperature-programmed desorption.

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Ru- - .

     

The reaction of copper(I) sulphide with a product of its oxidation copper(II) sulphate

The course of the reaction between copper(I) sulphide and copper(II) sulphate in SO₂ at 710–785 K was studied by the TG method under isothermal and non-isothermal conditions, as well as by the DTA method, X-ray analysis and scanning electron microscopy. It was established that the reaction is essentially dependent upon the initial composition of the substrate mixture, Cu₂SO₂ and Cu₂SO₂ being the chief intermediates in the reaction. Copper(I) oxide appears as the permanent final product of the reaction of interest. The reaction network, with the intermediate stages depending on the initial compositions in the temperature range studied, has been demonstrated.

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Zusammenfassung Der Verlauf der Reaktion von Kupfer(I)-sulfid mit Kupfer(II)-sulfat wurde in SO₂ bei 710–785 K durch isotherme und nichtisotherme Thermogravimetrie sowie DTA, Röntgenanalyse und Scanning-Elektronenmikroskopie untersucht. Es wurde festgestellt, daß die Reaktion wesentlich von der Ausgangszusammensetzung des Substratgemisches abhängt, wobei Cu₂SO₂ und Cu₂SO₄ die vorherrschenden intermediären Produkte der Reaktion sind. Kupfer(I)-oxid tritt als Endprodukt auf. Der die intermediären, im untersuchten Temperaturbereich von der Ausgangszusammensetzung abhängigen Reaktionsschritte in sich einschließende Reaktionsverlauf wird dargelegt.

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710–785 , , . , . Cu₂SO₂ Cu₂SO₄, . , .

     

Upper Bound to the Expectation Value of the Squared Hamiltonian

An upper bound to the expectation value of the squared Hamiltonian H ² is derived which relies on replacing products of certain operators with products of the matrix representations of said operators to reduce the computational demands of H ². An example is given which shows the strength of the bound and an application with the Temple lower bound is shown.     

Heats of adsorption of CO2 and NH3 on natural mordenites

The heats of adsorption of CO₂ and NH₃ were studied for sodium, lithium, calcium and decationized forms of natural mordenites. The exchange of Na⁺ for Ca²⁺ leads to increasing adsorption heats at low coverages. For CO₂ the region of elevated heats corresponds to the formation of Ca²⁺ ... CO₂ adsorption complexes. Two molecules of NH₃ probably interact with each Ca²⁺ ion (or with the Li⁺ ions in Li-mordenite). The heats of adsorption of NH₃ on decationized mordenite are much higher than those on calcium mordenite.

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Zusammenfassung Adsorptionswärmen von CO₂ und NH₃ an der Na-, Li-, Ca- und dekationisierten Form von natürlichem Mordenit wurden bestimmt. Der Austausch von Na⁺ gegen Ca²⁺ führt zu einer Erhöhung der Adsorptionswärmen bei geringen Bedeckungen. Bei CO₂ erfolgt im Bereich hoher Adsorptionswärmen die Bildung des Adsorptionskomplexes Ca²⁺ ...CO₂. Mit jedem Ca²⁺-Ion (bzw. Li⁺-Ion im Li-Mordenit) treten wahrscheinlich zwei NH₃-Moleküle in Wechselwirkung. An dekationisiertem Mordenit sind die Adsorptionswärmen von NH₃ höher als an Ca-Mordenit.

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, , . . Ca²⁺ ... CO₂. B , , ( -). , -.

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The authors would like to thank Dr. I. A. Belitsky for supplying the sample of natural mordenite. They also thank Professor S. P. Zhdanov for his interest and encouragement of this work.     

Zur Totalsynthese von Human-Sekretin

Summary The synthesis of the heptacosapeptide amide with the primary structure of Human-secretin is described. For this purpose 7 fragments were designed, i.e. H-Gly-Leu-Val-NH₂ 25–27b,Z-Arg(Z ₂)-Leu-Leu-Gln-OH 21–24,Z-Arg(Z ₂)-Leu-Gln-OH 18–20,Z-Arg(Z ₂)-Glu(OtBu)-Gly-Ala-OH 14–17,Z-Arg(Z ₂)-Leu-OH 12–13,Z-Thr(tBu)-Ser(tBu)-Glu(OtBu)-Leu-Ser(tBu)-OH 7–11,Adoc-His(Adoc)-Ser(tBu)-Asp(OtBu)-Gly-Thr(tBu)-Phe-OH 1–6 these fragments were consequently assembled to the overall protected total sequence using the Wünsch/Weygand-method with dicyclohexylcarbodiimide. After deprotection by exposure to trifluoroacetic acid in presence of 1,2-ethanedithiol and water as scavenger, the isolated crude product was purified by column chromatography on CM-Sepharose, fast flow. This synthetized Human-secretin showed the full biological activity in comparison to Porcine-secretin.

Herrn Prof. Dr. E. Bayer zum 65. Geburtstag gewidmet.     

[Fe(phen)3]2+ aquation in aqueous polyacrylamide solution

The aquation of tris(1, 10-phenanthroline) iron(II) has been studied in aqueous polyacrylamide solutions. The rate increases up to 2.8 times at low polymer concentrations, and subsequently decreases. These effects are attributed to changes in the local water activity in the region of the complex.

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(1, 10-) (II) . 2,8 , . .

     

Formation of N-butane in the pyrolysis of ethylene [1]

Yields of n-C₄H₁₀ have been measured from the flow pyrolysis of C₂H₄ at 897 (±7) K. From 77 to 720 Torr the order of n-C₄H₁₀ formation was found to be 2.0±0.3 The rate constant for the reaction, was estimated to be 2.4(±0.6)×10^–4l mol^–1s^–1.

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-C₄H₁₀ C₂H₄ 897 (±7) . -C₄H₁₀ 77 720 2.0±0.3. 2C₂H₄C₂H₃+C₂H₅ 2,4 (±0,6)×10^{–4 –1–1}.