Thermal desorption of atmospheric organic pollutants enriched on charcoal

A technique of thermal vacuum desorption of charcoal, used in passive dosimeters to enrich organic pollutants of toxicological importance, is described. It combines the advantages of the classic procedure of using highly active charcoal followed by solvent desorption and the environmental one-step procedure of analyzing the whole thermally desorbed sample. For pollutants such as trichloroethylene, tetrachloroethylene, ether, benzene and ethanol, the recovery and reproducibility are satisfactory. The unexpected decomposition of halothane and ethylacetate at higher temperatures is caused by the catalytic activity of the charcoal, but this can be tolerated under constant operating conditions.

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Zusammenfassung Eine Methode zum Anreichem toxikologisch bedeutender organischer Luftverunreinigungen durch thermische Vakuumdesorption von Aktivkohle nach dem Einsatz in passiven Dosimetern wird beschrieben. Die Methode kombiniert die Vorteile der klassischen Prozedur unter Verwendung hochaktiver Kohle mit nachfolgender Desorption durch Lösungsmittel einerseits mit denen der Umwelt-Analyse der gesamten desorbierten Probe in einem Schritt andererseits. Für Luftverunreinigungen wie Trichlorethylen, Tetrachlorethylen, Ether, Benzen und Ethanol werden ausreichende Wiedergewinnung und Reproduzierbarkeit ermittelt. Die unerwartete Zersetzung von Halothan und Ethylacetat bei höheren Temperaturen wird auf die katalytische Wirkung der Aktivkohle zurückgeführt. Sie kann unter konstanten Versuchsbedingungen jedoch toleriert werden.

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, . . , - , , . .

     

Comportement thermique des benzènesulfonates de lithium,sodium et potassium

Résumé Le comportement thermique des benzènesulfonates de lithium, sodium et potassium a été étudié par TG et ATD à l'air et sous atmosphère d'azote.Dans la zone de stabilité des sels anhydres, nous avons mis en évidence des transformations réversibles (changements de phase cristalline) dont certaines ont fait l'objet de mesures calorimétriques.L'étude des résidus solides de la décomposition a montré une proportion importante de sulfates dans les produits obtenus dans l'air, alors que sous azote, il s'agissait surtout de sulfures. Les sulfites ne se présentent qu'en très faible quantité dans les deux cas.

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The thermal behaviour of benzènesulphonates of lithium, sodium and potassium has been investigated by TG and DTA in air and in an atmosphere of nitrogen.We have shown in the stability interval of the anhydrous salts reversible transformations (phase transitions), some of which were quantitatively studied by calorimetry.The radiocristallographic study of the solid residues has shown an important proportion of sulphates in the residues in air and of sulphides in an inert atmosphere. The sulphites were found in very small quantity in both cases.

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Zusammenfassung Das thermische Verhalten der Benzolsulfonate von Lithium, Natrium und Kalium wurde durch TG und DTA in Luft und in Stickstoff untersucht.Im Stabilitätsbereich der wasserfreien Salze wurden reversible Umwandlungen (Phasenübergänge) nachgewiesen, von denen einige quantitativ durch Kalorimetrie untersucht wurden.Das radiokristallographische Studium der festen Rückstände zeigte, daß in Luft ein bedeutender Anteil der Rückstände aus Sulfaten und in inerter Atmosphäre aus Sulfiden besteht. Sulfite wurden in beiden Fällen in sehr geringen Mengen gefunden.

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

     

Determination of organic- and carbonate-carbon in freshwater lake sediments by a microcombustion procedure

A microcombustion procedure specific for the determination of total-, organic- and carbonate-C in freshwater lake sediments is described. The procedure involves combustion of the sample at 650° to obtain organic-C. Total-C is obtained by combustion at 950° and carbonate-C calculated by difference. The procedure was evaluated by differential thermal analyses of representative sediments and known carbonate minerals. A procedure for the identification of dolomite in lake sediments by differential thermal analysis under CO₂ is also described.

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Zusammenfassung Es wurde über ein zur Bestimmung des Gesamt-, Karbonat- und organischen Kohlenstoffgehaltes von Süßwasserrückständen geeigneten Mikroverbrennungsverfahren berichtet. Durch Verbrennen bei 650° erhält man den organischen Kohlenstoff, durch Verbrennen bei 950° den Gesamtkohlenstoff. Der Karbonatkohlenstoff ergibt sich aus der Differenz. Die Methode wurde durch differentialthermoanalytische Prüfung von charakteristischen Sedimenten und bekannten Karbonatmineralien getestet. Ein Verfahren zur Identifizierung von Dolomit in Seesedimenten durch Differentialthermoanalyse unter CO₂ wurde ebenfalls beschrieben.

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Résumé On décrit une méthode spécifique de microcombustion pour déterminer la teneur en carbone total, organique et carbonate dans des sédiments des lacs à eau froide. On reçoit le C organique par combustion à 650°, le C total par combustion à 950° et le carbone à l'état de carbonate, par la différence. On a évalué le procédé par ATD des sédiments représentatifs et de minérais de carbonate connus. On a décrit une méthode pour identifier le dolomite dans les sédiments des lacs, par ATD sous CO₂.

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, , C . C 650° 950°C, , C . . , , CO₂.

     

Reactivity of hydrogen adsorbed on platinum black towards ethylene

TPD studies of the reactivity of hydrogen adsorbed on dispersed Pt-black towards ethylene at –90, 30 and 200°C indicate that molecular forms of hydrogen with E_des from 3 to 16 kcal/mol are reactive species.

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Pt- –90, 30, 200°C . , . 3 16 /.

     

Difference method of evaluation of dynamic integral thermogravimetric curves in decomposition of polypropylene

A new differential method of evaluating integral thermogravimetric records of the formation of volatile products during the degradation of polypropylene in air is presented. The method, applied to 0–100% conversion of the polymer to volatile products, may distinguish the initial presence of low molecular compounds in the polymer, as well as changes in the mechanism of degradation of the material.

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Zusammenfassung Es wird eine neue differentielle Methode zur Auswertung der die Bildung von flüchtigen Produkten während der Zersetzung von Polypropylen in Luft widerspiegelnden integralen thermogravimetrischen Kurven dargelegt. Mit der im Bereich 0–100% Konversion von Polymer zu flüchtigen Produkten anwendbaren Methode können sowohl die Anwesenheit niedermolekularer Verbindungen im Polymer als auch Veränderungen im Abbaumechanismus des Materials erkannt werden.

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, . , 0–100%- , , .

     

Dispersity of (Ru+Pd)/SiO2 catalysts and their properties in CO hydrogenation and ethane hydrogenolysis

The decreased activity of bimetallic catalysts obtained by the interaction of Ru₃(CO)₁₂ with Pd/SiO₂ in the synthesis of hydrocarbons from CO and H₂ and in ethane hydrogenolysis compared with Ru/SiO₂ is due to the dilution, of ruthenium by less active palladium atoms.

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, Ru₃(CO)₁₂ Pd/SiO₂, CO Ru/SiO₂ .

     

Oxidizing supported reagents, III. Oxidation of alcohols by new supported K2Cr2O7 reagents

Several new supported K₂Cr₂O₇ reagents are used in the oxidation of secondary alcohols. The influence of the number of active sites and the nature of solid support on the yield is discussed. The influence of the structure of alcohol on the yield of ketone is analyzed.

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K₂Cr₂O₇ . . .

     

Pressure-jump method in the dehydrogenation of propane over chromia-alumina-potassium oxide

The pressure-jump method was applied to the dehydrogenation of C₃H₈ over a Cr₂O₃–Al₂O₃–K₂O catalyst in a closed static reactor at 443°C. The rate equation proposed for initial kinetics was shown to apply to the dehydrogenation of C₃H₈.

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C₃H₈ Cr₂O₃–Al₂O₃–K₂O 443°C. , , , C₃H₈.

     

Dispersity and reducibility of the molybdenum oxide phase in SiO2, SiO2?Al2O3 and γ-Al2O3 supported molybdena catalysts

XRD, isothermal and temperature-programmed reduction (TPR) experiments were carried out with SiO₂, SiO₂–Al₂O₃ and -Al₂O₃ supported catalysts. Molybdena is in a more disperse state on supports containing more alumina and it is more reducible on SiO₂–Al₂O₃ than on SiO₂ or -Al₂O₃. TPR curves were shown to reflect connections between reduction kinetics and dispersity.

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-, , SiO₂, SiO₂–Al₂O₃ -Al₂O₃. , , SiO₂–Al₂O₃ SiO₂ -Al₂O₃. .

     

Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

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CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Kinetics and mechanism of hydrazine oxidation by oxygenated Co2(L-his)4O2 complex

The kinetics of Co₂ (L-his)₄O₂ reduction by hydrazine in aqueous solution has been studied and the rate constants, the energy and entropy of activation have been determined.

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, , Co₂ (L-)₄O₂ .

     

Kinetic equation of heterogeneous catalytic isotope exchange

A kinetic equation is derived for the bimolecular isotope exchange reaction between AX _n ^* and BX _m ^o , all atoms of element X in each molecule being equivalent. The equation can be generalized for homogeneous and heterogeneous catalytic isotope exchange.

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, AX _n ^* BX _m ^o , X . , - .

     

Transformations of cyclohexanol on a platinum-alumina catalyst: Effect of poisons

Vapor-phase dehydrogenation/dehydration of cyclohexanol has been investigated over a bifunctional platinum-alumina catalyst. The products of the reactions are cyclohexane, cyclohexene, benzene, cyclohexanone and phenol. Studies using the poisons CO, H₂S and NH₃ have been made in order to elucidate the nature of the sites responsible for the formation of the various products.

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/ џ . , , , . CO, H₂S NH₃ , .

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Part of the Ph. D. thesis of S. Sivasanker     

Comparative study of single-crystal dehydration of LiCOOH.H2O and Li2SO4·H2O

The kinetics of isothermal dehydration of two crystal hydrates with equivalent water molecule sublattices (LiCOOH.H₂O and LiSO₄.H₂O) was investigated in vacuum with a quartz crystal microbalance, and the dynamics of structural reorganization of the substances was studied by the synchrotron radiation method. Differences were found both in the nucleation stage and in the stage of reaction interface advance. The results indicate that the kinetic behaviour of isothermal decomposition of solids is determined by the structural reorganization of a metastable intermediate.

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Zusammenfassung Die Kinetik der isothermen Entwässerung zweier Kristallhydrate mit gleichartigen Teilgittern der Wassermoleküle wurde untersucht mittels isothermer TG im Vakuum und Synchrotron-Röntgenbeugung. Unterschiede zwischen beiden Materialien werden sowohl in der Keimbildungswie- wei in der Ausbreitungsphase gefunden. Die Ergebnisse zeigen, dass die Kinetik der isothermen Zersetzung fester Stoffe durch die strukturelle Reorganisation eines metastabilen Zwischenprodukts bestimmt wird.

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HCOOLi.H₂O Li₂SO₄.H₂O . , — . , . , .

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The authors would like to thank N. Kosova for experimental assistance.     

Kinetics of the catalytic transformation of isobutene into methacrylonitrile with NO on supported nickel oxide aerogel

Kinetic studies of the nitroxidation of isobutene by NO show that the reaction follows a redox mechanism in the temperature range of 300–400°C. This mechanism implies an interaction between dehydrogenated isobutene -allyl radical and atomic nitrogen due to the decomposition of NO by the reduced catalyst, which is then reoxidized.

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NO , 300–400°C. - , NO , .

     

Addition of HCl to a Cluster-Bound Vinylidene Ligand: Preparation and Structure of Ru5(μ3-SMe)(μ3-CMe)(μ-Cl)(μ-SMe)(μ-PPh2)2(CO)9·PhMe

Addition of aqueous HCl to Ru₅( ₃-C=CH₂)(-SMe)₂(-PPh₂)₂(CO)₁₀ afforded the structurally characterized carbyne complex Ru₅( ₃-SMe)( ₃-CMe)(-Cl)(-SMe)(-PPh₂)₂(CO)₉, formed by addition of H to the vinylidene ligand; a Cl atom bridges an Ru–Ru bond.     

Influence of Pr ions on the properties of Pd/SiO2 and Pt/SiO2 catalysts in oxidation of n-butane

It has been established that (M_VIII+Pr)/SiO₂ catalysts (M_VIII=Pd or Pt) obtained from organometallic precursors, have increased the dispersity of Pt, but their TN in deep oxidation of n-butane is by 3–6 times lower than that of unmodified M_VIII/SiO₂.

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(M_VIII+Pr)/SiO₂ ( M_VIII=Pd, Pt), , Pt, 3–6 - M_VIII/SiO₂.

     

Effect of free phosphine on the reactivity of phosphine-containing rhodium(I) complexes

The photolysis products of SO₂-pentane-NO mixtures are N₂O, H₂O and a compound designated as RNO. Kinetic data obtained by OC method confirm the previously proposed scheme of photolysis. Also studied was the photolysis of SO₂, NO and cyclohexane mixtures. From comparison of spectral characteristics of RNO and its analog 2-methyl-2-nitrosopropane, the probable structure of RNO is suggested.

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SO₂--NO N₂O, H₂O , RNO. , , . SO₂ NO . RNO 2--2- RNO.

     

Infrared studies of CO2(CO)8 adsorption on zeolites Y

Co₂(CO)₈ sublimed onto the surface of HY, CeY, CoY and two dealuminated forms of NaY zeolite is converted at room temperature to Co₄(CO)₁₂ and other surfacebound cobalt carbonyl species. The reaction proceeds in a different way on each of the above zeolites, depending also on their pretreatment.

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Co₂(CO)₈, HY, CeY, CoY NaY, Co₄(CO)₁₂ - . - .

     

Pure pseudoboehmite from sodium aluminate

The influence of the Na₂O/Al₂O₃ mole ratio in sodium aluminate, the pH and the temperature of precipitation upon physicochemical properties of pseudoboehmite obtained from sodium aluminate has been studied. A mole ratio of 11 and low pH are favorable for the preparation of pure alumina.

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Na₂O/Al₂O₃ , pH , . , Na₂ O/Al₂O₃=1 , pH, .