Thermodesorption of C2?C3 olefins from the surface of molybdenum sulfide

The interaction of ethylene and propylene with the surface of MoS₂ has been investigated by means of a thermodesorption technique. Two types of adsorption sites on the surface of MoS₂ have been detected. From one type of sites the olefin is desorbed without changes, whereas from the other in the form of conversion products. Propylene desorption has been shown to be accompanied with carbon deposition on the active sites.

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Microbial oxidation of mixtures of methylmercaptan and hydrogen sulfide

Refinery spent-sulfidic caustic, containing only inorganic sulfides, has previously been shown to be amenable to biotreatment withThiobacillus denitrificans strain F with complete oxidation of sulfides to sulfate. However, many spent caustics contain mercaptans that cannot be metabolized by this strict autotroph. An aerobic enrichment culture was developed from mixedThiobacilli and activated sludge that was capable of simultaneous oxidation of inorganic sulfide and mercaptans using hydrogen sulfide (H₂S) and methylmercaptan (MeSH) gas feeds used to simulate the inorganic and organic sulfur of a spent-sulfidic caustic. The enrichment culture was also capable of biotreatment of an actual mercaptancontaining, spent-sulfidic caustic but at lower rates than predicted by operation on MeSH and H₂S fed to the culture in the gas phase, indicating that the caustic contained other inhibitory components.     

Thermodesorption products of 1-butene from the surface of oxide catalysts

Thermodesorption of 1-butene from the surface of an Fe–Sb–O catalyst was carried out to suggest methods of continuous gas phase analysis by gas chromatography.

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Hydrate dissociation conditions for gas mixtures containing carbon dioxide,hydrogen, hydrogen sulfide,nitrogen, and hydrocarbons using SAFT

A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data.     

Synergism between molybdenum and lanthanum in the disproportionation of hydrogen peroxide into singlet oxygen

The catalytic disproportionation of hydrogen peroxide into singlet molecular oxygen was studied using the combined action of lanthanum(III) and molybdenum(VI). A synergistic effect was observed between both metals, resulting in a strong acceleration of the H2O2 disproportionation. An optimum in the catalytic activity was found at La/Mo and La/NaOH molar ratios of 4/1 and 1/3, respectively.     

Ignition of hydrogen–oxygen and stoichiometric hydrogen–methane–oxygen mixtures on hot wires at low pressures

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Removal of carbonyl sulfide and hydrogen sulfide from synthesis gas byChlorobium thiosulfatophilum

Applied Biochemistry and Biotechnology - The anaerobic, photosynthetic bacteriumChlorobium thiosulfatophilum utilizes CO2 as its carbon source and operates at the mesophilic temperature of...     

Pheumatoamperometric determination of cyanide,sulfide and their mixtures

A rapid pneumatoamperometric method for quantifying cyanide in the presence or absence of sulfide is described. The gaseous mixture of hydrogen cyanide and hydrogen sulfide is separated by inserting a short chromatographic column packed with silica gel between the reaction vessel used to generate the volatile acids and the porous gold electrode that the detects them. The detection limit is ca. 5 ng cyanide in 2 ml of solution regardless of sulfide content. The detection limit for sulfide is ca. 1.0 ng in 2 ml of solution when cyanide is present and ca. 0.7 ng in absence of cyanide. Both sulfite and nitrite interfere.     

Structure and stability of molybdenum sulfide fullerenes

MoS2 nanooctahedra are believed to be the smallest stable closed-cage structures of MoS2, i.e., the genuine inorganic fullerenes. Here a combination of experiments and density functional tight binding calculations with molecular dynamics annealing are used to elucidate the structures and electronic properties of octahedral MoS2 fullerenes. Through the use of these calculations MoS2 octahedra were found to be stable beyond nMo > 100 but with the loss of 12 sulfur atoms in the six corners. In contrast to bulk and nanotubular MoS2, which are semiconductors, the Fermi level of the nanooctahedra is situated within the band, thus making them metallic-like. A model is used for extending the calculations to much larger sizes. These model calculations show that, in agreement with experiment, the multiwall nanooctahedra are stable over a limited size range of 104-105 atoms, whereupon they are converted into multiwall MoS2 nanoparticles with a quasi-spherical shape. On the experimental side, targets of MoS2 and MoSe2 were laser-ablated and analyzed mostly through transmission electron microscopy. This analysis shows that, in qualitative agreement with the theoretical analysis, multilayer nanooctahedra of MoS2 with 1000-25 000 atoms (Mo + S) are stable. Furthermore, this and previous work show that beyond approximately 105 atoms fullerene-like structures with quasi-spherical forms and 30-100 layers become stable. Laser-ablated WS2 samples yielded much less faceted and sometimes spherically symmetric nanocages.     

The microdetermination of carbon dioxide,oxygen, carbon monoxide,and hydrogen in gaseous mixtures Krogh method

Summary The analysis of gases by theKrogh technique of entrapping a bubble under glycerol and exposing it to selective absorbents has been examined to assess its value as a means of determining quantitatively oxygen, carbon dioxide, carbon monoxide and hydrogen in volumes of sample of the microlitre order. The method, after modifications to accommodate for non-specificity of the absorption reagents, has given satisfactory performance, and it possesses the additional advantage of simplicity of apparatus.

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Zusammenfassung Das gasanalytische Verfahren vonKrogh, wonach eine Gasblase in Glycerin eingeschlossen und unter dem Mikroskop der Einwirkung selektiver Absorptionsmittel ausgesetzt wird, wurde geprüft, um seine Eignung zur quantitativen Bestimmung von Sauerstoff, Kohlendioxyd, Kohlenmonoxyd und Wasserstoff in Proben der Größenordnung von Mikrolitern festzustellen. Das Verfahren wurde modifiziert, um es der Verwendung nicht spezifischer Absorptionsreagenzien anzupassen, und läßt sich nun in befriedigender Form durchführen. Es bietet den zusätzlichen Vorteil der Einfachheit in apparativer Hinsicht.

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Résumé La technique d'analyse de gaz deKrogh qui consiste à emprisonner une bulle de gaz sous du glycerol et à l'exposer à des réactifs absorbants sélectifs a été éprouvée pour le dosage de l'oxygène, du gaz carbonique, de l'oxyde de carbone et de l'hydrogène sur des échantillons dont le volume est de l'ordre de grandeur du microlitre. La méthode a fourni des résultats satisfaisants après certaines modifications destinées à tenir compte de la non spécificité des réactifs absorbants; elle présente l'avantage complémentaire de la simplicité de l'appareillage mis en oeuvre.

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The author wishes to thank Mr.F. J. Woodman who initiated this work, and Mr.I. Waide for technical co-operation. This paper is published by permission of the Managing Director, United Kingdom Atomic Energy Authority (Industrial Group).     

Ab initio intermolecular potential energy surface and thermophysical properties of hydrogen sulfide

A six-dimensional potential energy hypersurface (PES) for two interacting rigid hydrogen sulfide molecules was determined from high-level quantum-mechanical ab initio computations. A total of 4016 points for 405 different angular orientations of two molecules were calculated utilizing the counterpoise-corrected supermolecular approach at the CCSD(T) level of theory and extrapolating the calculated interaction energies to the complete basis set limit. An analytical site-site potential function with eleven sites per hydrogen sulfide molecule was fitted to the interaction energies. The PES has been validated by computing the second pressure virial coefficient, shear viscosity, thermal conductivity and comparing with the available experimental data. The calculated values of volume viscosity were not used to validate the potential as the low accuracy of the available data precluded such an approach. The second pressure virial coefficient was evaluated by means of the Takahashi and Imada approach, while the transport properties, in the dilute limit, were evaluated by utilizing the classical trajectory method. In general, the agreement with the primary experimental data is within the experimental error for temperatures higher than 300 K. For lower temperatures the lack of reliable data indicates that the values of the second pressure virial coefficient and of the transport properties calculated in this work are currently the most accurate estimates for the thermophysical properties of hydrogen sulfide.     

The second limit of hydrogen + carbon monoxide + oxygen mixtures

Previous studies by Buckler and Norrish of the second limit of CO and O₂ mixtures containing small amounts (0.25–10%) of H₂ have been used to obtain the velocity constant of the reaction These estimates of k₃₃ = 3.9 × 10⁸ and 3.5 × 10⁸ liter² mole^?2 sec^?1 (M ? H₂) at 500° and 560°C, respectively, have been combined with other estimates over the range 300°–3500°K to give k₃₃ = 3.0 × 10⁸ exp (?3000/RT) for M ? Ar; the considerable scatter in the available points does not encourage any great confidence in this expression and may be attributed at least partly to the different molecules used as M by different workers. For KCl-coated and CsCl-coated vessels at 540°C, studies of the second limit of H₂ + O₂ mixtures, to which CO has been added, have indicated that with both the surfaces, the effect of CO on the limit is masked by changes in the surface nature. In the case of CsCl, the results have enabled a lower limit of about 0.6 to be obtained for the efficiency of CO relative to H₂ in the reaction Use of a computer treatment to interpret the second limit of CO + H₂ + O₂ mixtures in aged boric-acid-coated vessels at 500°C gives a value of m_CO = 0.74 ± 0.04 together with an estimate of k₃₂ (H + CO + M″ = HCO + M″)/k₄ = 0.022 ± 0.003, which leads to k₃₂ = 2.3 × 10⁸ liter² mole^?2 sec^?1 (M ? H₂) at 500°C.     

Stabilization of sulfide and sulfite and ion-pair chromatography of mixtures of sulfide, sulfite, sulfate and thiosulfate

Ion chromatography of sulfide, sulfite, sulfate and thiosulfate in a mixture is often difficult because of instability of sulfide and sulfite, poor separation of sulfide from common anions such as bromide or nitrate and similar elution-times for sulfite and sulfate. An ion-pair chromatographic method for the determination of these sulfur anions has been established by stoichiometric conversion of sulfide and sulfite into stable thiocyanate and sulfate, respectively, prior to the chromatographic run. Sulfate, thiosulfate and thiocyanate were resolved on an octadecylsilica column with an acetonitrile-water mobile phase containing tetrapropylammonium salt (TPA) as an ion-paring reagent, and thiosulfate and thiocyanate in the effluent could be measured with a photometric detector (220 nm) and sulfate with a suppressed conductivity detector. When an acetonitrile-water (6:94, v/v) mobile phase (pH 5.0) containing 15 mM TPA and small amounts of acetic acid was used at a flow-rate of 0.6 ml min(-1), the three anions could be eluted within 32 min. Calibration plots of peak height versus concentration for sulfide (detected as thiocyanate) and thiosulfate gave straight lines up to 35 and 60 microM, respectively. The calibration plot for sulfide coincided with that obtained by using thiocyanate. A calibration plot for sulfite, measured as sulfate, was also linear up to 135 microM and was in accord with that of sulfate. Each calibration plot gave a correlation coefficient greater than 0.999. For six replicates obtained for a mixture of 30.0 microM sulfide, 50.0 microM sulfite, 50.0 microM sulfate and 20.0 microM thiosulfate, the proposed method gave a mean value of 30.1 microM with a standard deviation (SD) of 0.77 microM and a relative standard deviation (RSD) of 2.6% for sulfide, 101 microM (SD = 3.5 microM, RSD = 3.5%) for the total of sulfite and sulfate and 20.1 microM (SD = 0.44 microM, RSD = 2.2%) for thiosulfate. Recoveries for sulfide, sulfite plus sulfate, and thiosulfate in hot-spring water samples using the proposed method were found to be quantitative.     

A simple synthesis of 2-methyl-1,4-dithiacycloheptane from diallyl sulfide and hydrogen sulfide

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, PP. 2669–2670, November, 1990.