Effect of zinc added to the Co/Al2O3 catalyst on the formation of carbon nanofilaments from methane and butadiene-1,3

The dynamics of carbon nanofilament growth from methane and butadiene-1,3 on Co-Zn/Al₂O₃ catalysts have been studied in the temperature range 500–750°C. The rate-limiting step in the growth of nanofilaments from butadiene is carbon atom diffusion through the bulk of the metal particle. In the case of methane, the process is controlled by one of the stages of hydrocarbon decomposition on the metal particle. The structure and morphology of the nanofilaments (composites) forming by the carbide cycle mechanism on fine zinc-promoted cobalt particles have been studied by electron microscopy and X-ray diffraction. The morphology and crystallographic properties of the nanofilaments depend on the ratio of the hydrocarbon decomposition rate (which is determined by the nature of the hydrocarbon) to the rate at which carbon atoms diffuse from their formation sites to the nanofilament formation sites (which is determined by the nature of the metal particle and by the carbon diffusion coefficient in the particle bulk). The properties of the resulting carbon nanofilaments can be controlled by varying the nature of the hydrocarbon to be decomposed and the reaction temperature and by introducing another metal into the cobalt particles.     

Catalytic dechlorination of aromatic chloride with supported palladium catalysts in alkaline 2-propanol: influence of hydrocarbon solvents

Summary Catalytic dechlorination of p-chloroanisole (p-chloromethoxybenzene) was carried out in a solution of NaOH in 2-propanol in the presence of Pd/Al₂O₃ or Pd/C at 40°C. When aromatic hydrocarbons such as toluene or benzene were added to the solution, the dechlorination rates were strongly suppressed. However, aliphatic hydrocarbons such as n-hexane or cyclohexane hardly affected the dechlorination rates.     

Phase behaviour of 1-methyl-3-octylimidazolium bis[trifluoromethylsulfonyl]imide with thiophene and aliphatic hydrocarbons: The influence of n-alkane chain length

This paper reports the results of a new experimental study on the capacity of an ionic liquid to extract a sulfur compound from its mixtures with aliphatic hydrocarbons. With this aim, liquid + liquid equilibrium data of ternary systems containing 1-methyl-3-octyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([C₈mim][NTf₂]), thiophene and n-hexane, n-heptane or n-hexadecane have been determined at T = 298.15 K. All systems showed high solubility of thiophene in the ionic liquid and low solubility of the ionic liquid in the n-alkane. The solute distribution coefficient decreases and the selectivity increases as the chain length of n-alkane increases. Both parameters are higher than unity in most of the cases. The experimental results have been correlated using NRTL activity coefficient model, and large deviations from experimental data have been found at high concentrations of thiophene with the heaviest hydrocarbons.     

Nonoxidative conversion of methane and <Emphasis Type="Italic">n</Emphasis>-pentane over a platinum/alumina catalyst

Methane adsorption on the Pt–H/Al₂O₃ and Pt/Al₂O₃ catalysts begins at Т = 475°C and is accompanied by the appearance of hydrogen in the reaction medium. At a higher temperature is raised to 550°C, the amount of adsorbed hydrogen increases to 1.1 and 0.8 mol/(mol Pt), respectively. According to the calculated degree of methane dehydrogenation on platinum sites at Т = 550°C, the Н/C ratio is 1.3 (at/at) for the Pt–H/Al₂O₃ catalyst and 1.5 (at/at) for the Pt/Al₂O₃ catalyst. The introduction of n-pentane into the reaction medium increases the yield of aromatic hydrocarbons (benzene and toluene) by a factor of 8.8 over the arene yield observed in individual n-pentane conversion. A mass spectrometric analysis of the arenes obtained with the Pt/Al₂O₃ catalyst has demonstrated that 37.5% of the adsorbed methane is involved in the methane–n-pentane coaromatization yielding benzene and toluene.     

Experimental Study of Liquid Hydrocarbons Pyrolysis to Acetylene in H2/Ar Plasma

Liquid hydrocarbons including n-hexane, cyclohexane and toluene are pyrolyzed in H₂/Ar plasma to investigate the effects of feedstock properties and key operating conditions (e.g., the feedstock specific input power and residence time) on the reaction performance. The experiments verify that the non-aromatic hydrocarbons show better chemical reactivity than partially aromatic substances. Meanwhile, the straight-chain alkanes and cycloalkanes have better yields of ethylene during the pyrolysis. The results also demonstrate that the pyrolysis reactions are almost completed within the first 0.8?ms in Ar/H₂ plasma independent of the feed substances (i.e., liquid hydrocarbons), where the increased feedstock specific input power enhances the reactant conversions and correspondingly raises the yields of acetylene. At a feedstock specific input power of 4.7?×?10⁴?kJ/kg, the n-hexane conversion is over 90?% and the yield of acetylene reaches 70?%. In addition, when using n-hexane as the feedstock, very little coke is formed during the course of reaction. Comprehensive comparisons of the current experiments with the data reported in the literature are made to point out the key influencing factors, i.e., the effective mass ratio of C/H (R _C/H) in the gaseous phase and the quench temperature. Both two factors would need to be enhanced in order to get a better performance. Finally, the improvements on the specific energy requirement of this process are discussed.     

Multilayered catalysts for fatty acid ester hydrotreatment into fuel range hydrocarbons

This study aims to investigate Ni–Mo/γAl₂O₃ and Ni–La/Zn-ZSM-5–γAl₂O₃ catalysts, which convert methyl esters into various compounds with a similar composition to those found in diesel fuels. The catalysts were synthesized by impregnation using two different routes and characterized by atomic absorption spectrometry, Brunauer–Emmett–Teller, and scanning electron microscopy. The acid strength distribution indicates a relatively high concentration of weak acid centers for both materials. The disposal of the catalysts into the reactor system is an important factor for driving the process toward the desired reaction products. The hydrodeoxygenation becomes important and paraffins are formed as intermediaries when Ni–Mo/γAl₂O₃ is first disposed into the reactor, whereas hydrocracking is poor and the dehydrocyclization does not occur in the case of Ni–La/Zn-ZSM-5–γAl₂O₃ as first layer. Triple-layered catalytic systems enhance the production of n-paraffins with high carbon number, mainly C17 and C18, which are important as diesel component. The effect of temperature was also studied and it was found that aromatics are mainly formed over double-layered catalytic systems by varying the temperature. In the case of triple-layered catalysts, the change in the product composition from saturated hydrocarbons with 12–18 carbon atoms to aromatics was observed by increasing the temperature from 420 to 445 °C. An interesting finding by the addition of n-octane in the feed was observed and the considerable increase in C8 aromatics involved the dehydrocyclization that occurred faster than hydrocracking.     

Gaschromatographische Untersuchung der Adsorptionseigenschaften von Silicalit und ZSM-5

High silica molecular sieves (silicalite, ZSM-5) were tested as adsorbents for gas chromatographic trace analysis. Therefore the retention behaviour of low-boiling organic compounds (hydrocarbons, halogenated hydrocarbons, amines, alcohols and ethers) on these materials was investigated. The specific retention volumes at different temperatures have been determined and elution orders and peak shapes were studied. The retention data allow a simple calculation of the breakthrough volumes (dynamic adsorption capacity) and the chromatographic characterisation of the adsorbents. Both nitrogen and oxygen containing compounds could not—or at least unreproducibely—be eluated up to 300°. The elution order and the peak shape of compounds with the same number of carbon atoms but different geometric and electronic structure (e.g.n-butenes;n-hexane, cyclohexane, benzene) can be explained by the action of exclusion effects and different diffusion barriers. On the basis of calculated breakthrough volumes we conclude that silicalite should be useful in the preconcentration of both saturated C₃–C₆ hydrocarbons and C₁–C₂ chlorinated hydrocarbons from gaseous streams.     

Application of the principle of congruence to ternary alkane mixtures

Excess enthalpies and excess volumes at 298.15 K and atmospheric pressure have been measured for mixtures of n-hexane + (an equimolar mixture of n-tridecane + n-nonadecane). The agreement of the results with the corresponding results for mixtures of n-hexane + n-hexadecane is interpreted as confirmation of the applicability of the principle of congruence to multicomponent mixtures.     

Cyclohexane transformations over metal oxide catalysts. 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al₂O₃, Al₂O₃—F, SiO₂, WO₃/ZrO₂, and La₂Î₃/ZrO₂, in cyclohexane ring opening to form n-hexane were studied. The most active catalyst is Rh/Al₂O₃. Cyclohexane hydrogenolysis to n-hexane also occurs over the Pt/Al_;>2O₃ and Pt/La₂Î₃/ZrO₂ catalysts. Ring opening over the Ru catalysts proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts (350—400 °C), but the ruthenium systems are less selective for n-hexane formation than Rh/Al₂O₃ catalysts. The effects of acid-basic properties of the support and the reaction conditions on the activities of the catalytic systems in cyclohexane ring opening was studied.     

Enthalpies of solution of <Emphasis Type="Italic">n</Emphasis>-alkanes in mixtures of MeCN with alkan-1-ols at 298.15 K. Relations between the thermodynamic properties of binary and ternary systems

The solution enthalpies of n-hexane, n-nonane, and n-undecane in mixtures of MeCN with EtOH, PrOH, and BuOH were determined by calorimetric method at 298.15 K. Relations between the thermodynamic properties of ternary systems and the properties of the binary solvents and the solute are discussed. To predict the enthalpies of solution of hydrocarbons in mixed solvents whose components have strongly different molar volumes (V ₂/V ₁ > 1.5), it is proposed to use the values that are additive in the volume fraction scale. The solution enthalpies of hydrocarbons in mixtures characterized by close molar volumes of the components strongly depend on the excess properties of the binary solvent.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1578–1582, August, 2004.     

Kinetics and mechanism of the autoxidation of pentaerythrityl tetraheptanoate at 180–220°C

A kinetic and mechanistic study of the autoxidation of liquid pentaerythrityl tetraheptanoate (PETH) at 180–220°C has been carried out utilizing a stirred-flow reactor. The results are consistent with the occurrence of a chain reaction scheme similar to that proposed for n-hexadecane autoxidation, namely, the formation of monohydroperoxides by the intermolecular abstraction reaction (3), the formation of α,γ- and α,δ-dihydroperoxides and α,γ- and α,δ-hydroperoxyketones by intramolecular peroxy radical abstraction reactions (4) and (4*), the bimolecular termination of peroxy radicals, reaction (6), and the rapid conversion of α,γ-hydroperoxyketones to the corresponding cleavage acids and methyl ketones, reaction (7). Comparisons of various rate parameters for the n-hexadecane and PETH systems reveal that the values of k₇ and (k₃/H atom)/(2 k₆)^1/2 are within experimental uncertainties identical for the two systems at 180°C. The proposed reaction scheme includes the concurrent formation of hydroxy radicals and hydroperoxyketone species. The results of kinetic analysis and the experimentally observed isomer distributions of primary and secondary monohydroperoxide products at high and low oxygen pressures suggest that ≈60% of the hydrogen abstractions from PETH at high oxygen pressures occur by hydroxy radicals.     

Phase Diagrams of the <Emphasis Type="Italic">n</Emphasis>-Decane–<Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane, <Emphasis Type="Italic">n</Emphasis>-Decane–Cyclododecane,and <Emphasis Type="Italic">n</Emphasis>-Hexadecane–Cyclododecane Systems

The n-decane–n-hexadecane–cyclododecane, n-decane–cyclododecane, and n-hexadecane–cyclododecane systems are studied by means of low-temperature differential thermal analysis using a differential scanning heat flow calorimeter. It is noted that all studied systems belong to the eutectic type. It is concluded that in the n-decane–n-hexadecane–cyclododecane system, the eutectic composition contains 85.0 wt % n-С₁₀Н₂₂, 4.0 wt % n-С₁₆Н₃₄, and 11.0 wt % С₁₂Н₂₄. It has a melting point of ?35.0°C.     

Study of <Emphasis Type="Italic">n</Emphasis>-hexane isomerization on Pt/SO<Subscript>4</Subscript>/ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts: Effect of the state of platinum on catalytic and adsorption properties

The state of surface Pt atoms in the Pt/SO₄/ZrO₂/Al₂O₃ catalyst and the effect of the state of platinum on its adsorption and catalytic properties in the reaction of n-hexane isomerization were studied. The Pt-X/Al₂O₃ alumina-platinum catalysts modified with various halogens (X = Br, Cl, and F) and their mechanical mixtures with the SO₄/ZrO₂/Al₂O₃ superacid catalyst were used in this study. With the use of IR spectroscopy (CO_ads), oxygen chemisorption, and oxygen-hydrogen titration, it was found that ionic platinum species were present on the reduced form of the catalysts. These species can adsorb to three hydrogen atoms per each surface platinum atom. The specific properties of ionic platinum manifested themselves in the formation of a hydride form of adsorbed hydrogen. It is believed that the catalytic activity and operational stability of the superacid system based on sulfated zirconium dioxide were due to the participation of ionic and metallic platinum in the activation of hydrogen for the reaction of n-hexane isomerization.     

State of disperse alloy particles catalyzing hydrocarbon decomposition by the carbide cycle mechanism: TEM and EDX studies of the Cu-Ni/Al2O3 and Cu-Co/Al2O3 catalysts

The state of disperse bimetallic alloy particles in the Cu-Ni/Al₂O₃ and Cu-Co/Al₂O₃ catalysts during their carbonization in butadiene-1,3 is studied by high-resolution electron microscopy and energy-dispersive X-ray analysis. During the formation of carbon nanofilaments by the carbide cycle mechanism, the catalyst is in a dissipative state such that the bimetallic particles vary in composition and have an anomalous component distribution in their bulk. The extrapolation of this state provides insight into the processes occurring in the dissipative system.     

GC�CMS Determination of PAHs in Fish Samples Following Salting-out-Assisted Solvent Extraction-Gel Permeation Chromatography

A fast and effective sample cleanup procedure for the quantification of polycyclic aromatic hydrocarbons (PAHs) in fish samples is presented. The procedure involved extraction of fish samples using acetonitrile and cleanup by an automated gel-permeation chromatography (GPC) following liquid?Cliquid partition into n-hexane. The extracted samples were analyzed by gas chromatography-mass spectrometry (GC?CMS). Electron ionization was employed in a single analysis for the determination of PAHs in the selected ion monitoring mode. Three different solvents were studied for the extraction step: acetonitrile/n-hexane, methanol/n-hexane and acetone/n-hexane. The best solvent was found to be acetonitrile/n-hexane. The cleanup technique resulted in a good separation of analytes from co-extractive matrix compounds.     

Excess volumes of binary mixtures of (p-xylene+an n-alkane)

A semi-continuous dilatometer for measuring excess volume is described. Excess volumes of p-xylene +n-hexane + n-octane, +n-decane, +n-dodecane, +n-tetradecane, and +n-hexadecane have been measured at 298.15 K as a function of composition.     

Polyynes and cyanopolyynes synthesis from the submerged electric arc: about the role played by the electrodes and solvents in polyynes formation

The products of the electric arc between graphite electrodes have been investigated by high performance liquid chromatography-diode-array detector (HPLC-DAD) analysis in various media: distilled water, liquid nitrogen, methanol, ethanol, n-hexane and benzene. In distilled water, hydrogen capped polyynes H-(CC)_n-H were the unique products demonstrating that carbon is supplied by the graphite electrodes while hydrogen is supplied by the solvent plasmalysis (in this case water plasmalysis). Arcing graphite electrodes in liquid nitrogen produces cyanopolyynes: NC-(CC)_n-CN demonstrating that in this case the end groups of the polyyne chains are supplied by molecular nitrogen plasmalysis caused by the electric arc. Graphite arcing in methanol and ethanol produces very clean solutions (by-products negligible or absent) of hydrogen-capped polyynes with C₈H₂ as the main product accounting for more than 70 mol percent of the total polyyne concentration. By replacing graphite electrodes with titanium electrodes in methanol or in ethanol, polyynes are not formed at all; only trace amounts of polycyclic aromatic hydrocarbons (PAHs) were detected. When arcing with graphite electrodes is conducted in n-hexane or in benzene, polyyne formation is accompanied by a significant production of PAH, especially in benzene. These results have been rationalized in terms of carbonization or coking tendency of a given solvent. The effect of using titanium electrodes in place of graphite electrodes has been investigated also in n-hexane and in benzene as well as the effects of very high electric current intensity employed to ignite and sustain the submerged electric arc.     

Low temperature isomerization of n-hexane on catalyst systems Al2O3/ZrO2/SO4/Pt

As a result of investigating low temperature isomerization of n-hexane at 130, 140, 150, 160°C in a flow reactor with a fixed bed of catalyst of the Al₂O₃/ZrO₂/SO₄/Pt type a ratio of components in the catalyst system was selected and process conditions were defined, which allow to obtain highly branched high-octane isomers with a yield of up to 40% relative to a transformed raw material. A kinetic model of the process was proposed and kinetic parameters were calculated.     

Emulsifying,Flocculating, and Physicochemical Properties of Exopolysaccharide Produced by Cyanobacterium Nostoc flagelliforme

The emulsifying, flocculating, and physicochemical properties of purified exopolysaccharide (EPS) of terrestrial cyanobacterium Nostoc flagelliforme cultured in liquid media were investigated. The EPS was defined as heteropolysaccharide composed by 41.2 % glucose, 21.1 % galactose, 21.0 % mannose, 2.5 % fructose, 3.6 % ribose, 1.7 % xylose, 0.6 % arabinose, 3.0 % rhamnose, 0.9 % fucose, and 4.3 % glucuronic acid. The EPS possessed higher intrinsic viscosity than other cyanobacterial strains as reported and displayed pseudoplastic behavior in aqueous solution. The EPS produced more stable emulsions with tested hydrocarbons and oils than xanthan gum, and the emulsification indexes with n-hexadecane, liquid paraffin, and peanut oil were higher than 50 %, indicating the strong emulsion-stabilizing capacity. The EPS showed peak flocculating rates of 93.5 and 86.1 % in kaolin and MgO suspension, respectively, and exhibited a better flocculation performance than Al₂(SO₄)₃ and xanthan gum. These results demonstrated that the EPS of N. flagelliforme was a very promising candidate for numerous industrial applications, as it had higher intrinsic viscosity, good emulsification activity, and excellent flocculation capability.     

Temperature dependence of the derived properties of mixtures containing chlorobenzene and aliphatic linear alkanes (C6–C12)

This article reports experimental densities, refractive indices and speeds of sound of the binary mixtures chlorobenzene?+?(n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane or n-dodecane) and speeds of sound of the ternary mixtures chlorobenzene?+?n-hexane?+?(n-undecane or n-dodecane) at 298.15?K and atmospheric pressure, over the whole concentration range. The corresponding derived properties were computed from the experimental data. The results were fitted by means of the Redlich–Kister equation for binary mixtures and the Nagata equation for ternary mixtures. A set of estimation methods were applied, and an interpretation in terms of structure and length of molecular chain of the n-alkane molecules was made.