Complete oxidation of short chain alkanes using a nanocrystalline cobalt oxide catalyst

Exceptionally high activity for the complete oxidation of propane is reported for the first time using a nanocrystalline cobalt oxide catalyst. The catalyst shows stable activity for prolonged time on stream and when the reaction temperature is cycled. Furthermore, the nanocrystalline catalyst demonstrates considerably higher activity than an alumina supported palladium catalyst, which is recognised as one of the most active reported. The high activity of the cobalt oxide catalyst is associated with the nanocrystalline nature of the material, which gives rise to new catalytically active surface sites. A broader comparison with other reported high activity catalysts emphasises the high efficacy of nanocrystalline cobalt oxide for total oxidation and demonstrates that it has significant potential for important applications, such as control of emissions from liquid petroleum gas powered vehicles and alkane volatile organic emissions from stationary sources.     

Alkanes and solvent dimers in successive extract fractions released from coal during liquefaction in a flowing-solvent reactor

Types of alkanes present in liquefaction product fractions released from coal during successive time—temperature intervals were examined by g.c.—m.s. Experiments were carried out in a flowing-solvent reactor where solubilized products are continuously removed from the reaction zone; tetralin, quinoline and hexadecane were used as the solvent. At 450°C (with 400 s holding) total conversions in tetralin, quinoline and hexadecane were 82.5, 74.7 and 24 wt% (daf), respectively. In tetralin, alkanes were released from coal more readily and at lower temperatures than in quinoline or hexadecane; m.s. signal intensities fell rapidly with increasing reaction temperature. In quinoline, lower intensities of alkane peaks were observed than in tetralin, although the trend with temperature was similar. In hexadecane however, the trend of intensity with temperature was reversed compared with liquefaction in tetralin or in quinoline; the range of alkanes detected was also smaller than in tetralin or in quinoline. The presence of alkenes in the hexadecane extracts suggested a pyrolytic mechanism for the thermal breakdown. Isoprenoid alkanes, pristane and phytane, were detected in the tetralin and quinoline extracts but not those prepared in hexadecane. Materials present in product mixtures and thought to originate with each solvent were briefly investigated: dimers were the most prominent species in tetralin extracts, with only low-intensity dimers being found in quinoline extracts and no apparent formation of higher homologues from hexadecane. These results were compared with the pattern of alkane release from coal during liquefaction in tetralin in a conventional minibomb reactor and in the pentane-soluble fraction of the total (unfractionated) extract from the F-S reactor.     

Organic geochemistry of the British Kimmeridge clay: 2. Acyclic isoprenoid alkanes in Kimmeridge shale oils

The C15---C20 isoprenoid alkane composition of Kimmeridge Clay shale oils produced by Fischer assay has been examined, and compared with the isoprenoid composition of corresponding bitumens. C16 and C18 isoprenoid alkanes are generally dominant in shale oils, while pristane (C19) and phytane (C20) dominate in bitumens. A significant proportion of the phytane in many shale oils is derived from simple evaporation of free (bitumen) phytane, while free pristane contributes less to shale oil composition. Some shale oil phytane and a large proportion of pristane is kerogen-derived. Certain shale oils contain lower concentrations of isoprenoid alkanes than corresponding bitumens, suggesting that some free alkane is thermally degraded during pyrolysis. Results thus indicate three sources for shale oil isoprenoid alkanes: thermal evaporation of free alkanes (particularly for phytane), kerogen decomposition, and possibly the cracking of higher homologues for C15---C19 alkanes. Kerogen-derived isoprenoids are suggested to arise by thermal desorption of adsorbed free alkane (particularly for phytane) and from C---O and C---C bonded species (excluding phytane) via postulated clay catalysed hydrogenation of initially formed alkenes. Comparison of shale oil and bitumen pristane/phytane ratios allows groups of oil shales to be defined, dependent on source composition, organic carbon content and maturity. Shale oil pristane/phytane ratios can also help to determine depositional environments and source composition, although maturity, shale mineralogy and competing alkene-forming pyrolytic reactions may also affect the ratios.     

Methodological approach to identify chemical oviposition stimulants from maize for European corn borer

The noncontingent distribution ofO. nubilalis Hbn. eggs on various corn varieties has allowed their classification as either favorable or nonfavorable hybrids. This classification is based on a chemical communication system using volatile compounds active at a distance from the insect or active when in contact with the insect as soluble sugar components. Under this hypothesis, gas chromatography is the best way of investigating for the chemical differences between corn silk extracts from the two types of hybrids. A first experiment, using a desorption-trapping system on Tenax coupled to a gas chromatograph showed a quantitative difference between two compounds from the two hybrids. A second experiment showed the advantages and disadvantages of this method and allowed the development of two complementary techniques: (1) direct extraction of corn silk with trichlorofluo-romethane and direct injection into a capillary column with an apolar stationary phase using an on-column system; and (2) extraction under vacuum of volatile compounds from corn silk and their trapping on Tenax, followed by a second desorption. This allows a direct injection on the same capillary column. The first technique allows identification by mass spectrometry of many alkanes with high molecular weights. The second technique seems to confirm the presence of phenylacetaldehyde. Both techniques show quantitative differences in the composition of corn silk extracts from favorable and nonfavorable hybrids; however, the biologically active chemicals remain unknown.     

Adsorption of iso-/n-butane on an anatase thin film: a molecular beam scattering and TDS study

Binding energies and adsorption probabilities have been determined for n/iso-butane adsorption on an anatase thin film grown on SrTiO₃(001) by means of thermal desorption spectroscopy (TDS) and molecular beam scattering. The sample has been characterized by X-ray diffraction (XRD) and Auger electrons spectroscopy (AES).     

Propane partial oxidation to acrolein over combined catalysts

A novel approach for the partial oxidation of propane to acrolein, based on the use of layers of combined catalysts in a single reactor, provides good yields of acrolein with selectivity above 62%. The results depend strongly on the layer configuration, and reveal new mechanistic features for the process. This revised version was published online in August 2006 with corrections to the Cover Date.     

Gas/liquid mass transfer processes in a carbon dioxide/alkane system

A gas/liquid mass transfer process has been studied using carbon dioxide/alkane systems in a stirred vessel. Four linear alkanes (n‐heptane, n‐octane, n‐decane and n‐dodecane) have been used as the liquid phase in the present paper, and they have been employed to study the influence of the carbon length upon the mass transfer velocity. The mass transfer along the liquid phase has been studied using the mass transfer coefficient of the liquid phase, k_L. Pure carbon dioxide has been employed as the phase in all cases for this reason. The effects of the power supplied to the liquid phase and the gas flow rate upon the absorption process have also been analysed. Finally, the equations that allow calculation of the mass transfer coefficients have been applied for these systems, with acceptable results. Copyright © 2005 Society of Chemical Industry     

Progress of vanadium phosphorous oxide catalyst for n-butane selective oxidation

The utilization of lighter alkanes into useful chemical products is essential for modern chemistry and reducing the CO₂ emission. Particularly, n-butane has gained special attention across the globe due to the abundant production of maleic anhydride (MA). Vanadium phosphorous oxide (VPO) is the most effective catalyst for selective oxidation of n-butane to MA so far. Interestingly, the VPO complex exists in more or less fifteen different structures, each one having distinct phase composition and exclusive surface morphology and physiochemical properties such as valence state, lattice oxygen, acidity etc., which relies on precursor preparation method and the activation conditions of catalysts. The catalytic performance of VPO catalyst is improved by adding different promoters or co-catalyst such as various metals dopants, or either introducing template or structural-directing agents. Meanwhile, new preparation strategies such as electrospinning, ball milling, hydrothermal, barothermal, ultrasound, microwave irradiation, calcination, sol–gel method and solvothermal synthesis are also employed for introducing improvement in catalytic performance. Research in above-mentioned different aspects will be ascribed in current review in addition to summarizing overall catalysis activity and final yield. To analyze the performance of the catalytic precursor, the reaction mechanism and reaction kinetics both are discussed in this review to help clarify the key issues such as strong exothermic reaction, phosphorus supplement, water supplement, deactivation, and air/n-butane pretreatment etc. related to the various industrial applications of VPO.     

A neural network (CSA-LSSVM) model for the estimation of surface tension of branched alkanes

The current study highlights the application of a model based on least square support vector machine (LSSVM) for prediction of surface tension of branched alkanes. An optimization algorithm, namely, coupled simulated annealing (CSA) was applied to the model. Surface tensions of alkanes show a specific interaction between adjacent molecules of the branched alkanes which affects the anisotropic dispersion force component of the surface energy. In this paper, surface tension of branched alkanes was studied in temperature range of 283.15 and 448.15 K. To evaluate the performance and accuracy of this model, statistical and graphical error analyses have been used simultaneously. By applying CSA-LSSVM on 600 data points and finding optimum parameters, the estimated values of surface tension of branched alkanes were compared with experimental data which showed a reasonable agreement with the experimental results. Results demonstrate that the model is precise and viable for prediction of solubility data. The model shows an overall R² and AARD% estimations of 0.9921 and 0.89%, respectively.     

Occurrences and distributions of normal alkanes and biological markers to detections of origin,environments, and maturation of crude oils in El Hamed oilfield,Gulf of Suez,Egypt

The gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS) analyses for crude oils from Kareem reservoir in the wells El Hamed-1, 3, and 5 are used to provide information on source organic matters input, depositional environment, and maturation level. Data include normal alkane and acyclic isoprenoids distribution, terpane, and sterane aliphatic biomarkers. Pristine/phytane (Pr/Ph), Pr/nC17, and Ph/nC18 ratios indicated mixed organic sources of organic matters (kerogen type II, III) dominantly (kerogen type III) with a less effect of biodegradation and mature stage of occurrence. The diasteranes/steranes ratio showed generally low ratios as in most marine carbonate sources, while algal-bacterial organic matter contribution for the oil samples suggested dependence on the predominance of C23 tricyclic terpane relative to the C19 tricyclic terpane, and the C25 tricyclic terpane greater than C24 tricyclic terpane. The gammacerane index indicated that a low-salinity environment of deposition for the initial organic matters existed in the analyzed samples.