Showing papers on "Hydrocarbon published in 2003"

The mechanism of methanol to hydrocarbon catalysis.

Abstract: The process of converting methanol to hydrocarbons on the aluminosilicate zeolite HZSM-5 was originally developed as a route from natural gas to synthetic gasoline. Using other microporous catalysts that are selective for light olefins, methanol-to-olefin (MTO) catalysis may soon become central to the conversion of natural gas to polyolefins. The mechanism of methanol conversion proved to be an intellectually challenging problem; 25 years of fundamental study produced at least 20 distinct mechanisms, but most did not account for either the primary products or a kinetic induction period. Recent experimental and theoretical work has firmly established that methanol and dimethyl ether react on cyclic organic species contained in the cages or channels of the inorganic host. These organic reaction centers act as scaffolds for the assembly of light olefins so as to avoid the high high-energy intermediates required by all “direct” mechanisms. The rate of formation of the initial reaction centers, and hence the d...

Reinterpreting literature sorption data considering both absorption into organic carbon and adsorption onto black carbon.

Abstract: We hypothesized that the sorption of polycyclic aromatic hydrocarbons (PAHs) to natural sediments and soils should consider both absorption into a biogenic/diagenetic organic carbon (OC) fraction and adsorption onto a combustion-derived, black carbon (BC) fraction. Here, two sets of literature data were reevaluated to illustrate that an OC absorbent and a BC adsorbent together can (1) account for sediment−pore-water distribution coefficients observed in the field that are greater than predicted by a simple focKoc partitioning model and (2) explain a group of nonlinear phenanthrene isotherms observed in the laboratory with a single value for the BC-normalized distribution coefficient (log KBC = 6.1 ± 0.04) and a Freundlich exponent (n ≈ 0.6 if log Koc = 4.0) that is strongly dependent on the Koc value selected.

Staged and/or patterned heating during in situ thermal processing of a hydrocarbon containing formation

Abstract: A method for treating a hydrocarbon containing formation is described. The method for treating a hydrocarbon containing formation may include heating a first volume (162) of the formation using a first set of heaters (158). A second volume (164) of the formation may be heated using a second set of heaters (158). The first volume may be spaced apart from the second volume by a third volume of the formation. The first volume, second volume, and/or third volume may be sized, shaped, and/or located to inhibit deformation of subsurface equipment caused by geomechanical motion of the formation during heating.

Carbon capacious Ni-Cu-Al2O3 catalysts for high-temperature methane decomposition

Abstract: Steady and efficient decomposition of methane can be achieved at 625–675 °C over copper-promoted (8–15 wt.% of copper) nickel catalysts prepared from a Feitknecht compound precursor. Such catalysts permit one to increase the yield of catalytic filamentous carbon (CFC) and control both microstructural and textural properties of CFC by varying the copper concentration in the catalyst. The maximal conversion of methane into hydrogen and carbon reaches 40% at 675 °C at the carbon capacity not lower than 700 g/g Ni under optimal conditions. The BET surface area of the CFC is 285.9 m 2 /g. The influence of promotion of nickel-containing catalysts with copper on the catalytic activity is discussed.

Evidence for an initiation of the methanol-to-olefin process by reactive surface methoxy groups on acidic zeolite catalysts.

Abstract: Recent progress reveals that, in the methanol-to-olefin (MTO) process on acidic zeolites, the conversion of an equilibrium mixture of methanol and DME is dominated by a “hydrocarbon pool” mechanism. However, the initial C−C bond formation, that is, the chemistry during the kinetic “induction period” leading to the reactive hydrocarbon pool, still remains unclear. With the application of a stopped-flow protocol, in the present work, pure surface methoxy groups [SiO(CH3)Al] were prepared on various acidic zeolite catalysts (H−Y, H−ZSM-5, H−SAPO-34) at temperatures lower than 473 K, and the further reaction of these methoxy species was investigated by in situ 13C MAS NMR spectroscopy. By using toluene and cyclohexane as probe molecules which are possibly involved in the MTO process, we show the high reactivity of surface methoxy species. Most importantly, the formation of hydrocarbons from pure methoxy species alone is demonstrated for the first time. It was found that (i) surface methoxy species react at ro...

Low-temperature hydrogen production from oxygenated hydrocarbons

Abstract: Disclosed is a method of producing hydrocarbons from oxygenated hydrocarbon reactants, such as glycerol, glucose, or sorbitol. The method can take place in the vapor phase or in the condensed liquid phase (preferably in the condensed liquid phase). The method includes the steps of reacting water and a water-soluble oxygenated hydrocarbon having at least two carbon atoms, in the presence of a metal-containing catalyst. The catalyst contains a metal selected from the group consisting of Group VIIIB transitional metals, alloys thereof, and mixtures thereof. These metals are supported on supports that exhibit acidity or the reaction is conducted under liquid-phase conditions at acidic pHs. The disclosed method allows the production of hydrocarbon by the liquid-phase reaction of water with biomass-derived oxygenated compounds.

Ab Initio Calculations for Hydrocarbons: Enthalpy of Formation, Transition State Geometry, and Activation Energy for Radical Reactions

Abstract: A quantum chemical investigation is presented for the determination of accurate kinetic and thermodynamic parameters for hydrocarbon radical reactions. First, standard enthalpies of formation are calculated at different levels of theory for a training set of 58 hydrocarbon molecules, ranging from C1 to C10, for which experimental data are available. It is found that the CBS-QB3 method succeeds in predicting standard enthalpies of formation with a mean absolute deviation of 2.5 kJ/mol, after a systematic correction of −1.29 kJ/mol per carbon atom and −0.28 kJ/mol per hydrogen atom. Even after a systematic correction, B3LYP density functional theory calculations are not able to reach this accuracy, with mean absolute deviations of 9.2 (B3LYP/6-31G(d)) and 12.9 kJ/mol (B3LYP/6-311G(d,p)), and with increasing deviations for larger hydrocarbons. Second, high-level transition state geometries are determined for 9 carbon-centered radical additions and 6 hydrogen additions to alkenes and alkynes and 10 hydrogen a...

Degradation and formation of polycyclic aromatic compounds during bioslurry treatment of an aged gasworks soil.

Abstract: The goals of this study were to investigate the relative degradation rates of polycyclic aromatic compounds (PACs) in contaminated soil, and to assess whether persistent oxidation products are formed during their degradation. Samples were taken on five occasions during a pilot-scale bioslurry treatment of soil from a former gasworks site. More than 100 PACs were identified in the soil, including unsubstituted polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs (alkyl-PAHs), heterocyclic PACs, and oxygenated PAHs (oxy-PAHs), such as ketones, quinones, and coumarins. During the treatment, the low molecular weight PAHs and heterocyclics were degraded faster than the high molecular weight compounds. The unsubstituted PAHs also appear to have degraded more quickly than the corresponding alkyl-PAHs and nitrogen-containing heterocyclics. No new oxidation products that were not present in the untreated soil were identified after the soil treatment. However, oxy-PAHs that were present in the untreated soil were generally degraded more slowly than the parent compounds, suggesting that they were formed during the treatment or that they are more persistent. Two oxidation products, 1-acenaphthenone and 4-oxapyrene-5-one, were found at significantly higher concentrations at the end of the study. Because oxy-PAHs can be acutely toxic, mutagenic, or carcinogenic, we suggest that this group of compounds should also be monitored during the treatment of PAH-contaminated soil.

Role of Hydrocarbon Deposits in the Enhanced Performance of Direct-Oxidation SOFCs

Abstract: We have examined the changes that occur in the performance of solid oxide fuel cells (SOFCs) with Cu-ceria-yttria-stabilized zirconia anodes at 973 K following exposure to various hydrocarbon fuels, including methane, propane, n-butane, n-decane, and toluene. For cells with Cu contents of 20 wt % or less, large increases were observed in the power densities for operation in after the anode had been exposed to any of the hydrocarbons except methane. The increased performance is completely reversible upon oxidation of the anode and subsequent reduction in The enhancement decreases with increasing Cu content, implying that the deposits improve the connectivity of the metallic phase in the anode. Impedance spectra taken on cells before and after exposure to hydrocarbon fuels confirm that the conductivity of the anode improves after exposure. Temperature-programmed oxidation and weight changes were used to show that the deposits that enhance performance correspond to of the anode and are probably not graphitic. Measurements of the open-circuit voltages in hydrocarbon fuels suggest that equilibrium is established with partial oxidation products and that the chemical structure of the deposits change upon current flow. Finally, the implications of these results for operation of SOFC on hydrocarbons without added steam and with low copper contents are discussed. © 2003 The Electrochemical Society. All rights reserved.

Photoenhanced toxicity of aqueous phase and chemically dispersed weathered Alaska North Slope crude oil to Pacific herring eggs and larvae.

Abstract: The photoenhanced toxicity of weathered Alaska North Slope crude oil (ANS) was investigated in the eggs and larvae of Pacific herring (Clupea pallasi) with and without the chemical dispersant Corexit® 9527. Oil alone was acutely toxic to larvae at aqueous concentrations below 50 μg/L total polycyclic aromatic hydrocarbons (tPAH), and median lethal (LC50s) and effective concentrations (EC50s) decreased with time after initial oil exposure. Brief exposure to sunlight (∼2.5 h/d for 2 d) significantly increased toxicity 1.5- to 48-fold over control lighting. Photoenhanced toxicity only occurred when oil was present in larval tissue and increased with increasing tPAH concentration in tissue. Ultraviolet radiation A (UVA) treatments were less potent than natural sunlight, and UVA + sunlight caused greater toxicity than sunlight alone. The toxicity of chemically dispersed oil was similar to oil alone in control and UVA treatments, but oil + dispersant was significantly more toxic in the sunlight treatments. The chemical dispersant appeared to accelerate PAH dissolution into the aqueous phase, resulting in more rapid toxicity. In oil + dispersant exposures, the 96-h no-observed-effect concentrations in the UVA + sunlight treatment were 0.2 μg/L tPAH and 0.01 μg/g tPAH. Exposure of herring eggs to oil caused yolk sac edema, but eggs were not exposed to sun and UVA treatment did not cause phototoxicity. These results are consistent with the hypothesis that weathered ANS is phototoxic and that UV can be a significant and causative factor in the mortality of early life stages of herring exposed to oil and chemically dispersed oil.

Molecular dynamics simulations of end-to-end contact formation in hydrocarbon chains in water and aqueous urea solution.

Abstract: We probe the urea-denaturation mechanism using molecular dynamics simulations of an elementary “folding” event, namely, the formation of end-to-end contact in the linear hydrocarbon chain (HC) CH3(CH2)18CH3. Electrostatic effects are examined using a model HC in which one end of the chain is positively charged (+0.2e) and the other contains a negative charge (−0.2e). For these systems multiple transitions between “folded” (conformations in which the chain ends are in contact) and “unfolded” (end-to-end contact is broken) can be observed during 4 ns molecular dynamics simulations. In water and 6 M aqueous urea solution HC and the charged HC fluctuate between collapsed globular conformations and a set of expanded structures. The collapsed conformation adopted by the HC in water is slightly destablized in 6 M urea. In contrast, the end-to-end contact is disrupted in the charged HC only in aqueous urea solution. Despite the presence of a large hydrophobic patch, on length scales on the order of ∼8−10 A “denat...

Removal of Dibenzothiophene from Model Diesel by Adsorption on Carbon Aerogels for Fuel Cell Applications

Abstract: Carbon aerogels (CAs) were studied as adsorbents for the desulfurization of liquid hydrocarbon fuels for fuel cell applications. A synthetic mixture of dibenzothiophene (DBT) and n-hexadecane (n-HD) was used as a model for sulfur contaminated diesel fuel. Carbon aerogels with two different average pore sizes (4 and 22 nm) were synthesized, characterized, and tested for adsorption of DBT at ambient temperature and atmospheric pressure. The approach-to-equilibrium was monitored, and adsorption isotherms were measured. The CA with the larger average pore size had a higher sulfur adsorption rate and a higher capacity for DBT. The isotherms were best represented by the Freundlich model. According to the Langmuir isotherm, the adsorption capacities of the 4 nm CA and 22 nm CA were 11.2 and 15.1 mg S/g dry CA, respectively. The CAs were found to selectively adsorb DBT over naphthalene, which is a chemically similar but non-sulfur containing organic compound, when both are present in solution. However, the presen...

Adsorption of Unsaturated Hydrocarbons on Pd(111) and Pt(111): A DFT Study

Abstract: The adsorption of unsaturated hydrocarbons on metallic surfaces is of fundamental and applied interest, in view of its implications as a model system for catalysis in the refining industry. In particular, the relation between the type of hydrocarbon and its adsorption strength on metallic surfaces remains an open question. Thus, we propose a comparative DFT study of the adsorption of several relevant hydrocarbons on the catalytically relevant Pd(111) and Pt(111) surfaces. The key adsorption features (structural, electronic, energetic, and spectroscopic) are analyzed in a consistent way for two olefins (ethylene, 1-butene), one aromatic (benzene), one alkyne (acetylene), and one diolefin (1,3-butadiene). Whereas ethylene and 1-butene are adsorbed in a di-σ mode, the flat adsorption of benzene takes place in a bridge position. For acetylene, the adsorption occurs in a 3-fold hollow site, whereas 1,3-butadiene adsorbs in a tetra-σ configuration whatever the coverage. In the latter case, a vibrational analysi...

Adsorption equilibria of methane, ethane, ethylene, nitrogen, and hydrogen onto activated carbon

Abstract: Adsorption equilibria of single components for pure methane, ethane, ethylene, hydrogen, and nitrogen onto activated carbon adsorbent (Calgon Co.) were measured. The results were obtained with a static volumetric method at 293.15 K, 303.15 K, and 313.15 K and at pressures up to 2 MPa. Experimental data were correlated by the Langmuir−Freundlich equation. Isosteric enthalpies of adsorption were calculated and shown according to surface loading.

Comparative Oxidation and Net Emissions of Methane and Selected Non-Methane Organic Compounds in Landfill Cover Soils

Abstract: The surface emissions of methane (CH4) and non-methane organic compounds (NMOCs) were determined at two different areas at a French landfill: a permanently covered and fully vegetated area (40 cm coarse sand + 80 cm of loam) and a temporarily covered area (40 cm of coarse sand). The 37 NMOCs quantified in the landfill gas samples included alkanes (C1-C10), alkenes (C1-C4), halogenated hydrocarbons (including (H)CFCs), and aromatic hydrocarbons. Both positive and negative CH4 fluxes ranging from -0.01 to 0.008 g m(-2) d(-1) were measured from the permanently covered cell. However, high spatial variation was observed, and a hot spot with a high flux (10 g m(-2) d(-1)) was identified. A higher CH4 emission occurred from the temporarily covered cell (CH4 flux of 49.9 g m(-2) d(-1)) as compared to the permanently covered cell. The NMOC fluxes from the permanently covered zone were all very small with both positive and negative fluxes in the order of 10(-7) to 10(-5) g m(-2) d(-1). Higher and mainly positive NMOC fluxes in the order of 10(-5) to 10(-4) g m(-2) d(-1) were obtained from the temporarily covered zone. The lower emission from the permanently covered and fully vegetated cell was attributable to the thicker soil layer, which functions as microbial habitat for methanotrophic bacteria. The NMOC oxidation capacity was investigated in soil microcosms incubated with CH4. Maximal oxidation rates for the halogenated aliphatic compounds varied between 0.06 and 8.56 microg (g of soil)(-1) d(-1). Fully substituted hydrocarbons (tetrachloromethane, perchloroethylene, CFC-11, CFC-12, and CFC-113) were not degraded in the presence of CH4 and O2. Benzene and toluene were rapidly degraded, giving very high maximal oxidation rates (28 and 39 microg (g of soil)(-1) d(-1)). On the basis of the emission measurements and the batch experiments conducted, a general pattern was observed between emissions and biodegradability of various NMOCs. The emissions mainly consisted of compounds that were not degradable or slowly degradable, while an uptake of easily degradable compounds was registered. As an example, perchloroethylene, trichloromethane, CFC-11, and CFC-12 were emitted, while atmospheric consumption of aromatic hydrocarbons and lower chlorinated hydrocarbons such as vinyl chloride, dichloromethane, and chloromethane was observed. This study demonstrates that landfill soil covers show a significant potential for CH4 oxidation and co-oxidation of NMOCs. Under certain conditions, landfills may even function as sinks for CH4 and selected NMOCs, like aromatic hydrocarbons and lower chlorinated compounds.

A Coupled Hydrophobic-Hydrophilic Model for Predicting Secondary Organic Aerosol Formation

Abstract: The formation of secondary organic aerosol (SOA) results from the absorption of gas-phase organic oxidation products by airborne aerosol. Historically, modeling the formation of SOA has relied on relatively crude estimates of the capability of given parent hydrocarbons to form SOA. In more recent work, surrogate organic oxidation products have been separated into two groups, hydrophobic and hydrophilic, depending on whether the product is more likely to dissolve into an organic or an aqueous phase, respectively. The surrogates are then allowed to partition only via the dominant mechanism, governed by molecular properties of the surrogate molecules. The distinction between hydrophobic and hydrophilic is based on structural and physical characteristics of the compound. In general, secondary oxidation products, because of low vapor pressures and high polarities, express affinity for both the organic and aqueous aerosol phases. A fully coupled hydrophobic-hydrophilic organic gas-particle partitioning model is presented here. The model concurrently achieves mass conservation, equilibrium between the gas phase and the organic aerosol phase, equilibrium between the gas phase and the aqueous aerosol phase, and equilibrium between molecular and ionic forms of the partitioning species in the aqueous phase. Simulations have been performed using both a zero-dimensional model and the California Institute of Technology three-dimensional atmospheric chemical transport model. Simultaneous partitioning of species by both mechanisms typically leads to a shift in the distribution of products to the organic aerosol phase and an increase in the total amount of SOA predicted as compared to previous work in which partitioning is assumed to occur independently to organic and aqueous phases.