Showing papers on "Hydrocarbon published in 2002"

Assessing the combined roles of natural organic matter and black carbon as sorbents in sediments.

Abstract: We hypothesized that two mechanisms, absorption into natural organic matter and adsorption onto combustion-derived black carbon (BC), act in parallel to bind polycyclic aromatic hydrocarbons (PAHs) to Boston Harbor sediments. To focus on BC-adsorption, we removed the non-BC fraction by combusting near shore sediments at 375 °C for 24 h under air, leaving ca. 16% of the reduced carbon. The isotherm for pyrene sorption onto our combusted sediment was nonlinear with a Freundlich exponent of 0.62 ± 0.12 and a BC-normalized distribution coefficient (μg/kgBC)/(μg/L)n of 106.25±0.14. Pyrene sorption to untreated sediment was reasonably estimated using Kd = foc 104.7 + fBC 106.25 Cw(0.62-1) where foc was the non-BC organic carbon content, 104.7 was the organic carbon-normalized absorption coefficient for pyrene (L/kgoc), fBC was the BC content, and Cw was the dissolved pyrene concentration (μg/L). C/H/N ratios indicated that our environmental BC differed substantially from NIST diesel soot, possibly due to inclus...

Measurement of Activity Coefficients at Infinite Dilution in Ionic Liquids Using the Dilutor Technique

Abstract: Activity coefficients at infinite dilution have been measured with the dilutor technique for 20 solutes (alkanes, alkenes, cyclic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, and water) in the ionic liquids 1-methyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and 1-ethyl-3-methylimidazolium ethylsulfate. The measurements were carried out in the temperature range between 293.15 K and 333.15 K. The selectivities at infinite dilution ( = / ) for the separation of aliphatics from aromatics and n-hexane from 1-hexene are presented and discussed. From the results it can be concluded that the ionic liquids investigated show different advantages compared to those of the entrainers actually used for the separation of aliphatic from aromatic hydrocarbons by extractive distillation or extraction.

Speciation of gas-phase and fine particle emissions from burning of foliar fuels.

Abstract: Fine particle matter with aerodynamic diameter 70% by mass) PM2.5 are chemically speciated by gas chromatography/mass spectrometry. Expressed as a percent of PM2.5 mass, emission ranges by organic compound class are as follows: n-alkane (0.1-2%), polycyclic aromatic hydrocarbon (PAH) (0.02-0.2%), n-alkanoic acid (1-3%), n-alkanedioic acid (0.06-0.3%), n-alkenoic acid (0.3-3%), resin acid (0.5-6%), triterpenoid (0.2-0.5%), methoxyphenol (0.5-3%), and phytosterol (0.2-0.6%). A molecular tracer of biomass combustion, the sugar levoglucosan is abundant and constitutes a remarkably narrow PM2.5 mass range (2.8-3.6%). Organic chemical signatures in PM2.5 from open combustion of fine fuels differ with those of residential wood combustion and other related sources, making them functional for source-receptor modeling of PM. Inorganic matter [PM2.5 - (organic compounds + elemental carbon)] on average is estimated to make up 8% of the PM2.5. Wavelength dispersive X-ray fluorescence spectroscopy and ion chromatography identify 3% of PM2.5 as elements and water-soluble ions, respectively. Compared with residential wood burning, the PM2.5 of fine fuel combustion is nitrate enriched but shows lower potassium levels. Gas-phase C2-C13 hydrocarbon and C2-C9 carbonyl emissions are speciated by respective EPA Methods T0-15 and T0-11A. They comprise mainly low molecular weight C2-C3 compounds and hazardous air pollutants (48 wt % of total quantified volatile organic carbon).

Heterogeneous photocatalytic oxidation of benzene, toluene, cyclohexene and cyclohexane in humidified air: comparison of decomposition behavior on photoirradiated TiO2 catalyst

Abstract: Gas–solid heterogeneous photocatalytic decomposition of benzene, toluene, cyclohexane and cyclohexene over TiO 2 was studied at room temperature, and their reactivities were compared. Catalyst deactivation was ascribed to the formation of the carbon deposits on TiO 2 surface, and the formation and decomposition behavior of the carbon deposits affected the decomposition rate. Deactivated TiO 2 catalysts were photochemically regenerated in the presence of water vapor, and the carbon deposits were decomposed to CO x .

The West Falmouth oil spill after thirty years: the persistence of petroleum hydrocarbons in marsh sediments.

Abstract: The long-term fate of petroleum hydrocarbons in marsh sediments (West Falmouth, MA) contaminated in 1969 by the spill of the barge Florida was investigated. A 36-cm-long sediment core was collected in August 2000, and sediment extracts were analyzed by gas chromatography (GC) and comprehensive two-dimensional gas chroma tography (GC×GC). The latter technique is capable of separating 1 order of magnitude more compounds than the former and was used to observe whether any compositional changes in the unresolved complex mixture (UCM) occurred. No evidence of petroleum residues was detected in the top 6 cm (0−6 cm) and the lower 8 cm (28−36 cm) of the core. However, the central sections (6−28 cm) were dominated by a UCM in the boiling range of n-C13−n-C25 alkanes, consistent with a No. 2 fuel oil source. The 12−14- and 14−16-cm sections had the highest concentrations of UCM (∼8 mg g-1). These values are similar to concentrations observed shortly after the spill. Initial GC×GC analysis revealed that only the n-...

Combination of non-thermal plasma and heterogeneous catalysis for oxidation of volatile organic compounds: Part 1. Accessibility of the intra-particle volume

Abstract: The treatment of polluted air streams containing volatile organic compounds (VOCs) by a non-thermal plasma (NTP) is an alternative to conventional thermal and thermo-catalytical techniques, especially for low hydrocarbon concentrations (

An oft-studied reaction that may never have been: direct catalytic conversion of methanol or dimethyl ether to hydrocarbons on the solid acids HZSM-5 or HSAPO-34.

Abstract: Using highly purified reagents and careful tests, we show that methanol and dimethyl ether are apparently unreactive on the two most important methanol-to-hydrocarbon catalysts, HZSM-5 and HSAPO-34. Thus, none of the "direct" mechanisms involving two to four carbon atoms in intermediates such as oxonium ylides, carbenes, carbocations, and free radicals are applicable. Only the "indirect" route (hydrocarbon pool) is an established mechanism for this chemistry. An active catalyst requires a hydrocarbon pool that typically begins with products from organic impurities in the feed, carrier gas, or the solid acid itself. Impurities may also play important roles in other reactions catalyzed by solid acids.

Extraction of polycyclic aromatic hydrocarbons from soot and sediment: solvent evaluation and implications for sorption mechanism.

Abstract: Soot contains high levels of toxic compounds such as polycyclic aromatic hydrocarbons (PAHs). Extraction of PAHs from soot for quantitative analysis is difficult because the compounds are extremely tightly bound to the sorbent matrix. This study was designed to investigate the effect of solvent type on PAH extraction yield, to identify the most optimal solvent for PAH extraction from soot, and to gain insight into the mechanism of PAH sorption to soot in aquatic environments. To that end, different types of soot as well as coal, charcoal, and sediments containing soot-like material were extracted with seven organic solvents. Large differences in extraction recoveries were observed among solvents, with relative values as low as 16% as compared to the best extracting solvent. These differences were much larger for soot than for sediments. Dichloromethane, which to date is the most widely used solvent for soot and sediment extractions, appeared to be the overall worst extractant, whereas toluene/methanol (1:...

Efficient evolution of hydrogen from liquid cycloalkanes over Pt-containing catalysts supported on active carbons under “wet–dry multiphase conditions”

Abstract: Highly efficient evolution of hydrogen is achieved in the dehydrogenation of cycloalkanes such as cyclohexane, methylcyclohexane, and decalin over Pt catalyst supported on active carbon (AC) under “wet–dry multiphase conditions”. Formation rate of hydrogen is largely dependent on reaction conditions such as reactant/catalyst ratio, temperature, and support. The highest initial rate of formation of hydrogen, k =8.0×10 −3 mol min −1 , was obtained in the dehydrogenation of cyclohexane over Pt/AC at 623 K and the reactant/catalyst ratio=3.3 ml g −1 . The addition of second metals such as Mo, W, Re, Rh, Ir, and Pd on the carbon-supported Pt catalysts enhances the dehydrogenation rate due to the promotion of CH bond cleavage and/or desorption of aromatic products. A physical mixture of Pt/AC and Pd/AC catalysts exhibits higher activities than the monometallic Pt/AC catalyst owing to the synergistic effects of spillover, migration, and recombination of hydrogen over Pt and Pd catalysts.

Development of catalysts suitable for hydrogen or syn-gas production from biomass gasification

Abstract: Tri-metallic and ternary oxide structures were prepared, characterised and tested for two fixed-bed catalytic applications: the reforming of methane with steam and CO2; and for conditioning the gas produced by biomass steam gasification in a fluidised bed of olivine particles, with the aim of drastically reducing high and low molecular weight hydrocarbon concentrations in the product gas. Methane conversions higher than 90% were achieved for a synthetic gas feed mixture (similar of that produced in biomass gasification) using the catalyst formulation LaNi0.3Fe0.7O3 at 800°C: the space time under reaction conditions was 0.05 s, and no carbon was formed for reaction periods of up to 150 h . The catalyst contained in a secondary fixed-bed reactor placed after the gasifier was able to convert about 90% by weight of the tar present in the raw gas at 800°C: the space time under reaction conditions was 0.45 s , during which time no coke formation was observed on the catalyst surface.

A study of steam reforming of hydrocarbon fuels on Pd/ceria

Abstract: Differential steam-reforming rates were measured for methane, ethane, n -butane, n -hexane, 2,4-dimethylhexane, n -octane, cyclohexane, benzene, and toluene over 1 wt.% Pd/ceria between 620 and 770 K and were compared to rates observed on 1 wt.% Pd/alumina and 1 wt.% Pt/ceria. The H 2 O:C ratios at which stable rates were observed on Pd/ceria depended on the hydrocarbon, varying from less than 1:1 for methane to 3:1 for 2,4-dimethylhexane. In the series of alkanes from methane to n -hexane, for a H 2 O:C ratio of 2:1, the only products were CO, CO 2 , and H 2 O and the rate of formation of CO 2 and CO increased with carbon number. Benzene was also selectively converted to CO x and H 2 , but at lower rates than the alkanes with the exception of methane. For 2,4-dimethylhexane and n -octane, a significant amount of cyclohexane was observed in the initial products and cyclohexane was selectively converted to benzene at low conversions. Steam reforming of toluene also gave benzene as the initial product. FTIR measurements of Pd/ceria under methane-steam-reforming conditions indicate the formation of carbonates on the ceria. Pd/alumina showed significantly lower rates than Pd/ceria and much lower CO 2 :CO ratios in the initial products, implying ceria plays an important role in the reaction. Pt/ceria gave rates and selectivities that were essentially identical to that of Pd/ceria. The implications of these results for hydrocarbon fuel processing are discussed.

The evolution of multicomponent systems at high pressures: VI. The thermodynamic stability of the hydrogen–carbon system: The genesis of hydrocarbons and the origin of petroleum

Abstract: The spontaneous genesis of hydrocarbons that comprise natural petroleum have been analyzed by chemical thermodynamic-stability theory. The constraints imposed on chemical evolution by the second law of thermodynamics are briefly reviewed, and the effective prohibition of transformation, in the regime of temperatures and pressures characteristic of the near-surface crust of the Earth, of biological molecules into hydrocarbon molecules heavier than methane is recognized. For the theoretical analysis of this phenomenon, a general, first-principles equation of state has been developed by extending scaled particle theory and by using the technique of the factored partition function of the simplified perturbed hard-chain theory. The chemical potentials and the respective thermodynamic Affinity have been calculated for typical components of the H–C system over a range of pressures between 1 and 100 kbar (1 kbar = 100 MPa) and at temperatures consistent with those of the depths of the Earth at such pressures. The theoretical analyses establish that the normal alkanes, the homologous hydrocarbon group of lowest chemical potential, evolve only at pressures greater than ≈30 kbar, excepting only the lightest, methane. The pressure of 30 kbar corresponds to depths of ≈100 km. For experimental verification of the predictions of the theoretical analysis, a special high-pressure apparatus has been designed that permits investigations at pressures to 50 kbar and temperatures to 1,500°C and also allows rapid cooling while maintaining high pressures. The high-pressure genesis of petroleum hydrocarbons has been demonstrated using only the reagents solid iron oxide, FeO, and marble, CaCO3, 99.9% pure and wet with triple-distilled water.

Bacterial aerobic degradation of benzene, toluene, ethylbenzene and xylene

Abstract: Several aerobic metabolic pathways for the degradation of benzene, toluene, ethylbenzene and xylene (BTEX), which are provided by two enzymic systems (dioxygenases and monooxygenases), have been identified. The monooxygenase attacks methyl or ethyl substituents of the aromatic ring, which are subsequently transformed by several oxidations to corresponding substituted pyrocatechols or phenylglyoxal, respectively. Alternatively, one oxygen atom may be first incorporated into aromatic ring while the second atom of the oxygen molecule is used for oxidation of either aromatic ring or a methyl group to corresponding pyrocatechols or protocatechuic acid, respectively. The dioxygenase attacks aromatic ring with the formation of 2-hydroxy-substituted compounds. Intermediates of the “upper” pathway are then mineralized by eitherortho-ormeta-ring cleavage (“lower” pathway). BTEX are relatively water-soluble and there-fore they are often mineralized by indigenous microflora. Therefore, natural attenuation may be considered as a suitable way for the clean-up of BTEX contaminants from gasoline-contaminated soil and groundwater.

Alumina and silica supported metal catalysts for the production of carbon nanotubes

Abstract: Catalytic activity of iron, cobalt and a mixture of iron and cobalt supported on Al 2 O 3 and SiO 2 has been investigated in the production of carbon nanotubes (NTs). The supports are obtained from different methods. Acetylene was used as the source of carbon and nitrogen as the carrier gas. The pyrolysis of hydrocarbon was carried out at 500, 600 and 700 °C. The effect of other reaction parameters such as rate of flow of the hydrocarbon, carrier gas and the reaction time has also been investigated. Transmission electron microscope (TEM) was used to follow the quality and nature of NTs formed. It was observed that a good quality and quantity of multiwall carbon nanotubes (MWNTs) were produced when alumina prepared from aluminum isopropoxide and deposited with a mixture of iron and cobalt catalysts was used.

Detection of Anaerobic Metabolites of Saturated and Aromatic Hydrocarbons in Petroleum-Contaminated Aquifers

Abstract: Recent investigations have demonstrated that several classes of petroleum hydrocarbons are susceptible to anaerobic decay, including alkanes and mono- and polycyclic aromatic compounds. In previous work, benzylsuccinates were shown to be useful indicators of in situ anaerobic alkylbenzene metabolism. In the present study, we sought to determine whether metabolites of alkanes and naphthalenes could similarly be used as indicators of the intrinsic decomposition of these compounds in petroleum-contaminated aquifers. Such metabolites include succinate derivatives of n-alkanes, cyclic alkanes, and alkylaromatic hydrocarbons as well as naphthoic acids. Using gas chromatography−mass spectrometry (GC−MS), we analyzed trimethylsilyl-derivatized organic extracts from six hydrocarbon-contaminated groundwaters for MS fragment ions indicative of such anaerobic metabolites. Geochemical indicators in these aquifers suggested the prevalence of anaerobic processes. In the groundwaters of the contaminated sites, we found c...

Plasma Pyrolysis of Methane to Hydrogen and Carbon Black

Abstract: The plasma-driven gas-phase thermal decomposition of methane yielding hydrogen and solid-phase carbon has been suggested as an environmentally friendly alternative to conventional methods of producing hydrogen from natural gas. The advantage of the process is that hydrogen is obtained directly from methane without producing CO2 as a byproduct. The process was experimentally examined using a modified version of a dc plasma reactor originally developed for the conversion of methane to acetylene. Carbon yields of 30%, a factor of 6 increase, with a corresponding decrease in acetylene yield were obtained by simply increasing the residence or reaction time. A detailed kinetic model that includes the reaction mechanisms resulting in the formation of acetylene and heavier hydrocarbons through benzene is described. A model for solid carbon nucleation and growth is included. The model is compared to experimental results and is used to examine process optimization.

Plasma Thermal Conversion of Methane to Acetylene

Abstract: This paper describes a re-examination of a known process for the direct plasma thermal conversion of methane to acetylene. Conversion efficiencies (% methane converted) approached 100% and acetylene yields in the 90–95% range with 2–4% solid carbon production were demonstrated. Specificity for acetylene was higher than in prior work. Improvements in conversion efficiency, yield, and specificity were due primarily to improved injector design and reactant mixing, and minimization of temperature gradients and cold boundary layers. At the 60-kilowatt scale cooling by wall heat transfer appears to be sufficient to quench the product stream and prevent further reaction of acetylene resulting in the formation of heavier hydrocarbon products or solid carbon. Significantly increasing the quenching rate by aerodynamic expansion of the products through a converging–diverging nozzle led to a reduction in the yield of ethylene but had little effect on the yield of other hydrocarbon products. While greater product selectivity for acetylene has been demonstrated, the specific energy consumption per unit mass of acetylene produced was not improved upon. A kinetic model that includes the reaction mechanisms resulting in the formation of acetylene and heavier hydrocarbons, through benzene, is described.

Emissions of Aldehydes and Ketones from a Two-Stroke Engine Using Ethanol and Ethanol-Blended Gasoline as Fuel

Abstract: Besides aliphatic gasoline, ethanol-blended gasoline intended for use in small utility engines was recently introduced on the Swedish market. For small utility engines, little data is available showing the effects of these fuels on exhaust emissions, especially concerning aldehydes and ketones (carbonyls). The objective of the present investigation was to study carbonyl emissions and regulated emissions from a two-stroke chain saw engine using ethanol, gasoline, and ethanol-blended gasoline as fuel (0%, 15%, 50%, 85%, and 100% ethanol). The effects of the ethanol-blending level and mechanical changes of the relative air/fuel ratio, lambda, on exhaust emissions was investigated, both for aliphatic and regular gasoline. Formaldehyde, acetaldehyde, and aromatic aldehydes were the most abundant carbonyls in the exhaust. Acetaldehyde dominated for all ethanol-blended fuels (1.2-12 g/kWh, depending on the fuel and lambda), and formaldehyde dominated for gasoline (0.74-2.3 g/kWh, depending on the type of gasoline and lambda). The main effects of ethanol blending were increased acetaldehyde emissions (30-44 times for pure ethanol), reduced emissions of all other carbonyls exceptformaldehyde and acrolein (which showed a more complex relation to the ethanol content), reduced carbon monoxide (CO) and ntirogen oxide (NO) emissions, and increased hydrocarbon (HC) and nitrogen dixodie (NO2) emissions. The main effects of increasing lambda were increased emissions of carbonyls and nitrogen oxides (NOx) and reduced CO and HC emissions. When the two types of gasoline are considered, benzaldehyde and tolualdehyde could be directly related to the gasoline content of aromatics or olefins, but also acrolein, propanal, crotonaldehyde, and methyl ethyl ketone mainly originated from aromatics or olefins, while the main source for formaldehyde, acetaldehyde, acetone, methacrolein, and butanal was saturated aliphatic hydrocarbons.

Exploring the potential of mesoporous silica, SBA-15, as an adsorbent for light hydrocarbon separation

Abstract: Equilibrium adsorption isotherms for methane, ethane, ethylene, acetylene, propane, and propylene have been measured for the first time on mesoporous silica, SBA-15, and the data are analyzed by using the Langmuir−Freundlich adsorption isotherm model. The adsorption capacities for ethylene and propylene are found to be higher than those for corresponding alkanes. Likewise, adsorption of acetylene is more pronounced as compared to ethylene. The isosteric heats of adsorption for various adsorbates estimated by the Clausius−Clapeyron equation are higher for olefins and acetylene and are comparable with those reported for π-complexation based systems. Such a trend has in turn suggested a higher affinity of SBA-15 framework for alkenes over corresponding alkanes, which has been examined in terms of the textural characteristics of SBA-15. It is suggested that SBA-15 can potentially be a good adsorbent for separation of light hydrocarbons.

Catalytic partial-oxidation of methane on a ceria-supported platinum catalyst for application in fuel cell electric vehicles

Abstract: Fuel cell developers are investigating the generation of hydrogen from light hydrocarbons, such as methane or natural gas, for fuelling polymer electrolyte fuel cells (PEFCs) This study demonstrates generation of H 2 and CO by catalytic partial-oxidation of CH 4 in air at atmospheric pressure on a ceria-supported platinum catalyst prepared by a novel solution-combustion method where platinum is present in ionically-substituted form These catalysts at different platinum loadings showed methane conversion and hydrogen selectivity of 90 and 97%, respectively Interestingly, there is little carbon deposition in the catalytic reactor even after prolonged reaction time

Plasma-assisted production of hydrogen from hydrocarbons

Abstract: This paper is dedicated to the discussion of possible plasma applications for hydro- gen-rich gas production from hydrocarbons. Different types of plasma, both thermal and nonequilibrium ones, are under consideration. A special attention is devoted to experimental and theoretical results on hydrocarbon conversion in nonequilibrium plasma of pulse microwave discharge. A comparison of plasma methods and conventional catalytic technol- ogy is presented as well.