Showing papers on "Hydrocarbon published in 1999"

Organic aerosol formation from the oxidation of biogenic hydrocarbons

Abstract: A series of outdoor chamber experiments has been used to establish and characterize the significant atmospheric aerosol-forming potentials of the most prevalent biogenic hydrocarbons emitted by vegetation. These compounds were also studied to elucidate the effect of structure on aerosol yield for these types of compounds. Because oxidation products partition between the gas and aerosol phases, the aerosol yields of the parent biogenic hydrocarbons depend on the concentration of organic aerosol into which these products can be absorbed. For organic mass concentrations between 5 and 40 µg m^(-3), mass-based yields in photooxidation experiments range from 17 to 67% for sesquiterpenes, from 2 to 23% for cyclic diolefins, from 2 to 15% for bicyclic olefins, and from 2 to 6% for the acyclic triolefin ocimene. In these photooxidation experiments, hydroxyl and nitrate radicals and ozone can contribute to consumption of the parent hydrocarbon. For bicyclic olefins (α-pinene, β-pinene, Δ^3-carene, and sabinene), experiments were also carried out at daytime temperatures in a dark system in the presence of ozone or nitrate radicals alone. For ozonolysis experiments, resulting aerosol yields are less dependent on organic mass concentration, when compared to full, sunlight-driven photooxidation. Nitrate radical experiments exhibit extremely high conversion to aerosol for β-pinene, sabinene, and Δ^3-carene. The relative importance of aerosol formation from each type of reaction for bicyclic olefin photooxidation is elucidated.

Methane formation from long-chain alkanes by anaerobic microorganisms.

Abstract: Biological formation of methane is the terminal process of biomass degradation in aquatic habitats where oxygen, nitrate, ferric iron and sulphate have been depleted as electron acceptors. The pathway leading from dead biomass to methane through the metabolism of anaerobic bacteria and archaea is well understood for easily degradable biomolecules such as carbohydrates, proteins and lipids1,2. However, little is known about the organic compounds that lead to methane in old anoxic sediments where easily degradable biomolecules are no longer available. One class of naturally formed long-lived compounds in such sediments is the saturated hydrocarbons (alkanes)3,4,5. Alkanes are usually considered to be inert in the absence of oxygen, nitrate or sulphate6, and the analysis of alkane patterns is often used for biogeochemical characterization of sediments7,8. However, alkanes might be consumed in anoxic sediments below the zone of sulphate reduction9,10, but the underlying process has not been elucidated. Here we used enrichment cultures to show that the biological conversion of long-chain alkanes to the simplest hydrocarbon, methane, is possible under strictly anoxic conditions.

Estimate of global atmospheric organic aerosol from oxidation of biogenic hydrocarbons

Abstract: The results from a series of outdoor chamber experiments establishing the atmospheric aerosol-forming potential of fourteen terpenoid hydrocarbons have been used to estimate the annual amount of secondary organic aerosol formed globally from compounds emitted by vegetation. Hydroxyl radical, ozone, and nitrate radical oxidation each contribute to aerosol formation in full-photooxidation experiments; because oxidation by nitrate radical under ambient, remote conditions is likely to be negligible, parameters describing aerosol formation from hydroxyl radical and ozone reaction only are developed. Chamber results, temporally and spatially resolved, compound-specific estimates of biogenic hydrocarbon emissions, and hydroxyl radical and ozone fields are combined to lead to an estimate for atmospheric secondary organic aerosol formed annually from biogenic precursors of 18.5 Tg, a number smaller than the previously published estimate of 30–270 Tg [Andreae and Crutzen, 1997].

Adsorption-Partitioning Uptake of Nine Low-Polarity Organic Chemicals on a Natural Sorbent

Abstract: Sorption of comparatively nonpolar organic chemicals by natural solids not only can be predominated by partitioning with organic matter but also can reflect a substantial contribution from adsorption at low relative concentration. Sorption of nine polycyclic aromatic hydrocarbons (PAHs) and chlorinated benzenes (CBs) was investigated on a subsurface aquitard through batch study, with results interpreted by a composite adsorption-partitioning model. For both PAHs and CBs, the low-concentration adsorption slope and the coefficient for partitioning each correlated well with Kow; however, PAHs consistently sorbed more strongly than CBs at given Kow. For all chemicals, adsorption contributions were only important at low relative concentration and could be successfully modeled by assuming either Langmuir-type or Polanyi-type isotherms. Isotherms for all liquid chemicals fell on a single isotherm when plotted on a Polanyi basis (adsorbed volume per mass of sorbent versus adsorption potential density), providing ...

Catalytic Conversion of Palm Oil to Hydrocarbons: Performance of Various Zeolite Catalysts

Abstract: The catalytic cracking of palm oil to fuels was studied in a fixed bed microreactor operated at atmospheric pressure, a reaction temperature of 350−450 °C and weight hourly space velocities (WHSVs) of 1−4 h-1. HZSM-5, zeolite β, and ultrastable Y (USY) zeolites with different pore sizes were used to study the effects of reaction temperature and WHSV on the conversion of palm oil and yields of gasoline. The performances of HZSM-5−USY and HZSM-5−zeolite β hybrid catalysts containing 10, 20, and 30 wt % HZSM-5 were investegated. Potassium-impregnated K−HZSM-5 catalysts with different potassium loadings were used to study the effect of acidity on the selectivity for gasoline formation. The major products obtained were organic liquid product (OLP), hydrocarbon gases, and water. HZSM-5 catalyst gave conversion of 99 wt % and a gasoline yield of 28 wt % at a reaction temperature of 350 °C and WHSV of 1 h-1 and was the best among the three zeolites tested. The HZSM-5−USY hybrid catalyst performed better than USY ...

Plasma chemical vapor deposition of hydrocarbon films: The influence of hydrocarbon source gas on the film properties

Abstract: Hydrocarbon films were prepared by electron cyclotron resonance plasma deposition from different hydrocarbon source gases at varying ion energies. The source gases used were the saturated hydrocarbons CH4, C2H6, C3H8, C4H10 (n- and iso-) and the unsaturated hydrocarbons C2H4 and C2H2 as well as mixtures of these gases with hydrogen. Film deposition was analyzed in situ by real-time ellipsometry, and the resulting films ex situ by ion-beam analysis. On the basis of the large range of deposition parameters investigated, the correlation between hydrocarbon source gas, deposition parameters, and film properties was determined. The film properties are found to be influenced over a wide range not only by the energy of the impinging ions, but also by the choice of source gas. This is in contrast to a widely accepted study where no dependence of the film properties on the source gas was observed, this being ascribed to a “lost-memory effect.” A strong correlation was found between the hydrogen content of the films and the film properties. This strong correlation is explained on the basis of the random-covalent-network model.

Quantification of aerobic biodegradation and volatilization rates of gasoline hydrocarbons near the water table under natural attenuation conditions

Abstract: Aerobic biodegradation and volatilization near the water table constitute a coupled pathway that contributes significantly to the natural attenuation of hydrocarbons at gasoline spill sites. Rates of hydrocarbon biodegradation and volatilization were quantified by analyzing vapor transport in the unsaturated zone at a gasoline spill site in Beaufort, South Carolina. Aerobic biodgradation rates decreased with distance above the water table, ranging from 0.20 to 1.5 g m−3 d−1 for toluene, from 0.24 to 0.38 g m−3 d−1 for xylene, from 0.09 to 0.24 g m−3 d−1 for cyclohexene, from 0.05 to 0.22 g m−3 d−1 for ethylbenzene, and from 0.02 to 0.08 g m−3 d−1 for benzene. Rates were highest in the capillary zone, where 68% of the total hydrocarbon mass that volatilized from the water table was estimated to have been biodegraded. Hydrocarbons were nearly completely degraded within 1m above the water table. This large loss underscores the importance of aerobic biodradation in limiting the transport of hydrocarbon vapors in the unsaturated zone and implies that vapor-plume migration to basements and other points of contact may only be significant if a source of free product is present. Furthermore, because transport of the hydrocarbon in the unsaturated zone can be limited relative to that of oxygen and carbon dioxide, soil-gas surveys conducted at hydrocarbon-spill sites would benefit by the inclusion of oxygen- and carbon-dioxide-gas concentration measurements. Aerobic degradation kinetics in the unsaturated zone were approximately first-order. First-order rate constants near the water table were highest for cyclohexene (0.21–0.65 d−1) and nearly equivalent for ethylbenzene (0.11–0.31 d−1), xylenes (0.10–0.31 d−1), toluene (0.09–0.30 d−1), and benzene (0.07–0.31 d−1). Hydrocarbon mass loss rates at the water table resulting from the coupled aerobic biodgradation and volatilization process were determined by extrapolating gas transport rates through the capillary zone. Mass loss rates from groundwater were highest for toluene (0.20–0.84 g m−2 d−1), followed by xylenes (0.12–0.69 g m−2 d−1), cyclohexene (0.05–0.15 g m−2 d−1), ethylbenzene (0.02–0.12 g m−2 d−1), and benzene (0.01–0.04 g m−2 d−1). These rates exceed predicted rates of solubilization to groundwater, demonstrating the effectiveness of aerobic biodgradation and volatilization as a combined natural attenuation pathway.

Effect of salt on the mechanism of adsorption of aromatics on activated carbon.

Abstract: The effect of KCl on the adsorption of phenol, toluene, and benzene on activated carbon, with different degrees of surface oxygenation, was investigated Different trends of salt effect were observed for each compound The observed KCl effects were interpreted on the basis of electrical charge neutralization on the carbon surface and the adsorbate molecules, water adsorption, and the “salt out” effect In particular, water adsorption was found to be crucial in reducing the adsorption capacity of the activated carbon The influence of water adsorption was more pronounced on carbon surfaces with higher amounts of oxygen-containing groups This was additionally confirmed by measurements using flow microcalorimetry

Hydrocarbon selectivity model for the gas-solid Fischer-Tropsch synthesis on precipitated iron catalysts

Abstract: The kinetics of the gas−solid Fischer−Tropsch (FT) synthesis over a commercial Fe−Cu−K−SiO2 catalyst was studied in a continuous spinning basket reactor. Experimental conditions were varied as follows: reactor pressure of 0.8−3.2 MPa, H2/CO feed ratio = 0.5−2.0, and a space velocity of 0.5−2.0 × 10-3 Nm3 kgcat-1 s-1 at a constant temperature of 523 K. A new product distribution model for linear hydrocarbons is proposed. Deviations from conventional Anderson−Schulz−Flory distribution can be quantitatively described with an α-olefin readsorption product distribution model. The experimentally observed relatively high yield of methane, relatively low yield of ethene, and both the exponential decrease of the olefin-to-paraffin ratio and the change of the chain growth parameter with chain length can all be predicted from this new model. It combines a mechanistic model of olefin readsorption with kinetics of chain growth and termination on the same catalytic sites. The hydrocarbon formation is based on the surf...

Aging of 1,3-diaminopropane plasma-deposited polymer films: Mechanisms and reaction pathways

Abstract: In the course of plasma deposition of organic–polymeric thin films, radicals are incorporated into the growing film. These radicals initiate spontaneous oxidation reactions that continue over many weeks when the plasma polymers are stored in air. These reactions and their products have been previously studied in detail for spectroscopically simple, hydrocarbon-based plasma polymers. In this investigation, the aging of 1,3-diaminopropane (DAP) plasma polymer samples was monitored by XPS and FTIR in order to study how the oxidative reaction pathways might differ in a plasma-deposited material that is initially rich in amine groups. The freshly deposited DAP plasma polymer consisted of a random hydrocarbon network with a considerable amount of unsaturation and a high concentration of nitrogen-containing functional groups, mainly primary/secondary amines and imines. These groups strongly influenced the aging reactions: in contrast to hydrocarbon-based material where hydrogen abstraction and reaction of carbon-centered radicals with in-diffusing oxygen result in a wide range of oxidative products, both XPS and FTIR identified a rather narrow range of products (mainly amides and similar groups) in DAP plasma polymers even after extensive aging for more than 2 years. Reaction routes based on oxidation and/or hydrolysis of nitrogen functional groups, and involving primary as well as secondary reactions, are proposed to account for the spectroscopic data. The structure of the aged DAP plasma polymer appeared to be stable, and did not undergo more extensive oxidation, in contrast to hydrocarbon plasma polymers. In particular, carboxylic acid groups and carbamates were not detected. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2191–2206, 1999

Processes for the production of hydrocarbons, power and carbon dioxide from carbon-containing materials

Abstract: Apparatus and processes for producing power, liquid hydrocarbons and carbon dioxide from heavy feedstocks, using a partial oxidation reactor to produce a synthesis gas, a Fischer-Tropsch reactor to convert the synthesis gas to hydrocarbon products and tail gases containing hydrogen and carbon dioxide, and a combined cycle plant to produce power from steam generated by recovering heat from the reactors and from combustible tail gases. By varying operating conditions and utilizing hydrogen for recycle to the Fischer-Tropsch reactor and/or hydrocracking wax products to produce lighter hydrocarbons, the process can selectively maximize the production of power, hydrocarbons or carbon dioxide. In preferred embodiments, the Fischer-Tropsch reactor can be a slurry reactor and can employ an iron-based catalyst.

Deep oxidation of methane over zirconia supported Ag catalysts

Abstract: Zirconia supported silver catalysts were studied for deep oxidation of methane. The catalyst structure was examined by XRD, XPS, STEM-EDX, HR-TEM and UV–Vis spectroscopy and related to the catalyst activity. Methane conversion strongly depends on Ag state and dispersion. At low Ag loading ( + were studied for comparison. High conversion of methane was found only in zeolite catalysts containing a large amount of silver, some of which was in particle form. The reaction rate on zirconia-supported Ag particles is 0.77 order in methane and 0.37 order in oxygen. The reaction products, carbon dioxide and water, do not affect the methane oxidation rate in levels up to of 1.7 and 3.5 mol% in the feedgas, respectively. The active phase under reaction conditions for both low and high Ag loading is the oxygen covered metallic Ag surface, as was confirmed by XPS and UV–Vis spectrometry.

Autothermal process for the production of olefins

Abstract: A process and catalyst for the partial oxidation of paraffinic hydrocarbons, such as ethane, propane, naphtha, and natural gas condensates, to olefins, such as ethylene and propylene. The process involves contacting a paraffinic hydrocarbon with oxygen in the presence of hydrogen and a catalyst under autothermal process conditions. Preheating the feed decreases oxygen consumption and increases the net hydrogen balance. The catalyst comprises a Group 8B metal, preferably, a platinum group metal, and at least one promoter selected from Groups 1B, 6B, 3A, 4A, and 5A, optionally supported on a catalytic support, such as magnesia or alumina. In preferred embodiments, the support is pretreated with a support modifier selected from Groups 1A, 2A, 3B, 4B, 5B, 6B, 1B, 3A, 4A, 5A, the rare earth lanthanides, and the actinides. A modified fluidized bed reactor is disclosed for the process.

Microbial desulfurization of a crude oil middle-distillate fraction: analysis of the extent of sulfur removal and the effect of removal on remaining sulfur

Abstract: Rhodococcus sp. strain ECRD-1 was evaluated for its ability to desulfurize a 232 to 343°C middle-distillate (diesel range) fraction of Oregon basin (OB) crude oil. OB oil was provided as the sole source of sulfur in batch cultures, and the extent of desulfurization and the chemical fate of the residual sulfur in the oil after treatment were determined. Gas chromatography (GC), flame ionization detection, and GC sulfur chemiluminesce detection analysis were used to qualitatively evaluate the effect of Rhodococcus sp. strain ECRD-1 treatment on the hydrocarbon and sulfur content of the oil, respectively. Total sulfur was determined by combustion of samples and measurement of released sulfur dioxide by infrared absorption. Up to 30% of the total sulfur in the middle distillate cut was removed, and compounds across the entire boiling range of the oil were affected. Sulfur K-edge X-ray absorption-edge spectroscopy was used to examine the chemical state of the sulfur remaining in the treated OB oil. Approximately equal amounts of thiophenic and sulfidic sulfur compounds were removed by ECRD-1 treatment, and over 50% of the sulfur remaining after treatment was in an oxidized form. The presence of partially oxidized sulfur compounds indicates that these compounds were en route to desulfurization. Overall, more than two-thirds of the sulfur had been removed or oxidized by the microbial treatment.

Hydrocarbon measurements during tropospheric ozone depletion events : Evidence for halogen atom chemistry

Abstract: During the Arctic Tropospheric Ozone Chemistry 1996 (ARCTOC 96) field campaign (March 29 to May 15, 1996), in situ measurements of C2-C8 hydrocarbons, selected C1-C2 halocarbons, and carbon monoxide were carried out at Ny Alesund, Svalbard (78°55′N, 11°56′E). Two major tropospheric ozone depletions were observed during this period. In each case, concurrent depletion of alkanes and ethyne but no significant changes in benzene, chloromethane, or CO mixing ratios were detected. The change in the propane/benzene ratio can be used as evidence for the presence of chlorine radicals. Time integrated chlorine and bromine atom concentrations were calculated from the concentration changes of light alkanes and ethyne, respectively. At background ozone mixing ratios (O3 > 30 ppbv) our calculations yielded no significant integrated halogen atom concentrations (Cl: 5 ± 14 × 108 s cm−3, Br: 9 ± 42 × 1010 s cm−3). During major ozone depletion events, these values increase by more than a factor of 10 to values of about 1010 s cm−3 (Cl) and 5 × 1012 s cm−3 (Br). For such events the observed ozone losses can be explained quantitatively with these data. Our results show that free bromine atoms appear to be the major cause for ozone depletion (more than 92%). The contribution of chlorine atoms to the ozone loss is of the order of 1% or less. Highest integrated chlorine and bromine atom concentrations were found at lowest ozone mixing ratios and reached up to 1.4 × 1010 and 1.4 × 1013 s cm−3, respectively. A closer analysis reveals that during each ozone depletion event the integrated chlorine atom concentration increases earlier than the integrated bromine atom concentration and remains at high levels for a longer period of time. The bromine atom concentration starts to increase when ozone mixing ratios are below 15–20 ppbv and reaches very high levels for ozone <5 ppbv. The integrated chlorine concentration appears to be anticorrelated to the ozone mixing ratio (r2 = 0.811), whereas the integrated bromine concentration was found to be anticorrelated to the logarithm of the ozone mixing ratio (r2 = 0.895).