Decomposition Of Hydrocarbons Research Articles

Decomposition of long-chain petroleum hydrocarbons by Fenton‐like processes: Effects of ferrous iron source, salinity and temperature

Batch experiments were conducted to examine the effects of ferrous iron source, soil salinity and temperature on degradation of long-chain petroleum hydrocarbons by Fenton-like processes. The results show that over 70%, 50% and 25% of aliphatic C16-C21, C21-C35 and C35-C40, respectively, was eliminated at a H2O2 dose of 1.5%. The decomposition rate of petroleum hydrocarbons was similar to each other for ferrous sulfate and magnetite while the capacity of pyrite to trigger Fenton-driven decomposition of long-chain aliphatic petroleum hydrocarbons was weaker, as compared to ferrous sulfate and magnetite. The decomposition rate of aromatic hydrocarbons decreased with increasing length of carbon chain in the ferrous sulfate and magnetite systems, but the opposite was observed in the pyrite system. The effect of Fenton-like process on degradation of long-chain petroleum hydrocarbons was enhanced by increased temperature. At a temperature of 60 °C, the enhancement of Fenton process outweighed the adverse effects from potential loss of H2O2 due to elevated temperature. The use of magnetite as a source of ferrous iron was likely to prevent consumption of Fe2+ by complexation with chloride ion from occurring and consequently effectively eliminated the inhibitory effect of salinity on Fenton reaction.

Evaluation of aromatic hydrocarbon decomposition catalyzed by the dioxygenase system and substitution of ferredoxin and ferredoxin reductase.

In this study, the catalytic activity and kinetic characteristics of the aromatic hydrocarbon dioxygenase system and the possibility of substituting its ferredoxin and ferredoxin reductase components were evaluated. The genes encoding toluene dioxygenase and toluene dihydrodiol dehydrogenase were cloned from Pseudomonas putida F1, and the corresponding enzymes were overexpressed and purified to homogeneity. Oxidative hydroxylation of toluene to cis-toluene dihydrodiol was catalyzed by toluene dioxygenase, and its subsequent dehydrogenation to 3-methylcatechol was catalyzed by toluene dihydrodiol dehydrogenase. The specific activity of the dioxygenase was 2.82U/mg-protein, which is highly remarkable compared with the values obtained in previous researches conducted with crude extracts or insoluble forms of enzymes. Kinetic parameters, as characterized by the Hill equation, were vmax = 497.2μM/min, KM = 542.4μM, and nH = 2.2, suggesting that toluene dioxygenase has at least three cooperative binding sites for toluene. In addition, the use of alternative ferredoxins and reductases was examined. Ferredoxin cloned from CYP153 could transfer electrons to the iron sulfur protein component of toluene dioxygenase. The ferredoxin could be reduced by ferredoxin, rubredoxin, and putidaredoxin reductases of CYP153, alkane-1 monooxygenase, and camphor 5-monooxygenase, respectively. The results provide useful information regarding the effective enzymatic biotreatment of hazardous aromatic hydrocarbon contaminants.

Analysis of graphene films grown on copper foil at 845 °C by intermediate pressure chemical vapor deposition

Chemical vapor deposition (CVD) is the widely accepted method for synthesis of large area graphene from thermal decomposition of hydrocarbons. However, the high temperature (above 1000 °C) requirement is the major drawback of this technique. The present study is an effort towards growing graphene on copper foil using methane at a temperature of 845 °C without incorporation of any additional energy sources. This is achieved by tailoring the growth parameters at 8 mbar in thermal chemical vapor deposition. The effect of total pressure and the effect of growth-supporting gases on the growth and number of layers of graphene were analyzed to select a favorable deposition condition. Graphene formation and its uniformity were examined by Raman spectroscopy, SEM, optical microscopy, AFM and TEM analysis. No studies till date, have reported a growth temperature as low as 845 °C for complete graphene coverage on copper by thermal CVD using methane as the precursor. The low temperature can reduce the thermal budget for graphene production to a certain extent.

Carbon Chain Length Dependence of Graphene Formation via Thermal Decomposition of Alkenes on Pt(111)

Graphene layers were prepared by isothermal decomposition of different unsaturated hydrocarbons on Pt(111) single crystal surface and characterized by SRPES and LEED. Four different alkenes (ethene, propene, 1-pentene, 1-hexene) were used in order to elucidate the eventual role of the carbon chain length in the graphene growth kinetics. The process of dehydrogenation was followed stepwise from sample temperatures of 160 K (molecular adsorption) to over 1000 K, at which the surface carbon remains almost exclusively in the form of graphene. Reaction intermediates were identified for each alkene and the corresponding reaction rates were determined. The attachment of carbon during the thermally activated growth of graphene islands on Pt(111) and similar metals is predicted to proceed via prior formation of small clusters or chains in order to overcome a large energetic and spatial barrier which exists between a single adsorbed C atom (monomer) and the graphene layer. In accordance with this assumption the gro...

Soot formation in diluted laminar ethene, propene and 1-butene diffusion flames at elevated pressures

Soot formation characteristics of ethene, propene, and 1-butene, the most abundant unsaturated intermediates in thermal decomposition of paraffinic hydrocarbons, were investigated in laminar diffusion flames stabilized on a co-flow burner installed in a high-pressure combustion chamber with optical access. All three olefins were diluted with nitrogen to produce sooting but non-smoking diffusion flames at desired pressures. Pressure range was 1–2.5 bar with 1-butene, and 1–8 bar with propene and ethene. Upper pressure limits of 1-butene and propene were established by their respective vapour pressure characteristics. The spectral soot emission technique, in which radiation emitted by the soot within the flame was collected as line-of-sight intensity and spectrally resolved over the range 690–945 nm, was used to measure radially-resolved temperature and soot volume fraction. The carbon mass flow rates of the three fuels were kept constant at 0.505 mg/s to facilitate direct comparison among the fuels at elevated pressures. With the same dilution level, the sooting propensity increased from ethene to 1-butene as expected; however, the pressure sensitivity of propene and 1-butene differed significantly from that of ethene. Soot yields in both propene and 1-butene flames showed a much weaker dependence on pressure than the soot in ethene flames. In the decomposition of propene and 1-butene, allyl radical and 1,3-butadiene are known to form in critical quantities leading to formation of higher molecular growth species specifically six-membered ring aromatics, and presence of these simple aromatics is argued to play a role in lowering the pressure sensitivity of the soot in C3 and C4 olefin flames.

Catalyst Based on Sludge Derived from Wastewater Treatment of Textile Industry

Study of the catalytic properties of residual sludge from effluent treatment plants of two textile industries -located in Quito Ecuador- with different dye finishing processes. The sludges were firstly dried at 110, 125 and 140°C to analyze the effect of the temperature on the mechanical strength, then they were calcined at 300, 600 and 900°C to verify the influence of the calcination temperature on the surface properties. The structural characterization was performed with: elemental analysis, infrared spectroscopy FTIR, nitrogen adsorption, X-ray diffraction, programmed temperature reduction TPR and SEM images. The catalytic properties were studied with a thermal decomposition of glycerol and different types of oil. It is concluded that the best conditions to obtain a catalytic material from these residual sludges, were: 110°C and 600°C for drying and calcination, respectively. The catalyst with a specific area of 31.73 m2/g and presence of Cr2+ and Zn0, provided higher weight loss in the thermal decomposition reaction for glycerol and the catalyst with the specific area of 30.36 m2/g and a metallic content of Fe0 promotes higher decomposition for heavy hydrocarbons. Due to the metallic content, and the physisorption and chemisorptions capability the residual sludges of textiles industries have catalytic activity and can be used for hydrocarbon decomposition.

Carbon deposition on Ni-based catalyst with TiO2 as additive during the syngas methanation process in a fluidized bed reactor

Syngas methanation is a crucial step in industry to produce synthetic natural gas, but the Ni-based catalysts for this reaction often deactivate severely because of carbon formation. Tests were carried out in a pressurized fluidized bed methanation reactor in order to analyze the carbon deposition on the nickel-based methanation catalysts with TiO2 as additive (Ni-Ti/Al2O3) and a conventional Ni-based catalyst (Ni/Al2O3). Test results showed that Ni-Ti/Al2O3 performed better compared to Ni/Al2O3. At higher operating temperature (823 K), CO conversion on Ni-Ti/Al2O3 was 13.6% higher than that on Ni/Al2O3, CH4 yield was 39.7% higher and CH4 selectivity was even 64.7% higher for Ni-Ti/Al2O3 compared to Ni/Al2O3. The raw and spent catalysts were characterized with XRD, EDS and N2 adsorption-desorption measurements to describe the carbon deposits on them. The characterization results indicated that elemental carbon appeared on the surface of the catalysts after methanation reaction and with the increase in reaction temperature, the carbon deposition was getting more serious. The deposited carbon blocked the tiny porous channels of the catalysts and caused a drastic change in the surface topography, which led to the degradation of the catalysts’ performance. The TiO2 additive provided a physical barrier to hydrocarbon adsorption and decomposition on the catalyst surface and the oxygen vacancies on Ni-Ti/Al2O3 acted as the active sites to promote the removal carbon on the Ni particles. Thus, the TiO2 additive can enhance the anti-coking properties and catalytic activity of Ni-Ti/Al2O3 compared to Ni/Al2O3. These findings aid in further improvement and optimization of highly carbon-resistant catalysts.

Isolation, identification and evaluation of oil hydrocarbon decomposing bacteria from contaminated areas of oil fields

Microbialbiodegradation is known as an effective and harmless method to overcome environmental pollution with oil hydrocarbon. Some bacterial species were isolated from the Sarvestan oilfields (Iran, Fars province), then identified and applied for oil hydrocarbon decomposition. A carbon-free minimum medium (CFMM) containing 1% crude oil was used to isolate bacteria through incubation at 30°C in the dark at 200 rpm for 7 days. Different methods were used to identify the hydrocarbon oil decomposing bacteria: gram staining, squalene hydrolysis, catalase, production of arginine dihydrolase, gelatin liquefaction, hydrogen sulfide production, levan production, methyl red, oxidase, nitrite reduction, oxidative/fermentative, starch hydrolysis and Tween-80 hydrolysis tests. Nine different oil decomposing bacterial species were isolated. All the species grew well at 28 and 35°C, while four isolates containing of Bacillus sp. SA13, Pantoea sp. SA1112, Pseudomonas aeruginosa sp. SA21, and Bacillus sp. SA23 were capable of growing in a temperature of up to around 42°C. The minimum salt tolerance for isolates, except for Enterobacter sp. SA711, was 8%; Bacillus sp. SA212 had the highest tolerance of 15% sodium chloride. Acinetobacter sp. SA172, Enterobacter sp. SA711, Pseudomonas sp. SA75, Bacillus sp. SA212 and Bacillus sp. SA23 had the most growth rate in the CFMM. The highest percentages of oil removal obtained were 89% for Enterobacter sp. SA711, 86% for Acinetobacter sp. SA172, and 68% for Pseudomonas sp. SA75. The three isolated bacterial strains from the contaminated soil of the Sarvestan area had a good ability to degrade oil hydrocarbon. Therefore, they could be used commercially for the bioremediation of this region.

Structural transformations of highly porous nickel catalysts during ethanol conversion towards hydrogen

In this work, we report a liquid-phase reduction method to prepare porous non-supported amorphous nickel catalysts with high surface areas (65–250 m2/g). A highly crystalline face center cubic Ni (fcc-Ni) catalyst with 110 m2/g surface area was also prepared by frontal crystallization of the amorphous nickel catalyst. The catalytic activity and stability of these catalysts for ethanol decomposition was investigated at different time on stream (TOS) to understand structural transformations occurring at the early stages of catalyst activation-deactivation. Activity vs. TOS results obtained at 473 K show that on the amorphous catalysts the conversion increases from about 50% to 60–75% reaching a steady value at ∼30 h TOS, which remains constant during the observed 96 h of TOS. The fcc-Ni catalyst initially exhibits a higher conversion (∼85%), however, it quickly deactivates to a conversion in the similar range as the amorphous catalysts. It is also shown that BET surface areas of amorphous catalysts decreases during hydrogen pretreatment at 473 K due to crystallization, grain growth, and sintering. The structure of amorphous catalysts continuously refines to form a combination of fcc-Ni and hexagonal close-packed nickel (hpc-Ni) phases, as well as nickel carbide (Ni3C) and carbon layers that stabilize catalytic activity. The structure of the fcc-Ni catalyst remains unchanged during the 96 h TOS experiment indicating that carbon deposition might cause its initial deactivation. At 523 K, the amorphous catalyst shows 100% conversion, which remains constant during 96 h of TOS, while the fcc-Ni crystalline catalyst initially exhibits 95% conversion and then slowly deactivates to ∼80% at 96 h TOS. Thus at 523K the stabilized amorphous catalyst does not deactivate under the same TOS compared to the crystalline fcc-Ni catalyst, showing that the active sites on these catalysts are different. The findings of this work suggest that the liquid-phase reduction method can be used to prepare active and stable catalysts for reactions involving decomposition of alcohols and hydrocarbons to produce hydrogen.

Catalytic processing of non-condensable pyrolysis gas from plastics: Effects of calcium supports on nickel-catalyzed decomposition of hydrocarbons and HCl sorption

Non-condensable pyrolysis gas is a suitable source of hydrocarbons for energy applications. The purpose of this study was to develop a catalytic process for selective decomposition of unsaturated hydrocarbons in the pyrolysis gas as these species compromise the operation of gas engines, gas turbines and fuel cells. The effect of different calcium supports, namely CaCO3, Ca(OH)2, CaO and their mixtures, on the performance of Ni-based catalytic sorbents during the decomposition of hydrocarbons and HCl sorption from non-condensable pyrolysis gas of mixed plastics was investigated. The plastic mixture containing low density polyethylene (40%), polypropylene (40%), polystyrene (10%) and polyvinyl chloride (10%) was initially pyrolyzed at 600 °C producing condensable oils and non-condensable gases. The non-condensable gases were further treated in a subsequent reactor at 700 °C in the presence of catalytic sorbents. All catalytic sorbents were effective for HCl sorption, decreasing the HCl concentration in the gas stream below detectable levels. However, the choice of calcium support had a substantial effect on the catalytic decomposition of hydrocarbons and the properties of produced carbon deposits. CaCO3, Ca(OH)2 and their mixture at 1:1 ratio by mass loaded with Ni showed higher catalytic activity towards the decomposition of hydrocarbons compared to CaO and a mixture containing CaO, CaCO3 and Ca(OH)2 at 1:1:1 ratio by mass. Furthermore, carbon deposits produced on the surface of Ni supported on CaCO3, Ca(OH)2 and their mixture contained multi-walled carbon nanotubes, whereas carbon deposits produced on Ni supported on CaO and the mixture containing CaO had non-filamentous morphology. The observed results can be attributed to the low BET specific surface areas and pore volumes of CaO-containing catalytic sorbents which could limit the dispersion of Ni resulting in low catalytic activity.

Influence of the Crystal Structure of Titanium Oxide on the Catalytic Activity of Rh/TiO2 in Steam Reforming of Propane at Low Temperature.

Solid oxide fuel cells (SOFCs) with liquefied petroleum gas (LPG) reduce CO2 emissions due to their high-energy-conversion efficiency. Although SOFCs can convert LPG directly, coking occurs easily by decomposition of hydrocarbons, including C-C bonds on the electrode of fuel cell stacks. It is therefore necessary to develop an active steam pre-reforming catalyst that eliminates the hydrocarbons at low temperature, in which waste heat of SOFCs is used. Herein, we show that the crystal structure of the TiO2 that anchors Rh particles is crucial for catalytic activity of Rh/TiO2 catalysts for propane pre-reforming. Our experimental results revealed that strong metal support interaction (SMSI) induced during H2 pre-reduction were optimized over Rh/TiO2 with a rutile structure; this catalyst catalyzed the reaction much more effectively than conventional Rh/γ-Al2 O3 . In contrast, the SMSI was too strong for Rh/TiO2 with an anatase structure, and the surface of the Rh particles was therefore covered mostly with partially reduced TiO2 . The result was very low activity.

Analyzing the impact of reaction models on the production of hydrocarbons from thermally upgraded oil shales

Reaction parameters significantly affect oil production from shales by means of heating and in-situ upgrading. In this study, we perform numerical simulations of two chemical reaction models, which are mainly used in the research of kerogen pyrolysis and subsequent hydrocarbon decomposition in organic-rich porous media. They are the Braun and Burnham model and Wellington model. In these forward numerical simulations, we present the influence of the two reaction models on hydrocarbon production. The Braun and Burnham reaction model shows more vigorous kerogen and subsequent decomposition reactions and more hydrocarbon production than the Wellington model. A local sensitivity analysis identifies the reaction parameters with the highest influence on productivity, and the most sensitive outputs. A data-worth analysis identifies the most valuable observation data to be measured for the best prediction of total hydrocarbon production. We find that the most valuable observation data is the cumulative production of heavy oil in the Braun and Burnham model and of light oil in the Wellington model, respectively. Once we determine the maximum allowable prediction uncertainty and the expected measurement uncertainty, the observation data to be measured for the minimization of prediction uncertainty can be obtained.

BIOESTIMULACIÓN Y BIORREMEDIACIÓN DE RECORTES DE PERFORACIÓN CONTAMINADOS CON HIDROCARBUROS

The drilling of wells for extracting natural gas generates large quantities of drill cuttings contaminated with hydrocarbons. The use of bioremediation methods can reduce the concentration of hydrocarbons in these materials to an acceptable level. Three soils from the central and north zones of the state of Tamaulipas, Mexico, were assayed by mixing them with drill cuttings contaminated with hydrocarbons to find out the ability of soil to perform the bioremediation of hydrocarbons impregnated in the drill cuttings. The biostimulation of soil microorganisms with N and P on the decomposition of hydrocarbons in these mixtures was evaluated. Mixtures of soil and drill cuttings contaminated with hydrocarbons from natural gas extraction wells were poured and incubated in bioremediation cells of 1.0 × 1.2 × 0.4 m for one year. The rate of soil:drill cuttings in these mixtures was 1:1.5. Two agricultural soils and one soil of natural vegetation were studied. Based on the organic carbon content in the mixtures, N and P (urea and monoammonium phosphate) were added, in sufficient amounts to induce a ratio C:N:P of 100:10:1 in the mixture. The hydrocarbons concentration decreased significantly when the drill cuttings, mixed with soil, were incubated in the cells with addition of N and P, reaching 3000 mg/kg of total hydrocarbons, which is the maximum limit allowed in the agricultural soils by the official Mexican standard NOM-138-SEMARNAT/SSA1-2012. Plants of corn ( Zea mays ) were developed in bioremediated cuttings. The studied soils induced decomposition of hydrocarbons impregnated in drill cuttings and therefore allowed for the bioremediation of cuttings. Biostimulation of soil microorganisms with nutrients N and P, humidity and aeration increased the decomposition of hydrocarbons and fostered the bioremediation of drill cuttings.

Modeling of Block of Reactors of High-Temperature Pyrolysis Process Line

The results from mathematical modeling of a block of reactors of a high-temperature hydrocarbon pyrolysis line are presented. Models of tube furnaces for homogeneous pyrolysis with variously designed coils are described as ideal-displacement reactors. Application of a determinative approach to the reaction mechanism and determination of the kinetic parameters for thermal decomposition of hydrocarbons and their use for describing the processes occurring in SRT-1 and SRT-2 pyrolysis furnaces showed agreement between the calculated relationships and the experimental data.

SYNTHESIS OF FINELY DISPERSED VANADIUM CARBIDE (VC<sub>0.88</sub>) USING NANOFIBROUS CARBON

The paper presents the experimental data on the synthesis of finely dispersed powder of vanadium carbide (VC 0.88 ). Vanadium carbide was prepared by the reduction of vanadium oxide (III) with nanofibrous carbon (NFC) in the induction furnace under an argon atmosphere. NFC is a product of catalytic decomposition of light hydrocarbons. The main characteristic of a NFC is a high specific surface area (~150 000 m 2 /kg), which is significantly higher than that of soot (~50 000 m 2 /kg). The content of impurities in the NFC is at the level of 1 % wt. Based on the analysis of the state diagram of the V – C system, the composition of the charge and the upper temperature limit of the carbide formation reaction for obtaining vanadium carbide in the powder state are determined. Based on the thermodynamic analysis, the temperature of the onset of the carbothermic reduction reaction of vanadium oxide (III) at various CO pressures was determined. The characteristics of vanadium carbide were studied using X-ray and elemental analyzes, pycnometric analysis, scanning electron microscopy using local energy dispersive X-ray microanalysis (EDX), low-temperature adsorption of nitrogen, followed by determination of the BET specific surface area, sedimentation analysis, synchronous thermogravimetry and differential scanning calorimetry (TG/DSC). The material obtained at optimal parameters is represented by a single phase – vanadium carbide VC 0.88 . The powder particles were predominantly aggregated. The average size of the particles and the aggregates equaled 9.2 – 9.4 μm within a wide range of size distribution. The specific surface value of the obtained samples was 1800 – 2400 m 2 /g. Oxidation of vanadium carbide began from the temperature of ~430 °C and practically ends at ~830 °C. Optimum parameters of synthesis are the ratio of reagents according to stoichiometry to obtain carbide of composition VC 0.88 at a temperature of 1500 – 1600 °С and a holding time of 20 minutes. It is shown that for this process nanofibrous carbon is an effective reducing agent and that vanadium oxide (III) is almost completely reduced to carbide VC 0.88

Synthesis of Fine Vanadium-Carbide (VC0.88) Powder Using Carbon Nanofiber

The synthesis of fine vanadium-carbide (VC0.88) powder is considered. To produce the vanadium carbide, vanadium(III) oxide is reduced by means of carbon nanofiber in an induction furnace with an argon atmosphere. The carbon nanofiber is produced by the catalytic decomposition of light hydrocarbons. The specific surface of the carbon nanofiber is very high: ~150000 m2/kg, as against ~50000 m2/kg for soot. The impurity content in the carbon nanofiber is 1 wt %. By analysis of the phase diagram of the V–C system, the batch composition and the upper temperature limit in carbide formation may be determined such that vanadium carbide is formed as powder. Thermodynamic analysis yields the initial temperature at which the vanadium( III) oxide is reduced in a furnace with different CO pressures. The characteristics of the vanadium carbide are determined by the following methods: X-ray phase and elementary analysis; pycnometric analysis; scanning electron microscopy with local energy dispersion X-ray microanalysis (EDX); low-temperature nitrogen adsorption with subsequent determination of the specific surface by the BET method; sedimentation analysis; and synchronous thermogravimetric analysis and differential scanning calorimetry (TG/DSC). The material obtained with optimal reduction parameters consists of a single phase: vanadium carbide VC0.88. The powder particles are predominantly clumped together in aggregates. The mean size of the particles and aggregates is 9.2–9.4 μm, with a broad size distribution. The specific surface of the samples is 1800–2400 m2/kg. Oxidation of vanadium carbide begins at about 430°C and is practically over at 830°C. Optimal synthesis requires stoichiometric proportions of the reagents in the production of vanadium carbide VC0.88 at 1500–1600°C, with 20-min holding. In this process, carbon nanofiber effectively produces the carbide as the reduction product. The vanadium(III) oxide is reduced practically completely to VC0.88.

Effects of Multiple Pulses on Decomposition of Hydrocarbons for Hydrogen Production

Hydrogen production on vehicle is under development by using plasma discharges working in high-pressure condition over 1.5 atm. The original fuel for the system is methane (CH4) or propane (C3H8). For this purpose, mainly dielectric barrier discharge nonthermal plasma system is employed with high-voltage pulse of width 5– $30~\mu \text{s}$ and maximum amplitude 13 kV. This wide pulse is composed of multiple of 5- $\mu \text{s}$ pulse. In this system, no production of COx is expected. The decomposition rate of hydrocarbon depends on the applied pulsewidth. The phenomena of multiple pulse effects are discussed with use of multiple pulse decomposition model.

Gas generation and its isotope composition during coal pyrolysis: The catalytic effect of nickel and magnetite

Pyrolysis experiments were conducted at 370–550 °C for 72 h in closed gold capsules to investigate the effect of nickel and magnetite on gas generation from coal in the absence and presence of water.Nickel had a great catalytic effect on the yield, molecular and carbon and hydrogen isotope composition of generated gases. The methane yields increased significantly while heavy hydrocarbon gas yields decreased substantially due to the catalysis of nickel both in the absence and presence of water. The nickel catalysis caused an increase of δ13CCH4 value in the absence of water and a decrease of δ13CCH4 value in the presence of water. Results of molecular and carbon isotopic composition of hydrocarbons indicate that nickel could catalyze the decomposition of high-molecular-weight organic matter and Fischer-Tropsch-type (FTT) reactions both of which were responsible for the increased methane yield. FTT reactions catalyzed by transition metals are an important pathway for methane generation, especially in the presence of water. The catalytic decomposition of organic matter and FTT reactions also caused an increase of δ2HCH4 value both in the presence and absence of water. CO2 yield and 13CCO2 value increased obviously in the presence of nickel due to the catalytic decomposition of organic matter.In experiments without added water, addition of magnetite enhanced CO2 yield at all temperatures but only enhanced methane yield slightly at high temperature (430–550 °C). The increased CO2 and methane yields can be attributed to the oxidative decomposition of long-chain hydrocarbons via redox reactions between magnetite and hydrocarbons. In experiments with added water, addition of magnetite only caused a slight increase of methane and CO2 yields at 500 °C and 550 °C but did not influence their yields at 370–450 °C, indicating that water inhibited the effect of magnetite on methane and CO2 generation at low temperature. The addition of magnetite did not have systematic influence on carbon and hydrogen isotopes of hydrocarbon gases and carbon isotopes of CO2. Generally, the influence of magnetite on gas generation was very small.

Molecular and Kinetic Models for High-Rate Thermal Degradation of Polyethylene.

Thermal degradation of polyethylene is studied under the extremely high rate temperature ramps expected in laser-driven and X-ray ablation experiments-from 1010 to 1014 K/s in isochoric, condensed phases. The molecular evolution and macroscopic state variables are extracted as a function of density from reactive molecular dynamics simulations using the ReaxFF potential. The enthalpy, dissociation onset temperature, bond evolution, and observed cross-linking are shown to be rate dependent. These results are used to parametrize a kinetic rate model for the decomposition and coalescence of hydrocarbons as a function of temperature, temperature ramp rate, and density. The results are contrasted to first-order random-scission macrokinetic models often assumed for pyrolysis of linear polyethylene under ambient conditions.

Decomposition of Gasoline Hydrocarbons by Natural Microorganisms in Japanese Soils

Characterizing the mechanisms by which natural microorganisms in soil decompose gasoline hydrocarbons is of fundamental importance for a better understanding of natural attenuation and/or for predicting contaminant transport and fate in soils. To examine whether and how gasoline hydrocarbons can be decomposed under general environmental conditions, the decomposition of 10 major components generally contained in commercially available gasoline was analyzed in three arbitrarily selected Japanese soil samples. Gasoline hydrocarbons, especially aromatic hydrocarbons, are easily adsorbed by the tested Japanese soils, with straight chain hydrocarbons decomposing faster than branched hydrocarbons. Saturated monocyclic hydrocarbons were less easily decomposed than unsaturated monocyclic hydrocarbons. Enhancement of microbial decomposition of gasoline hydrocarbons requires a continuous supply of oxygen together with nutrients for the microorganisms.