Carbon nanotube-supported metal catalysts for NOx reduction using hydrocarbon reductants. Part 1:catalyst preparation, characterization and NOx reduction characteristics

A dual catalyst system for the Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR), including distinct low and high temperature formulations, is proposed as a means to abate NOx emissions from diesel engines. Given that satisfactory high temperature HC-SCR catalysts are already available, this work focuses on the development of an improved low temperature formulation. Pt supported on multiwalled carbon nantubes (MWCNTs) was found to exhibit superior NOx reduction activity in comparison with Pt/Al2O3, while the MWCNT support displayed a higher resistance to oxidation than activated carbon. Refluxing the MWCNT support in a 1:1 mixture of H2SO4 and HNO3 prior to the metal deposition step proved to be beneficial for the metal dispersion and the NOx reduction performance of the resulting catalysts. This support effect is ascribed to the increased Brønsted acidity of the acid-treated MWCNTs, which in turn enhances the partial oxidation of the hydrocarbon reductant. Further improvements in the HC-SCR performance of MWCNT-based formulations were achieved using a 3:1 Pt–Rh alloy as the supported phase.

Sulphate-promotion and structure-sensitivity in hydrocarbon combustion over Rh2/AlO3 catalysts

A series of Rh2/AlO3 catalysts have been prepared using untreated or pre-sulphated alumina supports. The effect of support sulphation on catalyst activity towards propene and propane combustion has been explored as a function of Rh loading. Light-off temperatures for the total oxidation of both hydrocarbons decrease with increasing Rh content, associated with a transition from small oxidic clusters to large metallic Rh particles. Sulphate promotes both propene and propane combustion equally, with the magnitude of promotion exhibiting only a weak loading dependence. Enhanced catalytic performance is accompanied by Rh reduction and sintering. © 2006 Elsevier B.V. All rights reserved.

Promoter effects in the polymerisation of a mixed hydrocarbon feed with silica-supported BF3

The activity of a silica-supported BF3–methanol solid acid catalyst in the cationic polymerisation of an industrial aromatic C9 feedstock has been investigated. Reuse has been achieved under continuous conditions. Titration of the catalyst acid sites with triethylphosphine oxide (TEPO) in conjunction with 31P MAS NMR shows the catalyst to have two types of acid sites. Further analysis with 2,6 di-tert-butyl-4-methylpyridine (DBMP) has revealed the majority of these acid sites to be Brønsted in nature. The role of α-methylstyrene in promoting resin polymerisation via chain transfer is proposed.

Trichloroethylene fate and transport studies and biodegradation kinetics in the saturated zone

Permeable reactive barriers (PRB) are constructed from soil solid amendments to support the growth of bacteria that are capable of degrading organic contaminants. The objective of this study was to identify low-cost soil solid amendments that could retard the movement of trichloroethylene (TCE) while serving as long-lived carbon sources to foster its biodegradation in shallow groundwater through the use of a PRB. The natural amendments high in organic carbon content such as eucalyptus mulch, compost, wetland peat, organic humus were compared based on their geophysical characteristics, such as pHw, porosity and total organic carbon (TOC), and as well as TCE sorption potentials. The pHw values were within neutral range except for pine bark mulch and wetland peat. All other geophysical characteristics of the amendments showed suitability for use in a PRB. While the Freundlich model showed better fit for compost and pine bark mulch, the linear sorption model was adequate for eucalyptus mulch, wetland peat and Everglades muck within the concentration range studied (0.2-0.8 mg/L TCE). According to these results, two composts and eucalyptus mulch were selected for laboratory column experiments to evaluate their effectiveness at creating and maintaining conditions suitable for TCE anaerobic dechlorination. The columns were monitored for pH, ORP, TCE degradation, longevity of nutrients and soluble TOC to support TCE dechlorination. Native bacteria in the columns had the ability to convert TCE to DCEs; however, the inoculation with the TCE-degrading culture greatly increased the rate of biodegradation. This caused a significant increase in by-product concentration, mostly in the form of DCEs and VC followed by a slow degradation to ethylene. Of the tested amendments eucalyptus mulch was the most effective at supporting the TCE dechlorination. The experimental results of TCE sequential dechlorination took place in eucalyptus mulch and commercial compost from Savannah River Site columns were then simulated using the Hydrus-1D model. The simulations showed good fit with the experimental data. The results suggested that sorption and degradation were the dominant fate and transport mechanisms for TCE and DCEs in the column, supporting the use of these amendments in a permeable reactive barrier to remediate the TCE.

Computational fluid dynamics (CFD) based approach to consequence assessment of accidental release of hydrocarbon during storage and transportation

This thesis investigated the risk of accidental release of hydrocarbons during transportation and storage. Transportation of hydrocarbons from an offshore platform to processing units through subsea pipelines involves risk of release due to pipeline leakage resulting from corrosion, plastic deformation caused by seabed shakedown or damaged by contact with drifting iceberg. The environmental impacts of hydrocarbon dispersion can be severe. Overall safety and economic concerns of pipeline leakage at subsea environment are immense. A large leak can be detected by employing conventional technology such as, radar, intelligent pigging or chemical tracer but in a remote location like subsea or arctic, a small chronic leak may be undetected for a period of time. In case of storage, an accidental release of hydrocarbon from the storage tank could lead pool fire; further it could escalate to domino effects. This chain of accidents may lead to extremely severe consequences. Analyzing past accident scenarios it is observed that more than half of the industrial domino accidents involved fire as a primary event, and some other factors for instance, wind speed and direction, fuel type and engulfment of the compound. In this thesis, a computational fluid dynamics (CFD) approach is taken to model the subsea pipeline leak and the pool fire from a storage tank. A commercial software package ANSYS FLUENT Workbench 15 is used to model the subsea pipeline leakage. The CFD simulation results of four different types of fluids showed that the static pressure and pressure gradient along the axial length of the pipeline have a sharp signature variation near the leak orifice at steady state condition. Transient simulation is performed to obtain the acoustic signature of the pipe near leak orifice. The power spectral density (PSD) of acoustic signal is strong near the leak orifice and it dissipates as the distance and orientation from the leak orifice increase. The high-pressure fluid flow generates more noise than the low-pressure fluid flow. In order to model the pool fire from the storage tank, ANSYS CFX Workbench 14 is used. The CFD results show that the wind speed has significant contribution on the behavior of pool fire and its domino effects. The radiation contours are also obtained from CFD post processing, which can be applied for risk analysis. The outcome of this study will be helpful for better understanding of the domino effects of pool fire in complex geometrical settings of process industries. The attempt to reduce and prevent risks is discussed based on the results obtained from the numerical simulations of the numerical models.

Efficient Computation of Electromagnetic Waves in Hydrocarbon Exploration Using the Improved Numerical Mode Matching (NMM) Method

In this study, we developed and improved the numerical mode matching (NMM) method which has previously been shown to be a fast and robust semi-analytical solver to investigate the propagation of electromagnetic (EM) waves in an isotropic layered medium. The applicable models, such as cylindrical waveguide, optical fiber, and borehole with earth geological formation, are generally modeled as an axisymmetric structure which is an orthogonal-plano-cylindrically layered (OPCL) medium consisting of materials stratified planarly and layered concentrically in the orthogonal directions.

In this report, several important improvements have been made to extend applications of this efficient solver to the anisotropic OCPL medium. The formulas for anisotropic media with three different diagonal elements in the cylindrical coordinate system are deduced to expand its application to more general materials. The perfectly matched layer (PML) is incorporated along the radial direction as an absorbing boundary condition (ABC) to make the NMM method more accurate and efficient for wave diffusion problems in unbounded media and applicable to scattering problems with lossless media. We manipulate the weak form of Maxwell's equations and impose the correct boundary conditions at the cylindrical axis to solve the singularity problem which is ignored by all previous researchers. The spectral element method (SEM) is introduced to more efficiently compute the eigenmodes of higher accuracy with less unknowns, achieving a faster mode matching procedure between different horizontal layers. We also prove the relationship of the field between opposite mode indices for different types of excitations, which can reduce the computational time by half. The formulas for computing EM fields excited by an electric or magnetic dipole located at any position with an arbitrary orientation are deduced. And the excitation are generalized to line and surface current sources which can extend the application of NMM to the simulations of controlled source electromagnetic techniques. Numerical simulations have demonstrated the efficiency and accuracy of this method.

Finally, the improved numerical mode matching (NMM) method is introduced to efficiently compute the electromagnetic response of the induction tool from orthogonal transverse hydraulic fractures in open or cased boreholes in hydrocarbon exploration. The hydraulic fracture is modeled as a slim circular disk which is symmetric with respect to the borehole axis and filled with electrically conductive or magnetic proppant. The NMM solver is first validated by comparing the normalized secondary field with experimental measurements and a commercial software. Then we analyze quantitatively the induction response sensitivity of the fracture with different parameters, such as length, conductivity and permeability of the filled proppant, to evaluate the effectiveness of the induction logging tool for fracture detection and mapping. Casings with different thicknesses, conductivities and permeabilities are modeled together with the fractures in boreholes to investigate their effects for fracture detection. It reveals that the normalized secondary field will not be weakened at low frequencies, ensuring the induction tool is still applicable for fracture detection, though the attenuation of electromagnetic field through the casing is significant. A hybrid approach combining the NMM method and BCGS-FFT solver based integral equation has been proposed to efficiently simulate the open or cased borehole with tilted fractures which is a non-axisymmetric model.

(Table 1) Summary of low-molecular-weight hydrocarbon concentrations, organic carbon contents, Rock-Eval pyrolysis and lithology at DSDP Leg 79 Holes

A series of core samples taken during Cruise 79 of Glomar Challenger, drilling offshore Morocco (Mazagan Plateau), is analyzed for their low-molecular-weight hydrocarbon contents. Fifty-four samples from DSDP Holes 544A, 545, 547A, and 547B, deep frozen on board immediately after recovery, are studied by a hydrogen-stripping/thermovaporization technique combined with capillary gas chromatography. Thirty-eight compounds in the C2-C8 molecular range, including saturated, olefinic, and aromatic hydrocarbons, are identified. Because of large differences in organic carbon contents, the total C2-C8 hydrocarbon concentrations vary from about 20 to 1500 ng/g dry sediment weight in the whole sample series. Organic-carbon normalized values are about 3.2 x 10**4 ng/g Corg for Lithologic Subunits IIIA and IIIB at Site 545 (Cenomanian to Aptian) and 1.0 x 10**5 ng/g Corg for Unit V at Site 547 (Cenomanian to Albian) reflecting the slightly more advanced maturity stage at the latter site. Values exceeding 10**5 ng/g Corg (Site 545) and 2 x 10**5 ng/g Corg (Site 547) are associated with samples that are very lean in organic carbon and are generally rich in carbonate. These samples are enriched by small amounts of gaseous hydrocarbons. A detailed study of individual hydrocarbon concentrations, plotted against depth, reveal additional indications for migration phenomena. At Site 547, for instance, the most mobile hydrocarbons studied (e.g., ethane) appear to migrate by diffusion or a related process from more than 700 m depth toward the surface.

(Table 1) Low molecular weight hydrocarbon concentrations and organic carbon contents at DSDP Hole 71-511

C2-C8 hydrocarbons (36 compounds identified) from 56 shipboard sealed, deep-frozen core samples of DSDP Leg 71, Site 511, Falkland Plateau, South Atlantic, were analyzed by a combined hydrogen stripping-thermovaporization method. Concentrations, which represent hydrocarbons dissolved in the pore water and adsorbed to the mineral surfaces of the sediment, vary from 24 ng/g of dry weight sediment in Lithologic Unit 4 to 17,400 ng/g in Lithologic Unit 6 ("black shale" unit). Likewise, the organic carbon normalized C2-C8 hydrocarbon concentrations range from 104 to 3.5 x 105 ng/g Corg. The latter value is more than one order of magnitude lower than expected for petroleum source beds in the main phase of oil generation. The low maturity at 600 meters depth is further supported by light hydrocarbon concentration ratios. The change of the kerogen type from Lithologic Unit 5 (Type III) to 6 (Type II) is evidenced by changes in the C6 and C7 hydrocarbon composition. Redistribution phenomena are observed close to the Tertiary-Cretaceous unconformity and at the contact between the "black shale" unit and the overlying Cretaceous chalks and claystones. Otherwise, the low molecular weight hydrocarbons in Hole 511 are formed in situ and remain at their place of formation. The core samples turned out to be contaminated by large quantities of acetone, which is routinely used as a solvent during sampling procedures onboard Glomar Challenger.

(Table 1) Hydrocarbon gas composition of sediment and gas hydrate collected in video-guided grabs from Chapopote

In the Campeche Knolls, in the southern Gulf of Mexico, lava-like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level. Chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt, which chilled and contracted after discharge. The site also includes oil seeps, gas hydrate deposits, locally anoxic sediments, and slabs of authigenic carbonate. Asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the Gulf of Mexico.

Hydrocarbon analyses of submarine mud volcanoes (MV) in the Kumano forearc basin

Twelve submarine mud volcanoes (MV) in the Kumano forearc basin within the Nankai Trough subduction zone were investigated for hydrocarbon origins and fluid dynamics. Gas hydrates diagnostic for methane concentrations exceeding solubilities were recovered from MVs 2, 4, 5, and 10. Molecular ratios (C1/C2<250) and stable carbon isotopic compositions (d13C-CH4 >-40 per mil V-PDB) indicate that hydrate-bound hydrocarbons (HCs) at MVs 2, 4, and 10 are derived from thermal cracking of organic matter. Considering thermal gradients at the nearby IODP Sites C0009 and C0002, the likely formation depth of such HCs ranges between 2300 and 4300 m below seafloor (mbsf). With respect to basin sediment thickness and the minimum distance to the top of the plate boundary thrust we propose that the majority of HCs fueling the MVs is derived from sediments of the Cretaceous to Tertiary Shimanto belt below Pliocene/Pleistocene to recent basin sediments. Considering their sizes and appearances hydrates are suggested to be relicts of higher MV activity in the past, although the sporadic presence of vesicomyid clams at MV 2 showed that fluid migration is sufficient to nourish chemosynthesis-based organisms in places. Distributions of dissolved methane at MVs 3, 4, 5, and 8 pointed at fluid supply through one or few MV conduits and effective methane oxidation in the immediate subsurface. The aged nature of the hydrates suggests that the major portion of methane immediately below the top of the methane-containing sediment interval is fueled by current hydrate dissolution rather than active migration from greater depth.

Analyses of hydrocarbon gases and sulphate in sediments from the King George Basin, Antarctica

Thermogenic hydrocarbons, formed by the thermal alteration of organic matter, are encountered in several piston core stations in the King George Basin, Anatarctica. These hemipelagic sediments are being deposited in an area of active hydrothermalism, associated with the back-arc spreading in the Bransfield Strait. The lateral extent of sediments infiltrated by the hydrothermally influenced interstitial fluids is characterized by basalt diapiric intrusions and is delineated by an acoustically turbid zone in the sediments of the eastern part of the basin. Iron-sulphide-bearing veins and fractures cut across the sediment in several cores; they appear to be conduits for flow of hydrothermally altered fluids. These zones have the highest C2+ and ethene contents. The thermogenic hydrocarbons have molecular C1/(C2 + C3) ratios typically < 50 and delta13CH4 values between -38? and -48?, indicating an organic source which has undergone strong thermal stress. Several sediment cores also have mixed gas signatures, which indicate the presence of substantial amounts of bacterial gas, predominantly methane. Hydrocarbon generation in the King George Basin is thought to be a local phenomenon, resulting from submarine volcanism with temperatures in the range 70-150°C. There are no apparent seepages of hydrocarbons into the water column, and it is not believed that significant accumulation of thermogenic hydrocarbons reside in the basin.

Seasonal variation of n-alkanes and polycyclic aromatic hydrocarbon concentrations in PMsub(10) samples collected at urban sites of São Paulo state, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Treatment of phenanthrene and benzene using microbial fuel cells operated continuously for possible in situ and ex situ applications

Bioelectrochemical systems could have potential for bioremediation of contaminants either in situ or ex situ. The treatment of a mixture of phenanthrene and benzene using two different tubular microbial fuel cells (MFCs) designed for either in situ and ex situ applications in aqueous systems was investigated over long operational periods (up to 155 days). For in situ deployments, simultaneous removal of the petroleum hydrocarbons (>90% in term of degradation efficiency) and bromate, used as catholyte, (up to 79%) with concomitant biogenic electricity generation (peak power density up to 6.75 mWm−2) were obtained at a hydraulic retention time (HRT) of 10 days. The tubular MFC could be operated successfully at copiotrophic (100 ppm phenanthrene, 2000 ppm benzene at HRT 30 days) and oligotrophic (phenanthrene and benzene, 50 ppb each, HRT 10 days) substrate conditions suggesting its effectiveness and robustness at extreme substrate concentrations in anoxic environments. In the MFC designed for ex situ deployments, optimum MFC performance was obtained at HRT of 30 h giving COD removal and maximum power output of approximately 77% and 6.75 mWm−2 respectively. The MFC exhibited the ability to resist organic shock loadings and could maintain stable MFC performance. Results of this study suggest the potential use of MFC technology for possible in situ/ex situ hydrocarbon-contaminated groundwater treatment or refinery effluents clean-up, even at extreme contaminant level conditions.