Showing papers by "Mexican Institute of Petroleum published in 2008"
TL;DR: The antibacterial properties of silver modified montmorillonites from Pellegrini Lake, Argentina were tested in growth inhibition of Escherichia coli bacteria as discussed by the authors, and the results showed that the antibacterial activity is generated by the Ag + present in the clay, as confirmed by X-ray photoelectronic spectroscopy (XPS); however the overall antibacterial performance is affected by the availability of the ionic silver to be in contact with the bacteria.
Abstract: The antibacterial properties of silver modified montmorillonites from Pellegrini Lake, Argentina were tested in growth inhibition of Escherichia coli bacteria. Montmorillonite was first submitted to different treatments: (a) calcination at 550 °C for 3 h and (b) grinding during 300 s. After that, the samples were loaded with silver by ion exchange. Structural characterization was performed by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), and BET specific surface area measurements. Scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTM) showed that metallic silver nanoparticles precipitates over the clay surface after silver modification. Nevertheless, the displacement of the (0 0 1) reflection observed by XRD in the calcined sample, and the diminution in Na + content evaluated by energy dispersive X-ray spectroscopy (EDXS), indicate that Ag ions were interchanged in the structure of the clays. Both samples showed good antibacterial activity against E. coli , measured by the disk susceptibility and the minimum inhibitory concentration (MIC) tests. The ground montmorillonite required a lower MIC than the thermally treated, although the last one presented a bigger inhibition zone in the disk method. The results shows that the antibacterial activity is generated by the Ag + present in the clay, as confirmed by X-ray photoelectronic spectroscopy (XPS); however the overall antibacterial properties are affected by the availability of the ionic silver to be in contact with the bacteria.
249 citations
TL;DR: In this paper, the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent were characterized by Raman spectroscopy.
Abstract: This work presents the results obtained in the development of Mo/γ-Al2O3 catalysts and their evaluation in the oxidative desulfurization (OD) process of diesel fuel using hydrogen peroxide as the oxidizing reagent. The catalysts were prepared by equilibrium adsorption using several molybdenum precursors and aluminas with different acidity values. They were characterized by Raman spectroscopy. The effect of the reaction time, reaction temperature, nature of solvent, concentration of solvent and hydrogen peroxide, content of molybdenum and phosphate in the catalysts were investigated. The results showed that the activity for sulfur elimination depends mainly on the presence of hepta- and octamolybdates species on the catalyst support and the use of a polar aprotic solvent. Likewise, the presence of phosphate markedly increases the sulfur elimination. In this way, it is possible to reduce sulfur level in diesel fuel from about 320 to less than 10 ppmw at 333 K and atmospheric pressure. Additionally, on the basis of the results obtained a mechanistic proposal for this reaction is described, as an oxidation mechanism by nucleophilic attack of the sulfur atom on peroxo species of hepta- and octamolybdates, but a mechanism involving the singlet oxygen presence can be discarded.
229 citations
TL;DR: The results of the MILAGRO campaign as discussed by the authors showed that PM 2.5 and PM 1 concentrations showed a marked impact of road traffic emissions (at rush hours), with levels of coarse PM remaining elevated during daytime.
Abstract: Levels of PM 10 , PM 2.5 and PM 1 and chemical speciation of PM 10 and PM 2.5 were measured during the MILAGRO campaign (1st to 31st March 2006, but extended in some cases until 6th April) at four urban, one suburban, two rural background and two rural sites, with different degree of industrial influence, in the Mexico City Metropolitan Area (MCMA) and adjacent regions. PM 10 and PM 2.5 daily levels varied between 50–56μg/m 3 and 24–46μg/m 3 at the urban sites, 22–35μg/m 3 and 13–25μg/m 3 at the rural sites, and 75μg/m 3 and 31μg/m 3 at the industrial hotspot, lower than those recorded at some Asian mega-cities and similar to those recorded at other Latin American cities. At the urban sites, hourly PM 2.5 and PM 1 concentrations showed a marked impact of road traffic emissions (at rush hours), with levels of coarse PM remaining elevated during daytime. At the suburban and rural sites different PM daily patterns were registered according to the influence of the pollution plume from MCMA, and also of local soil resuspension. The speciation studies showed that mineral matter accounted for 25–27% of bulk PM 10 at the urban sites and a higher proportion (up to 43%) at the suburban and rural sites. This pattern is repeated in PM 2.5 , with 15% at urban and 28% at suburban and rural sites. Carbonaceous compounds accounted for a significant proportion at the urban and industrial sites (32–46% in PM 10 , and 51–55% in PM 2.5 ), markedly reduced at the suburban and rural sites (16–23% in PM 10 , and 30% in PM 2.5 ). The secondary inorganic aerosols accounted for 10–20% of bulk PM 10 at urban, suburban, rural and industrial sites, with a higher proportion (40%) at the industrial background site. A relatively high proportion of nitrate in rural sites was present in the coarse fraction. Typically anthropogenic elements (As, Cr, Zn, Cu, Pb, Sn, Sb, Ba, among others) showed considerably high levels at the urban sites; however levels of particulate Hg and crustal trace elements (Rb, Ti, La, Sc, Ga) were generally higher at the suburban site. Principal component analysis identified three major common factors: crustal, regional background and road traffic. Moreover, some specific factors were obtained for each site.
202 citations
TL;DR: In this article, an electrochemical evolution of the interface formed by carbon steel exposed to artificial seawater with nutrients in the presence and absence of mixed cultures that contain sulfate-reducing bacteria (SRB) is characterized by electrochemical impedance spectroscopy (EIS).
197 citations
TL;DR: In this article, the effect of a combined biostimulation-bioaugmentation treatment applied to a silty-loam soil polluted with a complex mixture of total petroleum hydrocarbons (TPH) was investigated.
158 citations
TL;DR: In this article, the potential ability of single-walled carbon nanotubes (SWCNTs) to act as free-radical scavengers has been investigated, and the results from these analyses suggest that, once a first radical is attached to the nanotube, further additions are increasingly feasible.
Abstract: Density functional theory calculations have been used to model the potential ability of single-walled carbon nanotubes (SWCNT) to act as free-radical scavengers. The reactions of a (5,5) SWCNT fragment with six different radicals have been studied, and for hydroxyl radical, which is the most reactive and dangerous from all of the studied set, up to four additions were modeled. Energetic considerations show that, once a first radical is attached to the nanotube, further additions are increasingly feasible, suggesting that SWCNTs can act as free-radical sponges. For reactions with OH radicals, subsequent additions are expected to lead to products where the OHs are distributed in groups rather than regularly spread on the nanotube. Because nanotubes with none or an even number of OH groups attached are stable (nonradical) species that can be used for other purposes, their properties were analyzed in terms of global reactivity indexes and density of states (DOS). The results from these analyses suggest that, ...
148 citations
TL;DR: In this paper, new compounds of alkylamides derived from α-amino acids were tested as corrosion inhibitors for carbon steel in an aqueous solution of hydrochloric acid.
114 citations
TL;DR: In this paper, a representation theorem of the correlation type for an inhomogeneous region embedded in a homogeneous space is considered and it is concluded that, in the resulting field, the energy is equipartitioned.
105 citations
TL;DR: In this article, the authors showed that the presence of Cu facilitates the reduction of the Ni at lower temperatures, and the reduction peaks were attributed to the adjacent Cu and Ni atoms which could be forming a bimetallic Cu-rich phase.
102 citations
TL;DR: In this paper, the authors measured the densities and viscosities of (N,N-dimethylformamide + water) with a vibrating tube densimeter, while two different Cannon-Fenske viscosimeters were used for the viscosity measurements.
Abstract: Densities and viscosities of (N,N-dimethylformamide + water) have been measured from T = (283.15 to 353.15) K in the entire mole fraction composition. Densities are measured with a vibrating tube densimeter, while two different Cannon-Fenske viscosimeters are used for the viscosity measurements. Excess molar volumes and viscosity deviations from the composition weighted average of the pure component viscosities are calculated from experimental measurements and represented with Redlich–Kister equations. Excess molar volumes present negative deviations from ideality at all investigated temperatures and become more negative with decreasing temperature. Viscosity deviations are positive for all the temperatures and mole fractions considered in this work.
102 citations
TL;DR: In this paper, an efficient method for anchoring Pt clusters (e.g., 6nm in size) on the surfaces of N-doped multi-walled carbon nanotubes (MWNTs-CN x ) using a relatively simple method consisting of a hydrothermal treatment of Na 2 [PtCl 6 ]··6H 2 O and Ndoped nanotube dispersed in acetic acid was reported.
TL;DR: A series of copolymers derived from styrene (S), n-butyl acrylate (BuA), and vinyl acetate (VA) monomers were prepared by emulsion polymerization to improve some physical properties of Mexican crude oils (MCOs) as discussed by the authors.
Abstract: A series of copolymers derived from styrene (S), n-butyl acrylate (BuA), and vinyl acetate (VA) monomers were prepared by emulsion polymerization to improve some physical properties of Mexican crude oils (MCOs). Once obtained, the copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, size-exclusion chromatography (SEC), and thermogravimetric analysis (TGA). Later, they were dissolved in toluene and were added to both light and heavy MCOs; the pour point temperature and apparent viscosity of these mixtures were carefully evaluated. Results indicate that styrene and vinyl acetate (SVA) copolymers show a good pour point depressant performance for both types of crude oils. The apparent viscosity dependence on temperature for light and heavy crude oils, mixed with copolymers, was also established. It was observed that, in general, the addition of copolymers decreases the apparent viscosity of both light and heavy crude oils above 35 °C.
TL;DR: In this article, the synthesis, characterization and photoactivity for the MTBE decomposition on Au/TiO2-Al2O3 and Au/ TiO2 sol-gel synthesized photocatalysts are reported.
Abstract: The synthesis, characterization and photoactivity for the MTBE decomposition on Au/TiO2–Al2O3 and Au/TiO2 sol–gel synthesized photocatalysts are reported. The semiconductor supports TiO2, and TiO2–Al2O3 were prepared by gelling titanium and aluminum alkoxides, whereas gold nanoparticles were prepared by the deposition–precipitation method with urea. Reference Au-supported photocatalysts were also prepared using the incipient impregnation method. Nitrogen adsorption as well as XRD, UV–vis and STEM-EDAX spectroscopies was used to characterize the solids. A shift of the band gap to the visible region was observed in gold-supported solids. The Eg band of the supports was shifted to the lower energy region for gold-supported catalysts. UV–vis characterization showed a gold plasmon surface resonance band (∼560 nm) in catalysts showing particles >7.0 nm. It is showed that the photocatalytic decomposition of MTBE in water (500 ppm) carried out with visible-light source (λ 495 nm) strongly depend of the Au particle size (6.4–25 nm). The catalysts with gold particle size ≤7.5 nm are the most active. It is proposed that in the catalyst with gold particle 7.0 nm the plasmon surface resonance band plays an important role in the photoactivity behavior.
TL;DR: In this article, a three-phase heterogeneous plug-flow reactor model was developed to describe the behavior of residue hydroprocessing in a multi-fixed-bed reactor system, considering gas-liquid and liquid-solid mass-transfer phenomena and incorporating reactions such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodeasphaltenization (HDAs), and hydrocracking (HCR) as well as hydrogen consumption.
Abstract: A three-phase heterogeneous plug-flow reactor model was developed to describe the behavior of residue hydroprocessing in a multi-fixed-bed reactor system. The model considers gas–liquid and liquid–solid mass-transfer phenomena and incorporates reactions such as hydrodesulfurization (HDS), hydrodenitrogenation (HDN), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrocracking (HCR) as well as hydrogen consumption. HDS reaction was described by Langmuir–Hinshelwood kinetics while the rest of the reactions were modeled with power law kinetics. To estimate kinetic parameters, experiments were carried out in a multi-reactor pilot plant loaded with a triple catalyst system under the following operating conditions: 380–420 °C temperature and 0.25–1.0 h −1 liquid hourly space velocity (LHSV), keeping constant hydrogen-to-oil (H 2 /oil) ratio at 891 std m 3 /m 3 and pressure at 9.81 MPa. Model predictions showed good agreement with experimental data in the range of the studied operating conditions. The model was also applied for simulating an industrial scale residue hydroprocessing unit with multi-bed adiabatic reactors and hydrogen quenching.
TL;DR: In this article, the structural and photoluminescence properties of nanocrystalline ZrO 2 :Dy 3+ were characterized and the highest efficiency was obtained for 0.5% of Dy 3+.
TL;DR: In this paper, a set of vapor pressure osmometry experiments investigating the asphaltene agglomeration inhibition by commercial and new inhibitor molecules in toluene and o-diclorobenzene were performed.
Abstract: Applying chemical additives (molecule inhibitors or dispersants) is a common way to control asphaltene agglomeration and precipitation. Until now, it has not been clear why under some conditions the flocculation inhibitors do not inhibit (and may also promote) the asphaltene agglomeration, and why increasing the additive concentration may lead to the diminishing of their efficacy. To clarify this issue, we performed a set of vapor pressure osmometry experiments investigating the asphaltene agglomeration inhibition by commercial and new inhibitor molecules in toluene and o-diclorobenzene. Monte Carlo computer modeling was carried out to interpret some unexpected trends of the averaged molar mass of the Puerto Ceiba asphaltene clusters at different concentrations of inhibitor, assuming that inhibitor efficiency is directly related to their adsorption on the surface of asphaltene. It is shown that the self-assembly of inhibitor molecules, induced by relative lyophilic or lyophobic interactions with a solvent...
TL;DR: In this paper, the authors used EDTA and citric acid (CA) as organic chelating additives during preparation of NiMo catalysts with wide-pore ZrO 2 -TiO 2 mixed oxides as carrier.
Abstract: Ethylenediamine tetraacetic acid (EDTA) and citric acid (CA) were used as organic chelating additives during preparation of NiMo catalysts with wide-pore ZrO 2 –TiO 2 mixed oxides as carrier. A clear beneficial effect of using either chelator was evident when sulfided catalysts were tested in dibenzothiophene hydrodesulfurization (DBT HDS at 320 °C and 5.72 MPa, batch reactor) although the optimum concentration of EDTA and CA to obtain materials of maximized activity was different to each other (Ni/EDTA = 1 and Ni/CA = 1/2). These molar ratios seemed to correspond to total impregnated nickel chelation. Augmented chelator concentration resulted in catalysts of decreased hydrodesulfurizating properties probably due to delayed sulfidation of complexated molybdenum that could be formed by reaction of Mo 6+ containing species with organic additive excess. In a pseudo-first-order kinetic constant basis, the best catalyst prepared with EDTA had similar HDS activity to that of the optimized formulation with CA ( k HDS values of 7.8 × 10 −5 and 7.3 × 10 −5 m 3 /kg cat s, respectively), both formulations being clearly superior to a NiMo/ZrO 2 –TiO 2 catalyst prepared with no organic additive ( k HDS ∼ 4.7 × 10 −5 m 3 /kg cat s). Characterization by thermal analyses (TGA, DTA) and infrared spectroscopy pointed out to delayed Ni 2+ sulfidation as the main cause of HDS activity improvement in catalysts prepared in presence of either organic chelator.
TL;DR: In this paper, three different supports were prepared with distinct magnesia-alumina ratio x ǫ = MgO/(MgO+Al 2 O 3 ) = 0.01, 0.1 and 0.5.
TL;DR: In this paper, a stochastic model for predicting corrosion damage evolution in active sites, applicable under professional practice conditions, is presented, where the damage of a material and its evolution are determined from the damage state at a given time instant and the rate of damage occurrence.
TL;DR: Capillary viscometry was used to determine the kinematic viscosity of the binary systems composed of N-methylpyrrolidone+monoethanolamine and N-mixture of tetramethylene sulfone+diethanolamine as discussed by the authors, at eight different temperatures in the range 303.15-373.15
TL;DR: In this paper, the morphology and crystalline structure of cadmium sulphide nanoparticles were measured by high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD), respectively.
TL;DR: In this paper, an effect of zeolite with alumina as a support for heavy oil hydroprocessing is presented. But, the results indicate that the combination of ultra-stable zeolites and alumina is able to produce bi-modal type of pores in the catalyst which may contribute to a better combination of hydrodesulfurization (HDS), hydrodemetallization (HDM), and the selective cracking of asphaltene over the acidic catalysts.
TL;DR: In this paper, the binding energies of Pt in the alloys were determined by XPS and Polarization curves were obtained by Rotating Disk Electrode technique in 0.5 M H2SO4 to determine the electrocatalytic activity of the mechanically alloyed powders.
TL;DR: In this article, a support for hydrotreating Al2O3-SiO2 mixed oxide has been investigated, and the results indicated that the effect of support is responsible for forming different catalytic sites.
TL;DR: Good agreement found between the calculated and the available experimental data supports the methodology used in this work, as well as the data reported here for the first time.
Abstract: Density functional theory has been used to model the reaction of OH with L-phenylalanine, as a free molecule and in the Gly-Phe-Gly peptide. The influence of the environment has been investigated using water and benzene as models for polar and non-polar surroundings, in addition to gas phase calculations. Different paths of reaction have been considered, involving H abstractions and addition reactions, with global contributions to the overall reaction around 10% and 90% respectively when Phe is in its free form. The ortho-adducts (o-tyrosine) were found to be the major products of the Phe + OH reaction, for all the modeled environments and especially in water solutions. The reactivity of phenylalanine towards OH radical attacks is predicted to be higher in its peptidic form, compared to the free molecule. The peptidic environment also changes the sites’ reactivity, and for the Gly-Phe-Gly + OH reaction H abstraction becomes the major path of reaction. The good agreement found between the calculated and the available experimental data supports the methodology used in this work, as well as the data reported here for the first time.
TL;DR: In this paper, the presence of Lewis acid sites was determined by FTIR-pyridine adsorption spectroscopy, and the results indicated that an activation treatment is needed to obtain an optimal Pd°/PdO ratio for these species.
TL;DR: In this article, the Mie(n,m) model fluids were calculated for six pairs of parameters m and n. The authors showed that after certain re-scaling of fluid density, the corresponding states rule can be applied for the calculations of the thermodynamic properties of the model fluids, and for some real substances.
TL;DR: In this article, the effective interaction between a sphere with an open cavity (lock) and a spherical macroparticle (key), both immersed in a hard sphere fluid, is studied by means of Monte Carlo simulations.
Abstract: The effective interaction between a sphere with an open cavity (lock) and a spherical macroparticle (key), both immersed in a hard sphere fluid, is studied by means of Monte Carlo simulations. As a result, a two-dimensional map of the key-lock effective interaction potential is constructed, which leads to the proposal of a self-assembling mechanism: There exists trajectories through which the key-lock pair could assemble avoiding trespassing potential barriers. Hence, solely the entropic contribution can induce their self-assembling even in the absence of attractive forces. This study points out the solvent contribution within the underlying mechanisms of substrate-protein assembly∕disassembly processes, which are important steps of the enzyme catalysis and protein mediated transport.
TL;DR: In this article, the results of multiple weld repairs in the same area in seamless API X-52 microalloyed steel pipe were analyzed by means of tension tests, Charpy-V impact resistance and Vickers hardness of the welds.
TL;DR: In this paper, the synthesis of multimetallic hydrotalcite-like (HT) materials is reported, by means of an easy environmentally friendly method, where product washing or purification steps are eliminated.
Abstract: Synthesis of multimetallic hydrotalcite-like (HT) materials is reported, by means of an easy environmentally friendly method. Product washing or purification steps are eliminated. It provides a via...