Trace Sulfur Research Articles

Contribution of aboveground plants, the rhizosphere and root-free-soils to total COS and DMS fluxes at three key growth stages in rice paddies

Carbonyl sulfide (COS) and dimethyl sulfide (DMS) are trace sulfur gases that contribute substantially to sulfate aerosols or cloud condensation nuclei in the upper and lower atmosphere and therefore play great roles in the earth's radiative balance. COS and DMS fluxes in rice (Oryza sativa L.) have been measured previously in rice paddies, and this study was designed to further investigate the role of aboveground plants, the rhizosphere and the root-free-soils in the exchange of COS and DMS by comparing COS and DMS fluxes among planted plots (PP), non-planted plots (NPP), plots with aboveground plants just cut before test (plants-cut plots, PCP) at three key growth stages (tillering, jointing–booting and mature stage). The average COS fluxes in NPP, PCP, and PP were 10.5±3.8, 6.1±4.6, and −12.3±5.0pmolm−2s−1, suggesting that COS emission from root-free-soils (10.5pmolm−2s−1) was surpassed by uptake of the rhizosphere (−4.4pmolm−2s−1) and aboveground plants (−18.4pmolm−2s−1). DMS emission rates were 60.5±25.2, 20.2±7.3 and 30.8±10.8pmolm−2s−1 in PP, NPP and PCP, respectively. Calculated DMS emission from the aboveground plants, rhizosphere and the root-free-soils were 29.7, 10.6 and 20.2pmolm−2s−1, accounting respectively for 49.0%, 17.6% and 33.4% of total DMS emission. Directly measured COS and DMS fluxes from aboveground plants averaged −14.2±7.2 and 22.3±10.6pmolm−2s−1, approximating that of −18.4 and 29.7pmolm−2s−1 calculated by subtracting fluxes in PP and PCP, respectively. Preliminary diurnal flux observation at jointing–booting stage revealed significant linear correlation between COS uptake rates by above ground plants (MFCOS) and photosynthesis rates (Pn) with a MFCOS/Pn slope of 0.48pmolμmol−1. DMS emission from the aboveground plants was also found to be significantly increased with temperature.

Higher alcohols from syngas using a K/Ni/MoS2 catalyst: Trace sulfur in the product and effect of H2S-containing feed

Two types of experiments have been performed related to the higher alcohol synthesis from syngas over a K–Ni–MoS2 catalyst which beforehand has been operated for 1000h on stream in sulfur-free syngas. In the first experimental part, sulfur-free syngas was used as feed and the condensed liquid product was found to contain 67ppmw sulfur, while the sulfur concentration in the gas was 19ppmv. The gas phase was found to contain mainly COS and H2S, while the liquid phase contained methanethiol (13.8ppmwS), ethanethiol (10.6ppmwS), dimethyl sulfide (21.3ppmwS), ethyl methyl sulfide (12.2ppmwS), unidentified sulfur compounds (7.9ppmwS) together with some dissolved COS (0.5ppmwS) and H2S (1.2ppmwS).In the second experimental part, the effect of feeding syngas containing 170ppm H2S compared to a sulfur-free syngas was studied, while all products were carefully monitored online. The presence of H2S in the syngas was found to increase CO conversion, but the largest change was found in product selectivity. The hydrocarbon selectivity greatly increased at the expense of alcohol selectivity, while the alcohol distribution shifted towards longer alcohols (increased C2+OH/MeOH ratio). From product yields it became clear that most of the increased CO conversion with H2S in the feed was due to increased methane formation (and CO2 formation due to the water–gas shift reaction). The presence of H2S in the feed greatly increased the concentration of all sulfur compounds. Together with COS, formation of thiols (methanethiol and ethanethiol) was especially favored by the presence of H2S. The thioether concentration also increased, however, to a much lower extent.

Element profile and chemical environment of sulfur in a giant clam shell: Insights from μ-XRF and X-ray absorption near-edge structure

We used micro X-ray fluorescence (μ-XRF) to investigate element profiles of sulfur in the inner layer of an aragonitic clam shell (Hippopus hippopus), and we used sulfur K-edge X-ray absorption near-edge structure (XANES) to evaluate the local environment of sulfur in aragonitic (H. hippopus, freshwater pearl mussel Hyriopsis sp.) and calcitic (Japanese scallop Mizuhopecten yessoensis) bivalve shells. The spectra of S K-edge XANES collected from bivalve shells and S-bearing organic and inorganic reference materials indicated that inorganic sulfate was present in marine aragonitic and calcitic bivalve shells. However, XANES results did not permit us to discriminate between organic and inorganic sulfate in freshwater aragonitic shells. The first-order fluctuations of sulfur in the inner shell layer showed clear annual fluctuations, with sulfur concentrations being lower during periods of faster growth. Our results suggest that trace sulfur profiles in aragonitic shells could be the result of cyclic changes of shell growth related to insolation or some influencing factors of shell growth.

Characterization of trace contaminants in syngas from the thermochemical conversion of biomass

Sampling and analysis procedures are described that have been developed and validated for the detailed characterization of trace organic and inorganic contaminants in purified syngas generated from an integrated biorefinery (IBR). A dynamic dilution sampling system was employed to minimize the potential loss of polar organic and particulate species during the sampling of the syngas. Sample collection media included a combination of filters, adsorbent cartridges, and evacuated canisters. Results were generated for up to 165 syngas contaminants generated from the conversion of rice hull and wood chip feedstocks over a 3-day test period from a pilot IBR having a biomass conversion capability of 10 to15 dry tons per day. Special emphasis was placed on the characterization of trace sulfur species (H2S, SO2, and inorganic sulfates), nitrogen species (NH3, HNO3, NO2, and inorganic nitrates), chlorine species (HCl and inorganic chlorides), tars (organic particulates), and inorganic particulate matter (elemental species) since these materials are known contaminants that can adversely affect catalysts used in subsequent conversion of syngas to fuels. The dynamic dilution sampling system was shown to reliably collect trace contaminants in the syngas, collected both before and after the IBR syngas purification system. The detection limits for most chemical species were found to be in the low ppb range. The total average concentrations of all particulate contaminants using filter sampling media were in good agreement with PM2.5 measurements using a real-time particulate monitoring instrument. It was found that the purified syngas contained very low levels of contaminants, and that the syngas from this biorefinery would be suitable for subsequent catalytic conversion to liquid fuels over extended periods of biorefinery operation.

Simple and sensitive method for the measurement of volatile alkyl mercaptans in gasoline for remote field deployment

Trace sulfur species, such as elemental sulfur, hydrogen sulfide, and volatile alkyl mercaptans, adversely affect silver based devices, such as gasoline level sensors, used in most vehicles. Identification and measurement of the sulfur species are key to developing a process control and/or treatment system to solve the problem at the refinery, prior to product distribution. A new and innovative method was developed for the analysis of specific mercaptan species in gasoline, and is reported here. The initial sample treatment stage is precipitation and stabilization of mercaptans as silver mercaptides. This stabilization could be successfully utilized in the field to mitigate the instability of mercaptans in gasoline samples. Another advantage of this step is that silver nitrate (AgNO3) precipitation concentrates the mercaptans allowing for trace level detection. The silver mercaptides are converted to pentafluorobenzyl derivatives and analyzed by gas chromatography (GC) with mass spectrometric (MS) detection. Results based on this technique show that alkyl mercaptans can be accurately measured in the full scan mode of MS with a limit of detection (LOD) of 0.02mg/L when a 100mL gasoline sample is used. The recovery of mercaptans spiked into gasoline was 85 to 120% (n=5). Gasoline producers will find knowing the exact levels of mercaptans in their products a useful tool to avoid distribution delays.

Sulphur poisoning of the SOFC cathode material La0.6Sr0.4CoO3-δ

Abstract The oxygen exchange kinetics of La0.6Sr0.4CoO3-δ was investigated at 700 °C and p(O2) = 0.10 bar by in-situ conductivity relaxation measurements. The experiments were performed for 1000 h in an O2–Ar atmosphere with and without 50 ppm SO2. For post-test analyses, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDXS) and analytic transmission electron microscopy (TEM) were applied. Elemental depth profiles were obtained by X-ray photoelectron spectroscopy (XPS). The decrease in the chemical oxygen exchange coefficient kchem by a factor of 10 during the course of 1000 h indicated that an accumulation of traces of sulphur (estimated to the range of ppb) in the form of SrSO4 can lead to a significant degradation even in nominally pure O2–Ar. The exposure to 50 ppm of SO2 for 1000 h caused a severe degradation in kchem by a factor of 3000. Post-test analyses showed that the perovskite phase La0.6Sr0.4CoO3-δ is decomposed into SrSO4 and La2O2SO4 within the first 500 nm of the surface, and a nano-crystalline Co-rich phase, which is located in the depth range of 500–1400 nm.

Interactions of mineral dust with pollution and clouds: An individual-particle TEM study of atmospheric aerosol from Saudi Arabia

Aerosol particles from desert dust interact with clouds and influence climate on regional and global scales. The Riyadh (Saudi Arabia) aerosol campaign was initiated to study the effects of dust particles on cloud droplet nucleation and cloud properties. Here we report the results of individual-particle studies of samples that were collected from an aircraft in April 2007. We used analytical transmission electron microscopy, including energy-dispersive X-ray spectrometry, electron diffraction, and imaging techniques for the morphological, chemical, and structural characterization of the particles.Dust storms and regional background conditions were encountered during four days of sampling. Under dusty conditions, the coarse (supermicrometer) fraction resembles freshly crushed rock. The particles are almost exclusively mineral dust grains and include common rock-forming minerals, among which clay minerals, particularly smectites, are most abundant. Unaltered calcite grains also occur, indicating no significant atmospheric processing. The particles have no visible coatings but some contain traces of sulfur. The fine (submicrometer) fraction is dominated by particles of anthropogenic origin, primarily ammonium sulfate (with variable organic coating and some with soot inclusions) and combustion-derived particles (mostly soot). In addition, submicrometer, iron-bearing clay particles also occur, many of which are internally mixed with ammonium sulfate, soot, or both. We studied the relationships between the properties of the aerosol and the droplet microphysics of cumulus clouds that formed above the aerosol layer. Under dusty conditions, when a large concentration of coarse-fraction mineral particles was in the aerosol, cloud drop concentrations were lower and droplet diameters larger than under regional background conditions, when the aerosol was dominated by submicrometer sulfate particles.

Applications of planar microfluidic devices and gas chromatography for complex problem solving

The application of planar microfluidic devices in GC for the separation of components of interest otherwise difficult to separate in a single analysis is presented. A variety of configurations were used for parallel chromatography, column effluent splitting, back flushing, selectivity tuning, valve less switching and column isolation, heart cutting, and comprehensive multidimensional chromatography. The synergies of recently commercialized planar microfluidic devices combined with the resolving power of fused-silica capillary columns are demonstrated. Difficult separations were accomplished in one single analysis, such as light hydrocarbons in air with high-moisture content, fixed gases in hydrocarbons, trace sulfur containing compounds in natural gas, and oxygenated compounds in hydrocarbons, among others.

Study on Mineral Elements in Salvia roborwskii from the Qinghai-Tibet Plateau

The contents of trace elements, including aluminum, barium, beryllium, calcium, cobaltium, chromium, copper, iron, potassium, lanthanum, lithium, magnesium, manganese, sodium, nickel, phosphorus, lead, sulfur, silicon, titanium, vanadium, and zinc, were determined by ICP-AES. The mean concentrations of the 22 elements were as follows: K>Ca>Mg>Fe>Al>Na>S>P>Ba>Ti>Mn>Zn>Sr>Cu>Ni=Cr>Pb>V>Li=La>Co>Be. Principal components analysis of SPSS was applied to study the characteristic elements in Salvia roborwskii. Five principal components which accounted for 89.288% of the total variance were extracted from the original data. The first factor accounted for 56.401% of the total variance, which meant that aluminum, barium, beryllium, calcium, and cobaltium were the characteristic elements in S. roborwskii. This useful new method was used to evaluate the quality of S. roborwskii, and to provide the scientific foundation for its utilization and further research.

Novel Alkylborate–Dithiocarbamate Lubricant Additives: Synthesis and Tribophysical Characterization

Boron-based lubricant additives have recently received significant attention, because of their wear-reducing and frictional properties and low pollution. At the same time, dithiocarbamate complexes with different metals have a long history of being used as multifunctional additives to lubricants. In this study, novel, environmentally friendly additives containing alkylborate and dithiocarbamate groups with alkyl or methylbenzyl substitutes in one molecule were studied. Tribological tests were performed with the additives admixed in a mineral oil using steel-on-steel contacts in a four-ball tribometer. Borate derivatives of different dithiocarbamate ligands were synthesized by several step reactions to investigate tribochemical properties of boron, sulfur, and nitrogen combined in one selected compound. Viscous liquid products were characterized by multinuclear 1H, 13C, and 11B NMR spectroscopy. The surface morphology and the elemental composition of the tribofilms were investigated using an optical profiler and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS). It was found that some of these novel compounds provide better antiwear performance and similar frictional properties compared with a commercially available ZnDTP package. Traces of sulfur in the tribofilms formed with both 0.2 and 1.0 wt% of alkylborate–dithiocarbamate compounds in a mineral oil were detected with EDS.

H 2S stability and separation performance of cobalt oxide silica membranes

This work investigates the effect of hydrogen sulfide (H 2S) exposure on cobalt oxide silica (CoO x Si) xerogels and membranes to determine their robustness under sour gas conditions. Fourier transform infra-red spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed no detectable traces of sulfur or any sulfur compounds in CoO x Si xerogels exposed to 50 ppm H 2S in helium (He) at 200 and 500 °C. Similarly N 2 adsorption showed no significant change of average pore size or pore volume of the xerogel samples after 48 h of H 2S exposure. Gravimetric analysis of the xerogels showed that the H 2S adsorbs on the CoO x Si surface, possibly by physisorption as no H 2S sorption was observed during post-testing analysis with XPS. A CoO x Si membrane was exposed to varied dosings of H 2S in He over a period of 160 h at 200 °C, including an additional testing with 3.2 vol% H 2O vapour. It was observed that exposure to H 2S resulted in a temporary reduction in single gas permeation with the largest effect occurring with the highest concentration of H 2S. These results are attributed to physisorbed H 2S on the CoO x Si surface, thus slightly impeding the diffusion of He. H 2O exposure and H 2S + H 2O exposure showed similar reversible effects to that of H 2S individually, leading to the conclusion that there was no significant interaction between H 2S, H 2O and the CoO x Si surface. Although H 2S permeation was initially measured through the membrane, this quickly became undetectable for the remainder of the experiment. As a result, the CoO x Si membrane concentrated H 2S to 70 ppm in the retentate stream from a maximum feed H 2S 50 ppm concentration.

Determination of trace sulfate ion in liposome doxorubicin with capillary electrophoresis

A capillary electrophoretic method for the determination of the trace sulfate ion in liposome doxorubicin has been developed with potassium nitrate as the background electrolyte. The components and pH of the buffer solution, the concentration of electroosmotic flow modifier and the separation voltage on the separation were studied in detail. The optimized electrophoretic conditions were as follows: capillary column diameter 50 microm, total length 60 cm and effective length 51.5 cm, 20 mmol/L potassium nitrate buffer solution (pH 7.0) containing 0.4 mmol/L cetyltrimethylammonium chloride (CTAC) as the electroosmotic flow modifier, an applied voltage of -15 kV (reversed polarity) and a detection wavelength of 202 nm. Under the optimized capillary electrophoresis separation conditions, sulfate ion and chloride ion in the liposome doxorubicin breaking emulsion were separated successfully within 3 min, and the relative standard deviations of migration time and peak area of sulfate ion were less than 0.01% and 1.0% respectively. The detection limit was 5 microg/L. This method has been proved to be simple, sensitive and accurate, and also has been applied to determine sulfate ion in liposome doxorubicin sample with satisfactory results.

Capture of Trace Sulfur Gases from Binary Mixtures by Single-Walled Carbon Nanotube Arrays: A Molecular Simulation Study

Adsorption of H(2)S and SO(2) pure gases and their selective capture from the H(2)S-CH(4), H(2)S-CO(2), SO(2)-N(2), and SO(2)-CO(2) binary mixtures by the single-walled carbon nanotubes (SWNT) are investigated via using the grand canonical Monte Carlo (GCMC) method. It is found that the (20, 20) SWNT with larger diameter shows larger capacity for H(2)S and SO(2) pure gases at T = 303 K, in which the uptakes reach 16.31 and 16.03 mmol/g, respectively. However, the (6,6) SWNT with small diameter exhibits the largest selectivity for binary mixtures containing trace sulfur gases at T = 303 K and P = 100 kPa. By investigating the effect of pore size on the separation of gas mixtures, we found that the optimized pore size is 0.81 nm for separation of H(2)S-CH(4), H(2)S-CO(2), and SO(2)-N(2) binary mixtures, while it is 1.09 nm for the SO(2)-CO(2) mixture. The effects of concentration and temperature on the selectivity of sulfide are also studied at the optimal pore size. It is found that the concentration (ppm) of sulfur components has little effect on selectivity of SWNTs for these binary mixtures. However, the selectivity decreases obviously with the increase of temperature. To improve the adsorption capacities, we further modify the surface of SWNTs with the functional groups. The selectivities of H(2)S-CO(2) and SO(2)-CO(2) mixtures are basically uninfluenced by the site density, while the increase of site density can improve the selectivity of H(2)S-CH(4) mixture doubly. It is expected that this work could provide useful information for sulfur gas capture.

Analytical Constraints on the Measurement of the Sulfur Isotopic Composition and Concentration of Trace Sulfate in Phosphorites: Implications for Sulfur Isotope Studies of Carbonate and Phosphate Rocks

The aim of this study was to evaluate the existing methods for extracting trace sulfate from francolite and measuring its concentration and sulfur isotope composition. Phosphatic rocks were chemically and thermally treated to remove non-structural SO(4)2- in francolite, which would otherwise be inadvertently included in geochemical analyses of the structurally-bound sulfate. Acetic acid (10% v/v) proved to be effective in removing calcite, dolomite and ankerite without affecting francolite. To remove all 'easily' soluble sulfates, such as Ca-sulfates and adsorbed sulfate, rinsing with 10% v/v NaCl had to be repeated several times for most samples. For subsequent S isotope determination sample combustion at 600 degrees C was found to be an efficient way to remove non-francolite S-bearing phases. From a number of SO(4)2- detection methods tested, ICP-AES proved to be the most accurate. For francolite-sulfate recovery, our recommended protocol involved repeated rinsing of powdered phosphorites with 10% NaCl as well as NaOCl, and testing of the filtrate for SO(4)2- in each wash. If only S isotope compositions are needed, combustion at 600 degrees C with a subsequent de-ionised water rinse could be undertaken instead of repeated NaOCl rinsing for studies of both francolite and carbonate. Re-analysis of previously published data, using the new protocol, provided evidence that the use of this protocol considerably improves data quality.

Hydrometallurgical processing of a Nigerian sphalerite in hydrochloric acid: Characterization and dissolution kinetics

This study is concerned with the physio-chemical characterization and investigation of the dissolution kinetics of a Nigerian sphalerite in hydrochloric acid (HCl). The effects of HCl concentration, temperature, particle diameter, stirring speed, solid/liquid ratio on the leaching of sphalerite were investigated. The XRF analysis showed that the sphalerite mineral consists of zinc and sulphur as major elements with Fe, Sn, Ag, K, Sb, Ca and Pb occurring as minor or trace elements. The XRD examination confirmed the originality of the sphalerite sample and it revealed the presence of associated minerals such as ilmenite (FeTiO 3), pyrite (FeS 2), siderite (FeCO 3), α-quartz and cassiterite (SnO 2). Optical microscopic examination also supported the above. The leaching experiments showed that sphalerite dissolution in HCl increases with acid concentration and temperature, but decreases with particle diameter and solid/liquid ratio. In HCl 4 M and at 80 °C, about 91.80% of sphalerite was dissolved within 120 min using − 112 + 63 μm particle diameter and solid/liquid ratio of 10 g/L. The activation energy calculated from the experimental data was 39.09 kJ/mol, while the reaction order, Arrhenius constant and reaction constant of 0.24, 13.46 s − 1 and 2.21 ± 0.4 × 10 3 were computed for the process respectively. Kinetic data analysis indicated that the rate determining step for the dissolution process followed a surface chemical reaction and the reaction data fitted shrinking core model for spherical particles. Finally, the XRD analysis of the post-leaching residue provided evidence for the presence of silica and traces of sulphur in the residual solid.

Rebekah's 5p: A Case Study from Surface Analytics

Correspondence: m.petty@LSALtd.co.uk http://www.lsaltd.co.uk One day recently, one of my daughters, Rebekah, who was fi ve at the time, came to tell me that she had swallowed a fi ve-pence piece. I was not too concerned by this news. The fi ve-pence piece was quite small in comparison to Rebekah and I knew that both would part company within a day or two. However, I am a Yorkshire man. I was troubled by the potential loss of fi ve pence. So, with the aid of my son’s metal detector, we followed the progress of the fi ve pence through Rebekah. Our divinings indicated that the coin would reappear after about a day and a half. Sure enough, the coin emerged as predicted and was unscathed except for the fact that it had now changed colour. Rebekah’s fi ve-pence piece had turned a very deep and vivid blue. Intrigued by this transformation, I and my colleagues at LSA decided to try to fi nd out what changes had occurred to the coin on its travels through Rebekah. We began by taking an Auger electron spectrum of the surface of blue stain. It came as no surprise to fi nd traces of sulphur, chlorine, calcium, nitrogen and sodium along with substantial amounts of carbon, oxygen and copper. Carbon, oxygen, sulphur and chlorine are often found on air-exposed surfaces, whilst the calcium and sodium may be a residue from the soap and water used to wash the coin (normally samples are analysed as received, but in this case. . .). Interestingly, we did not detect any nickel on the surface as you might expect on a cupronickel-plated coin. The next stage in our investigation was to see how these elements varied with depth. By following the signals from the elements as we etched into the coin with an argon ion beam, we produced a composition depth profi le through the blue stain on Her Majesty’s cheek (see Fig. 1). The chlorine, calcium, nitrogen and sodium were only present at the very surface. Much to our surprise, as we etched into the surface the sulphur signal rose dramatically. The blue stain was composed of three distinct layers on top of the cupronickel plating. The outer two layers were chiefl y copper and sulphur, whilst the inner layer contained nickel and sulphur. In contrast, a control fi ve-pence piece from “petty” cash gave the composition depth profi le in Fig. 2. In this case, only a thin surface oxide was present. So, we can conclude that the anaerobic environment within Rebekah’s gut has produced a relatively thick sulphide multilayer on the surface of the coin. No children or animals were harmed in the performance of this experiment. But do not try this at home! Surface Analytics is Loughborough Surface Analysis Ltd (www.lsaltd.co.uk) and Midlands Surface Analysis (www. midsurfanalysis.co.uk) working in strategic alliance. We provide a surface chemical analysis and depth profi ling service. Areas of application include,

The impact of sulfur on the performance of a solid oxide fuel cell (SOFC) system operated with hydrocarboneous fuel gas

The impact of thiophene in the fuel gas of a commercial solid oxide fuel cell (SOFC) system is investigated for concentrations up to 400 ppmV. Based on the measured voltage–current curves, an empiric correlation for the estimation of the expectable power output of the investigated SOFC system when operated with sulfur containing fuel gases is derived. An interrelation between the open circuit voltage (OCV) and the sulfur concentration of the investigated hydrocarboneous fuel gas is presented and discussed based on corresponding model simulations. The reduction of the steam reforming (STR) activity of the anode cermet material and of the catalytic partial oxidation catalyst used for the fuel gas processing in the investigated SOFC system are found important factors regarding the power output reduction induced by sulfur traces in the fuel gas of SOFCs.

Sulfur trace determination in petroleum products by isotope dilution ICP-MS using direct injection by thermal vaporization (TV-ICP-IDMS)

An accurate, sensitive, and fast method for direct determination of total sulfur in petroleum products after thermal vaporization of an isotope-diluted sample was developed by using ICP-MS. (34)S-labelled dibenzothiophene spike was used for the isotope dilution step. The isotope-diluted sample was injected into a thermal vaporizer which was directly connected by a heated transfer line to the plasma torch. Sample transport was achieved by using a helium gas flow, and the isotope ratio (34)S/(32)S was determined within seconds after injection. No other sample preparation other than the simple and fast isotope dilution step, which enables accurate and sensitive determination of sulfur at high sample throughputs, is necessary. Thus, this technique fits all needs for routine analyses. Validation of the TV-ICP-IDMS method was carried out by analyzing the certified gas oil reference materials BCR672 and BCR107. Comparison of results for noncertified low- and high-boiling samples, obtained from an ICP-IDMS microwave-assisted digestion method, also resulted in very good agreement. The low detection limit of 40 ng/g and the large dynamic range of TV-ICP-IDMS fulfill all necessities to allow analysis of sulfur in different petroleum products, e.g., even at the low concentration level of 'sulfur-free' gasoline.

A global sensitivity study of sulfur chemistry in a premixed methane flame model using HDMR

AbstractThe use of complex mechanisms is increasing within models describing a range of important chemical processes, including combustion. Parameters describing chemical reaction rates and thermodynamics can often be very uncertain. Highlighting the main parameters contributing to predictive uncertainty is an important part of model development. However, due to the computational cost of the models and their nonlinearity, traditional methods for sensitivity analysis are often not suitable. The high‐dimensional model representation (HDMR) method was developed to express the input–output relationship of a complex model with a high‐dimensional input space. A fully functional surrogate model can be constructed with low computational effort. First‐ and second‐order sensitivity indices can then be calculated in an automatic way, over large input parameter ranges. These provide an importance ranking for the input parameters. An extension to the existing set of HDMR tools is developed in this work, where the number of HMDR component functions can be reduced to explore large dimensional input spaces very efficiently. The HDMR tools are demonstrated for a case study of a one‐dimensional low‐pressure premixed methane flame model doped with trace sulfur and nitrogen species. Uncertainties in rate constants and thermodynamic data are considered, leading to a study of 176 input parameters. Using the new HDMR tools, the use of screening methods such as the Morris method, which aim to identify unimportant parameters beforehand, can generally be avoided. However, in certain cases, a combination of a screening method and HDMR is computationally more efficient than using HDMR alone. The final ranking of important parameters is shown to be critically dependent on the uncertainty ranges chosen due to the nonlinearity of the model. The study demonstrates that the proposed HDMR method provides a powerful tool for general application to global sensitivity analysis of complex chemical mechanisms. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 742–753, 2008

Molecular speciation of sulfur in solid oxide fuel cell anodes with X-ray absorption spectroscopy

Two sets of solid oxide fuel cell (SOFC) electrode assemblies from different manufacturers were run under different operating conditions with different sulfur exposure, and then subjected to X-ray absorption spectroscopy (XAS) at the sulfur K (1s) edge. Within the detection limits of the spectrometer, pristine fuel electrodes (anodes) show no traces of sulfur. The anodes operated with sulfur-containing natural gas and H 2S doped natural gas show spectra rich in sulfur structures. Two other electrodes run with sulfur-containing natural gas, one with a sulfur filter and the other without, show an XAS spectrum with a very broad peak, covering the entire sulfur absorption range, and thus not allowing for identification of specific sulfur signatures. These appear to be the first ever reported sulfur XAS data on SOFC anodes, and the XAS technique shows promise to resolve some hitherto unsolved issues on sulfur poisoning of SOFC, particularly regarding the molecular speciation of the sulfur components.