Sulfur Evolution Research Articles

Thermodynamic and Kinetic Analysis of Ca-Based Oxygen Carrier in Chemical-Looping Combustion

Chemical-looping combustion (CLC) is a promising technology to capture carbon dioxide (CO2) inherently and conveniently without the additional apparatus. At present, for some metal oxide oxygen carriers, the high costs and the positive hazards to the environment inhibit the developing of CLC systems. The feasibility of using CaSO4 oxygen carrier in the CLC system is studied in this paper. Through the thermodynamic analysis, the carbon deposition and the sulfur evolution are studied in the reaction between CaSO4 and a typical syngas. In addition, providing that hydrogen (H2) is fed as the gaseous fuel in the CLC system, the kinetic analysis is investigated on the reduction of CaSO4 by H2 and the oxidation of calcium sulfide (CaS) by oxygen (O2) through the thermo-gravimetric apparatus (TGA). The kinetic models are built on the reduction and the oxidation of the oxygen carrier. The results calculated from the models agree well with the experimental data. Finally, the possible reaction mechanisms for the reduction and the oxidation are explored.

SULFUR ABUNDANCES IN THE ORION ASSOCIATION B STARS

Sulfur abundances are derived for a sample of ten B main-sequence star members of the Orion association. The analysis is based on LTE plane-parallel model atmospheres and non-LTE line formation theory by means of a self-consistent spectrum synthesis analysis of lines from two ionization states of sulfur, SII and SIII. The observations are high-resolution spectra obtained with the ARCES spectrograph at the Apache Point Observatory. The abundance distribution obtained for the Orion targets is homogeneous within the expected errors in the analysis: A(S)=7.15+/-0.05. This average abundance result is in agreement with the recommended solar value (both from modelling of the photospheres in 1-D and 3-D, and meteorites) and indicates that little, if any, chemical evolution of sulfur has taken place in the last ~4.5 billion years. The sulfur abundances of the young stars in Orion are found to agree well with results for the Orion nebulae, and place strong constraints on the amount of sulfur depletion onto grains as being very modest or nonexistent. The sulfur abundances for Orion are consistent with other measurements at a similar galactocentric radius: combined with previous results for other OB-type stars produce a relatively shallow sulfur abundance gradient with a slope of -0.037+/-0.012 dex/kpc.

Sulfur evolution from coal combustion in O 2/CO 2 mixture

O 2/CO 2 coal combustion technology is considered as one of the most promising technologies for CO 2 sequestration due to its economical advantages and technical feasibility. It is significant to study the sulfur transfer behavior of coal in O 2/CO 2 atmosphere for organizing combustion properly and controlling SO 2 emission effectively. To clarify the effect of atmosphere on the sulfur transfer behavior, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) system was employed to study the formation behavior of sulfur-containing gas species from Xuzhou bituminous coal pyrolysis in CO 2 atmosphere compared with that in N 2 atmosphere. Also the SO 2 formation behaviors during Xuzhou bituminous coal combustion in O 2/N 2 and O 2/CO 2 atmospheres were investigated. Results show that COS is preferentially formed during the coal pyrolysis process in CO 2 atmosphere rather than in N 2 atmosphere. When temperature is above 1000 K, sulfate in the CO 2 atmosphere begins to decompose due to the reduction effect of CO, which comes from the CO 2 gasification. During coal combustion process, replacing N 2 with CO 2 enhances the SO 2 releasing rate. SO 2 emission increases first and then decreases as O 2 fraction increases in the O 2/CO 2 mixture. XPS result of the ash after combustion indicates that higher O 2 concentration elevates the sulfur retention ability of the mineral matter in the coal.

Investigation of sulfur forms and transformation during the co-combustion of sewage sludge and coal using X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to investigate the characteristics and evolution of sulfur (S) in mixtures of bituminous coal and sewage sludge (SS) and their chars during isothermal combustion. Five groups of mixtures with SS content of 0%, 10%, 20%, 30% and 100%, were examined at different burn-off ratios ( β) of 0, 30%, 50%, 70% and 100%. The S in the coal mainly exist as the forms of mercaptan (S1), sulfide (S2), thiophene (S3), sulfoxide (S4), sulfone (S5) and sulfate (S6). During the coal combustion process, the content of S1 and S2 decreased, while that of S3 and S5 increased in the early stage and decreased in the late stage. The S4 content increased throughout the entire process of combustion. Small amount of S6 was detected, showing a fluctuated pattern. The trend of S1, S2, S5 and S6 in SS was alike with that in coal, whereas S4 decreased at the end of combustion. The changing process of S3 in SS was opposite to that of coal, while the composition of S in the mixtures resulted from the mixing of coal and SS. The transformation of each functional group during co-combustion were correlated with their transformation characteristics during the mono-combustion of coal and SS, and no obvious interaction was observed, which demonstrated that the coal-origin and SS-origin sulfur in mixtures kept their own characteristics in the combustion. SS may accumulate on the solid surface as α increase, resulting its significant influence on the evolution of each form of S. When α was low, most of the S-contained functional groups presented the characteristics of coal. The percentage of coal-origin functional groups declined as α increased. The transforming trends of most functional groups were similar with that of SS when α reached 30%.

Effect of Ceria on the Sulfation and Desulfation Characteristics of a Model Lean NO x Trap Catalyst

The effect of ceria addition on the sulfation and desulfation characteristics of a model Ba-based lean NO x trap (LNT) catalyst was studied. According to DRIFTS and NO x storage capacity measurements, ceria is able to store sulfur during catalyst exposure to SO2, thereby helping to limit sulfation of the main (Ba) NO x storage phase and maintain NO x storage capacity. Temperature programmed desulfation experiments revealed that desulfation of a model ceria-containing catalyst occurred in two stages, corresponding to sulfur elimination from the ceria phase at ~450 °C, followed by sulfur loss from the Ba phase at ~650 °C. Significantly, the ceria-containing catalyst displayed relatively lower sulfur evolution from the Ba phase than its non-ceria analog, confirming that the presence of ceria lessened the degree of sulfur accumulation on the Ba phase.

Oxidation of heavy nonferrous metal and iron sulfides via a chain mechanism

Gaseous sulfur monoxide (SO) is experimentally found to be a primary intermediate product in the oxidation of nonferrous metal and iron monosulfides. This finding is used to develop a theory for the chain oxidation of metal sulfides to form oxysulfide complexes MSO x and gaseous SO. The main steps of the metal sulfide oxidation via a chain mechanism are thermodynamically characterized. The Gibbs energies of the oxidation reactions are shown to decrease in the absolute value relative to the type of sulfide as follows: FeS, Ni3S2, CoS, NiS, ZnS, PbS, CdS, CuS, and Cu2S. The thermodynamic probability of all steps of the chain oxidation of the monosulfides with the evolution of gaseous atomic oxygen and sulfur is estimated.

High-performance liquid chromatography coupled to ultraviolet diode array detection and electrospray ionization mass spectrometry for the analysis of intermediates produced in the initial steps of the photocatalytic degradation of sulfonated azo dyes

High-performance liquid chromatography coupled to ultraviolet diode array detection and electrospray ionization mass spectrometry was applied to monitor the photocatalytic degradation mediated by TiO 2 of three sulfonated monoazo dyes (Orange I, Orange II, and Ethylorange) present in aqueous solution. Photobleaching, organic carbon, nitrogen and sulfur evolution were also followed during the process. Delayed carbon mineralization was observed with respect to both dyes disappearance and photobleaching, due to the formation of transient intermediate compounds which were in turn completely degraded. Among the intermediates produced during the initial degradation steps the formation of several hydroxylated derivatives, mostly coloured, was evidenced. The MS 2 spectra allowed one to formulate hypothesis about the OH attack positions; a peculiar reactivity of the azo moiety was shown by Orange I and Orange II.

A study on the thermal decomposition of coal-derived pyrite

The thermal behavior of coal-derived pyrite as well as ferrous sulfide compound during heat treatments was investigated by temperature-programmed decomposition–mass spectrometer analysis (TPD–MS) and X-ray diffraction (XRD) measurements. An influence of atmosphere on pyrite and FeS decomposition and the interaction between pyrite and a coal-like environment were examined. The results showed that pyrite decomposition under inert atmosphere occurred in steps and the different transition states with Fe/S value were formed during heat treatments. The final solid state under helium contained only Fe (1− x) S phase. The presence of carbon support and hydrogen could promote pyrite transfer and change the sulfur evolution behavior during decomposition process. However, hydrogen was the principal factor which could determine the presence of iron phase in the final products.

Thermodynamic Investigation of Carbon Deposition and Sulfur Evolution in Chemical Looping Combustion with Syngas

Chemical looping combustion (CLC) with syngas, a synthesized gas mixture of CO, H2, CO2, H2O(g), N2, and H2S, was investigated using thermodynamic simulation, with focus on carbon deposition and sulfur evolution in CLC. Five metal oxides, such as NiO, CuO, Fe2O3, Mn3O4, and CoO, were selected as oxygen carriers for CLC application. Different influencing factors on the formation of carbon deposits were investigated, including pressure, fuel reactor (FR) temperature, oxygen excess number Φ (denoting the availability of lattice oxygen in the oxygen carrier to the fuel), and fuel gas composition. Higher temperature and larger oxygen excess number Φ inhibited the formation of carbon deposits while the pressurized condition caused the opposite. The increase of H2O(g) and CO2 fraction in syngas reduced carbon deposition while, in contrast, a larger H2S occurrence in syngas led to more carbon deposits to be formed. A sensitivity analysis to the different factors revealed that carbon deposition was mainly determin...

ABUNDANCE PATTERN OF METAL-RICH STARS FROM 14 OLD AND 24 YOUNG STARS

The metallicities and abundance ratios, [X/Fe], of 12 elements—C, Na, Mg, Si, S, Ca, Ti, Cr, Ni, Y, Zr, and Ce—are determined for 14 old and 24 young metal-rich stars based on high resolution, high S/N spectra obtained with the HIDES spectrograph attached to the 1.88 m telescope of Okayama Astrophysical Observatory (Okayama, Japan). The results show that there is no any significant difference in the [X/Fe] versus [Fe/H] trend for these elements between the two groups of stars. This is consistent with the kinematics of the two groups of stars being similar to that of the thin disk. In connection with the abundance analysis, we found that iron abundances from Fe II lines are generally higher than those from Fe I lines for cool metal-rich stars. In particular, the [S/Fe] ratio strongly depends on stellar temperature. In view of this, the chemical evolution of the element sulfur can only be traced by selecting solar-type stars within a critically narrow temperature range. Inspecting a large sample of metal-rich stars, we found that young metal-rich stars generally have kinematics similar to that of the local thin disk, while old metal-rich stars show two different kinematic distributions, one with V LSR ~ −10kms−1 and the other with V LSR ~ −50kms−1. Abundances of this new population of old metal-rich stars with a slight lag in the Galactic rotation have already been investigated by the present authors. We compared the abundance patterns for the three groups of metal-rich stars, and did not find any significant difference in abundance ratios for the elements investigated. These results indicate an inhomogeneous metallicity enhancement but similar nucleosynthesis history for the Galactic evolution of the thin disk from the beginning to the present.

Sulphur abundances from the S i near-infrared triplet at 1045 nm

Context. Unlike silicon and calcium, sulphur is an -element which does not form dust. Some of the available observations of the evolution of sulphur with metallicity indicate an increased scatter of sulphur to iron ratios at low metallicities or even a bimodal distribution, with some stars showing constant S/Fe at all metallicities and others showing an increasing S/Fe ratio with decreasing metallicity. In metal-poor stars S i lines of Multiplet 1 at 920 nm are not yet too weak to permit to measure the sulfur abundance A(S), however in ground-based observations they are severely a ected by telluric lines. Aims. We investigate the possibility to measure sulphur abundances from S i Mult. 3 at 1045 nm lines, which lie in the near infra-red. These are slightly weaker than those of Mult. 1, but lie in a range not a ected by telluric lines. Methods. We investigate the lines of Mult. 3 in the Sun (G2V), Procyon (F5V), HD 33256 (F5V), HD 25069 (G9V) and Eri (HD 22049, K2V). For the Sun and Procyon the analysis has been performed with CO 5 BOLD 3D hydrodynamical model atmospheres, for the other three stars, for which hydrodynamical simulations are not available, the analysis has been performed using 1D model atmospheres. Results. For our sample of stars we find a global agreement of A(S) from lines of di erent multiplets. Conclusions. Our results suggest that the infrared lines of Mult. 3 are a viable indicator of the sulphur abundance which, because of the intrinsic strength of this multiplet, should be suitable to study the trend of [S/Fe] at low metallicities.

Sulphur abundances in disk stars as determined from the forbidden λ10821 [S I] line

Aims: In this paper we aim to study the chemical evolution of sulphur in the galactic disk, using a new optimal abundance indicator: the [SI] line at 10821 A. Similar to the optimal oxygen indicators, the [OI] lines, the [SI] line has the virtues of being less sensitive to the assumed temperatures of the stars investigated and of likely being less prone to non-LTE effects than other tracers. Methods: High-resolution, near-infrared spectra of the [SI] line are recorded using the Phoenix spectrometer on the Gemini South telescope. The analysis is based on 1D, LTE model atmospheres using a homogeneous set of stellar parameters. Results: The 10821 A [SI] line is suitable for an abundance analysis of disk stars, and the sulphur abundances derived from it are consistent with abundances derived from other tracers. We corroborate that, for disk stars, the trend of sulphur-to-iron ratios with metallicity is similar to that found for other alpha elements, supporting the idea of a common nucleosynthetic origin.

The sources and evolution of sulfur in the hypersaline Lake Lisan (paleo-Dead Sea)

δ 34S values in gypsum are used to evaluate the fate of sulfur in the hypersaline Lake Lisan, the late Pleistocene precursor of the Dead Sea (70–14 ka BP), and applied as a paleo-limnological tracer. The Ca-chloride Lake Lisan evolved through meromictic periods characterized by precipitation of authigenic aragonite and holomictic episodes characterized by enhanced gypsum precipitation. The lake deposited two major gypsum units: the “Lower Gypsum unit” (deposited at ∼56 ka) showing δ 34S values of 18–20‰, and the “Upper Gypsum unit” (deposited at 17 ka) displaying significantly higher δ 34S values of 26–28‰. Laminated and disseminated gypsum, residing within the aragonite, exhibit δ 34S values in the range of − 26‰ to 1‰. The isotopic composition of the gypsum was dictated by freshwater sulfate input that replenished the upper layer of the lake (the mixolimnion), bacterial sulfate reduction (BSR) that occurred under the anoxic conditions of the lower brine (the monimolimnion), and mixing between these two layers. During meromictic periods, the sulfate reservoir in the lower brine was replenished by precipitation of gypsum from the upper layer, and its subsequent dissolution due to sulfate deficiency induced by BSR activity. This process describes a “sulfur pump” mechanism and its effect on δ 34S in the water can be modeled by a modified Rayleigh distillation equation. Steady state δ 34S values (∼40‰) were reached in the lower brine after long meromictic periods. Following overturn episodes, induced by diminishing freshwater input and lake level decline, large quantities of δ 34S enriched gypsum precipitated. The negative δ 34S values in laminated and disseminated gypsum provide evidence for BSR activity in the lower brine that removed isotopically depleted sulfides from the water column, causing significant isotopic enrichment of remaining sulfate. Following the lake desiccation, the sediments were exposed and the latter sulfides oxidized and re-crystallized as gypsum.

On the Galactic chemical evolution of sulfur

Department of Astronomy, University of Texas, Austin, TX 78712-1083, USAe-mail: ryde@astro.uu.seReceived ; acceptedAbstract. Sulfur abundances have been determined for ten stars to resolve a debate in the literature on theGalactic chemical evolution of sulfur in the halo phase of the Milky Way. Our analysis is based on observationsof the Si lines at 9212.9, 9228.1, and 9237.5 ˚A for stars for which the S abundance was obtained previously frommuch weaker Si lines at 8694.0 and 8694.6 ˚A. In contrast to the previous results showing [S/Fe] to rise steadilywith decreasing [Fe/H], our results show that [S/Fe] is approximately constant for metal-poor stars ([Fe/H]<∼−1)at [S/Fe] ≃ +0.3. Thus, sulfur behaves in a similar way to the other α elements, with an approximately constant[S/Fe] for metallicities lower than [Fe/H] ≃ −1. We suggest that the reason for the earlier claims of a rise of [S/Fe]is partly due to the use of the weak Si 8694.0 and 8694.6˚A lines and partly uncertainties in the determinationof the metallicity when using Fei lines. The Si 9212.9, 9228.1, and 9237.5˚A lines are preferred for an abundanceanalysis of sulfur for metal-poor stars.

Sulphur-bearing species as chemical clocks for low mass protostars?

We present observations of H2S, SO and SO2 towards a sample of Class 0 and Class I sources. The H2S abundances rule out its formation in the gas phase and we assume that it is released from grain mantles. Applying a model of the evolution of the sulphur chemistry first used in the study of hot cores, we show that this model can reproduce the results of our observations even for the relatively low temperatures and densities of these sources. We demonstrate that the chemical evolution of sulphur bearing species is a potentially valuable probe of chemical timescales in low mass star forming regions. Overall, the model indicates that Class I sources are at a later chemical evolutionary stage than their Class 0 counterparts, with an average dierence in chemical age of at least 3 10 3 years and an upper limit on the age of the Class I sources of a few times 10 5 years.

Simultaneous organic nitrogen and sulfate removal in an anaerobic GAC fluidised bed reactor

A granular activated carbon (GAC) anaerobic fluidised bed reactor treating vinasse from an ethanol distillery of sugar beet molasses was operated for 250 days under three different organic loading rates. The reactor showed good performance in terms of organic matter removal and methane production but an anomalous behaviour in terms of unusual high concentrations of molecular nitrogen and low concentration of hydrogen sulphide in the biogas. The analysis of the different nitrogenous and sulphur compounds and the mass balances of these species in the liquid and gas phases clearly indicated an uncommon evolution of nitrogen and sulphur in the reactor. Up to 55% of the TKN and up to 80% of the sulphur disappear in the liquid phase. This is the opposite to any previously reported results in the bibliography. The new postulated anaerobic process of ammonia and sulphate removal seems to follow the mechanism: SO4 = +2 NH4+-->S + N2 + 4H2O (delta G degree = -47.8 kJ/mol).

Cross-sectional transmission electron microscopy investigation of the dead layer of ZnS:Ag,Al phosphors in field emission displays

The dead surface layer of blue-emitting ZnS:Ag,Al phosphor with Al metallized thin film in high-voltage field emission displays (FEDs) has been investigated by means of cross-sectional transmission electron microscopy. From these observations, it was found that electron irradiation at 6 keV excitation causes the decomposition of ZnS and the subsequent evolution of sulfur in the topmost surface layer ∼30 nm, and also causes the formation of lattice defects within the electron penetration depth of ∼300 nm in a life-end stage. When this evidence was taken into account, it was estimated that the decomposition rate of ZnS and the formation rate of lattice defects depend mainly on the degree of crystallinity and the atomic-scale surface roughness of ZnS phosphor particles. Necessary characteristics of ZnS:Ag,Al phosphors for longer luminescence lifetime in FEDs were suggested in this work.

New process for simultaneous removal of nitrogen and sulphur under anaerobic conditions

A granular activated carbon (GAC) anaerobic fluidised-bed reactor treating vinasse from an ethanol distillery of sugar beet molasses was operated for 90 days, the first 40 days of start-up followed by 50 days of operation at constant organic loading rate of 1.7 g COD/Ld . The reactor showed good performance in terms of organic matter removal but an anomalous behaviour in terms of unusual high concentrations of molecular nitrogen in the biogas. The analysis of the different nitrogenous and sulphur compounds and the mass balances of these compounds in the liquid and gas phases clearly indicated an uncommon evolution of nitrogen and sulphur in the reactor. About 50% of the nitrogen entering the reactor as total Kjeldahl nitrogen (TKN) was removed from the liquid phase appearing as N 2 in the gas phase. Simultaneously, only 20% of the S–SO 4 2− initially present in the influent appears as S–S 2−in the effluent or S–H 2S in the biogas, indicating that 80% of the sulphur is removed. This behaviour has not been reported previously in the literature. These observations may suggest a new anaerobic removal process of ammonia and sulphate according to an uncommon mechanism involving simultaneous anaerobic ammonium oxidation and sulphate reduction.

Evolution of sulfur during pyrolysis of petroleum kerogens.

Sulphur K edge spectroscopy was used to differentiate types of sulphur present in petroleum asphaltenes and kerogens. A simplified model of the near edge structure enabled quantification of the different sulphur forms. The evolution of the sulphur edge following pyrolysis of kerogens confirms that thiophenic sulphur is more stable than organic sulphide forms. Pyrite retained in the kerogens may partially transform to iron sulphate during air storage. During pyrolysis FeS2 is regenerated and subsequently converted to FeS, contributing to the release of H2S. The results show that exchange between organic and mineral forms of sulphur is limited.

Can a relaxation technique be used to validate clouds and sulphur species in a GCM?

The Hamburg version of the European Centre for Medium-Range Weather Forecasting (ECMWF) general circulation model, ECHAM4, developed for climate studies, is used to study the hydrological cycle and the atmospheric sulphur cycle. A technique, the Newtonian relaxation, is introduced to compare results from the model with measurements of cloud parameters and sulphur species concentrations. The model is forced by ECMWF analyses to simulate September 1993, and results are compared to observations on different spatial and temporal scales: monthly mean horizontal satellite data, daily mean averages at European and Canadian stations and aircraft soundings over the north Atlantic off the Canadian coast. The model is able to reproduce monthly mean horizontal distributions of liquid water path and precipitation. Daily mean precipitation fluxes and the temporal evolution of gaseous and particulate sulphur also agree quite well with observations. Based on this comparison with observations the performance of two different cloud physics parametrizations is discussed. These experiments indicate that variables like relative humidity, cloud cover and precipitation are controlled by the large-scale dynamics, whereas the cloud water content depends on the parametrization of the cloud microphysics. Coupling of the model-calculated sulphate mixing ratios to the cloud microphysics improves the model's sulphate distribution but slightly worsens the agreement between calculated and observed precipitation.