Organic Sulfur Species Research Articles

Investigation on structural features of Shengli lignite through oxidation under mild conditions

Structural features of Shengli lignite (SL) were investigated through ruthenium ion-catalyzed oxidation and oxidations in aqueous hydrogen peroxide (AHPO) and sodium hypochlorite (ASHC) under mild conditions. The results suggest that SL is rich in condensed aromatic species and hydroxyl-, methoxy-, and/or methyl-substituted benzene rings, and –CH2CH2– is a dominant bridged linkage connecting aromatic rings in SL. Aliphatic linkages connecting three aromatic rings also exist in SL. Most of the organic matter in SL was converted into soluble fractions in either AHPO or ASHC. The products from SL oxidation in AHPO are rich in hydroxyl- and/or methoxyl-substituted benzoic acids, alkanoic acids (AAs), and long-chain alkanedioic acids (ADAs), whereas those from SL oxidation in ASHC are mainly composed of benzene carboxylic acids, chloro-substituted short-chain AAs and ADAs. The nitrogen- or sulfur-containing species produced from SL oxidation provide important information on structural features of organic nitrogen and sulfur species in SL.

Arsenic binding to organic and inorganic sulfur species during microbial sulfate reduction: a sediment flow-through reactor experiment

Environmental context The use of water contaminated with arsenic for drinking and irrigation is linked to water and food borne diseases throughout the world. Although reducing conditions in soils and sediments are generally viewed as enhancing arsenic mobility in subsurface environments, we show they can actually promote As sequestration in the presence of reduced sulfur species and labile organic matter. We propose that sulfurisation of organic matter and subsequent binding of As to thiol groups may offer an innovative pathway for As remediation. Abstract Flow-through reactors (FTRs) were used to assess the mobility of arsenic under sulfate reducing conditions in natural, undisturbed lake sediments. The sediment slices in the FTRs were supplied continuously with inflow solutions containing sulfate and soluble AsIII or AsV and, after 3 weeks, also lactate. The experiment ran for a total of 8 weeks. The dissolved iron concentration, pH, redox potential (Eh), as well as aqueous As and sulfur speciation were monitored in the outflow solutions. In FTRs containing surface sediment enriched in labile organic matter (OM), microbial sulfate reduction led to an accumulation of organically bound S, as evidenced by X-ray absorption spectroscopy. For these FTRs, the inflowing dissolved As concentration of 20μM was lowered by two orders of magnitude, producing outflow concentrations of 0.2μM monothioarsenate and 0.1μM arsenite. In FTRs containing sediment collected at greater depth, sulfide and zero-valent S precipitated as pyrite and elemental S, while steady-state outflow arsenite concentrations remained near 5μM. The observations thus suggest that As sequestration is enhanced when sediment OM buffers the free sulfide and zero-valent S concentrations. An updated conceptual model for the fate of As in the anoxic As–C–S–Fe system is presented based on the results of this study.

ChemInform Abstract: Nighttime Radical Observations and Chemistry

AbstractReview: 487 refs.

Nickel supported on zinc oxide nanowires as advanced hydrodesulfurization catalysts

A novel catalyst with deep hydrodesulfurization (HDS) capabilities was tested with the aim of producing ultra-low sulfur diesel oil. The catalyst consisted of a zinc oxide nanowire (ZnO NW)/alumina carrier impregnated with nickel (Ni) as the active phase. Based on the concept of reactive adsorption, it was hypothesized that enhanced metal–support interactions and short diffusion paths between Ni and ZnO NWs could lead to improved activity and sulfur uptake capacity. Long ZnO NWs (10–15μm) were produced in bulk quantities using an atmospheric plasma jet reactor. In situ heating studies of Ni impregnated ZnO NW samples revealed better Ni dispersion, greater Ni-support interaction, and smaller Ni particle sizes when compared to a support comprised spherical ZnO nanoparticles (NPs). The reactive adsorbent was tested for on-stream sulfur uptake with model diesel oil spiked with difficult-to-remove organic sulfur species. The data indicated high activity for deep de-sulfurization in the initial stages but the catalyst deactivated via coking after 16h. The coking appears to be due to cracking of aromatic species present in the model oil in the absence of adsorbed surface hydrogen. The initial activity of the catalyst with modest composition of nickel loading indicated the potential utility of the catalyst system involving ZnO NWs as support.

Nighttime radical observations and chemistry

The nitrate radical, NO(3), is photochemically unstable but is one of the most chemically important species in the nocturnal atmosphere. It is accompanied by the presence of dinitrogen pentoxide, N(2)O(5), with which it is in rapid thermal equilibrium at lower tropospheric temperatures. These two nitrogen oxides participate in numerous atmospheric chemical systems. NO(3) reactions with VOCs and organic sulphur species are important, or in some cases even dominant, oxidation pathways, impacting the budgets of these species and their degradation products. These oxidative reactions, together with the ozonolysis of alkenes, are also responsible for the nighttime production and cycling of OH and peroxy (HO(2) + RO(2)) radicals. In addition, reactions of NO(3) with biogenic hydrocarbons are particularly efficient and are responsible for the production of organic nitrates and secondary organic aerosol. Heterogeneous chemistry of N(2)O(5) is one of the major processes responsible for the atmospheric removal of nitrogen oxides as well as the cycling of halogen species though the production of nitryl chloride, ClNO(2). The chemistry of NO(3) and N(2)O(5) is also important to the regulation of both tropospheric and stratospheric ozone. Here we review the essential features of this atmospheric chemistry, along with field observations of NO(3), N(2)O(5), nighttime peroxy and OH radicals, and related compounds. This review builds on existing reviews of this chemistry, and encompasses field, laboratory and modelling work spanning more than three decades.

Taurine Biosynthesis by Neurons and Astrocytes

The physiological roles of taurine, a product of cysteine degradation and one of the most abundant amino acids in the body, remain elusive. Taurine deficiency leads to heart dysfunction, brain development abnormalities, retinal degradation, and other pathologies. The taurine synthetic pathway is proposed to be incomplete in astrocytes and neurons, and metabolic cooperation between these cell types is reportedly needed to complete the pathway. In this study, we analyzed taurine synthesis capability as reported by incorporation of radioactivity from [(35)S]cysteine into taurine, in primary murine astrocytes and neurons, and in several transformed cell lines (human (SH-SY5Y) and murine (N1E-115) neuroblastoma, human astrocytoma (U-87 MG and 1321 N1), and rat glioma (C6)). Extensive incorporation of radioactivity from [(35)S]cysteine into taurine was observed in rat glioma cells as well as in primary mouse astrocytes and neurons, establishing the presence of an intact taurine synthesis pathway in these cells. Interestingly, exposure of cells to cysteine or cysteamine resulted in elevated intracellular hypotaurine without a corresponding increase in taurine levels, suggesting that oxidation of hypotaurine limits taurine synthesis in cells. Consistent with its role as an organic osmolyte, taurine synthesis was stimulated under hypertonic conditions in neurons.

Sorbents for BioFueled SOFCs

Unlike internal combustion engines, fuel cells operate with very high efficiency even at small scale, offering significant benefits to distributed combined heat and power (CHP) systems utilizing bio-waste. However, effective utilization of biogas in a fuel cell requires removal of impurities such as sulfur and siloxanes. TDA Research Inc. (TDA) is developing a low-cost, high-capacity expendable sorbent that can remove both the <p>H2S and organic sulfur species in biogas to the ppb levels. This sorbent bed operates downstream of a bulk desulfurization system as a polishing bed to provide an essentially sulfur-free gas to the fuel cell. The sorbent can also be modified so that it can remove contaminants such as siloxanes in a single step. TDA is carrying out field demonstrations of our integrated gas clean-up units and biofueled SOFCs. The results from the sorbent development for biogas and field demonstrations will be presented in the meeting.

Modeling natural emissions in the Community Multiscale Air Quality (CMAQ) model – Part 2: Modifications for simulating natural emissions

Abstract. The Community Multiscale Air Quality (CMAQ) model version 4.6 has been revised with regard to the representation of chlorine (HCl, ClNO2) and sulfur (dimethylsulfide, or DMS, and H2S), and evaluated against observations and earlier published models. Chemistry parameterizations were based on published reaction kinetic data and a recently developed cloud chemistry model that includes heterogeneous reactions of organic sulfur compounds. Evaluation of the revised model was conducted using a recently enhanced data base of natural emissions that includes ocean and continental sources of DMS, H2S, chlorinated gases and lightning NOx for the continental United States and surrounding regions. Results using 2002 meteorology and emissions indicated that most simulated "natural" (plus background) chemical and aerosol species exhibit the expected seasonal variations at the surface. Ozone exhibits a winter and early spring maximum consistent with ozone data and an earlier published model. Ozone distributions reflect the influences of atmospheric dynamics and pollutant background levels imposed on the CMAQ simulation by boundary conditions derived from a global model. A series of model experiments reveals that the consideration of gas-phase organic sulfur chemistry leads to sulfate aerosol increases over most of the continental United States. Cloud chemistry parameterization changes result in widespread decreases in SO2 across the modeling domain and both increases and decreases in sulfate. Most cloud-mediated sulfate increases occurred mainly over the Pacific Ocean (up to about 0.1 μg m−3) but also over and downwind from the Gulf of Mexico (including parts of the eastern US). Geographic variations in simulated SO2 and sulfate are due to the link between DMS/H2S and their byproduct SO2, the heterogeneity of cloud cover and precipitation (precipitating clouds act as net sinks for SO2 and sulfate), and the persistence of cloud cover (the largest relative sulfate increases occurred over the persistently cloudy Gulf of Mexico and western Atlantic Ocean). Overall, the addition of organic sulfur chemistry increased hourly surface sulfate levels by up to 1–2 μg m−3 but reduced sulfate levels in the vicinity of high SO2 emissions (e.g., wildfires). Simulated surface levels of DMS compare reasonably well with observations in the marine boundary layer where DMS oxidation product levels are lower than observed. This implies either a low bias in model oxidation rates of organic sulfur species or a low bias in the boundary conditions for DMS oxidation products. This revised version of CMAQ provides a tool for realistically simulating the influence of natural emissions on air quality.

Distribution of iron and sulfur and their speciation in relation to degradation processes in wood from the Swedish warship Vasa

Wood samples from the Swedish warship Vasa were analysed by scanning electron microscopy and X-ray absorption spectroscopy with the focus on speciation and distribution of iron and sulfur compounds in the wood matrix. Both these elements were found at high concentration (10–100 mg g−1) in the surface region as a result of former accumulation of iron sulfides, elemental sulfur and reduced organic sulfur species (ROSS). Below the surface region, iron was the dominating element (1–10 mg g−1) present both as iron(II) and iron(III) compounds, which diffused into the wood matrix from corroding iron bolts and other iron items during the time in the sea (1628–1961). Electron microscopy results revealed that iron and sulfur are present in a variety of particles of different sizes and compositions in the surface region, in contrast to the interior where few particles were found. Here, the presence of iron compounds of nano-particle size inside the cell walls enables a close contact between the wood polymers and reactive oxygen species originating from reactions with iron compounds. The presence of ROSS seems to have played an important role as scavengers of reactive oxygen species. Samples with high iron : ROSS ratio displayed evident signs of degradation as indicated by depolymerisation of wood components accompanied by increased acidity due to low molecular organic acids. The observations strengthen the hypothesis of the pro-oxidative and antioxidant properties of iron and ROSS compounds, respectively, and that the chemical activities of these elements play crucial roles in the long term preservation of wooden maritime artefacts.

Phase Equilibria of Mixtures Containing Organic Sulfur Species (OSS) and Water/Hydrocarbons: VLE Measurements and Modeling Using the Cubic-Plus-Association Equation of State

We report new vapor−liquid equilibrium (VLE) data for dimethyl sulfide (DMS) in pure water, performed at three temperatures (303, 330, and 362 K) in the 1−8 MPa pressure range. The total system pressure was maintained introducing CH4. The inlet mole fraction of DMS was the same in all experiments, around 1.5 × 10−3 in the liquid phase. A “static-analytic” method was used for performing all of the measurements. The objective is to provide experimental VLE data for the dimethyl sulfide + CH4 + water system, for which no data are available in the open literature. These data will allow industry to model sulfur emissions. The new VLE data as well as the VLE data of some binary systems from the literature containing organic sulfur species + hydrocarbon, organic sulfur species + water, and some ternary systems containing organic sulfur species in hydrocarbons and water have been modeled successfully with the cubic-plus-association (CPA) equation of state. Useful remarks are presented about the application of Henry’s constant values to estimate binary interaction parameters of the CPA EoS for the description of whole vapor−liquid equilibria. The results using CPA EoS show that the cross association interactions in the methyl mercaptan + water system and ethyl mercaptan + water system should be considered. In aqueous mixtures of higher mercaptans, the consideration of such interactions does not improve the calculations, indicating that they are rather weak.

Direct Determination of Pyrite Content in Argonne Premium Coals by the Use of Sulfur X-ray Near Edge Absorption Spectroscopy (S-XANES)

Argonne premium coal samples are used by researchers worldwide as standards in coal research. The set consists of a suite of eight samples of varying rank from the United States. The sulfur X-ray near edge absorption spectroscopy (S-XANES) third-derivative analysis method uses a well-defined library of model compounds to curve fit each sample spectrum and enables sulfur speciation to within about 10 mol % for materials such as coals and kerogens. This direct, non-destructive characterization technique, used in conjunction with others, such as X-ray photoelectron spectroscopy, can provide valuable information about chemical and thermal sulfur transformations. The S-XANES third-derivative analysis method provides quantitative results for organic sulfur species in coal but has not been used to quantify inorganic sulfur forms to date. In general, the direct determination of the pyrite content, a metal sulfide, has been problematic. Through wet chemical methods, several of the Argonne premium coal samples are known to exceed 50 mol % pyrite but only show a weak pyrite feature in the S-XANES absorbance and third-derivative spectrum. We show that particle-size effects are responsible for attenuating the pyrite signal for high-pyrite-containing Argonne premium coals. Grinding techniques are discussed that decrease the particle size and produce spectra and results that are in better agreement with those from established wet chemical methods for pyrite determination.

Sulfur speciation in the upper Black Sea sediments

We report solid phase sulfur speciation of six cores from sediments underlying oxic, suboxic and anoxic-sulfidic waters of the Black Sea. Our dataset includes the five sulfur species [pyrite-sulfur, acid volatile sulfides (AVS), zerovalent sulfur (S(0)), organic polysulfides (RSx), humic sulfur] together with reactive iron and manganese, as quantified by dithionite extraction, and total organic carbon. Pyrite – sulfur was the major phase in all cores [200-400 µmol (g dry wt)- 1] except for the suboxic core. However, zerovalent sulfur and humic sulfur also reached very significant levels: up to about 109 and 80 µmol (g dry wt)- 1, respectively. Humic sulfur enrichment was observed in the surface fluff layers of the eastern central basin sediments where Unit-1 type depositional conditions prevail. Elemental sulfur accumulated as a result of porewater sulfide oxidation by reactive iron oxides in turbidities from the anoxic basin margin and western central basin sediments. The accumulation of elemental sulfur to a level close to that of pyrite-S in any part of central Black Sea sediments has never been reported before and our finding indicates deep basin turbidites prevent the build-up of dissolved sulfide in the sediment. This process also contributes to diagenetic pyrite formation whereas in the non-turbiditic parts of the deep basin water column formed (syngenetic) pyrite dominates the sulfur inventory. In slope sediments under suboxic waters, organic sulfur (humic sulfur + organic polysulfides) account for 33-42% of total solid phase S, indicating that the suboxic conditions favor organosulfur formation. Our study shows that the interactions between depositional patterns (Unit 1 vs. turbidite), redox state of overlying waters (oxic-suboxic-sulfidic) and organic matter content determine sulfur speciation and enable the accumulation of elemental sulfur and organic sulfur species close to a level of pyrite-S.

Unexpected extracellular and intracellular sulfur species during growth of Allochromatium vinosum with reduced sulfur compounds

Before its uptake and oxidation by purple sulfur bacteria, elemental sulfur probably first has to be mobilized. To obtain more insight into this mobilization process in the phototrophic purple sulfur bacterium Allochromatium vinosum, we used HPLC analysis and X-ray absorption near-edge structure (XANES) spectroscopy for the detection and identification of sulfur compounds in culture supernatants and bacterial cells. We intended to identify soluble sulfur compounds that specifically occur during growth on elemental sulfur, and therefore compared spectra of cultures grown on sulfur with those of cultures grown on sulfide or thiosulfate. While various unexpected oxidized organic sulfur species (sulfones, C-SO(2)-C, and sulfonates, C-SO(3)(-)) were observed via XANES spectroscopy in the supernatants, we obtained evidence for the presence of monosulfane sulfonic acids inside the bacterial cells by HPLC analysis. The concentrations of the latter compounds showed a tight correlation with the content of intracellular sulfur, reaching their maximum when sulfur began to be oxidized. None of the detected sulfur compounds appeared to be a specific soluble intermediate or product of elemental sulfur mobilization. It therefore seems unlikely that mobilization of elemental sulfur by purple sulfur bacteria involves excretion of soluble sulfur-containing substances that would be able to act on substrate distant from the cells.

Concentrations, sulfur isotopic compositions and origin of organosulfur compounds in pore waters of a highly polluted raised peatland

Sulfur cycling in peatlands plays a key role in their response to atmospheric deposition of acid sulfate; however, the role of dissolved organic sulfur species has received little attention. In this study, we assess the quantitative importance of dissolved organic sulfur species in a heavily polluted peatland and their role in sulfur cycling. Surface and pore waters from a raised peat bog have been analyzed for dissolved organic and inorganic species. Except in the surface water, organically bound sulfur dominates over sulfate sulfur and the organosulfur is predominantly in the humic fraction, which is not GC amenable. Two organosulfur compounds are present in the GC amenable fraction at all depths; a compound containing a benzene ring, sulfone and amide groups dominates while a compound closely similar to either benzothiazole or 1,2-benzisothiazole is present at 100–1000 times lower concentrations. Other organosulfur species were detected in some samples by GC–AED (gas chromatography–atomic emission detection) at similar or yet lower concentrations but not identifiable with GC–MS. In the shallowest parts of the peat, sulfur isotopic data on the humic and non-humic dissolved organic sulfur fractions show a pronounced difference, implying different sources for these organosulfur compounds. Humic organosulfur is 34S enriched, indicating a source for this component from breakdown of plant materials, which have similar δ34S (0.1‰ and 4.2‰). By contrast, the non-humic organosulfur is more 34S depleted at shallow depths (−11.7‰ in surface water), indicating an origin from reaction of bacterially produced sulfide (−9.9‰ in surface water) with dissolved organic material. Deeper in the peat the non-humic organosulfur becomes more 34S enriched (up to +6.8‰), which may result from either: (i) reactions between organic material and more 34S enriched sulfide; or (less likely) (ii) a shift to production of non-humic organosulfur by breakdown of humic compounds or plant material in the peat matrix.These data highlight the importance of organosulfur species relative to inorganic species in peatland groundwaters. Organosulfur species comprise the bulk of the dissolved sulfur budget and are involved in the bacterial cycling of sulfur in the peatland ecosystem.

Bmim]AlCl4 Ionic Liquid for Deep Desulfurization of Real Fuels

1-Butyl-3-methylimidazolium tetrachloroaluminate ionic liquid (IL) was synthesized and tested for its capability to extract organic sulfur species from real, refinery obtained hydrocarbon fuels. The fuels consisted of sulfur-rich gasoline and diesel as well as pretreated, partially desulfurized gasoline and diesel. The IL-extracted fuels were then analyzed for total sulfur, nitrogen, and chlorine. Total sulfur was significantly lowered in all tested fuels. Nitrogen levels were also significantly reduced mainly due to a pretreatment with molecular sieve. Only traces of chloride originating from the IL could be detected in three of the four samples after all extraction stages. Sulfur-speciation analyses revealed that some sulfur compounds in the feed were converted to new compounds.

Direct Characterization of Kerogen by X-ray and Solid-State 13C Nuclear Magnetic Resonance Methods

A combination of solid-state 13C NMR, X-ray photoelectron spectroscopy (XPS) and sulfur X-ray absorption near edge structure (S-XANES) techniques are used to characterize organic oxygen, nitrogen, and sulfur species and carbon chemical/structural features in kerogens. The kerogens studied represent a wide range of organic matter types and maturities. A van Krevelen plot based on elemental H/C data and XPS derived O/C data shows the well established pattern for type I, type II, and type III kerogens. The anticipated relationship between the Rock−Eval hydrogen index and H/C is independent of organic matter type. Carbon structural and lattice parameters are derived from solid-state 13C NMR analysis. As expected, the amount of aromatic carbon, measured by both 13C NMR and XPS, increases with decreasing H/C. The correlation between aromatic carbon and Rock−Eval Tmax, an indicator of maturity, is linear for types II and IIIC kerogens, but each organic matter type follows a different relationship. The average al...

The influence of oxidation with HNO3 on the surface composition of high-sulphur coals: XPS study

The study reported has been undertaken to characterise the changes taking place on the surface of the pyrite-free coal oxidised with nitric acid. The method applied for this purpose was XPS and the samples studied were high-sulphur brown coal Mequinenza from Spain and Labin from Croatia. It was found that the oxidative method of pyrite removal by using HNO3 enables to efficiently desulphurise coal surfaces. The changes on the coal surface as a result of the oxidation have been proved to depend on the individual characteristic of the coal studied. In general, the exposure to nitric acid leads to an increase in the content of oxidised organic sulphur species (sulphones and sulphoxides) on the coal surface. According to the susceptibility of a given coal surface to oxidation it is either enriched in the functional nitrogen groups as a result of HNO3 oxidation or the nitrogen species formed as a result of the oxidation are removed from the coal surface in gas form (NO or/and NO2).

Experiments on δ 34S mixing between organic and inorganic sulfur species during thermal maturation

Reduced sulfur species were studied to constrain isotopic exchange-mixing with synthetic polysulfide cross-linked macromolecules (PCLM), model sulfur containing molecules and natural sulfur-rich kerogen, asphalt and oil of the Dead Sea area. PCLM represents protokerogens that are rich in sulfur and thermally unstable. Mixing rates of PCLM with HS - (aq) (added as (NH 4) 2S (aq)) at low to moderate temperatures (50–200 °C) are rapid. Elemental sulfur and H 2S (gas) fully mix isotopes with PCLM during pyrolysis conditions at 200 °C. During these reactions significant structural changes of the PCLM occur to form polysulfide dimers, thiolanes and thiophenes. As pyrolysis temperatures or reaction times increase, the PCLM thermal products are transformed to more aromatic sulfur compounds. Isotopic mixing rates increase with increasing pyrolysis temperature and time. Polysulfide bonds (S–S) in the PCLM are responsible for most of these structural and isotopic changes because of their low stability. Conversely, sulfur isotope mixing does not occur between dibenzothiophene (aromatic S) or hexadecanthiol (C–SH) and HS - (aq) at 200 °C after 48 h. This shows that rates of sulfur isotope mixing are strongly dependent on the functionality of the sulfur in the organic matter. The order of isotopic mixing rates for organic matter is kerogen > asphalt > oil, which is inverse to their sulfur thermal stability. Asphalt and oil with more refractory sulfur show significantly lower isotopes mixing rates than the kerogen with more labile sulfur. Based on the findings of the present study we suggest that sulfur isotopes mixing can occur from early diagenesis into catagenesis and result in isotopic homogenization of the inorganic and organic reduced sulfur pools.

Stable sulfur isotope partitioning during simulated petroleum formation as determined by hydrous pyrolysis of Ghareb Limestone, Israel

Hydrous pyrolysis experiments at 200 to 365°C were carried out on a thermally immature organic-rich limestone containing Type-IIS kerogen from the Ghareb Limestone in North Negev, Israel. This work focuses on the thermal behavior of both organic and inorganic sulfur species and the partitioning of their stable sulfur isotopes among organic and inorganic phases generated during hydrous pyrolyses. Most of the sulfur in the rock (85%) is organic sulfur. The most dominant sulfur transformation is cleavage of organic-bound sulfur to form H 2S (gas). Up to 70% of this organic sulfur is released as H 2S (gas) that is isotopically lighter than the sulfur in the kerogen. Organic sulfur is enriched by up to 2‰ in 34S during thermal maturation compared with the initial δ 34S values. The δ 34S values of the three main organic fractions (kerogen, bitumen and expelled oil) are within 1‰ of one another. No thermochemical sulfate reduction or sulfate formation was observed during the experiments. The early released sulfur reacted with available iron to form secondary pyrite and is the most 34S depleted phase, which is 21‰ lighter than the bulk organic sulfur. The large isotopic fractionation for the early formed H 2S is a result of the system not being in equilibrium. As partial pressure of H 2S (gas) increases, retro reactions with the organic sulfur in the closed system may cause isotope exchange and isotopic homogenization. Part of the δ 34S-enriched secondary pyrite decomposes above 300°C resulting in a corresponding decrease in the δ 34S of the remaining pyrite. These results are relevant to interpreting thermal maturation processes and their effect on kerogen-oil-H 2S-pyrite correlations. In particular, the use of pyrite-kerogen δ 34S relations in reconstructing diagenetic conditions of thermally mature rocks is questionable because formation of secondary pyrite during thermal maturation can mask the isotopic signature and quantity of the original diagenetic pyrite. The main transformations of kerogen to bitumen and bitumen to oil can be recorded by using both sulfur content and δ 34S of each phase including the H 2S (gas). H 2S generated in association with oil should be isotopically lighter or similar to oil. It is concluded that small isotopic differentiation obtained between organic and inorganic sulfur species suggests closed-system conditions. Conversely, open-system conditions may cause significant isotopic discrimination between the oil and its source kerogen. The magnitude of this discrimination is suggested to be highly dependent on the availability of iron in a source rock resulting in secondary formation of pyrite.

The δ34S values of the early-cleaved sulfur upon low temperature pyrolysis of a synthetic polysulfide cross-linked polymer

Closed and open kinetic pyrolysis experiments were conducted at 200 °C on synthetic sulfur cross-linked polymer. Sulfur isotopic analyses of the released H 2S and the residual organic sulfur revealed large discrimination (6–9.5‰) between the early-formed, isotopically light H 2S and the residual organic sulfur. This indicates that there is a relatively large kinetic isotope effect during thermal alteration of organic sulfur. This large discrimination decreases as the reaction time increases. Isotope exchange between organic sulfur and inorganic sulfur species rapidly occur under closed system conditions. Therefore, we suggest that the early isotopic discrimination in closed system is minimized due to both gradual release of heavier sulfur isotope and isotopic exchange processes as the pyrolysis experiments advance. These results have significant geochemical implications for source rock–oil–H 2S correlations.