H2S Consumption Research Articles

Nitrite-dependent microbial utilization for simultaneous removal of sulfide and methane in sewers

Chemicals are commonly dosed in sewer systems to reduce the emission of hydrogen sulfide (H2S) and methane (CH4), incurring high costs and environmental concerns. Nitrite dosing is a promising approach as nitrite can be produced from urine wastewater, which is a feasible integrated water management strategy. However, nitrite dosing usually requires strict conditions, e.g., relatively high nitrite concentration (e.g., ∼200 mg N/L) and acidic environment, to inhibit microorganisms. In contrast to “microbial inhibition”, this study proposes “microbial utilization” concept, i.e., utilizing nitrite as a substrate for H2S and CH4 consumption in sewer. In a laboratory-scale sewer reactor, nitrite at a relatively low concentrations of 25–48 mg N/L was continuously dosed. Two nitrite-dependent microbial utilization processes, i.e., nitrite-dependent anaerobic methane oxidation (n-DAMO) and microbial sulfide oxidation, successfully occurred in conjunction with nitrite reduction. The occurrence of both processes achieved a 58 % reduction in dissolved methane and over 90 % sulfide removal in the sewer reactor, with microbial activities measured as 15.6 mg CH4/(L·h) and 29.4 mg S/(L·h), respectively. High copy numbers of n-DAMO bacteria and sulfide-oxidizing bacteria (SOB) were detected in both sewer biofilms and sediments. Mechanism analysis confirmed that the dosed nitrite at a relatively low level did not cause the inhibition of sulfidogenic process due to the downward migration of activity zones in sewer sediments. Therefore, the proposed “microbial utilization” concept offers a new alternative for simultaneous removal of sulfide and methane in sewers.

Detailed kinetics modeling of sulfur species evolution in alternating reducing/oxidizing atmosphere

Under conditions of deep load fluctuation, the furnace of a coal-fired boiler experiences alternating reduction/oxidation atmospheres, which directly impact the evolution of sulfur species. Building upon our previous mechanism (Model I), this study specifically considered the influence of alternating atmospheres and proposed a comprehensive reaction model (Model II), incorporating 8 additional elementary reactions. The relative error in predicting the concentration distribution of sulfur species was reduced from 18% (Model I) to 13% (Model II). In the alternating atmospheres, the predominant sulfur species remained as SO2 and H2S. Sensitivity analysis revealed that S, SH, SO, HSO, and HOSO were the critical free radicals. The new supplementary reactions (118) H2S + M = SH + H + M and (116) H2S + O2=HSO + OH played a significant role in the generation and consumption of H2S and SO2. Rate of production analysis demonstrated that the alternating atmosphere impacted the production and consumption primary free radicals like O/H/OH, thus potentially causing changes of S, SH, SO, HSO, and HOSO; moreover, it introduced new reaction pathways for SH and SO. Finally, a simplified reaction pathway for the sulfur species evolution was proposed. This study seeks to provide insights into the sulfur species evolution under the peak regulation conditions in coal-fired boilers.

A Polyoxometalate‐Based Pathologically Activated Assay for Efficient Bioorthogonal Catalytic Selective Therapy

AbstractSince polyoxometalates (POMs) can undergo reversible multi‐electron redox transformations, they have been used to modulate the electronic environment of metal nanoparticles for catalysis. Besides, POMs possess unique electronic structures and acid‐responsive self‐assembly ability. These properties inspired us to tackle the drawbacks of the copper‐catalyzed azide‐alkyne cycloaddition (CuAAC) reaction in biomedical applications, such as low catalytic efficiency and unsatisfactory disease selectivity. Herein, we construct molybdenum (Mo)‐based POM nanoclusters doped with Cu (Cu‐POM NCs) as a highly efficient bioorthogonal catalyst, which is responsive to pathologicallyacid and H2S for selective antibiofilm therapy. Leveraging the merits of POMs, the Cu‐POM NCs exhibit biofilm‐responsive self‐assembly behavior, efficient CuAAC‐mediated in situ synthesis of antibacterial molecules, and a NIR‐II photothermal effect selectively triggered by H2S in pathogens. The consumption of bacterial H2S at the pathological site by Cu‐POM NCs extremely decreases the number of persisterbacteria, which is conducive to the inhibition of bacterial tolerance and elimination of biofilms. Unlocked at pathological sites and endowed with NIR‐II photothermal property, the constructed POM‐based bioorthogonal catalytic platform provides new insights into the design of efficient and selective bioorthogonal catalysts for disease therapy.

Black Phosphorus Nanosheet/Tin Oxide Quantum Dot Heterostructures for Highly Sensitive and Selective Trace Hydrogen Sulfide Sensing

Conductometric detection of hydrogen sulfide (H2S) gas is highly desired in the fields of environmental protection and noninvasive human health assessment due to its unique merits of real-time monitoring, low cost, and high miniaturization. In this regard, semiconducting metal oxides, such as tin oxide (SnO2), have been extensively employed for H2S detection but suffer from constrained sensitivity, elevated operation temperature, and poor selectivity. To overcome these drawbacks, mixed-dimensional heterostructures of two-dimensional (2D) black phosphorus (BP) nanosheet-templated zero-dimensional (0D) SnO2 quantum dots (QDs) (BP/SnO2) were prepared in this work for trace H2S detection. The constituent ratio-optimized BP/SnO2 sensors showed a high response of 233.8 and swift response/recovery speeds of 16.4/9.5 s toward 5 ppm H2S and ultralow energy consumption at a relatively low operation temperature (10 mW@130 °C), rivaling or surpassing that of most of the sensors in recent academic reports and commercial products. Moreover, excellent repeatability, long-term stability, and selectivity were demonstrated. When exposed to 5 ppm H2S under 80% relative humidity, the sensor displayed a 75% response retention with respect to the dry case, revealing a favorable humidity tolerance. Furthermore, the BP/SnO2 sensors outperformed their reduced graphene oxide (rGO)- and molybdenum disulfide (MoS2)-templated counterparts in terms of response intensity and response/recovery speeds. Benefiting from the abundant p–n heterojunctions and sufficient material utility within the mixed-dimensional heterostructures, the as-prepared BP/SnO2 sensors showcased brilliant application prospects for energy-saving and portable H2S detection systems.

Telescoped boiling and cooling mechanisms triggered hydrothermal stibnite precipitation: Insights from the world’s largest antimony deposit in Xikuangshan China

AbstractSociety annually consumes 250% more Sb relative to the year 1960 and a sustainable supply of antimony depends critically on understanding the precipitation mechanism of stibnite (Sb2S3) that is the globally predominant source of this important technology metal. Previous solubility studies revealed that antimony is transported in mesothermal hydrothermal fluids mainly as the aqueous species thioantimonite (H2Sb2S4, HSb2S4−, Sb2S42−) and hydroxothioantimonite [Sb2S2(OH)2]. Thioantimonite can transform to hydroxothioantimonite with a decline of H2S concentration. However, whether this transition occurs in hydrothermal systems and its role in stibnite precipitation are unknown. In this work, bulk Sb isotope measurements for stibnite from the world’s largest Sb deposit in Xikuangshan China were conducted to address ore fluid evolution and stibnite precipitation mechanisms. The abundance of the stable antimony isotopes 121Sb and 123Sb were measured in stibnite from the Xikuangshan orebodies and reported as δ123Sb. The δ123Sb values show a trend of decreasing first and then increasing from proximal to distal parts of orebodies. This reveals that 123Sb had been preferentially partitioned from the ore fluid into stibnite first, then 123Sb remained preferentially dissolved in the ore fluid. These data indicate that the dominant Sb-complex transforms to Sb2S2(OH)2 from H2Sb2S4 with consumption of H2S. Speciation diagram considerations indicate that stibnite precipitation from the ore fluid was controlled by two telescoped processes: (1) boiling of the ore fluid induced a decrease in H2S that reduced the solubility of H2Sb2S4, and (2) subsequent cooling that induced a decrease in the solubility of Sb2S2(OH)2. This study highlights that understanding the controls of Sb isotope fractionation is critical to constrain fluid evolution and stibnite precipitation mechanisms in Sb-rich mineral systems. In particular, the stable Sb complex in the hydrothermal ore fluid may change during fluid evolution and affect the isotope fractionation mechanism.

Cable bacteria activity and impacts in Fe and Mn depleted carbonate sediments

The metabolic activities of cable bacteria enable the oxidation of sulfide to sulfate in anoxic sediment at depth through long distance electron transport coupled to the reductions of O2 and NO3−/NO2− in surface sediment. The spatial separation of oxidation and reduction half reactions requires modification of diagenetic models that assume electron donors and acceptors are coupled with each other locally within sedimentary deposits. In this study, we show that cable bacteria can become established and remain metabolically active in sulfidic, but Fe, Mn, and solid phase sulfide-depleted, carbonate muds from Florida Bay, USA. Sediment surface pH maxima reflecting electrogenic metabolism developed between 1 and 3 weeks in sediment incubated in laboratory microcosms with oxic overlying water. Cable filament cell abundances varied over time, with the increase initially focused within the subsurface, but by the end of experiments, cell abundances increased both in subsurface and oxic surface sediment. The development of cable bacteria activity in carbonate muds demonstrates that long-distance electron transport metabolism can utilize subsurface dissolved sulfide (e.g., H2S) as a sole reductant source for sustained periods without transition to Fe-sulfide and apparently without formation of an intermediate suboxic region associated with Fe and Mn cycling. H2S consumption occurs initially within the O2-NO3− rich oxic – suboxic zone and transitions to a dominant, but not exclusive, subsurface cable bacteria anodic zone. Once established, cable bacteria significantly altered sediment carbonate cycling. Thermodynamic calculations demonstrated that aragonite and hi-Mg-calcites were supersaturated (Ω ∼2.0–3.2) in the surface sediment layer (< 0.25 cm depth) and were undersaturated (Ω ∼ 0.2) in the anodic zone (1–2 cm depth). Hi-Mg-calcites and aragonite likely precipitated in the surface sediment and dissolved in the anodic region, the dissolution confirmed by elevated porewater Ca2+, Mg2+ concentrations. P cycling was coupled to remineralization of organic matter, carbonate mineral cycling, and apparently intracellular accumulation of polyphosphates. Thus, cable bacteria may play an important role in the acquisition of P by seagrasses in carbonate deposits where P is otherwise limited by irreversible adsorption and authigenic mineral precipitation.

Sinking particles in the Black Sea waters: Vertical fluxes of elements and pyrite to the bottom, isotopic composition of pyrite sulfur, and hydrogen sulfide production

The Black Sea is the largest anoxic basin with hydrogen sulfide at depths below 100 m. Anoxic condition significantly affects fluxes of particulate matter due to consuming organic material for sulfate reduction and syngenetic pyrite formation. Composition of sinking particles was studied for 6 water depths of the Black Sea (100–1750 m) with deployment period of over one year. As a result, the data on chemical and mineral composition of sinking particles including the contents of reduced sulfur species (acid volatile sulfides and Cr reducible species) and isotopic composition of Cr reducible sulfur species were obtained.Mineral composition of trapped material changes with depth mainly due to dissolution of plankton carbonate shells, which decreases to the bottom to reach 90%, and also due to oxidation of organic carbon (by 59%). While sinking, particulate matter loses Fe, S, U, Co, Mo, Tl, and Ag to the least extent. Framboidal pyrite appears in sinking particles in the upper part of anoxic water column shallower than 180 m. Its quantity increases down to the deeper waters amounting to 0.4 wt% of dry weight. The δ34S values in syngenetic pyrite from depths of 980, 1680, and 1775 m range from −42.2 to −42.6‰ vs. VCDT and were found to be close to those of sulfur isotopic composition in dissolved hydrogen sulfide.Based on a decrease of particulate organic carbon flux, the annual production of hydrogen sulfide in 2015–2016 was calculated to be 5.9 Tg H2S /year, the main part of which (80%) generates above a depth of about 980 m. Our estimate of H2S consumption for pyrite formation in the water column is 0.030 Tg H2S /year (0.5% of annual H2S production) which is believed insignificant for hydrogen sulfide balance in the Black Sea.

Impact of serine and serine synthesis genes on H2S release in Saccharomyces cerevisiae during wine fermentation

Excessive hydrogen sulfide (H2S) during fermentation causes undesirable sensory properties in wine. In yeast, serine functions as a precursor in the biosynthesis of S-containing compounds, which facilitates H2S consumption. To investigate the effect of serine on H2S release and the underlying mechanism, extracellular and intracellular serine levels were separately increased under fermentation conditions. The results show that, although the abundance of extracellular serine was ineffective in decreasing H2S levels, increased levels of intracellular serine levels from SER1 and SER2 overexpression reduced H2S release through increased consumption of sulfur metabolites. In contrast, SER33 overexpression significantly increased H2S release, and the metabolites and gene expression profile of the sulfur assimilation pathway indicates that SER33 regulated MET17, which mediated H2S release. Our study revealed valuable insights on the relationship between serine levels and H2S release, and may be helpful in understanding the H2S regulation mechanism in yeast during fermentation.

Synergistic decomposition of H2S into H2 by Ni3S2 over ZrO2 support via a sulfur looping scheme with CO2 enabled carrier regeneration

Commercially viable H2 production from H2S demands a well-designed and efficient technology concept with superior H2 yield. We propose a novel sulfur looping scheme that involves carrier sulfidation and CO2 enabled carrier regeneration to simultaneously utilize H2S and CO2, the two common industrial waste gases, for valuable H2 production. Using Ni3S2 as the active component, a high-performance sulfur carrier design is developed, where the selection of support is key. ZrO2 and MgAl2O4 supports were tested and both substantially improve the recyclability over cycles by imparting structural stability to Ni3S2. ZrO2 dramatically enhances the carrier performance, exhibiting a maximum increase of ~ 100% in sulfur uptake during the redox cycles compared to MgAl2O4. Furthermore, in fixed bed experiments at a high GHSV of 5000 hr-1, ZrO2 supported carrier maintained its superior performance over MgAl2O4 with a ~ 9.5% higher total H2S consumption. Density functional theory calculations were performed to unveil the role of supports. ZrO2 is identified as a support with bifunctional characteristics that not only improves textural properties of the carrier, but also catalytically decomposes H2S and induces a synergistic dynamic with Ni3S2. On the other hand, MgAl2O4 acts only as a conventional inert support for morphology modifications with negligible interaction with H2S. This work demonstrates a novel strategy for H2S and CO2 utilization and provides new insights into effective support selection aiding the design of a robust and efficient sulfur carrier.

Carbon consumption and adsorption-regeneration of H2S on activated carbon for coke oven flue gas purification.

Carbon consumption of activated carbon varies with sulfur-containing products. In this work, differential thermogravimetric (DTG), electron paramagnetic resonance (ESR), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD) we re used to reveal the adsorption-regeneration process of H2S and the effect of adsorption products on carbon consumption. The results show that H2S reacts with the C=C bond to form the C-S bond as an intermediate state, followed by the formation of elemental sulfur. It directly sublimates at approximately 380 °C, about 30 °C higher than the decomposition temperature of H2SO4. In the thermal regeneration process, the elemental sulfur in the form of monoclinic sulfur (S8) first breaks into infinitely long chain molecules (S∞) and then into small molecules, finally into sulfur vapor. The desorption of elemental sulfur consumes less oxygen and carbon functional groups, reducing the chemical carbon consumption by 59.8% than H2SO4; moreover, the compressive strength reduces less due to its slight effect on the disordered graphitic structure. H2S also reacts with the C=O bond to form H2SO3 or H2SO4. The desorption of H2SO3 does not require carbon consumption. The decomposition of H2SO4 needs to react with the C=C bond to release SO2, CO2, and CO, and the compressive strength of activated carbon significantly decreases. The carbon consumption originates from two aspects; the one from the regeneration of sulfur-containing products is more than twice the other one from the decomposition of oxygen-containing functional groups.

Conversion of H2S/O2/NO mixtures at different pressures. Experiments and kinetic modeling

The present study deals with the oxidation of H2S/NO mixtures, in the temperature range of 475–1400 K, at atmospheric pressure and 20 bar of manometric pressure. The experiments have been performed in two different set-ups, using tubular flow reactors, for different air excess ratios (λH2S = 0.3–6). A kinetic model has been updated with recent reactions from the literature. When NO is present, the oxidation of H2S at atmospheric pressure proceeds at slightly higher temperatures (25 K) with respect to neat H2S oxidation. At high pressure (20 bar), the experiments of the oxidation of H2S in the absence and presence of NO have been performed only at oxidizing conditions (λH2S = 2 and λH2S = 6), in order to avoid sulfur formation under reducing conditions. The outcomes of these experiments show that, in presence of NO, at the lowest temperature considered (475 K), at least 50% of H2S conversion for λH2S = 2 and 90% for λH2S = 6 is obtained. In order to further evaluate the influence of the presence of NO in H2S oxidation, additional experiments of neat NO oxidation have been performed. As NO2 formation is favored at high pressures and high O2 concentrations, the NO2-H2S interaction is thought to be responsible for the consumption of H2S, even at low temperatures (475 K). While the kinetic mechanism is able to reproduce the experimental results at atmospheric pressure, discrepancies are more relevant at high pressure (20 bar).

Morbidly obese subjects show increased serum sulfide in proportion to fat mass.

The importance of hydrogen sulfide is increasingly recognized in the pathophysiology of obesity and type 2 diabetes in animal models. Very few studies have evaluated circulating sulfides in humans, with discrepant results. Here, we aimed to investigate serum sulfide levels according to obesity. Serum sulfide levels were analyzed, using a selective fluorescent probe, in two independent cohorts [cross-sectionally in discovery (n = 139) and validation (n = 71) cohorts, and longitudinally in 82 participants from discovery cohort]. In the validation cohort, blood gene expression of enzymes contributing to H2S generation and consumption were also measured. In the discovery cohort, serum sulfide concentration was significantly increased in subjects with morbid obesity at baseline and follow-up, and positively correlated with BMI and fat mass, but negatively with total cholesterol, haemoglobin, serum ferritin, iron and bilirubin after adjusting by age, gender and fat mass. Fat mass (β = 0.51, t = 3.67, p < 0.0001) contributed independently to age-, gender-, insulin sensitivity- and BMI-adjusted serum sulfide concentration variance. Importantly, receiver operating characteristic analysis demonstrated the relevance of fat mass predicting serum sulfide levels, which was replicated in the validation cohort. In addition, serum sulfide concentration was decreased in morbidly obese subjects with impaired compared to those with normal fasting glucose. Longitudinally, weight gain resulted in increased serum sulfide concentration, whereas weight loss had opposite effects, being the percent change in serum sulfide positively correlated with the percent change in BMI and waist circumference, but negatively with bilirubin. Whole blood CBS, CTH, MPST, SQOR, TST and MPO gene expression was not associated to obesity or serum sulfide concentration. Altogether these data indicated that serum sulfide concentrations were increased in subjects with morbid obesity in proportion to fat mass and inversely associated with circulating markers of haem degradation.

New results of H2S oxidation at high pressures. Experiments and kinetic modeling

The present study deals with the oxidation of H2S at high pressures. In some local scenarios, combustion is seen as an alternative possibility for the use of sour gas mixtures containing H2S. Therefore, further research is needed in terms of H2S oxidation characteristics and kinetics, which might be useful for existing processes like the Claus process. Experiments have been performed in the present work in a flow reactor under diluted conditions at different manometric pressures (0.6, 10, 20 and 40 bar). The influence of oxygen concentration (λ = 1 and λ = 6), temperature (450–1100 K) and gas residence time (371/T(K)-9280/T(K), in seconds) have been studied. At a given pressure, increasing oxygen concentration shifts the onset of H2S conversion to lower temperatures and makes the H2S consumption more abrupt. Gas residence time has an important influence on the H2S oxidation behavior under the experimental conditions studied. A recent kinetic model by the authors has been updated with two new reactions, obtaining a good prediction of H2S oxidation over a wide variety of experimental conditions, both from this work and the literature. The formation of H2O2 species, favored at high pressures, is responsible for the importance of the two new reactions here proposed, improving the model predictions at high pressures. At atmospheric pressure, the reaction pathways obtained using the current mechanism, remain essentially unaltered in comparison with previous studies.

A novel study of sulfur-resistance for CO2 separation through asymmetric ceramic-carbonate dual-phase membrane at high temperature

Sulfur compounds present in high-temperature gases from various industrial sources have a negative influence on the permeability of different kinds of membranes. In this study, we present a general and efficient strategy to design and prepare two asymmetric membranes for CO2 separation that are resistant to H2S. The asymmetric membranes, mainly composed of one adsorbed layer for H2S consumption and one dense ceramic-carbonate layer for CO2 separation, show not only high CO2 permeation flux but also remarkably stable permeation behavior under an H2S-containing atmosphere. The sulfur-resistant stability times of the asymmetric membranes are approximately 10–12 times higher than the single ceramic-carbonate dual-phase membrane. The adsorbed layer of the asymmetric membranes can react with H2S to form Ce-O-S phases, gradually causing deactivation of the adsorbed layer. However, the adsorbed layer can be regenerated in the oxygen-containing gas stream above 850 °C, which can effectively remove the sulfur content from the adsorbed layer, making recycle of the membrane possible. Sulfur accumulated in the adsorbed layer of the membrane as a Ce2O2S phase, can be oxidized into SO2 under air stream and elemental sulfur (S) under a 2.5% O2/He gas stream. These asymmetric membranes thus possess high permeation stability in the H2S-containing atmosphere with good regenerability and also have potential in collection and removal of sulfur impurities from gas streams.

TOUGHREACT-CO2Bio – A new module to simulate geological carbon storage under biotic conditions (Part 1): The multiphase flow of CO2-CH4-H2-H2S gas mixtures

A new TOUGHREACT module named CO2Bio is introduced to simulate geological carbon storage (GCS) under biotic conditions. CO2Bio is developed by incorporating into TOUGHREACT an expanded thermodynamic model capable of predicting the mutual solubility of CO2-CH4-H2S-H2 gas mixtures and brine. Simple but robust thermophysical correlations are adopted in CO2Bio to calculate density, viscosity and enthalpy of CO2-CH4-H2S-H2 gas mixtures. CO2Bio can predict the kinetic microbial production and/or consumption of CO2, CH4, H2S, and H2 gases, and the multiphase flow of CO2-CH4-H2S-H2 gas mixtures and brine at deep geological formation conditions. The multiphase flow capabilities of CO2Bio are verified by comparing its simulation results with other reliable multiphase simulation programs including the ECO2N module of TOUGHREACT, the EOS7C module of TOUGH2, and CMG-GEM©. Simulated scenarios include injection of CO2 into a radial infinite acting saline aquifer, extraction of dissolved CH4 from CH4-saturated water by CO2 injection, and injection of CO2 mixed with H2S as an impurity into a saline aquifer. To verify the field-scale applicability of TOUGHREACT-CO2Bio, we conducted simulations for alternate injection of CO2 and brine into the Cushing-Drumright oil reservoir of Oklahoma where the supply of nutrients such as protein-rich matter was assumed to result in the stimulation of microbial production of H2 and CH4 from the degradation of n-alkanes. Our simulation results confirm that TOUGHREACT-CO2Bio is capable of predicting the multiphase flow of CO2-CH4-H2S-H2 gas mixtures and brine.

H2S conversion in a tubular flow reactor: Experiments and kinetic modeling

Oxidation of H2S at atmospheric pressure has been studied under different reaction atmospheres, varying the air excess ratio (λ) from reducing (λ = 0.32) to oxidizing conditions (λ = 19.46). The experiments have been carried out in a tubular flow reactor, in the 700-1400 K temperature range. The concentrations of H2S, SO2 and H2 have been determined and the experimental results have been simulated with a detailed chemical mechanism compiled in the present work. The experimental results obtained indicate that H2S consumption is shifted to lower temperatures as the stoichiometry increases, starting at 925 K for reducing conditions and at 700 K for the most oxidizing ones. The model reproduces well, in general, the experimental data from the present work, and those from the literature at high pressures. Supported by theoretical calculations, the isomerization of HSOO to HSO2 has been determined as an alternative and possible pathway to the final product SO2, from the key SH + O2 reaction.

Effect of Ce modification on the structural and catalytic property of Co-Mo/Mg(Al)O catalyst for water-gas shift reaction

A series of Mg-Al-Ce mixed oxides with (nMg2+)/(nCe3+ + nAl3+) = 5 and nCe3+/(nCe3+ + nAl3+) = 0 ∼ 7% were synthesized by co-precipitation method based on a hydrotalcite route and used as support to prepare Co-Mo sulfur-resistant water-gas shift (WGS) catalysts. The supports and catalysts were characterized by XRD, ICP, N2-physisorption, CO2-TPD, H2-TPR, H2S-TPS, TEM, and CO-IR. It is found that the catalytic performance and physicochemical property of the Co-Mo/Mg(Al)O catalyst are significantly influenced by the Ce modification. The addition of Ce effectively enhances the WGS activity and the highest activity is obtained on the Co-Mo/Mg(Al)O-CeO2 (5%) catalyst, where the activity at 623 K increases about 2.5 times. The results of H2S-TPS investigation show that in the presence of Ce, the H2S consumption peak shifts to lower temperatures and there is decrease of Mo sulfidation activation energy. Furthermore, HRTEM analysis shows that the addition of Ce (5%) results in decrease of MoS2 slab length and stacking number, and those of CO-IR characterization indicate increased exposure of surface MoS2 sites. It is suggested that the addition of Ce promotes the formation of MoS2 slabs that are smaller in size, leading to higher exposure of surface active sites and hence higher activity.

Comportamiento de torre de lavado a nivel de escala para la remoción de H2S de un reactor anaerobico de flujo ascendente

Nuestro equipo en esta oportunidad hizo una simulación de una torre de lavado, la cual la aplicamos en el reactor UASB, a manera de escala construimos una torre de lavado compuesta por difusores, una cama de sólidos hecha de material de esponja, un tubo de acrílico y todas las conexiones que conducen el biogás con H2S. Los componentes a eliminar y/o remover fueron los gases que salen del reactor, en especial del H2S (gas odorífero y toxico que a grandes concentraciones pude llevar a la muerte y como resultado de sus reacciones con el ambiente puede causar daños en las estructuras con la cual este en contacto) mediante la oxidación con el oxígeno disuelto que proveen las microalgas presentes en el agua de la laguna terciara utilizada. Esta torre de lavado la montamos en las instalaciones de CITRAR‐UNI con el permiso del operador y vimos el comportamiento que tiene esta torre, mediante los monitoreos de oxígeno disuelto, temperatura, pH y sulfatos que realizamos durante tres semanas de monitoreo. Como resultados obtuvimos que la torre de lavado sí oxidaba y removía la contracción de H2S, ya que cuando pasaba el tiempo se consumía el oxígeno disuelto, además de esto también en el monitoreo de sulfatos pudimos observar un aumento de este parámetro es decir la torre si estaba consumiendo en H2S, y por esta razón también disminuyo el olor fétido que produce este gas.

Experimental and Modeling Investigation of the Effect of H2S Addition to Methane on the Ignition and Oxidation at High Pressures

The autoignition and oxidation behavior of CH4/H2S mixtures has been studied experimentally in a rapid compression machine (RCM) and a high-pressure flow reactor. The RCM measurements show that the addition of 1% H2S to methane reduces the autoignition delay time by a factor of 2 at pressures ranging from 30 to 80 bar and temperatures from 930 to 1050 K. The flow reactor experiments performed at 50 bar show that, for stoichiometric conditions, a large fraction of H2S is already consumed at 600 K, while temperatures above 750 K are needed to oxidize 10% methane. A detailed chemical kinetic model has been established, describing the oxidation of CH4 and H2S as well as the formation and consumption of organosulfuric species. Computations with the model show good agreement with the ignition measurements, provided that reactions of H2S and SH with peroxides (HO2 and CH3OO) are constrained. A comparison of the flow reactor data to modeling predictions shows satisfactory agreement under stoichiometric conditions, while at very reducing conditions, the model underestimates the consumption of both H2S and CH4. Similar to the RCM experiments, the presence of H2S is predicted to promote oxidation of methane. Analysis of the calculations indicates a significant interaction between the oxidation chemistry of H2S and CH4, but this chemistry is not well understood at present. More work is desirable on the reactions of H2S and SH with peroxides (HO2 and CH3OO) and the formation and consumption of organosulfuric compounds.

High spatial resolution analysis of the distribution of sulfate reduction and sulfide oxidation in hypoxic sediment in a eutrophic estuary.

Bottom hypoxia and consequential hydrogen sulfide (H2S) release from sediment in eutrophic estuaries is a major global environmental issue. We investigated dissolved oxygen, pH and H2S concentration profiles with microsensors and by sectioning sediment cores followed by colorimetric analysis. The results of these analyses were then compared with the physicochemical properties of the bottom water and sediment samples to determine their relationships with H2S production in sediment. High organic matter and fine particle composition of the sediment reduced the oxidation-reduction potential, stimulating H2S production. Use of a microsensor enabled measurement of H2S concentration profiles with submillimetre resolution, whereas the conventional sediment-sectioning method gave H2S measurements with a spatial resolution of 10 mm. Furthermore, microsensor measurements revealed H2S consumption occurring at the sediment surface in both the microbial mat and the sediment anoxic layer, which were not observed with sectioning. This H2S consumption prevented H2S release into the overlying water. However, the microsensor measurements had the potential to underestimate H2S concentrations. We propose that a combination of several techniques to measure microbial activity and determine its relationships with physicochemical properties of the sediment is essential to understanding the sulfur cycle under hypoxic conditions in eutrophic sediments.