The reaction thermodynamics of hydrogen sulfide decomposition into hydrogen and diatomic sulfur

To verify a hypothesis about the electronic state of diatomic gaseous sulfur formed during the low-temperature catalytic decomposition of hydrogen sulfide, we carried out some experiments to examine elemental sulfur dissociation. As shown, after heating at ～1000?K, elemental sulfur sealed in quartz ampoules with metal catalysts followed by quenching at room temperature did not produce any visible changes on solid sulfur. However, conversion of solid sulfur into gaseous diatomic sulfur can be realized via intermediate interaction of melted sulfur with hydrogen in the presence of Pt followed by decomposition of H₂S formed on the surface of the metal catalyst at room temperature. It is suggested that the conversion of the singlet sulfur atoms into the ground triplet state becomes feasible only on the surface of metal catalysts resulted from the dissociation of hydrogen sulfide into adsorbed atomic species.     

Modifying effects of hydrogen sulfide on the rheometric properties of liquid elemental sulfur

Handling molten sulfur is inherently difficult due to liquid sulfur's extreme rheological behavior. Upon melting at 115°C, sulfur's viscosity remains low until reaching 160°C, the λ-transition region, where the viscosity increases to a maximum of 93,000 × 10⁻³ Pa s at 187°C. Within this study, our previous viscosity measurements for pure liquid elemental sulfur have been discussed along with new measurements on sulfur containing physically and chemically dissolved hydrogen sulfide (H₂S). H₂S is always incorporated into industrial sulfur which has been recovered through the modified Claus process in gas plants and oil refineries. Using the experimental data from this study, a semi-empirical correlation model was reported based on the reptation model of Cates to estimate the impact of H₂S on liquid sulfur's viscosity as a function of temperature. The equation can be applied to commercial sources of sulfur with 0–500 ppm of total dissolved H₂S.     

Dissociation of dihydrogen and hydrogen sulfide over a sulfided NiMo-alumina catalyst as evidenced by D2S-H2 isotopic exchange

To investigate the possible role of surface sulfur in the activation of dihydrogen, the reaction of D₂S with H₂ was carried out at 423 K on a presulfided NiMo-Al₂O₃ catalyst. The incorporation of D atoms in H₂ shows that the catalyst is capable of dissociating H₂S and H₂ into species which by recombination make the exchange of hydrogen atoms possible between these molecules. This can be considered as evidence of the involvement of surface sulfur in the activation of dihydrogen.     

Effects of H2S and process conditions in the synthesis of mixed alcohols from syngas over alkali promoted cobalt-molybdenum sulfide

The present work is an investigation of how the process conditions influence the synthesis of mixed alcohols from syngas over a K₂CO₃/Co/MoS₂/C catalyst. The emphasis in the investigations is upon the effects of H₂S in the syngas feed. However the effects of the temperature and of the partial pressures of H₂ and CO are also investigated. With or without H₂S in the feed the pre-sulfided catalyst requires an initiation period to reach a stabilized behavior, but the duration of this period depends upon the H₂S level. Operation with a feed containing more than 103 ppmv H₂S leads to a fairly rapid stabilization of the product distribution and ensures that higher alcohols are the dominant reaction products. With less than 57 ppmv H₂S in the feed the stabilization of the product distribution is much slower, and methanol is the dominant product. An investigation of the reaction kinetics indicates a high CO coverage and low hydrogen coverage. Hydrogen sulfide in the syngas feed generally promotes chain growth for both alcohols and hydrocarbons, but lowers the alcohol selectivity by enhancing the hydrocarbon formation. The highest alcohol productivity reached in these investigations was 0.276 g/g cat./h, and this was achieved at 350 °C, 100 bar, GHSV = 5244 h⁻¹, Feed: 49.9 vol% H₂, 50.1 vol% CO. Finally it is found that sulfur fed to the reactor as H₂S is incorporated into the condensed alcohol product, and the incorporation of sulfur species into the product continues for some time after H₂S has been removed from the feed. When the catalyst is operated with an S-free syngas feed, the amount of sulfur in the condensed liquid product decreases over time, but after 35 h of operation with an S-free syngas the alcohol product still contains 340 ppmw of sulfur. Thiols appear to be the dominant sulfur compounds in the product.     

Low Temperature Catalytic Decomposition of Hydrogen Sulfide into Hydrogen and Diatomic Gaseous Sulfur

A new catalytic reaction of hydrogen sulfide decomposition is discovered, the reaction occurs on metal catalysts in gas phase according to equation $$2{\text{H}}_{2} {\text{S}} \leftrightarrow 2{\text{H}}_{2} + {\text{S}}_{2}^{{({\text{gas}})}}$$ 2 H 2 S ? 2 H 2 + S 2 ( gas ) to produce hydrogen and gaseous diatomic sulfur, conversion of hydrogen sulfide at room temperature is close to 15 %. The thermodynamic driving force of the reaction is the formation of the chemical sulfur–sulfur bond between two hydrogen sulfide molecules adsorbed on two adjacent metal atoms in the key surface intermediate and elimination of hydrogen into gas phase. “Fingerprints” of diatomic sulfur adsorbed on the solid surfaces and dissolved in different solvents are studied. In closed vessels in adsorbed or dissolved states, this molecule is stable for a long period of time (weeks). A possible electronic structure of diatomic gaseous sulfur in the singlet state is considered. According to DFT/CASSCF calculations, energy of the singlet state of S₂ molecule is over the triplet ground state energy for 10.4/14.4 kcal/mol. Some properties of gaseous diatomic sulfur are also investigated. Catalytic solid systems, both bulk and supported on porous carriers, are developed. When hydrogen sulfide is passing through the solid catalyst immersed in liquid solvent which is capable of dissolving sulfur generated, conversion of hydrogen sulfide at room temperature achieves 100 %, producing hydrogen in gas phase. This gives grounds to consider hydrogen sulfide as inexhaustible potential source of hydrogen—a very valuable chemical reagent and environmentally friendly energy product.     

A new approach for hydrogen production in Claus sulfur recovery process

In this study, the decomposition of hydrogen sulfide and reforming of hydrocarbons were employed for producing hydrogen. Thermolysis of H₂S in the platinum-based catalytic reactor led to the production of hydrogen and sulfur. It is observed that the presence of catalyst increased the conversion of H₂S decomposition up to 99.6%. Also, the hydrocarbon content of acid gas stream (CH₄) was converted to syngas, especially hydrogen in a catalytic reforming process. The produced hydrogen was separated using a Pd/Ag membrane. The simulation results showed that hydrogen production in a sulfur recovery unit provided a green source of energy by incinerating gasses. By hydrogen production during the process, the molar flow rate of incinerating gasses reduced from 2555 to 621?Kmol/h. Moreover, the hazardous sulfur compounds of the stack were removed, while hydrogen was produced by 256?Kmol/hr.     

Boiling heat transfer characteristics of a sulfuric-acid flow in thermochemical iodine–sulfur cycle

The Japan Atomic Energy Agency has been conducting research and development on the thermo-chemical iodine–sulfur (IS) process, which is one of the most attractive water-splitting hydrogen production methods that uses nuclear thermal energy. The sulfuric acid decomposer is one of the key components of the IS process. The boiling heat transfer coefficients of sulfuric acid solutions are required to design the sulfuric acid decomposer. These coefficients were measured in aqueous solutions where the mole fraction of H₂O ranged from 0.17 to 0.37 (heat flux range from 16.9 kW/m² to 5.6 kW/m²) and compared with the empirical correlations formulated for binary mixtures. A combination of the Stephan–Körner correlation, using the empirical constant A₀ = 2.00, and the Nishikawa–Fujita correlation was used to predict the experimental results with an accuracy of ±10%.     

Production of H2 from catalytic partial oxidation of H2S in a short-contact-time reactor

Partial oxidation of H₂S over alumina catalysts in a short-contact-time reactor (SCTR) has been shown to yield hydrogen, sulfur and water as the predominant products. At a set temperature of 400 °C and a contact time of 13 ms, the conversion of H₂S is 64.6% with a H₂ selectivity of 20.8%, while the amount of SO₂ in the products was <0.5% of the input H₂S.     

Production of hydrogen and sulfur from hydrogen sulfide in a nonthermal-plasma pulsed corona discharge reactor

Hydrogen sulfide (H₂S) dissociation into hydrogen and sulfur has been studied in a pulsed corona discharge reactor (PCDR). Due to the high dielectric strength of pure H₂S (∼2.9 times higher than air), a nonthermal plasma could not be sustained in pure H₂S at discharge voltages up to 30 kV with our reactor geometry. Therefore, H₂S was diluted with another gas with lower dielectric strength to reduce the breakdown voltage. Breakdown voltages of H₂S in four balance gases (Ar, He, N₂, and H₂) have been measured at different H₂S concentrations and pressures. Breakdown voltages are proportional to the partial pressure of H₂S and the balance gas. With increasing H₂S concentrations, H₂S conversion initially increases, reaches a maximum, and then decreases. H₂S conversion and the reaction energy efficiency depend on the balance gas and H₂S inlet concentrations. H₂S conversion in atomic balance gases, such as Ar and He, is more efficient than that in diatomic balance gases, such as N₂ and H₂. These observations can be explained by proposed reaction mechanisms of H₂S dissociation in different balance gases. The results show that nonthermal plasmas are effective for dissociating H₂S into hydrogen and sulfur.     

Elemental sulfur production through regeneration of a SO2-adsorbed V2O5-CoO/AC in H2

H₂ regeneration of an activated carbon supported vanadium and cobalt oxides (V₂O₅-CoO/AC) catalyst–sorbent used for flue gas SO₂ removal is studied in this paper. Elemental sulfur is produced during the H₂-regeneration when effluent gas of the regeneration is recycled back to the reactor. The regeneration conditions affect the regeneration efficiency and the elemental sulfur yield. The regeneration efficiency is the highest at 330 °C, with SO₂ as the product. The production of elemental sulfur occurs at 350 °C and higher with the highest elemental sulfur yield of 9.8 mg-S/g-Cat. at 380 °C. A lower effluent gas recycle rate is beneficial to elemental sulfur production. Intermittent H₂ feeding strategy can be used to control H₂S concentration in the gas phase and increase the elemental sulfur yield. Two types of reactions occur in the regeneration, reduction of sulfuric acid to SO₂ by AC and reduction of SO₂ to elemental sulfur through Claus reaction. H₂S is an intermediate, which is important for elemental sulfur formation and for conversion of CoO to CoS that catalyzes the Claus reaction. The catalyst–sorbent exhibits good stability in SO₂ removal capacity and in elemental sulfur yield.     

Sulfur Nanoparticles Synthesis and Characterization from H2S Gas, Using Novel Biodegradable Iron Chelates in W/O Microemulsion

Sulfur nanoparticles were synthesized from hazardous H₂S gas using novel biodegradable iron chelates in w/o microemulsion system. Fe³⁺–malic acid chelate (0.05 M aqueous solution) was studied in w/o microemulsion containing cyclohexane, Triton X-100 and n-hexanol as oil phase, surfactant, co-surfactant, respectively, for catalytic oxidation of H₂S gas at ambient conditions of temperature, pressure, and neutral pH. The structural features of sulfur nanoparticles have been characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), diffused reflectance infra-red Fourier transform technique, and BET surface area measurements. XRD analysis indicates the presence of α-sulfur. TEM analysis shows that the morphology of sulfur nanoparticles synthesized in w/o microemulsion system is nearly uniform in size (average particle size 10 nm) and narrow particle size distribution (in range of 5–15 nm) as compared to that in aqueous surfactant systems. The EDS analysis indicated high purity of sulfur (>99%). Moreover, sulfur nanoparticles synthesized in w/o microemulsion system exhibit higher antimicrobial activity (against bacteria, yeast, and fungi) than that of colloidal sulfur.     

Kinetics of the reactive absorption of hydrogen sulfide into aqueous ferric sulfate solutions

The reactive absorption of H₂S into aqueous Fe₂(SO₄)₃ solutions, was studied in a stirred cell reactor operated batchwise with and without a flat interface. The temperature was varied from 25°C to 65°C and the concentrations of aqueous Fe₂(SO₄)₃ solutions ranged from 0.025 to . The corresponding initial pH values ranged from 2 to 0.8, respectively. Additional measurements were conducted at other pH values by addition of NaOH. The H₂S partial pressure was varied between 0 and . The rate of H₂S absorption was measured by recording the pressure drop as a function of time during batch absorption experiments. In this system the absorbed H₂S reacts with ferric iron and is oxidized to elemental sulfur. The kinetic results are in agreement with enhanced absorption due to a fast chemical reaction according to the film theory. The reaction of ferric sulfate and H₂S appears to proceed irreversibly and is first order in both the total concentrations of ferric iron and H₂S. The activation energy for the reaction was calculated to be .     

Physical solubility of hydrogen sulfide in several aqueous solvents

The solubility of hydrogen sulfide in several aqueous solutions was measured over the temperature range 25°C to 60°C. The solvents investigated in this work include 0 to 50% aqueous solutions of polyethylene glycol, ethylene glycol, methyldiethanolamine and diethanolamine. The amine solutions used in this work were neutralized by the addition of hydrochloric acid in order to suppress the hydrogen sulfide reaction (H₂S → H⁺ + HS^?) so that only the physical solubility of hydrogen sulfide would be measured. The solubility data determined in this work are expressed in terms of Henry's law. The Henry's law constants found in this work were correlated well by a particularly simple empirical formula based on the molecular weight of the solvent.     

Calorimetric study of reactions occurring between impregnated activated fibres and hydrogen sulphide

Activated carbon fibres, which exhibit high specific area and numerous active surface sites constitute very powerful adsorbents and are widely used in filtration to eliminate pollutants from liquid or gaseous effluents. The fibres studied in this work are devoted to the filtration of gaseous effluents containing very small amounts (few vpm) of hydrogen sulphide. To improve their fixation capacity towards H₂S the activated fibres are impregnated in an aqueous solution of potassium hydroxide and then thermally treated. The treatment leads to the deposition of crystallites of K₂CO₃ showing a great activity for H₂S gas in the presence of water vapour. The H₂S fixation mechanism proposed can be summarised as follow: K₂CO₃ and H₂S dissolve in a liquid aqueous solution formed on the fibre surface. Then carbonate ions and H₂S molecules react together almost completely to yield HS⁻ species. This mechanism has been validated and completed by the study of the thermal effects induced when the treated fibres are in contact with H₂S together with water vapour. The study has been carried out using a calorimetric method. The variations of standard enthalpy of reactions involved in the fixation mechanism are measured and compared to the data given by the thermodynamic tables for bulk solutions.     

Kinetics of sulfur transfer from H2S to digenite (Cu2−xS) at 500°C

The kinetics of sulfur transfer from H₂S to cuprous sulfide (digenite) at 500°C has been established by the resistance relaxation technique. The resistance measurements have been carried out by the van der Pauw method, which uses a four probe configuration. The rate of the forward reaction decreases with the increase in the activity of sulfur in the sulfide (rate a _s ^–0.55 ) while the rate of the backward reaction is found to be nearly independent of the sulfur activity. Based on these results, the rate limiting step for sulfur transfer reaction to digenite is shown to be: H₂S (g) + 2e^– = S^2–(ad) + H₂(g).     

Naphthoquinones Oxidize H2S to Polysulfides and Thiosulfate,Implications for Therapeutic Applications

1,4-Napththoquinones (NQs) are clinically relevant therapeutics that affect cell function through production of reactive oxygen species (ROS) and formation of adducts with regulatory protein thiols. Reactive sulfur species (RSS) are chemically and biologically similar to ROS and here we examine RSS production by NQ oxidation of hydrogen sulfide (H₂S) using RSS-specific fluorophores, liquid chromatography-mass spectrometry, UV-Vis absorption spectrometry, oxygen-sensitive optodes, thiosulfate-specific nanoparticles, HPLC-monobromobimane derivatization, and ion chromatographic assays. We show that NQs, catalytically oxidize H₂S to per- and polysulfides (H₂S_n, n = 2–6), thiosulfate, sulfite and sulfate in reactions that consume oxygen and are accelerated by superoxide dismutase (SOD) and inhibited by catalase. The approximate efficacy of NQs (in decreasing order) is, 1,4-NQ ≈ juglone ≈ plumbagin > 2-methoxy-1,4-NQ ≈ menadione >> phylloquinone ≈ anthraquinone ≈ menaquinone ≈ lawsone. We propose that the most probable reactions are an initial two-electron oxidation of H₂S to S⁰ and reduction of NQ to NQH₂. S⁰ may react with H₂S or elongate H₂S_n in variety of reactions. Reoxidation of NQH₂ likely involves a semiquinone radical (NQ^·−) intermediate via several mechanisms involving oxygen and comproportionation to produce NQ and superoxide. Dismutation of the latter forms hydrogen peroxide which then further oxidizes RSS to sulfoxides. These findings provide the chemical background for novel sulfur-based approaches to naphthoquinone-directed therapies.     

Chemistry of hydrogen sulphide under coal liquefaction conditions: 1. Modelling hydrogen transfer catalysis

The work reported here represents initial attempts to develop a complete kinetic and mechanistic understanding of the reaction chemistry of H₂S under coal liquefaction conditions, using both model systems and coal. Hydrogen sulphide was found to promote/catalyse the transfer of hydrogen from tetralin to 2-hydroxyquinoline (2-HOQ). The presence of H₂S can increase the rate of hydrogen transfer from tetralin to 2-HOQ by a factor of 10 compared with the same reaction run in the absence of H₂S. The energy of activation for hydrogen transfer was found to decrease by ≈5 kcal mol⁻¹ in the presence of H₂S. The presence of H₂S was also found to promote loss of oxygen from 2-HOQ to form small amounts of quinoline. No evidence of CC or CN bond cleavage in 2-HOQ was noted under any of the reaction conditions studied. These results suggest that the presence of H₂S reduces the temperatures necessary to promote effective hydrogen transfer from tetralin by 50–75 °C. Moreover, they imply that similar effects occur in H₂S-promoted coal liquefaction.     

Proteomic Insights into Sulfur Metabolism in the Hydrogen-Producing Hyperthermophilic Archaeon Thermococcus onnurineus NA1

The hyperthermophilic archaeon Thermococcus onnurineus NA1 has been shown to produce H₂ when using CO, formate, or starch as a growth substrate. This strain can also utilize elemental sulfur as a terminal electron acceptor for heterotrophic growth. To gain insight into sulfur metabolism, the proteome of T. onnurineus NA1 cells grown under sulfur culture conditions was quantified and compared with those grown under H₂-evolving substrate culture conditions. Using label-free nano-UPLC-MS^E-based comparative proteomic analysis, approximately 38.4% of the total identified proteome (589 proteins) was found to be significantly up-regulated (≥1.5-fold) under sulfur culture conditions. Many of these proteins were functionally associated with carbon fixation, Fe–S cluster biogenesis, ATP synthesis, sulfur reduction, protein glycosylation, protein translocation, and formate oxidation. Based on the abundances of the identified proteins in this and other genomic studies, the pathways associated with reductive sulfur metabolism, H₂-metabolism, and oxidative stress defense were proposed. The results also revealed markedly lower expression levels of enzymes involved in the sulfur assimilation pathway, as well as cysteine desulfurase, under sulfur culture condition. The present results provide the first global atlas of proteome changes triggered by sulfur, and may facilitate an understanding of how hyperthermophilic archaea adapt to sulfur-rich, extreme environments.     

H2S–CO2 Separation Using Room Temperature Ionic Liquid [BMIM][Br]

Solubility and selective absorption of hydrogen sulfide (H₂S) over carbon dioxide (CO₂) in a room temperature ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIM][Br]) has been evaluated under ambient temperature and pressure. [BMIM][Br] demonstrated its potential as a solvent for selective removal of H₂S from CO₂/H₂S mixture. Our investigation indicated that H₂S solubility in [BMIM][Br] is comparable to or better than that in commercially available MDEA-based solvents. Meanwhile, CO₂ solubility in [BMIM][Br] is lower than that in the same amine resulting in H₂S/CO₂ absorption selectivity of within 3.5 to 3.75. The solubility behavior is relatively maintained after 4 times absorption-desorption cycles. A computational molecular study suggested that intramolecular hydrogen bonding interaction between anion Br and hydrogen atom of H₂S could stabilize the complex and resulted lower complexation energy than CO₂ interaction with [BMIM][Br]. Based on the experiment results, a separation process employing [BMIM][Br] is proposed to control the CO₂/H₂S ratio existing in a natural gas feed.