Monomeric Sulfur Research Articles

Redox performance of trivalent iron iminodisuccinic acid in converting hydrogen sulfide to sulfur: A new complexed iron catalyst

A novel iron complex formed with tetrapotassium iminodisuccinate (IDSK4) was developed for catalytic conversion of hydrogen sulfide from industrial gases to monomeric sulfur, and a small-scale apparatus for the conversion of hydrogen sulfide in the laboratory was set up.The voltammetric curves of the system were generated with an electrochemical workstation, which indicated a quasireversible process. The catalytic capacity of the catalyst was saturated at 93.8% of the theoretical value for the trivalent iron complex.The open-circuit potential of the system was in the range −0.3 to −0.2 V, which provided full conversion of hydrogen sulfide, and after regeneration by air, it was restored to the initial potential.Full-cycle experiments showed that with increasing numbers of cycles, the open-circuit potential of the regenerated system was not fully restored to the initial value, thus requiring the design of a continuous absorption–regeneration system for industrial use. For safe treatment of hydrogen sulfide in industrial exhaust gases, a single-tower unit with absorption–regeneration cycles was used, and for safe treatment of hydrogen sulfide in combustible industrial gases, a double-tower unit with absorption–regeneration separation was used. The oxidation performance of the system was quickly monitored by measuring the open-circuit potential.

Unraveling the sulfur poisoning mechanism of N-doping KAl2O3 catalyst in simultaneous hydrolysis of COS and CS2 via experimental and theoretical study

The short lifetime and poor resistance to poisoning of hydrolysis catalysts restricted their application in the desulfurization of blast furnace gas. N doping was applied to enhance the low-temperature hydrolytic activity and stability of the catalysts, and the poisoning mechanisms of COS and CS2 were explored by a series of characterizations and DFT theoretical calculations. The results revealed that the N-modified catalyst could maintain 100 % COS conversion and more than 40 % CS2 conversion after 120 h reaction. The characterization results certified that reduced surface area, weakened surface basicity, and weakened COS and CS2 adsorption capacity were the main causes of catalyst poisoning. The deposited sulfur species on the catalyst were mainly monomeric sulfur and sulfate (Al2(SO4)3). The incorporation of N significantly reduced the production of Al2(SO4)3 and enhanced the protection of the Al active site by K, which in turn enhanced the resistance to poisoning. DFT theoretical calculations exhibited that the oxidation products of COS were mainly COSO2- and CO2SO-, while CS2 was easily converted to COS first and then further be oxidized. The addition of N made the oxidation intermediate species more difficult to generate, while the oxidation product SO2 was easier to desorb, which explained the improved catalyst resistance to poisoning.

Research on Real-Time Prediction of Hydrogen Sulfide Leakage Diffusion Concentration of New Energy Based on Machine Learning

China’s sour gas reservoir is very rich in reserves, taking the largest whole offshore natural gas field in China-Puguang gas field as an example, its hydrogen sulfide content reaches 14.1%. The use of renewable energy, such as solar energy through photocatalytic technology, can decompose hydrogen sulfide into hydrogen and monomeric sulfur, thus realizing the conversion and resourceization of hydrogen sulfide gas, which has important research value. In this study, a concentration sample database of a hydrogen sulfide leakage scenario in a chemical park is constructed by Fluent software simulation, and then a leakage concentration prediction model is constructed based on the data samples to predict the hydrogen sulfide leakage diffusion concentration in real-time. Several machine learning algorithms, such as neural networks, support vector machines, and deep confidence networks, are implemented and compared to find the model algorithm with the best prediction performance. The prediction performance of the support vector machine model optimized by the sparrow search algorithm is found to be the best. The prediction model ensures the accuracy of the prediction results while greatly reducing the computational time cost, and the accuracy meets the requirements of practical engineering applications.

Photocatalytic hydrogen energy recovery from sulfide-containing wastewater using thiol-UiO-66 modified Mn0.5Cd0.5S nanocomposites

The worldwide environmental pollution and energy crisis have become two main challenges currently. To this end, we aim to build a win–win strategy of clean hydrogen energy recovery with simultaneous environmental detoxification by treating sulfide-containing wastewater in a non-hazardous manner. In this study, we designed a heterostructure photocatalyst with in situ growth of MnCdS nanoparticles on thiol-functionalized UiO-66-based materials (UiOS-MCS). A series of characterization analyses showed that UiOS-MCS nanocomposites held favorable properties of efficient charge separation and migration, which thanked to well-matched band structure and tight interfacial contacts via thiol-linked bonds that greatly facilitated the transfer of photogenerated charge carriers. The optimal nanocomposite of 0.5UiOS-MCS exhibited excellent photocatalytic activity under visible light irradiation, with an impressive hydrogen evolution of 3179.36 μmol g−1 h−1 and a significant removal of sulfide contaminants in the wastewater of about 90%, selectively generating valuable oxidation product of monomeric sulfur. The mechanism analysis demonstrated that the main photoactive species required for hydrogen production by photoreduction (electrons) and sulfide removal by photooxidation (holes) were independent of each other, and that the electron-hole division of collaboration ensured an efficient and synergistic redox reaction. This work offers a promising strategy for the recovery of energy stored in wastewater and environmental remediation.

A Study on Elemental Sulfur Equilibrium Content in Mixtures of Methane, Carbon Dioxide, and Hydrogen Sulfide under Conditions of Natural Gas Pipeline Transmission

The effect of gathering pipeline pressure, temperature, and key components on the solubility of monomeric sulfur in high-sulfur-content natural gas is directly related to the prediction and prevention of sulfur deposition in surface gathering pipelines. Based on our previous study on a prediction model of sulfur solubility in gas with a new formula for the binary interaction coefficient between sulfur and H2S, a new gas–solid thermodynamic phase equilibrium solubility prediction model for monomeric sulfur in high-sulfur-content natural gas was improved based on the gas–solid phase equilibrium principle considering both physical and chemical solution mechanisms. Two new expressions for binary interaction coefficients between sulfur and CO2 and CH4, considering both temperature and solvent density, are proposed in this new solubility prediction model. In this paper, the main factors, such as the gathering pipeline pressure, gathering pipeline temperature, H2S, and CO2, affecting the solubility law of elemental sulfur in high-sulfur-content natural gas are investigated. The results show that the total solubility of elemental sulfur in high-sulfur-bearing natural gas tends to decrease with an increase in the gathering temperature, in which the increase in temperature promotes physical solution, and the physical solution mechanism prevails. Conversely, chemical solution is promoted, and the chemical solution mechanism prevails. With an increase in the gathering pressure, the total solubility of elemental sulfur in high-sulfur-content gas tends to increase, where the physical solubility decreases slightly at first and then increases continuously, with a pressure inflection point of about 2.0 MPa, and the pressure increase has a significant promoting effect on the chemical solubility of elemental sulfur. The increase in the H2S concentration promotes the solution of elemental sulfur in the gas phase in general and significantly promotes the chemical solution of elemental sulfur. The effect on elemental sulfur solubility can be neglected when the molar concentration of CO2 in the gas phase does not exceed 10%.

Study on H2S Occurrence in Low Sulfur Coal Seams

Coal samples from the Shanxi Shaping coal mine were selected to investigate the occurrence of H2S in low sulfur coal seams. The adsorption mechanism of coal to H2S was explored, and an occurrence equation for H2S in coal seams was fitted through adsorption experiment results. The results showed that under ambient temperature and pressure conditions, the H2S adsorbed by coal reached equilibrium within 24 h. The increase in H2S concentrations and the moisture content of coal samples resulted in an increase in the adsorption capacity of H2S. Chemical adsorption of H2S by the coal also occurred. The total sulfur content in the coal increased, and water promoted the conversion from H2S to sulfur in coal. After adsorption, most of the H2S remains in the coal structure in the form of inorganic sulfur, such as sulfur hydride, iron sulfide sulfur, and monomeric sulfur, and a small proportion of H2S is bonded in the structure of the coal in the form of organic sulfur such as thiophene, C-S-C, and C-SH. Therefore, the higher the total sulfur content in coal, the greater the occurrence of H2S. The total amount of H2S increased exponentially with the concentration of free H2S and the moisture content of coal at equilibrium. This meant that the total amount of H2S in the coal seam could be estimated by fitting an equation according to the concentration of free H2S and the moisture content of coal seams. The concentration of free H2S decreased linearly with the increase in moisture content of the coal, therefore, the concentration of H2S in space could be reduced by injecting water into coal seams.

New Insight into the Chemical Nature of the Plasmonic Nanostructures Synthesized by the Reduction of Au(III) with Sulfide Species.

We have studied the products of the controversial synthesis of HAuCl4 with Na2S, which include gold nanostructures (Au NSs) that absorb in the near-infrared (NIR) region and are highly promising for photothermal therapies and other nanomedical applications. From high-resolution transmission electron microscopy, X-ray absorption spectroscopy, and small-angle X-ray scattering, we have found that only metallic Au NSs are formed as a result of this synthesis, with no detectable amount of gold sulfide or other oxidized gold species that could account for the NIR absorption. Different sulfur species are adsorbed on the Au NSs, mainly sulfides (monomeric sulfur) and polysulfides, similar to what is found on the planar gold surfaces, therefore precluding the idea that thiosulfate or other oxidized species are the actual reducing agents for Au(III) ions. The presence of strongly adsorbed S species, which are difficult to remove from the gold surface, is of great importance for their applications as regards toxicity and use of postfunctionalization strategies to anchor biomolecules and/or to increase circulation time after administration.

Electrophilic Aromatic Substitution: New Insights into an Old Class of Reactions.

The classic SEAr mechanism of electrophilic aromatic substitution (EAS) reactions described in textbooks, monographs, and reviews comprises the obligatory formation of arenium ion intermediates (σ complexes) in a two-stage process. Our findings from several studies of EAS reactions challenge the generality of this mechanistic paradigm. This Account focuses on recent computational and experimental results for three types of EAS reactions: halogenation with molecular chlorine and bromine, nitration by mixed acid (mixture of nitric and sulfuric acids), and sulfonation with SO3. Our combined computational and experimental investigation of the chlorination of anisole with molecular chlorine in CCl4 found that addition-elimination pathways compete with the direct substitution processes. Detailed NMR investigation of the course of experimental anisole chlorination at varying temperatures revealed the formation of addition byproducts. Moreover, in the absence of Lewis acid catalysis, the direct halogenation processes do not involve arenium ion intermediates but instead proceed via concerted single transition states. We also obtained analogous results for the chlorination and bromination of several arenes in nonpolar solvents. We explored by theoretical computations and experimental spectroscopic studies the classic reaction of benzene nitration by mixed acid. The structure of the first intermediate in this process has been a subject of contradicting views. We have reported clear experimental UV/vis spectroscopic evidence for the formation of the first intermediate in this reaction. Our broader theoretical modeling of the process considers the effects of the medium as a bulk solvent but also the specific interactions of a H2SO4 solvent molecule with intermediates and transition states along the reaction path. In harmony with the obtained spectroscopic data, our computational results reveal that the structure of the initial π complex precludes the possibility of electronic charge transfer from the benzene π system to the nitronium unit. In contrast to usual interpretations, our computational results provide compelling evidence that in nonpolar, noncomplexing media and in the absence of catalysts, the mechanism of aromatic sulfonation with sulfur trioxide is concerted and does not involve the conventional σ-complex (Wheland) intermediates. Stable under such conditions, (SO3)2 dimers react with benzene much more readily than monomeric sulfur trioxide. In polar (complexing) media, the reaction follows the classic two-stage SEAr mechanism. Still, the rate-controlling transition state involves two SO3 molecules. The reactivity and regioselectivity in EAS reactions that follow the classic mechanistic scheme are quantified using a theoretically evaluated quantity, the electrophile affinity (Eα), which measures the stabilization energy associated with the formation of arenium ions. Examples of applications are provided.

Defective pyrite (100) surface: Anab initiostudy

The structural and electronic properties of sulfur monomeric defects at the FeS{sub 2}(100) surface have been studied by periodic density-functional calculations. We have shown that for a monomeric sulfur bound to an originally fivefold coordinated surface Fe site, the defect core features a triplet electronic ground state with unpaired spins localized on the exposed Fe-S unit. At this site, the iron and sulfur ions have oxidation states +4 and -2, respectively. This defect can be seen as produced via heterolytic bond breaking of the S-S sulfur dimer followed by a Fe-S redox reaction. The calculated sulfur 2p core-level shifts of the monomeric defects are in good agreement with experimental photoemission spectra, which allow a compelling assignment of the different spectroscopic features. The effect of water on the stability of the defective surface has also been studied, and it has been shown that the triplet state is stable against the wetting of the surface. The most important implications of the presence of the monomeric sulfur defect on the reactivity are also discussed.

Monomeric sulfur trioxide — generation, handling and reactions with fluoroolefins

Sulfur trioxide (SO 3) is one of the most widely used chemicals in the world. Several convenient procedures for the generation and handling of monomeric SO 3 will be discussed here. Also, the reaction of monomeric SO 3 with CF 2CF 2 and CF 2CFH will be described.

Oxidation of (Carboxyalkyl)thiopropionic Acid Derivatives by Hydroxyl Radicals. Mechanisms and Kinetics of Competitive Inter- and Intramolecular Formation of σ- and σ*-type Sulfuranyl Radicals

The substituent effects on kinetics and yields of specific intermediates and products for the one-electron oxidation by hydroxyl radicals of various (carboxylalkyl)thiopropionic acid derivatives, 3-(methylthio)propionic acid (3-MTPA), 3,3‘-thiodipropionic acid (3,3‘-TDPA), 3-(carboxymethylthio)propionic acid (3-CMTPA), and 2-(carboxymethylthio)succinic acid (2-CMTPA) have been investigated employing pulse radiolysis on the nanosecond to microsecond time scale, and γ-radiolysis. For each derivative, the initial step was a formation of a hydroxysulfuranyl radical proceeding with absolute rate constants of kOH+3-MTPA = 9.1 × 109 M-1 s-1 and kOH+3,3‘-TDPA = 5.8 × 109 M-1 s-1. The subsequent formation of one-electron-oxidized intermediates such as dimeric sulfur−sulfur (S∴S)-three-electron-bonded and monomeric sulfur−carboxylate oxygen (S−O)-bonded sulfide radical cations strongly depended on pH, thioether concentration, and the availability of α- or β-positioned carboxylate functions. A spectral resolution procedure permitted the quantification of all transients present in solution at any time after the pulse. Whereas both (S∴S)- and (S−O)-bonded intermediates were formed for 3-MTPA at neutral solution, electrostatic repulsion nearly prohibited the formation of dimeric (S∴S)-bonded intermediates between an overall negatively charged sulfide radical cation of 3,3‘-TDPA and a second nonoxidized, overall twice negatively charged, molecule of 3,3‘-TDPA. Neither sulfide radical cation complex (S∴S)+ was observed for 3-CMTPA and 2-CMPTA rationalized by a fast decarboxylation of the α-positioned carboxylate group, yielding α-(alkylthio)alkyl radicals which were the only products optically observed on the pulse radiolysis time scale. For 3,3‘-TDPA, the conversion of the initially formed hydroxysulfuranyl radicals into the (S−O)-bonded intermediates occurred unimolecularly with k ≅ 108 s-1 whereas the formation of the (S∴S)-bonded intermediates proceeded bimolecularly with k = (1.9−2.0) × 108 M-1 s-1. These processes did not occur competitively, as the intercepts of plots of pseudo-first-order rate constants for the formation of the S∴S bonded intermediates as a function of thioether concentration were too small (2.7 × 107 s-1) to contain the unimolecular rate constant for the formation of the (S−O)-bonded intermediate (k = 108 s-1). Therefore, a mechanism was proposed according to which initially formed hydroxysulfuranyl radicals rapidly converted into the σ*-type (S−O)-bonded intermediate. Subsequently, these either converted into (S∴S)-bonded radical cation complexes via a displacement of the carboxylate oxygen by a second nonoxidized sulfide function, or reversibly ring-opened to yield the monomeric sulfur-centered radical cation. The latter either associated with a nonoxidized sulfide or irreversibly cyclized to a σ-type (S−O)-bonded sulfuranyl radical.

The density of liquid sulfur near the polymerization temperature

We have measured the density of liquid sulfur as a function of temperature near the polymerization temperature. We measure between 424 and 445 K, with a precision in density of 2×10−5 and an accuracy of 5×10−4. We see upward shifts of the density within 3 K of the polymerization temperature of about 8×10−4 with each cycle in temperature; these shifts could be due to the reaction of the sulfur with the quartz cell, or to the persistence of metastable polymeric forms of sulfur. Thus we consider the data from the first heating run to be the best, since the sample was then the purest. Our results differ from those in the literature in that, while we see a change in slope at the transition, we do not see a sharp minimum or a singularity. We compare our data to two models of the sulfur polymerization as a second order phase transition: the mean field model [A. V. Tobolsky and A. Eisenberg, J. Am. Chem. Soc. 81, 780 (1959)] and the n→0 magnet model [S. J. Kennedy and J. C. Wheeler, J. Chem. Phys. 78, 1523 (1983)]. Both models assume that the sulfur forms linear polymers which are in an ideal solution in monomeric sulfur, and that the thermal expansions of monomeric and polymeric sulfur are linear within the temperature range under consideration. For the most physically reasonable choice of thermodynamic parameters for the models, the mean field model describes the data better than does the n→0 model. The n→0 model is superior if the change of specific volume on polymerization is adjusted. One possible explanation is that sulfur belongs in the n=1 universality class, not in the n→0 class.

ChemInform Abstract: PHOTOOXIDATION OF SULFUR DIOXIDE IN LOW‐TEMPERATURE MATRICES

AbstractMonomeres SO2 ist sowohl in inerten als auch in Sauerstoffmatrices photochemisch inaktiv.

Photooxidation of sulfur dioxide in low-temperature matrices

The mechanism of photoxidation of sulfur dioxide has been investigated at low temperatures. Monomeric sulfur dioxide was found to be photochemically inactive, and no evidence was found for the existence of (SO/sub 4/)* in an oxygen matrix. In contrast, the dimeric species, (SO/sub 2/)/sub 2/, was found to be readily photoxidized to sulfur trioxide in an oxygen matrix at 12 K.