Kinetics and Mechanism of low-Temperature Oxidation of H2S with Oxygen in the gas Phase

The possibility of the formation of polysulfides during oxidation of H₂ S with oxygen on oxide catalysts has been checked, and the sequence of the reaction stages at temperatures below the sulfur dew point determined. The amount of polysulfides formed during H₂ S oxidation has been found to exceed significantly that obtained in the reaction of sulfur with H₂ S. Polysulfides are concluded to be intermediates in H₂ S oxidation to sulfur. The rate of formation of SO₂ from sulfur vapor is shown to be negligibly low at 100-200°C. A reaction scheme involving the formation of sulfur from polysulfides and the formation of sulfur dioxide by direct oxidation of H₂ S is suggested.     

Microbial reduction of sulfur dioxide with pretreated sewage sludge and elemental hydrogen as electron donors

It has been demonstrated that heat- and alkali-pretreated sewage sludge may serve as an electron donor and carbon source for SO₂ reduction byDesulfovibrio desulfuricans. A continuousD. desulfuricans culture was operated for 6 mo with complete reduction of SO₂ to H₂S. The culture required only minor amounts of mineral nutrients in addition to pretreated sewage sludge. It has also been shown that the sulfate-reducing bacteriumDesulfotomaculum orientis can be grown on H₂ as an energy source, CO₂ as a carbon source, and SO₂ as a terminal electron acceptor. Complete reduction of SO₂ to H₂S was observed.     

Conversion of hydrogen sulfide to elemental sulfur byChlorobium thiosulfatophilum in a CSTR with a sulfur-settling separator

Chlorobium thiosulfatophilum may be used for the bioconversion of hydrogen sulfide to elemental sulfur or sulfate. Sulfur is the preferred product because of problems in the disposal of sulfate. A CSTR with a sulfur-settling separator has been used to preferentially produce and recover elemental sulfur. The simple nutritional requirements of the bacterium and differences in densities and average cell and sulfur particle sizes make a CSTR with a sulfur-settling separator attractive. A bench-scale study has been carried out to determine the optimum process conditions to maximize H₂S conversion, cell growth, elemental sulfur production, and to minimize sulfate production. The liquid effluent typically contained about 425–550 mg/L elemental sulfur. The sulfate concentration was maintained at levels below 100 mg/L. It was possible to remove up to 57 Μmol min⁻¹ L⁻¹ of H₂S from the gas stream. An experiment over a period of 392 h showed stable performance. For Presentation at the Fifteenth Symposium on Biotechnology for Fuels and Chemicals, Colorado Springs, CO.     

Continuous hydrogen photoproduction by Chlamydomonas reinhardtii

This study demonstrates, for the first time, that it is possible to couple sulfate-limited Chlamydomonas reinhardtii growth to continuous H₂ photoproduction for more than 4000 h. A two-stage chemostat system physically separates photosynthetic growth from H₂ production, and it incorporates two automated photobioreactors (PhBRs). In the first PhBR, the algal cultures are grown aerobically in chemostat mode under limited sulfate to obtain photosynthetically competent cells. Active cells are then continuously delivered to the second PhBR, where H₂ production occurs under anaerobic conditions. The dependence of the H₂ production rate on sulfate concentration in the medium, dilution rates in the PhBRs, and incident light intensity is reported.     

TiO2基固体超强酸的制备及光催化性能研究

半导体氧化物TiO2对很多有机污染物吸附较强、催化氧化活性高,因此它在环境污染治理方面扮演极其重要的角色,被广泛用于光催化处理多种有机物,但常规二氧化钛半导体光催化剂较低的量子效率(约4%)使其应用受到一定程度的制约[1]。1979年H ino[2]等首次报道无卤素型SO42-/M xO y固体超强酸体系以来,引起化学工作者极大关注。固体超强酸催化剂如SO42-/TiO2,SbF5/SiO2/TiO2等是一类新型酸催化剂,广泛用于酯化反应、苯衍生物烷基化、烯烃齐聚等。研究发现,基于SO42-改性的TiO2固体超强酸催化剂对于有机物具有较高的光催化氧化活性[3,4],…     

Microbial oxidation of mixtures of methylmercaptan and hydrogen sulfide

Refinery spent-sulfidic caustic, containing only inorganic sulfides, has previously been shown to be amenable to biotreatment withThiobacillus denitrificans strain F with complete oxidation of sulfides to sulfate. However, many spent caustics contain mercaptans that cannot be metabolized by this strict autotroph. An aerobic enrichment culture was developed from mixedThiobacilli and activated sludge that was capable of simultaneous oxidation of inorganic sulfide and mercaptans using hydrogen sulfide (H₂S) and methylmercaptan (MeSH) gas feeds used to simulate the inorganic and organic sulfur of a spent-sulfidic caustic. The enrichment culture was also capable of biotreatment of an actual mercaptancontaining, spent-sulfidic caustic but at lower rates than predicted by operation on MeSH and H₂S fed to the culture in the gas phase, indicating that the caustic contained other inhibitory components.     

Microbial reduction of SO2 as a means of byproduct recovery from regenerable,dry scrubbing processes for flue gas desulfurization

A project is under way at the University of Tulsa to investigate the reduction of SO₂ to H₂S by sulfate reducing bacteria (SRB) in co-culture with mixed fermentative heterotrophs. We have previously demonstrated that SO₂ is completely reduced to H₂S (contact times of 1–2 s) in cultures in which no redox poising agents were required and glucose served as the ultimate source of carbon energy. We have proposed that such a microbial process could be coupled with a Claus reactor to recover elemental sulfur as a byproduct of regenerable, dry scrubbing processes for flue gas desulfurization. The development of this process concept has continued with a study of the use of molasses as a source of carbon and reduced nitrogen, identification of important non-SRB heterotrophs in process cultures, and the identification of the end products of carbohydrate fermentation that serve as carbon and energy sources for the SRB and identification of the end products of SRB metabolism.     

Thermotropic Liquid Crystals of Double-Chain Zwit-terionic Surfactants (C16)2NCnS

A series of double-chain sulfobetain zwitterionic surfactants with varying carbon number of the intercharge group (spacer), (C₁₆H₃₃)₂NCH₃(CH₂)_nSO₃, where n=2, 3, 4, and 6, referred to as (C₁₆)₂NC_nS, were synthesized. The influence of the spacer length on the thermal behaviors of (C₁₆)₂NC_nS in their pure state was studied using thermogravimetry (TG), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction (XRD). Thermogravimetric analysis (TGA) showed that the thermal stability of (C₁₆)₂NC_nS lowered with increasing the spacer length. All compounds showed a complex polymorphism. Only for (C₁₆)₂NC₄S and (C₁₆)₂NC₆S, thermotropic liquid crystals were observed using POM. The former exhibited a smectic A (SmA) phase, whereas the latter formed a hexagonal columnar phase. These liquid crystals obtained both in the cooling and the second heating scans provided compelling evidence for the thermal stability of these compounds.     

Catalytically Promoted NOx Sorption by ZrO2-Based Oxides

Metal promoted zirconia-based oxide sorbents, such as Pt–ZrO₂/Al₂O₃ for NO _x have been investigated. To clarify the role of the catalyst component, sorption of NO and NO₂ was compared using the samples with and without Pt. The catalytic oxidation of NO to NO₂ and successively to nitrate ions is an important role for the Pt catalyst. The experimental results indicate that a high-temperature calcination is essential to remove residual Cl from Pt–ZrO₂–Al₂O₃ prepared from H₂PtCl₆ in order to provide more active NO _x sorption sites. Of M–ZrO₂–Al₂O₃ samples investigated, ruthenium as well as Pt demonstrated relatively good performance as a catalyst component in the sorbent. The FT-IR spectra after sorption of NO and NO₂ demonstrated a strong band attributed to stored nitrate ions. The Pt catalyst was more resistant to sulfur poisoning than a base metal catalyst. However, the NO _x sorptive capacities of the Pt–ZrO₂/Al₂O₃ sorbents were expected to be deteriorated in dilute SO₂ as far as observed from FT-IR spectra.     

Kinetic Study on the Selective Oxidation of H2S Containing Excess Water and Ammonia

The selective oxidation of hydrogen sulfide containing excess water and ammonia was studied over V₂O₅/SiO₂ catalysts. H₂S was successfully converted to elemental sulfur and ammonium thiosulfate (ATS) without considerable emission of sulfur dioxide. Kinetic studies were carried out to describe the complex reaction paths. This revised version was published online in June 2006 with corrections to the Cover Date.     

Thermodynamics of aqueous mixtures of sodium chloride,potassium chloride,sodium sulfate,and potassium sulfate at 25°C

Aqueous solutions of sodium chloride, potassium chloride, sodium sulfate, and potassium sulfate can be mixed in six ways to give ternary mixtures. Two of these have already been studied and results are now presented for the remaining four systems: H₂O–NaCl–K₂SO₄, H₂O–Na₂SO₄–K₂SO₄, H₂O–KCl–Na₂SO₄, and H₂O–KCl–K₂SO₄.     

A Radioisotope Flow-Circulation Tracer Method for Determination of Sulfur Uptake and Exchange

A combined radioactive flow-circulation tracer method has been developed and applied to a CoMo/Al₂O₃ catalyst for measurement of sulfur uptakes and of catalyst - gas phase sulfur exchange in the H₂S partial pressure range of 2–47 kPa and the temperature range of 373–673 K. Equilibrium between gas-phase and catalyst sulfur species was rapidly achieved. A substantial part of the sulfur uptake was retained as adsorbed (reversible) sulfur species. The exchange of sulfur increased with increase in temperature up to 573 K and in H₂S partial pressure up to 4 kPa.     

One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Their Sulfur Derivatives with H2SO4 Supported on Silica Gel or Alumina

The one-pot condensation of aromatic aldehydes, β-dicarbonyl compounds, and urea or thiourea in the presence of H₂SO₄ supported on silica gel or alumina (80% m/m) in refluxing n-hexane produces 3,4-dihydropyrimidin-2(1H)-ones and their sulfur derivatives in high to excellent yields.     

Effect of Zirconia Precursor on the Properties of ZrO2-SiO2 Sol-Gel Oxides

Sol-gel zirconia-silica oxides were synthesized with two zirconium precursors, zirconium n-butoxide and zirconium acetylacetonate, and two different hydrolysis catalysts, HCl and H₂SO₄. The samples prepared with HCl were additionally sulfated with a 1 M solution of H₂SO₄. Characterization was performed with FTIR and ²⁹Si-MAS-NMR spectroscopy, as well as with nitrogen adsorption. Because zirconium and silicon alkoxides have different hydrolysis rates, it was necessary to perform a pre-hydrolysis of the silicon alkoxide before mixing. The atom distribution in the ZrO₂-SiO₂ system depended on the zirconium precursor, which also determined the zirconium incorporation in the silica lattice, which was greater for zirconium acetylacetonate. The zirconium precursor also was responsible for the silanol concentration, which increases when samples were sulfated. Sulfating stabilizes the specific surface area. On sulfate samples calcined at 800°C BET areas larger than 500 m²/g were obtained.     

Darstellung und Eigenschaften von Heteropolykationenverbindungen,IV: Darstellung und Struktur von Natriumdodekaaluminogalliumsulfat-Ikosihydrat,Na[GaO4Al12(OH)24(H2O)12](SO4)4 ·xH2O mitx∼20

Summary A chemical analyses of Na[GaO₄(Al₁₂(OH)₂₄(H₂O)₁₂](SO₄)₄ ·xH₂O withx20 [a=17.861 (4) Å; F 3 m-T _d ² ;Z=4] in connection with a crystal structure investigation confirmed the tetrahedral coordination of the gallium atom by oxygen atoms, as well as the far extending statistical distribution of the crystal water in the structure. The syntheses was done by neutralization of a satured aqueous aluminium chloride solution, mixed with metallic gallium and sodium sulfate, by an aqueous sodiumhydroxide solution.

     

Removal of SO2 and the simultaneous removal of SO2 and NO from simulated flue gas streams using dielectric barrier discharge plasmas

A gas-phase oxidation method using dielectric barrier discharges (DBDs) has been developed to remove SO₂ and to simultaneously remove SO₂ and NO from gas streams that are similar to gas streams generated by the combustion of fossil fuels. SO₂ and NO removal efficiencies are evaluated as a function of applied voltage, temperature, and concentrations of SO₂, NO, H₂O_(g), and NH3. With constant H₂O_(g) concentration, both SO₂ and NO removal efficiencies increase with increasing temperature from 100 to 160°C. At 160°C with 15% by volume H₂0_(g), more than 95% of the NO and 32% of the S0₂ are simultaneously removed from the gas stream. Injection of NH₃ into the gas stream caused an increase in S0₂ removal efficiency to essentially 100%. These results indicate that DBD plasmas have the potential to simultaneously remove SO₂ and NO from gas streams generated by large-scale fossil fuel combustors.     

Removal of SO2 from Gas Streams by Oxidation using Plasma-Generated Hydroxyl Radicals

The key problem for the removal of SO₂ by electrical discharge methods is how to obtain the hydroxyl radicals at high concentration and large production rates. With the micro-gap discharge method, O₂ and H₂O in simulated gas streams (N₂/O₂/H₂O/SO₂) are ionized into a large number of OH^. radicals to oxidize SO₂ into SO₃ which reacts with H₂O forming H₂SO₄ droplets at 120 °C in the absence of any catalyst or absorbent. The droplets are captured with an electrostatic precipitator. As a result, conversion of SO₂ to primarily H₂SO₄ is limited by the generation of OH^. radicals. By increasing the reduced field and concentrations of O₂ and H₂O, the amount of OH^. radicals increase resulting in more removal of SO₂ from gas streams. The removal efficiency of SO₂ reaches 100% when the residence time is only 0.74 s. Therefore, a new gas-phase oxidation method for removal of SO₂ without NH₃ additive is found.     

Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO₄ was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT] _o , fractional-order in [substrate] _o , and inverse fractional-order in [H⁺]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D₂O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH₃C₆H₄SO₂NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics.     

Aluminium anodising in low acidity sulphate baths: growth mechanism and nanostructure of porous anodic films

Overall kinetic and chronopotentiometric studies were performed during Al anodising in H₂SO₄, 0–5% w/v, bath solutions pure and saturated by Al₂(SO₄)₃. Peculiarities in film growth mechanism and nanostructure in these cases appeared, like significant differences of porosity and its dependence on film thickness, different critical current density above which pitting appears, salt deposition on pitted surface regions in saturated bath, etc. The different conditions inside pores are responsible for this behaviour like almost depletion of H⁺ during a long initial transient stage in the first case, supersaturation and formation of Al₂(SO₄)₃ nanoparticle micelles on pore surface in the second case, etc. Differences in film growth mechanism also appeared between these and alike baths at higher acidity. Anodising in low acidity saturated baths shows superiority for growing low porosity films at specific conditions. New technologies may be suggested to produce optimal films of desired structure.     

Comparison of the fermentability of enzymatic hydrolyzates of sugarcane bagasse pretreated by steam explosion using different impregnating agents

Sugarcane bagasse is a potential lignocellulosic feedstock for ethanol production, since it is cheap, readily available, and has a high carbohydrate content. In this work, bagasse was subjected to steam explosion pretreatment with different impregnation conditions. Three parallel pretreatments were carried out, one without any impregnation, a second with sulfur dioxide, and a third with sulfuric acid as the impregnating agent. The pretreatments were performed at 205°C for 10 min. The pretreated material was then hydrolyzed using celluloytic enzymes. The chemical composition of the hydrolyzates was analyzed. The highest yields of xylose (16.2 g/100 g dry bagasse), arabinose (1.5 g/100 g), and total sugar (52.9 g/100 g) were obtained in the hydrolysis of the SO₂-impregnated bagasse. The H₂SO₄-impregnated bagasse gave the highest glucose yield (35.9 g/100 g) but the lowest total sugar yield (42.3 g/100 g) among the three methods. The low total sugar yield from the H₂SO₄-impregnated bagasse was largely due to by-product formation, as the dehydration of xylose to furfural. Sulfuric acid impregnation led to a three-fold increase in the concentration of the fermentation inhibitors furfural and 5-hydroxymethylfurfural (HMF) and a two-fold increase in the concentration of inhibitory aliphatic acids (formic, acetic, and levulinic acids) compared to the other two pretreatment methods. The total content of phenolic compounds was not strongly affected by the different pretreatment methods, but the quantities of separate phenolic compounds were widely different in the hydrolyzate from the H₂SO₄-impregnated bagasse compared with the other two hydrolyzates. No major differences in the content of inhibitors were observed in the hydrolyzates obtained from SO₂-impregnated and non-impregnated bagasse. The fermentability of all three hydrolyzates was tested with a xylose-utilizing Saccharomyces cerevisiae strain with and without nutrient supplementation. The hydrolyzates of SO₂-impregnated and nonimpregnated bagasse showed similar fermentability, whereas the hydrolyzate of H₂SO₄-impregnated bagasse fermented considerably poorer.