Elimination Of Sulfur Research Articles

Trimetallic NiMoW and CoMoW catalysts supported on SBA-15 modified with titania or zirconia for deep hydrodesulfurization

SBA-15, Ti-SBA-15 and Zr-SBA-15 were used to prepare trimetallic CoMoW and NiMoW catalysts in order to inquire into the effect of the support’s composition on the catalytic performance in deep hydrodesulfurization (HDS). Supports and catalysts were characterized by N2 physisorption, X-ray diffraction, temperature-programmed reduction, scanning electron microscopy (SEM-EDX) and high-resolution transmission electron microscopy. The catalytic activity was determined in the simultaneous HDS of dibenzothiophene and 4,6-dimethyldibenzothiophene. The most important characteristics of the SBA-15 material were preserved in the titania and zirconia-containing supports and the trimetallic catalysts. The deposited metal oxide species (NiO, CoO, MoO3 and WO3) were well-dispersed. NiMoW catalysts were substantially more active in deep HDS than the corresponding CoMoW ones. Titania and zirconia addition to the supports resulted in higher HDS activity of NiMoW and CoMoW catalysts, being this effect larger for the Ni-promoted samples. The NiMoW/Zr-SBA-15 catalyst was the most active for the elimination of sulfur from both dibenzothiophene and 4,6-dimethyldibenzothiophene. Its activity was twice higher than that of the NiMoW/SBA-15 analog. This was attributed to the high dispersion of the deposited metal species in the sulfided NiMoW/Zr-SBA-15 sample. Regarding the catalysts’ selectivity, it depended more strongly on the promoter used than on the support’s chemical composition.

Kinetic Analysis of the Thermal Decomposition of a Synthetic Mercury Jarosite

Jarosites are widely used in the hydrometallurgical industry of zinc to eliminate iron and other impurities contained in the concentrates. However, these compounds can also incorporate elements of significant environmental concern such as Tl+, Hg2+, Pb2+, Cd2+, Cr(VI), and As(V). In this work, the characterization of a synthetic mercury jarosite and its thermal decomposition kinetics are reported. XRD and FTIR analyses confirm that a mercury jarosite—Hg0.40(H3O)0.2]Fe2.71(SO4)2.17(OH)4.79(H2O)0.44—was successfully synthesized. Four mass loss events were observed by thermogravimetric analysis at 290 °C, 365 °C, 543 °C, and 665 °C. The third event corresponds to mercury decomposition into mercury oxide, whilst the forth is related to the jarosite to hematite transformation determined by X-ray diffraction starting at around 600 °C. According to the kinetic parameters (activation energy and frequency factor) of the thermal decomposition process, the fourth stage required the highest energy (Ea = 234.7 kJ∙mol−1), which corresponds to elimination of sulfur and oxygen from the jarosite lattice. Results show that jarosite-type compounds have the capability to incorporate heavy metals into their structure, retaining them even at high temperatures. Therefore, they can be used as a remediation strategy for heavy metals, such as mercury and others elements of environmental concern.

AN EFFICIENT METHOD FOR THE SYNTHESIS OF 2-THIAZOLEACETIC ACID N -SULFONYL AMIDINES

A three-step method was designed and developed on the basis of retrosynthetic analysis for the synthesis of hybrid molecules containing a thiazole ring and an N-sulfonyl amidine fragment, connected by a methylene linker. The mechanism of the last step involves the formation of intermediate 1,2,3,4-thiatriazoles and their transformation into the final products as a result of the elimination of molecular nitrogen and sulfur.

An efficient method for the synthesis of 2-thiazoleacetic acid N-sulfonyl amidines

A three-step method was designed and developed on the basis of retrosynthetic analysis for the synthesis of hybrid molecules containing a thiazole ring and an N-sulfonyl amidine fragment, connected by a methylene linker. The mechanism of the last step involves the formation of intermediate 1,2,3,4-thiatriazoles and their transformation into the final products as a result of the elimination of molecular nitrogen and sulfur.

Hydrogen cold plasma for the effective reduction of graphene oxide

We report the reduction of GO by hydrogen cold plasma as an effective alternative to the usual chemical (with harsh reducing agents) or physical (through high-temperature treatments) methods. The hydrogen plasma is generated through microwave radiation and the reduction is performed barely above room temperature, avoiding structural degradation of the graphene oxide. Three commercial GOs, with several oxygen and sulfur contents, have been used in this study. As a consequence of the exposure to the hydrogen plasma, the oxygen content is decreased in large extent while sulfur is scarcely removed. Thus a two-stage methodology consisting of a simple water treatment under reflux conditions of GO (to remove sulfur) and further treatment with H2 plasma is proposed. The combination of both steps allows the total elimination of sulfur while achieving very high degrees of reduction, lowering the initial oxygen content by more than 60%. These degrees of reduction are comparable to those obtained when the reduction is carried out by using the standard procedure with NaBH4 on the same materials. The reduction with hydrogen plasma clearly shows advantages over the conventional reduction procedures due to its simplicity: no chemicals or high temperatures are needed, and the procedure is very fast.

Improving the Desulfurization Degree of High-Grade Nickel Matte via a Two-Step Oxidation Roasting Process

Generally, sulfur elimination from nickel matte was incomplete in the one-step oxidation roasting process. In this work, X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectroscopy, and chemical analysis of the roasted products were carried out to explain this phenomenon. The results indicated that the melting of heazlewoodite was the main limiting factor. Thereafter, the oxidation mechanism of high-grade nickel matte from room temperature to 1000 °C was studied. It was found that the transformation from heazlewoodite (Ni3S2) to nickel sulfide (NiS) took place from 400 °C to 520 °C. Considering that the melting temperature of NiS was much higher than that of Ni3S2, a low-temperature roasting step was suggested to suppress the melting of heazlewoodite. Under the optimum conditions (520 °C for 120 minutes followed by 800 °C for 80 minutes), the degree of desulfurization reached 99.52 pct. These results indicated that the two-step oxidation roasting method could be a promising process for producing low-sulfur calcine from high-grade nickel matte.

Kinetic Assessment of the Simultaneous Hydrodesulfurization of Dibenzothiophene and the Hydrogenation of Diverse Polyaromatic Structures

The elimination of sulfur from fossil fuels via hydrodesulfurization (HDS) is paramount to produce cleaner fuels. Ultradeep HDS refers to reducing sulfur in fuels below the 10 ppm level. Nevertheless, under such conditions, dibenzothiophenes (DBTs) are to be desulfurized in the presence of highly complex aromatic structures that possibly exert inhibitory effects. Therefore, this contribution presents a kinetic study of the inhibition effect of diverse aromatic structures: naphthalene (NP), fluorene (FL), and phenanthrene (PHE), on the HDS of dibenzothiophene over a sulfided NiMo/γ-Al2O3 catalyst. Kinetic modeling was based on the Langmuir–Hinshelwood–Hougen–Watson (LHHW) formalism and was submitted to regression analyses with the reparametrized form of the Arrhenius and van’t Hoff equations. Before addressing inhibition effects, the kinetics of the HDS of DBT was revisited. In this sense, observations were better fitted when considering that the two parallel pathways for the HDS of DBT, i.e., the so-calle...

New Conduct in the Adsorptive Removal of Sulfur Compounds by New Nickel–Molybdenum Adsorbent

The article states the first preparation of NiMo layered double hydroxide (LDH) adsorbent for the removal of dibenzothiophene (DBT) form n-heptane solution and desulfurization of gas oil. The existence of (Mo6+) in Ni2+Mo6+ LDH was proven by X-ray photoelectron spectroscopy (XPS), while X-ray diffraction and X-ray fluorescence patterns, Fourier transform infrared spectra, scanning electron microscopy images, and differential scanning calorimetry–thermogravimetric analysis and Brunauer–Emmett–Teller analysis were applied for the composition and surface characterizations. Experimentally, NiMo LDH exhibited a different conduct in the adsorption elimination of sulfur in the existence of aromatics; the sulfur uptake was increased with the increase of the aromatic content in accordance with its own highly charged surface as a result of the formation of +4 balancing charges between Ni2+and Mo6+ through the brucite layers. The material achieved adsorption capacity of 48.8 mg g–1 sulfur for DBT at 25 °C follows a ...

Suitability of used frying oil for co-processing with atmospheric gas oil

This work study the catalytic co-hydroprocessing of used frying oil (UFO) with atmospheric gas oil (AGO), paying particular attention to the effect of UFO on the hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) efficiency, the products selectivities and its influence on fuel properties. Hydrotreating experiments were performed in a pilot plant for diesel hydrodesulphurization using a commercial catalyst of NiMo/Al2O3, temperature 320–350 °C, pressure 5.5 MPa, WHSV 2 h-1, UFO content 20–50 wt% and H2/feed ratio 500–1200 NL/L. At the operating conditions used, a total conversion of the triglycerides of UFO was obtained with a 96–99% sulfur elimination. This produced a slightly increase of the HDS/HDN rates during the co-processing, without irreversible effects over its activity and important variation in some properties such as cetane index, density 15 °C or kinematic viscosity 40 °C. The main products obtained were paraffins with 15 and 17 atoms of carbons and light gases such as CO2 and CH4, which imply that the catalyst used stimulates decarboxylation reactions in detriment of hydrodeoxygenation reactions.

Empirical Study of Treatment of Sour Gas by New Technology

The use of multistage, fluidized beds of continuous recycles reveals economically and technically attractive for both adsorption of stack gas SO2 and sequential conversion to elemental sulfur. This paper studies the adsorption process behavior of SO2 removal in one bed reactor which is filled with zinc oxide nano catalysts. The performance of catalytic bed is analyzed experimentally and theoretically by measuring the rate of mass transfer, NA, in this work. Sulfur elimination from gas is the major purpose of the handled experiments. The specific surface area (15, 20 and 25 m2/m3) as a effective parameter on mass transfer area and the particle diameter (40, 60 and 80 nm) as feed driving force on the amount of NA are evaluated.

Optimization of Lithotrophic Activities of Acidithiobacillus ferrooxidans toward Significant Reduction of Sulfur and Ash from Low Rank Bitumen

ABSTRACTIn the present study, the potential application of Acidithiobacillus ferrooxidans for elimination of ash and sulfur from bitumen was investigated in batch experiments. A comparison between the bioleaching and abiotic treatments indicated that A. ferrooxidans cells enhanced ash and pyritic sulfur removal by 20 and 59%, respectively. The X-ray diffraction profiles of the samples indicated the precipitation of some mineral elements inside of bitumen decreased the bioleaching performance after 9 days from beginning of the experiments. The effects of bitumen particle size (X1), agitation speed (X2) and initial pH (X3) as interfacial factors each at three levels on the ash removal (Y1) and pyritic sulfur removal (Y2) were investigated by response surface methodology as a statistical design of the experiment. On the basis of quadratic models applied to the performance of the bioleaching process, 66.42% of the pyritic sulfur and 50.88% of the ash could be removed after 9 days under optimal conditions, namely a bitumen particle size of 100 µm, an agitation speed of 80 rpm, and initial pH of 2.

New approach of synthesis of phosphate–sulfates with NZP-type structure

New approach of phosphate–sulfate synthesis, preventing sulfur elimination was proposed. It implies sulfur encasement into intermediate with heightened thermal resistance, thus the synthesis temperature of phosphate–sulfate could be increased, and crystallization can be performed. This method is considered to be capable by example of obtaining of Pb2/3FeZr(PO4)7/3(SO4)2/3 ceramic. It was synthesized by means of sol–gel method via formation of intermediate PbSO4, which encased sulfur and eventually led to formation of mentioned before phosphate–sulfate. Obtained sample was characterized via X-ray, IR, combined DTA–TG, SEM and microprobe electron analysis. Crystal structure and unit cell parameters were derived from least-squares refinement of powder X-ray diffraction data (NZP-type, sp. gr. $${\text{R}}\bar{3}{\text{c}}$$ , a = 8.6339 A, c = 23.2991 A, V = 1504.1 A3). Thermal expansion (α a = 0.96·10−6, α c = 3.24·10−6, α av = 1.76·10−6 K−1) of compound also has been studied. There is a wide area of interest, due to development of ceramics with low thermal expansion.

Graded ZnS/ZnSxO1−x heterostructures produced by oxidative photolysis of zinc sulfide: Structure, optical properties and photocatalytic evolution of molecular hydrogen

Abstract The photolysis of microcrystalline and single crystal ZnS on the ambient air was found to result in the formation of metallic zinc clusters and radical sulfur species additionally to the elimination of sulfur in reactions with oxygen and generation of S vacancies. The latter process results in the formation of a graded alloyed ZnO x S 1−x layer with a continuously decreasing content of sulfur and increasing content of oxygen from the bulk to the surface of the crystals. These photolytic changes are observed within the surface layer with a thickness of 50–80 nm which is comparable to the depth of light penetration into the ZnS crystals. Coupling of ZnS to ZnO, both via pre-photolysis thermal oxidation of ZnS in the dark or by in situ formation of ZnO via the oxidative photocorrosion of ZnS accelerates the photolysis considerably, most probably, as a result of directed and opposite flow of the electrons and holes within the graded ZnO x S 1−x layer and suppression of the electron-hole recombination. The ZnS/ZnS x O 1−x heterostructures revealed a relatively high photocatalytic activity in hydrogen evolution from water/ethanol mixtures under illumination with the UV light with a quantum yield of up to 1.6% in the absence of any co-catalysts. The dependence between the rate of photocatalytic hydrogen formation and the duration of ZnS photolysis was found to be dome-shaped one as a result of the interplay of two factors—(i) an increase of the probability of the spatial separation of the electron and hole within the ZnO x S 1−x layer and (ii) a decrease of the probability of ethanol oxidation by the holes with an increase in the ZnS x O 1−x layer thickness (or photolysis duration as an equivalent). In the optimal conditions the rate of photocatalytic H 2 evolution was 30 times higher than that for original non-photolyzed ZnS owing to the unique graded structure of the alloyed zinc oxysulfide layer produced by the oxidative photolysis.

Interconversion and selective reactivity of sulfur dioxide reduction intermediates inserted on graphene oxide

Graphene oxide, MPGO, was obtained by oxidation of graphite microparticles by a H2SO4/KMnO4/H2O2 mixture followed by thermal exfoliation. Non‐thermal plasma treatment of MPGO under SO2 atmosphere resulted in the insertion of the oxidized intermediates only. Refluxing this material in CS2 (46 °C) showed sulfur elimination and interconversion of the oxidized into non‐oxidized intermediates with an energetic barrier of ΔG‡ = 25.81 kcal mol−1 without decarboxylation. The episulfide content in modified MPGO increases with respect to the oxidized intermediates when increasing temperature. Modification of MPGO with SO2 at 630 °C presented exclusively the non‐oxidized intermediate. These results support the hypothesis that there are two major reactions with different energetic demand in the SO2 reduction on carbons: desulfurization and decarboxylation. The selectivity of thiolysis and aminolysis towards the intermediates inserted in the MPGO matrix allowed the amino‐thiolysis of a sample containing both intermediates with the insertion of the amino group on the episulfide site followed by an intramolecular thiolysis with double functionalization of the matrix. Copyright © 2016 John Wiley & Sons, Ltd.

Computational insights into cycloadditions of thioisomünchnones with acetylenes: how does sulfur escape from cycloadducts?

The spontaneous loss of sulfur or isocyanate from transient 7-thia-2-azabicyclo[2.2.1]hept-5-en-3-ones, which are initially formed by 1,3-dipolar cycloadditions of thioisomünchnones with acetylenic dipolarophiles, is the key step in the chemoselective syntheses of pyridin-2-ones or thiophenes. The way by which sulfur is released has been the subject of previous studies pointing to a concerted retro-cheletropic mechanism as a more favorable route than the alternative stepwise pathway. The latter however, is apparently prevalent for elimination of isocyanate. Working with a conformationally-restricted bicyclic thioisomünchnone that undergoes facile cycloaddition with acetylenes, sulfur elimination has now been interrogated by experiment and theoretical calculations at the M06-2X and M11 methods in combination with the 6-311++G(d,p) basis set, which unveil rather a sigmatropic shift via the intermediacy of thiirane species. These results provide new vistas and synthetic opportunities in mesoionic cycloadditions.

Magnetically Responsive Core–Shell Fe3O4@C Adsorbents for Efficient Capture of Aromatic Sulfur and Nitrogen Compounds

Elimination of aromatic sulfur and nitrogen compounds via selective adsorption is an effective method for the purification of transportation fuels to meet the increasingly stringent environmental requirements. Since the adsorption processes proceed in liquid phases, separation and recycling of adsorbents should be greatly facilitated if they were endowed with magnetism. In the present study, magnetically responsive core–shell microspheres, Fe3O4@C, which comprise a magnetite core and a carbon shell with a thickness adjustable from 47 to 97 nm, were fabricated for the adsorption of aromatic sulfur and nitrogen compounds. The carbon shell derived from the carbonization of a resorcinol–formaldehyde polymer possesses abundant porosity with a hierarchical structure, which is highly active in the capture of aromatic sulfur and nitrogen compounds despite the absence of any active metal sites such as Cu(I) and Ag(I). Our results show that the Fe3O4@C adsorbents with BET surface areas ranging from 227 to 264 m2 g–...

Spectroscopic investigation of sulfur-resistant Pt/K2O/ZrO2/TiO2/Al2O3 NSR/LNT catalysts

An alternative ternary support oxide material and its K2O and Pt functionalized counterparts in the form of Pt/K2O/Al2O3/ZrO2/TiO2 with different K2O loadings were synthesized. Structural and morphological properties of the catalysts were characterized via XRD and BET techniques in comparison to a conventional Pt/20Ba/Al benchmark NSR/LNT catalyst. Comprehensive in-situ FTIR and TPD analysis revealed that increasing the K2O loading in the Pt/K2O/AZT system leads to an increase in NOx Storage Capacity (NSC) at the expense of the formation of bulk-like sulfates requiring higher temperature for complete sulfur elimination with H2(g). Observed delicate trade-off between NSC and sulfur poisoning tendencies of the currently investigated family of AZT-based NSR/LNT catalysts implies that Pt/5.4K2O/AZT is a promising catalyst revealing comparable NSC within the temperature range of 473–673K to that of the conventional Pt/20Ba/Al benchmark catalyst, while exhibiting superior sulfur tolerance and regeneration characteristics.

Sulfur elimination by oxidative desulfurization with titanium-modified SBA-16

TiO2-modified mesoporous SBA-16 and titanium-substituted mesoporous SBA-16 were developed and tested in the oxidative desulfurization (ODS) of dibenzothiophene prevailing in liquid fuel. Pure TiO2 was used as reference. The titania-based catalysts were characterized by chemical analysis, XRD, EDX and TEM. The titanium state as tetrahedral (in Ti-SBA-16 sample) or octahedral (in TiO2/SBA-16 sample) coordination surrounding in the silicate matrix was determined by XPS, UV–vis DRS, FTIR, Raman and XANES. We assessed the impact exerted on performance of different reaction variables, including (nature and amount of the active catalytic species, phase system, molar ratio of oxidant H2O2 and DBT, reaction temperature, nature of the substrate and reuse of catalysts). In addition, we carried out a kinetic study and the activation energy was determined. We achieved 90% of S removal from a 0.2wt.% dibenzothiophene solution at 60°C in less than 1h of reaction. The best catalytic results are obtained with high exposed surface of nanometric TiO2 species of TiO2/SBA-16 sample. The activated catalyst is very active in ODS reaction and can be reused four times with no loss in activity.

Formation of Mercury Sulfide from Hg(II)-Thiolate Complexes in Natural Organic Matter.

Methylmercury is the environmental form of neurotoxic mercury that is biomagnified in the food chain. Methylation rates are reduced when the metal is sequestered in crystalline mercury sulfides or bound to thiol groups in macromolecular natural organic matter. Mercury sulfide minerals are known to nucleate in anoxic zones, by reaction of the thiol-bound mercury with biogenic sulfide, but not in oxic environments. We present experimental evidence that mercury sulfide forms from thiol-bound mercury alone in aqueous dark systems in contact with air. The maximum amount of nanoparticulate mercury sulfide relative to thiol-bound mercury obtained by reacting dissolved mercury and soil organic matter matches that detected in the organic horizon of a contaminated soil situated downstream from Oak Ridge, TN, in the United States. The nearly identical ratios of the two forms of mercury in field and experimental systems suggest a common reaction mechanism for nucleating the mineral. We identified a chemical reaction mechanism that is thermodynamically favorable in which thiol-bound mercury polymerizes to mercury-sulfur clusters. The clusters form by elimination of sulfur from the thiol complexes via breaking of mercury-sulfur bonds as in an alkylation reaction. Addition of sulfide is not required. This nucleation mechanism provides one explanation for how mercury may be immobilized, and eventually sequestered, in oxygenated surface environments.

Experimental and theoretical study of fluidized bed for SO 2 recovery as sulfur from effluent gases from sulfur production unit

Abstract This paper studies the adsorption process behavior of SO 2 removal in one fluidized bed reactor which is filled with aluminum oxide catalysts. The performance of catalytic bed is analyzed experimentally and theoretically in this work. Sulfur elimination from gas is the major purpose of the handled experiments. The influence of bed height, bed width, diameter of aluminum oxide particles which affects the mass transfer surface area, operating conditions such as temperature and pressure which affects the mass transfer coefficient and rate of reaction and also superficial velocity of inlet gas which affects the residence time are measured and discussed. Results show the increase in the percentage of SO 2 removal with increasing sorbent aluminum content and bed height. The increase in the percentage of SO 2 removal with increase of operating temperature (0.41%), pressure (0.21%), superficial velocity (0.5%), bed diameter (0.16%), bed height (0.58%), and surface area (0.63%) and with decrease of particle diameter (0.54%) are obtained. The applied mathematical model can predict the experimental data with an average accuracy of 92%.