Oxidative Desulfurization Mechanism Research Articles

Engineering high specific surface area over poly (ionic liquids)-derived molybdenum-silica hybrid materials for enhanced oxidative desulfurization

Generally, the high specific surface area of catalysts with a highly uniform dispersion of active centers is beneficial for the improvement of catalytic performance in a reaction. Herein, a kind of mesoporous molybdenum-silica hybrid materials was successfully prepared via one-pot calcination method using molybdenum-based poly (ionic liquids) as template and active metal sources, which was characterized in detail and evaluated in the oxidative desulfurization of organosulfur in fuel. The experimental results indicated that the prepared samples possessed not only high specific surface area, but also a highly uniform dispersion of active sites in the sample. Under mild operating condition, the typical sample (PILMo/Si-400) with a BET area of 597.6 m2/g can achieve the complete desulfurization in 30 min without any additional organic extractant. After recycling for seven times, the desulfurization for PILMo/Si-400 can still reach 100 %. In addition, the possible mechanism for oxidative desulfurization was discussed according to the radical trapping experiments.

Ultra-deep oxidative desulfurization of high sulfur liquid fuels with molybdenum carbide@carbon loaded on N-doped graphene

A new composite Mo2C@NC/NrGO, with very small and well-distributed molybdenum carbide (Mo2C) nanoparticles on N-doped graphene, was prepared via carbonization of the tricomponent composite PMo12-PEI/GO comprising phosphomolybdic acid (H3PMo12O40·xH2O), polyethyleneimine (PEI), and graphene oxide (GO). The as-prepared Mo2C@NC/NrGO exhibited outstanding oxidative desulfurization (ODS) performance and achieved the ultra-deep desulfurization of liquid fuel under mild conditions, which was attributed to the synergistic effect of extraction and catalytic oxidation. In particular, catalytic oxidation played a dominant role, which originated from the excellent characteristics of Mo2C@NC/NrGO, such as the small size and even distribution of Mo2C on graphene, as well as the improved activation of oxidant by the electronic transfer of N-doped graphene to Mo2C. For oxidative desulfurization (ODS) of 4000 ppm of DBT, Mo2C@NC/NrGO showed the high kinetic constant (＞0.35 min−1), which can make 4000 ppm of DBT removed completely within 10 min. A HO• radical mechanism for oxidative desulfurization (ODS) of fuel oils was revealed on the basis of radical experiments and electron paramagnetic resonance (EPR). Moreover, the prepared catalyst presented a good recyclability for six runs with no significant loss of activities. Overall, Mo2C@NC/NrGO could be suggested as a prospective catalyst for ODS.

HPW/PAM Catalyst for Oxidative Desulfurization-Synthesis, Characterization and Mechanism Study

In this work, polyacrylamide (PAM) was first used in the loading of heteropoly acids, and then the HPM/PAM-n catalyst was synthesized by simple reaction. The FTIR and SEM measurements showed that the HPM/PAM-n (n = 10,000, 20,000, 30,000) was successfully synthesized. In addition, the HPM/PAM-n effect on desulfurization was measured, which showed the optimal desulfurization efficiency. The optimal process condition for HPM/PAM-10000 desulfurization was optimized by a single-factor experiment. The optimal condition was as follows: The temperature was 60 °C, the amount of the catalyst was 0.2 g, the oxygen to sulfur ratio was 16, and the reaction time is 100 min. The catalyst was suitable for recycled use, and the desulfurization efficiency was high after 10 times. In the end, the oxidative desulfurization mechanism was put forward.

Synthesis BiVO4 modified by CuO supported onto bentonite for molecular oxygen photocatalytic oxidative desulfurization of fuel under visible light

A highly photocatalytic activity of bismuth vanadate (BiVO4) modified by CuO was synthesized loaded onto the bentonite (BTT) and applied to photocatalytic oxidative desulfurization of model oil. The photocatalyst was characterized by XRD, SEM, EDS, FT-IR, XPS and UV–vis DRS. The influences of the mass ratio of cata./model oil, the flow rate of molecular oxygen and the irradiation time on the photocatalytic oxidative desulfurization of model oil were investigated by using molecular oxygen as the oxidant. The sulfur removal performances and products of the photocatalytic oxidative desulfurization of benzothiophene (BT), dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in model oil under visible light were also discussed. The results showed that the photocatalytic activity of CuO modified BiVO4/BTT for organic sulfur compounds under visible light was significantly higher than that of BiVO4 and BiVO4/BTT. Its oxidative desulfurization reactions for BT, DBT, 4-6DMDBT were the pseudo-first-order reaction, and the desulfurization activity as well as apparent activation energy followed the order of DBT > 4,6-DMDBT > BT. The photocatalytic oxidative desulfurization mechanism of CuO-BiVO4/BTT was analyzed through the calculated band gap, valence band and conduction band position. The recycling experiment presented that DBT removal by CuO-BiVO4/BTT still reached 81.5% after ten cycles.

Synthesis, Characteristic and Application of PAM Catalysts for Oxidative Desulfurization

Oxidative desulfurization has been widely used in the desulfurization process for petroleum production. But conventional oxidative desulfurization catalyst was low desulfurization efficiency, low recycle use, and the mechanism was unclear. In this work, polyacrylamide (PAM) was first used in the loading of heteropolyacids and was used in oxidative desulfurization, which was prepared by simple reaction of each of the heteropolyacids and PAM. The optimal process condition for the catalyst was chosen by the single factor experiment. The optimal condition was as follows: the temperature was 60°C, the amount of the catalyst was 0.2 g, the oxygen to sulfur ratio was 16, and the reaction time is 100 minutes. Besides, the cycle use experiment indicated the desulfurization efficiency was high after 10 times. In the end, the oxidative desulfurization mechanism was put forward. The catalyst had a good industrial development prospect.

Biomimetic oxygen activation and electron transfer mechanism for oxidative desulfurization

Construction of biomimetic catalytic systems is recognized as one of the most prospective, but is challenging approaches to achieve efficient aerobic oxidative transformations. Herein, a green aerobic oxidative desulfurization (AODS) biomimetic system was designed, which combined an Anderson polyoxometalate (POM) -based ionic liquid (IL) with deep eutectic solvent (DES). The 3-(pyridine-1-ium-1-yl) propane-1-sulfonate]3 Co(OH)6Mo6O18 {abbreviate as [PyPS]3Co(OH)6Mo6O18} combined high catalytic activity and stability with perfect synthetic availability on the desulfurization of diesel. Also, excellent recoverability showing little decrease in activity after 5 cycles has aroused the great interest. Cyclic voltammogram measurement shows conclusive evidence of oxygen activation with a 17-fold current density increase, further confirming the reduction of the aerobic oxidation reaction barrier. It revealed the biomimetic oxygen activation and synergistic electron transfers mechanism for ODS, which may provide a new insight into the construction of biomimetic system in the future.

Insight into the oxidative desulfurization mechanism of aromatic sulfur compounds over Ti-MWW zeolite: A computational study

Abstract The mechanism of aromatic sulfur compounds oxidized on Ti-MWW zeolite with H2O2 was studied by density functional theory. The results show that the adsorption capacity of solvents on Ti-η2-OOH decreases in the order of CH3COCH3> CH3OH > CH3CN > H2O. The energy barriers of thiophene on different active centers are in the order of Ti-η2-OOH-CH3CN benzothiophene > dibenzothiophene >4, 6-dimethyldibenzothiophene, confirming that Ti-MWW could provide sufficient space for the aromatic sulfur compounds with relatively large molecular size and has an excellent oxidation desulfurization performance. Our results address the controversy over the oxidation desulfurization reactivity of aromatic sulfur compounds by Ti-MWW in experimental studies and provide insights to further studies.

Extraction combined catalytic oxidation desulfurization of petcoke in ionic liquid under mild conditions

The desulfurization of high-sulfur petcoke under mild condition is a great challenge due to the structurally stable aromatic ring skeleton with a large steric hindrance of sulfur compounds. Herein, by using polyoxometalate ionic liquid [Bmim]3PW12O40 and H2O2 as catalyst and oxidant, respectively, the sulfur content in the petcoke was reduced from 4.46 wt% to 2.85 wt% in green solvent [Bmim]BF4. Moreover, the reaction performed at a mild temperature (80 °C), significantly lower than that in the industrial methods (≥1700 °C). It realized the conversion of high-sulfur petcoke from waste to resources. The experimental results indicated that sulfides in petcoke were oxidized to sulfate, sulfone and sulfoxide, while SO2 was not produced in the process of desulfurization. The possible oxidative desulfurization mechanism was proposed based on the series of characterizations.

Deep desulfurization of liquid fuels with molecular oxygen through graphene photocatalytic oxidation

A simple extraction and photocatalytic oxidative desulfurization (EPODS) system for model oil was successfully developed on the basis of as-prepared graphene oxide (GO), air, formic acid (MeA), and acetonitrile (MeCN). Under UV radiation, the main reaction conditions influencing sulfur removal were systematically investigated, including the amount of GO, the volume ratio of MeCN to model oil, the amount of MeA, the initial S-concentration, air/N2 bubbling, different sulfur compounds, and fuel composition. The reactivities of different sulfur compounds decreased in the order of benzothiophene>dibenzothiophene (DBT)>4,6-dimethyldibenzothiophene, and this was attributed to the influences of the electronic structure of the lowest-lying triplet state of each species and to steric hindrance. The photocatalytic oxidative desulfurization mechanism was investigated using radical scavenger experiments, gas chromatography-mass spectrometry, electron spin-resonance spectroscopy, and density functional theory. DBT was initially extracted into the MeCN phase and then oxidized to the mixed oxidation products including sulfone. This was accomplished by the produced HO2 and HO, which mainly originated from the oxygen-containing functional groups with absorbed O2, ambient H+, and the additional electrons at the zigzag edge and at the defect sites of GO. This work presents a promising approach to the highly-efficient removal of heterocyclic aromatic sulfur compounds from liquid fuels with an ultra-low dosage of carbon catalyst under mild conditions. Additionally, it provides insights into the fundamental knowledge on the origin of GO activity and the nature of the active oxygen functional groups in the photocatalytic process.

Deep-desulfurization of the petroleum diesel using the heterogeneous carboxyl functionalized poly-ionic liquid

Acidic carboxyl functionalized poly(ionic liquid) (CFPIL) has been synthesized and characterized by various techniques like FT-NMR,Fourier transform infrared spectroscopy (FTIR). In this work, deep oxidative desulfurization of model oil (thiophene dissolved in iso-octane) byCFPIL catalyst was carried out in presence of 30 wt% H2O2 solution as an oxidant. The effects of the hydrogen peroxide, amount of CFPIL,temperature-time and recyclability are scrutinized systematically. It was found that the effective molar proportion of H2O2 to sulfur was 4:1 at 70 °Cin 180 min with 0.6 g catalyst, removing 100% thiophene from model oil. This method has shown high efficiency for the removal of thiophene,which is difficult to remove from the oil than benzothiophene and dibenzothiophene. Additionally, an oxidative desulfurization mechanism hasbeen proposed according to the experimental results. This catalytic system by CFPIL offers advantages such as higher efficiency, low amount ofionic liquid, simple work up for separating oil from the catalyst and ease of recycling. This protocol inclines to show that diesel fuels in industrycan be purified to sulfur-free or ultra-low sulfur fuels by further deep oxidative desulfurization with CFPILs after hydrodesulfurization.

Transition metal salts of H4PMo11VO40 for efficient H2S removal in the liquid redox process

Several transition metal (Cu2+, Fe3+, Zn2+, Mn4+, and Cr6+) salts of H4PMo11VO40 were prepared and their solutions were used initially for H2S removal in the liquid redox process. H2S removal tests were performed by dynamic absorption experiments. Among these polyoxometalates, that with the Cu2+ cation was found to have pronounced H2S removal performance with the removal efficiency of up to 98%. The relevant oxidative desulfurization mechanism and the role of Cu2+ were studied.

Deep-desulfurization of the petroleum diesel using the heterogeneous carboxyl functionalized poly-ionic liquid

Abstract Acidic carboxyl functionalized poly(ionic liquid) (CFPIL) has been synthesized and characterized by various techniques like FT-NMR, Fourier transform infrared spectroscopy (FTIR). In this work, deep oxidative desulfurization of model oil (thiophene dissolved in iso-octane) by CFPIL catalyst was carried out in presence of 30 wt% H 2 O 2 solution as an oxidant. The effects of the hydrogen peroxide, amount of CFPIL, temperature-time and recyclability are scrutinized systematically. It was found that the effective molar proportion of H 2 O 2 to sulfur was 4:1 at 70 °C in 180 min with 0.6 g catalyst, removing 100% thiophene from model oil. This method has shown high efficiency for the removal of thiophene, which is difficult to remove from the oil than benzothiophene and dibenzothiophene. Additionally, an oxidative desulfurization mechanism has been proposed according to the experimental results. This catalytic system by CFPIL offers advantages such as higher efficiency, low amount of ionic liquid, simple work up for separating oil from the catalyst and ease of recycling. This protocol inclines to show that diesel fuels in industry can be purified to sulfur-free or ultra-low sulfur fuels by further deep oxidative desulfurization with CFPILs after hydrodesulfurization.

Graphene-Analogue Hexagonal BN Supported with Tungsten-based Ionic Liquid for Oxidative Desulfurization of Fuels

Graphene-analogue hexagonal boron nitride (G-h-BN), as a novel few-layer material, was prepared and used as a support to coat with tungsten-based ionic liquid (IL) in oxidative desulfurization. Designed G-h-BN supported with tungsten-based IL (IL/G-h-BN) heterogeneous catalyst was characterized by atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. This few-layer material supported with IL strategy makes the usage amount of IL reduce remarkably, which not only presents excellent catalytic activity but also is superior to homogeneous catalysts of ILs themselves. Additionally, compared with the multilayer hexagonal boron nitrides (M-h-BN) or commercial bulk BN supported with IL, the IL/G-h-BN catalyst exhibited better catalytic activity in oxidation of dibenzothiophene, reaching 99.3% sulfur removal. The adsorption and catalytic oxidative desulfurization mechanism was further studied by gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction and UV-diffuse reflectance spectroscopy. Moreover, the IL/G-h-BN catalyst could be recycled five times with little decrease in catalytic activity.

Oxidative desulfurization using ordered mesoporous silicas as catalysts

Ordered mesoporous silicas with structures of MCM-41, MCM-48 and SBA-15 were synthesized. Oxidative desulfurization activities of dibenzothiophene and 4,6-dimethyl dibenzothiophene on the mesoporous silicas were investigated using tert-butyl hydroperoxide as an oxidant. Textures and surface properties of the synthesized mesoporous silicas were studied by X-ray diffraction, N2-sorption, FT-IR and NH3-temeprature programmed desorption. The results show that oxidative desulfurization catalytic activities increase with surface area and surface acidity of the mesoporous silicas. Oxidative desulfurization mechanism on MCM-41 was investigated by the addition of surface silanol inhibitor such as acetic acid, water and triethylolamine or silylation of surface silanol groups using trimethylchlorosilane. A hypothetical mechanism based on surface silanol-mediated oxidation desulfurization is proposed. Oxidative desulfurization activities for Mo catalysts supported on MCM-41 were also investigated to identify the difference in oxidative desulfurization mechanism between MoO3 catalysts and pure mesoporous silicas.

Catalytic oxidative desulfurization mechanism in Lewis–Brønsted complex acid

Lewis–Brønsted complex acid, such as BF3, SnCl4, FeCl3, or ZnCl2-CH3COOH, can enhance thiophenic compound oxidation using solid oxidants. The catalytic oxidative mechanism was studied here. For the catalysis of the complex acid system, Lewis acid was the core, improving the Brønsted acidity of the system, promoting the dissolution of oxidant in the system, and finally catalyzing the oxidation of sulfur in the oil. For the oxidation of thiophenic compound, dibenzothiophene (DBT) was oxidized to its sulfone, but benzothiophene (BT) and thiophene (T) were oxidized to some unidentified products besides the sulfones or sulfoxides. These unidentified products originated from the oxidation of unsaturated bonds on thiophenic compounds. The electronic property of unsaturated bonds, which included bond order and π orbital occupancy, was used to explain the reactivity of unsaturated bonds on those compounds. On the basis of mechanism obtained, the catalysis for the oxidation of sulfur against olefins was controlled.

Kinetics and mechanism for oxidative desulfurization of fuels catalyzed by peroxo-molybdenum amino acid complexes in water-immiscible ionic liquids

Three peroxo-molybdenum amino acid complexes (PMAACs) were synthesized and characterized. Their catalytic activities for oxidation of dibenzothiophene (DBT) in extraction and catalytic oxidative desulfurization system (ECODS) were evaluated using different ionic liquids. Comparing with simple catalyst Na 2MoO 4·2H 2O in ECODS, PMAACs were effective wide-ranging catalysts and exhibited high desulfurization efficiency not only in water-miscible IL [bmim]BF 4 but also in water-immiscible [bmim]PF 6, [omim]BF 4 and [omim]PF 6. Especially 4,6-dimethyldibenzothiophene (4,6-DMDBT), the most difficult refractory compound in HDS, could be completely removed under optimal conditions. The reaction mechanism and desulfurization differences between using Na 2MoO 4·2H 2O catalyst and PMAACs in water-miscible and water-immiscible ionic liquids have been investigated and explained by UV–vis. Kinetic parameters of the oxidation of DBT, BT and 4,6-DMDBT were studied.

Deep oxidative desulfurization with task-specific ionic liquids: An experimental and computational study

A series of task-specific acidic ionic liquids (TSILs), immiscible with oil, halogen-free and containing –COOH group in the cations, were used for oxidative desulfurization as both the catalyst and extractant. The removal of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from model diesel at 298 K could reach 96.7% and 95.1%, respectively. The TSIL could be recycled 5 times without any apparent loss of the catalytic activity. Meanwhile, the structures, acidities and interactions between the cation and the anion of TSILs have been investigated by density functional theory (DFT) method, and found that catalytic properties of TSILs are close related to the structures, acidities and extraction capabilities. Furthermore, an oxidative desulfurization mechanism has been proposed.

Optimization of Oxidative Desulfurization of Dibenzothiophene Using a Coordinated Ionic Liquid as Catalytic Solvent

Oxidative desulfurization (ODS) of dibenzothiophene (DBT) in n-octane with hydrogen peroxide/acetic acid using a quaternary ammonium coordinated ionic liquid (IL) (C4H9)4NBr · 2C6H11NO as catalytic solvent has been studied. The ODS mechanism by coordinated ionic liquid [(C4H9)4NBr · 2C6H11NO] was also carried out. The sulfur-containing compounds in model oil were extracted into ionic liquid phase and oxidized to their corresponding sulfones by H2O2. The effect factors for desulfurization of model oil were investigated in detail by means of monofactorial and orthogonal experiments (L16(4)4). The results showed that the desulfurization efficiency of model oil could reach 98.6% under the optimal conditions of oxidation time, oxidation temperature, molar ratio of H2O2/sulfur (O/S), and volume ratio of model oil to coordinated ionic liquid were 30 min, 50°C, 16, and 1, respectively. The influences to the desulfurization efficiency of DBT decreased in the following order: volume ratio of model oil to coordinated ionic liquid (C4H9)4NBr · 2C6H11NO (Vmodel oil/VIL) > molar ratio of O/S > oxidation temperature > oxidation time, according to extreme analysis of the orthogonal test. The coordinated ionic liquid (C4H9)4NBr · 2C6H11NO can be recycled 5 times without a significant decrease in desulfurization.

THIONO COMPOUNDS, 7. OXIDATION OF THIOAMIDES IN RELATION TO ADVERSE BIOLOGICAL EFFECTS1

Abstract Thioacetamide, thioacetamide S-oxide (1), and thiopivalamide S-oxide (8) were oxidized with H2O2 in H2 18O to generate the corresponding amides with at least 50% 18O incorporation; hydrolysis of the S-oxides to the amides or 18O exchange with the amides occurs much more slowly. When 1 and trifluorothioacetamide (6) were oxidized with three and four equivalents of H2O2, respectively, in the presence of benzylamine, N-acetylbemylamine (5) and N-benzyltrifluoroacetamide (7) were isolated in respective yields of 17% and 37%. These results are interpreted as evidence for an oxidative desulfurization mechanism involving nucleophilic attack at the carbon atom of an S,S-dioxide or trioxide intermediate as the major pathway; a minor pathway may involve the intermediacy of an oxathiirane S -oxide (3) or dioxide (4) species. Understanding is added to the behavior of S-oxides in aqueous solution, as well as to thermal stability in deuterochloroform. Also reported are studies of the preparation and properties...