Desulfurization Of Thiophene Research Articles

ZSM-5-Ln(Pc)2 catalyzed oxygen oxidation of thiophene

Abstract Direct oxidative desulfurization of thiophene with oxygen catalyzed by ZSM-5-Ln(Pc) 2 (NO 2 ) 6 (NH 2 ) 2 (Pc = phthalocyanine) was conducted. The precursor Ln(PcTn) 2 (Ln = Ce, Pr, Er, PcTn = tetra-substituted nitro phthalocyanine) was synthesized with programmed heating under nitrogen atmosphere. Then, the precursor was partially reduced by Na 2 S so the compound Ln(Pc) 2 (NO 2 ) 6 (NH 2 ) 2 (Ln = Ce, Pr, Er) was obtained, which was then anchored onto ZSM-5 zeolites through the formation of secondary amine. The catalyst was characterized by XRD, SEM, XPS, and N 2 adsorption–desorption. For the oxidation of thiophene with oxygen, the catalyst showed remarkable catalytic activity.

Theoretical insight into the desulfurization of thiophene on Pt(1 1 0): A density functional investigation

Adsorption and desulfurization of thiophene on Pt(110) are investigated using self-consistent periodic density functional theory (DFT), and the reaction network is mapped out for elaborating the possible desulfurization processes. Thiophene has two types of adsorption geometries on Pt(110), Upright and Flat adsorptions. The S atom inclines to sp3 nonequivalent hybridization in all the adsorption structures of thiophene, whereas the C atom alters between sp2 and sp3 hybridization determined by the interaction modes between the adsorbate and the surface Pt atoms. The extent of molecular distortion of thiophene on Pt(110) is correlated to the HOMO–LUMO gap of the molecule and the interaction with the surface. Thermodynamic and kinetic analysis of the elementary steps suggest that direct desulfurization pathway is most favorable for the hydrodesulfurization of thiophene on Pt(110). This desulfurization process exhibits lower CS bond activation energy but higher conversion barrier compared to the situation of thiophene on Pt(111).

Investigation of Photocatalytic Oxidative-Extraction Desulfurization of Simulation Gasoline

Photocatalytic Oxidative-Extraction Desulfurization (Photo-cat-EODS) of thiophene, the main sulfur-containing compound of catalytic cracking (FCC) gasoline, has been investigated in heterogeneous photocatalysis process using WO3/ZnO composite as photocatalyst and air was used as the oxidant. Extraction process was also employ followed by the photocatalytic oxidative process to remove the oxidative products using acetonitrile as the extractant. Furthermore, orthogonal experiments method was used to optimize the processing parameters.

Monodispersed Ag nanoparticles loaded on the surface of spherical Bi2WO6 nanoarchitectures with enhanced photocatalytic activities

Spherical Bi2WO6 nanoarchitectures with scale of 2–4 μm were prepared by a hydrothermal reaction using bismuth nitrate and ammonium tungstate as raw materials. Ag was deposited on the surface of Bi2WO6via a following facile photoreduction process. The as-prepared samples were characterized by UV-Vis-DRS, BET, XRD, XPS, FE-SEM, and HR-TEM. The results revealed that the monodispersed metallic Ag nanoparticles with average size of 10–15 nm were deposited on the surface of the spherical Bi2WO6 nanoarchitectures. The photocatalytic activities of the samples were evaluated by the photodegradation of RhB and thiophene under visible light irradiation. The results showed that Ag loading greatly improved the photocatalytic activity of Bi2WO6, and the content of loading silver has an impact on the catalytic activity of Bi2WO6. The 0.5at%Ag-loaded Bi2WO6 sample exhibited the best photocatalytic activity in both the decolorization of RhB and desulfurization of thiophene. In addition, the mechanism for the enhancement of the photocatalytic activity of Ag-loaded Bi2WO6 was also investigated by comparison of their PL spectra.

Sonocatalytic Oxidative Desulfurization of Thiophene and Its Derivatives

Abstract Currently, the sulfur level in diesels is limited to 10 and 15 ppm in Europe and USA respectively, since the organosulfur compounds available in fuels emit corrosive SO2 gases into atmosphere during combustion, thus leading to acid rain. A lot of processes such as hydrodesulfurization (HDS), oxidative desulfurization (ODS) etc. have been used to reduce sulfur level in fuels and ODS, which is alternative to conventional HDS, is much more efficient in removing benzothiophene (BT), dibenzothiophene (DBT) and their alkyl derivatives as compared with HDS and more economical. One of very powerful oxidation systems used in ODS is H2O2-formic acid and removal of alkyl-substituted derivatives of T, BT and DBT with this oxidation system is easier than that with H2O2-phosphotungstic acid catalyst system due to the steric hindrance of alkyl groups adjacent to sulfur atom because phosphotungstic acid is a bulky catalyst. In this work, oxidative desulfurization reactions of the model compounds, thiophene (T), 2-methylthiophene (2-MT) and 2,5-dimethylthiophene (2,5-DMT), which have the lowest reactivity in ODS, on sonication at low H2O2 (O)/F (formic acid)/S (organosulfur solution) volume ratios were carried out sequentially in the presence of tetrabutylammonium bromide (TBAB) as phase transfer catalyst at 30 and 40 °C. First, the solution of the relevant model sulfur compound in n-heptane was put into a steel batch reactor and later, reactions were performed by adding mixture of 35% H2O2, formic acid and TBAB onto the organic phase. After each reaction cycle, the aqueous phase was removed by a separation funnel and the oxidative desulfurization reaction of the remaining treated organic phase was repeated three or four times with reuse of the same amounts of fresh hydrogen peroxide, formic acid and TBAB as in the first reactions at 30 and 40 °C for 15 min. After every reaction cycle, the sulfur compounds in heptane were analyzed by using GC with Sulfur Chemiluminescence Detector. Afterwards, the oxidative desulfurization reactions of the model sulfur compounds in heptane were performed for only one cycle in sonoreactor with total amount of oxidation reagents H2O2, formic acid and the same amount of TBAB used in the former multi-cycle reactions at 30 and 40 °C for 15 and 60 min. It was observed that the total conversions of model sulfur compounds obtained from multicycle reactions were higher than its conversions obtained from single-cycle reactions with total amount of oxidation reagents used in the multicycle reaction. The same method was also applied to diesel fuel sample and it was shown that high sulfur removal is reached.

Oxidative desulfurization of benzothiophene and thiophene with WOx/ZrO2 catalysts: Effect of calcination temperature of catalysts

Oxidative desulfurization (ODS) of model fuel containing benzothiophene (BT) or thiophene (Th) has been carried out with WOx/ZrO2 catalyst, which was calcined at various temperatures. Based on the conversion of BT in the model fuel, it can be shown that the optimum calcination temperature of WOx/ZrO2 catalyst is around 700°C. The most active catalyst is composed of tetragonal zirconia (ZrO2) with well dispersed polyoxotungstate species and it is necessary to minimize the contents of the crystalline WO3 and monoclinic ZrO2 for a high BT conversion. The oxidation rate was interpreted with the first-order kinetics, and it demonstrated the importance of electron density since the kinetic constant for BT was higher than that for Th even though the BT is larger than Th in size. A WOx/ZrO2 catalyst, treated suitably, can be used as a reusable active catalyst in the ODS.

Density Functional Theory Study of the Adsorption and Desulfurization of Thiophene and Its Hydrogenated Derivatives on Pt(111): Implication for the Mechanism of Hydrodesulfurization over Noble Metal Catalysts

Desulfurization of thiophene and its hydrogenated derivatives on Pt(111) are studied using self-consistent periodic density functional theory (DFT), and the hydrodesulfurization network is mapped out. On Pt(111), thiophene has two types of adsorption configurations (parallel cross-bridge and partially tilted bridge-hollow), and for its hydrogenated derivates, the molecule is gradually lifted up from the surface with the addition of hydrogen atoms. In all the adsorbed thiophenic compounds, the S atom is always sp3 hybridized; the C atom in the methylene group is always sp3 hybridized, whereas it is either sp2 or sp3 hybridized in the methyne group, depending on how the group interacts with the surface Pt atoms. On the basis of the thermodynamic and kinetic analysis of the elementary steps, a direct desulfurization pathway is proposed for the hydrodesulfurization of thiophene on Pt(111). In contrast to the common thought that hydrogenation toward aromatic organosulfur compounds would make desulfurization easier, the present work clearly demonstrates that hydrogenations of thiophene on Pt(111) do not reduce the energy barrier for the C–S bond cleavage.

Modeling aspects of hydrodesulfurization by molybdenum hydride compounds: Desulfurization of thiophene and benzothiophene and C–S bond cleavage of dibenzothiophene

The molybdenum hydride complexes Mo(PMe 3) 5H 2 and Mo(PMe 3) 4H 4 are capable of cleaving the C–S bonds of thiophene, benzothiophene and dibenzothiophene. For example, Mo(PMe 3) 5H 2 reacts with thiophene to give the η 5-thiophene and butadiene–thiolate complexes, (η 5-C 4H 4S)Mo(PMe 3) 3 and (η 5-C 4H 5S)Mo(PMe 3) 2(η 2-CH 2PMe 2). These complexes are also obtained from the reaction between Mo(PMe 3) 4H 4 and thiophene under photochemical conditions, whereas at elevated temperatures thiophene is desulfurized to liberate but-1-ene. Similarly, Mo(PMe 3) 4H 4 desulfurizes benzothiophene at elevated temperatures to liberate ethylbenzene, while the arylthiolate complex Mo(PMe 3) 4(SC 6H 4Et)H 3 is obtained photochemically. Furthermore, Mo(PMe 3) 4H 4 cleaves the C–S bond of dibenzothiophene to give [η 6,κ 1-C 6H 5C 6H 4S]Mo(PMe 3) 2H.

Optimization of oxidative desulfurization of thiophene using Cu/titanium silicate-1 by box-behnken design

The oxidative desulfurization of thiophene in a synthetic mixture of thiophene and iso-octane was investigated with copper loaded titanium silicate-1 (TS-1) catalyst in presence of hydrogen peroxide as oxidising agent and the conversion was enhanced by 22% at 240 min on addition of 1.05 wt.% copper in TS-1. The optimal design of experiments using box-behnken method was employed to evaluate the effects of individual process variables such as, reaction temperature, amount of catalyst and moles of hydrogen peroxide per mole of thiophene and their optimum values were found to be 70 °C, 0.45 g (22.5 mol/L of iso-octane) and 19.9 mol (in 20 ml of iso-octane), respectively, to achieve a conversion of 93%. The influence of mass transfer effects on the desulfurization reaction was minimized by selecting proper degree of agitation and catalyst size. An empirical kinetic model was used to interpret the rate data. The apparent activation energy was found to be 28.67 kJ/mol.

Deep Extractive Desulfurization of Gasoline with xEt3NHCl·FeCl3 Ionic Liquids

xEt3NHCl·FeCl3 (x = 1.4−1.8) ionic liquids were synthesized by mixing Et3NHCl and anhydrous FeCl3 at 80 °C. These were liquid at room temperature, with low viscosities, and exhibited remarkable abilities in effective desulfurization of thiophene in n-octane and fluid catalytic cracking (FCC) gasoline. Among them, 1.6Et3NHCl·FeCl3 showed the highest sulfur removal. The anionic species FeCl4− existed in 1.6Et3NHCl·FeCl3 ionic liquid, as detected by electrospray ionization−mass spectrometry (ESI−MS), and the ionic liquid was stable in air and moisture. Sulfur-free (<10 mg/L) gasoline could be obtained after extraction twice using an ionic liquid/oil volume ratio of 1. The ionic liquid could be recycled 10 times by distillation with a slight decrease in activity.

Polymer-Bound Oxidovanadium(IV) and Dioxidovanadium(V) Complexes As Catalysts for the Oxidative Desulfurization of Model Fuel Diesel

The Schiff base (Hfsal-dmen) derived from 3-formylsalicylic acid and N,N-dimethyl ethylenediamine has been covalently bonded to chloromethylated polystyrene to give the polymer-bound ligand, PS-Hfsal-dmen (I). Treatment of PS-Hfsal-dmen with [V(IV)O(acac)(2)] in the presence of MeOH gave the oxidovanadium(IV) complex PS-[V(IV)O(fsal-dmen)(MeO)] (1). On aerial oxidation in methanol, complex 1 was oxidized to PS-[V(V)O(2)(fsal-dmen)] (2). The corresponding neat complexes, [V(IV)O(sal-dmen)(acac)] (3) and [V(V)O(2)(sal-dmen)] (4) were similarly prepared. All these complexes are characterized by various spectroscopic techniques (IR, electronic, NMR, and electron paramagnetic resonance (EPR)) and thermal as well as field-emission scanning electron micrographs (FE-SEM) studies, and the molecular structures of 3 and 4 were determined by single crystal X-ray diffraction. The EPR spectrum of the polymer supported V(IV)O-complex 1 is characteristic of magnetically diluted V(IV)O-complexes, the resolved EPR pattern indicating that the V(IV)O-centers are well dispersed in the polymer matrix. A good (51)V NMR spectrum could also be measured with 4 suspended in dimethyl sulfoxide (DMSO), the chemical shift (-503 ppm) being compatible with a VO(2)(+)-center and a N,O binding set. The catalytic oxidative desulfurization of organosulfur compounds thiophene, dibenzothiophene, benzothiophene, and 2-methyl thiophene (model of fuel diesel) was carried out using complexes 1 and 2. The sulfur in model organosulfur compounds oxidizes to the corresponding sulfone in the presence of H(2)O(2). The systems 1 and 2 do not loose efficiency for sulfoxidation at least up to the third cycle of reaction, this indicating that they preserve their integrity under the conditions used. Plausible intermediates involved in these catalytic processes are established by UV-vis, EPR, (51)V NMR, and density functional theory (DFT) studies, and an outline of the mechanism is proposed. The (51)V NMR spectra recorded for solutions in methanol confirm that complex 4, on treatment with H(2)O(2), is able to generate peroxo-vanadium(V) complexes, including quite stable protonated peroxo-V(V)-complexes [V(V)O(O)(2)(sal-dmen-NH(+))]. The (51)V NMR and DFT data indicate that formation of the intermediate hydroxido-peroxo-V(V)-complex [V(V)(OH)(O(2))(sal-dmen)](+) does not occur, but instead protonated [V(V)O(O)(2)(sal-dmen-NH(+))] complexes form and are relevant for catalytic action.

The Photooxidative Desulfurization of Thiophene with Tetrabutylammonium Bromide as a Phase Transfer Catalyst

Photochemical oxidative desulfurization of thiophene with tetrabutylammonium bromide (TBAB) as phase transfer catalyst was studied. The effects of the TBAB addition and pH on the desulfurization yield of thiophene were investigated. The cycle model of desulfurization of thiophene with TBAB was proposed. The results show that the desulfurization yield of thiophene in n-octane is 80.6% for a 2-hr photoirradiation under the conditions of air flow at 150 mL/min, V (n-octane):V (water) = 1:1, pH = 12, and 0.1 g of TBAB as catalyst. The photooxidation kinetics of thiophene is first-order with rate constant of 0.5702 hr−1 and half-life of 1.22 hr.

Oxidation of Thiophene over Modified Alumina Catalyst under Mild Conditions

Thiophene is a typical thiophenenic sulfur compound that exists in flow catalytic cracking gasoline. Oxidation desulfurization of thiophene was conducted with hydrogen peroxide and formic acid over a series of modified alumina catalysts. The copper oxide modified alumina catalyst was an active catalyst for thiophene oxidation with a 91.2% sulfur removal rate in the oxidation system, while the other oxides less actively modified alumina. The oxidation of thiophene was achieved under mild reaction conditions, and the high conversion of thiophene was easy to be achieved by increasing the reaction temperature or reaction time. The sulfur removal rate of thiophene was enhanced when a phase transfer agent was added in the oxidation system but was reduced with the addition of aromatics.

Meaningful Differences in Spectral Performance, Thermal Behavior, and Heterogeneous Catalysis between Ammonium Molybdate Tetrahydrate and Its Adduct of β-Cyclodextrin

A novel molecule-ion adduct of ammonium molybdate tetrahydrate (AMT) with beta-cyclodextrin (CD) was prepared in this work. Significant differences in spectral properties between AMT and the adduct AMT-beta-CD were observed by a series of experimental probes, such as powder X-ray diffraction, Fourier transformation infrared spectroscopy, and Raman spectroscopy. Field emission scanning electron microscopy showed that, although the crystal growth of AMT-beta-CD was dominated by the molecular stacking of AMT, the size and morphology of the adduct were rather different from those seen in free AMT. The difference in stacking forms was attributed to the contribution of the molecule-ion interaction between AMT and beta-CD. A drastic improvement in thermal stability of AMT and beta-CD after adduct formation was observed by thermogravimetry analysis, which was confirmed by controlled sintering measurements. This revealed that the adduct interaction between them played an important role in mediating the thermal decomposition process of the adducted components. Furthermore, our results indicated that AMT and its adduct had a different performance in the catalytic desulfurization of thiophene and its derivatives. The fact that the catalytic efficiency of AMT was decreased after adduct formation implied there was a complexation between AMT and beta-CD. Besides, several unusual molecular ions--NH(3)(+), NH(2)(+), and NH(+)--were simultaneously found with gas chromatography coupled to time-of-flight mass spectrometry of free AMT.

Removal of Thiophene from Coking Benzene over SO42−/Fe2O3 Solid Acid under Mild Conditions

Desulfurization of thiophene in coking benzene with n-butanol as an alkylating agent over SO42−/Fe2O3 solid superacid at 353 K and atmospheric pressure was investigated. The acidity of the catalyst was measured by temperature-programmed desorption (TPD) of ammonia, and the result confirms that the SO42−/Fe2O3 catalyst has a high acid strength. The sample after reaction was detected by gas chromatography−mass spectrometry (GC-MS), and the results show that thiophene has been removed completely.

Desulfurization of Thiophene on Au/TiC(001): Au−C Interactions and Charge Polarization

Photoemission and first-principles DF calculations were used to study the interaction of thiophene with TiC(001) and Au/TiC(001) surfaces. The adsorption strength of thiophene on TiC(001) is weak, and the molecule desorbs at temperatures below 200 K. The molecule binds to Ti centers of TiC(001) through its sulfur atom with negligible structural perturbations. In spite of the very poor desulfurization performance of TiC(001) or Au(111), a Au/TiC(001) system displays a hydrodesulfurization activity higher than that of conventional Ni/MoS(x) catalysts. The Au<-->TiC(001) interactions induce a polarization of electron density around Au which substantially increases the chemical reactivity of this metal. Au nanoparticles drastically increase the hydrodesulfurization activity of TiC(001) by enhancing the bonding energy of thiophene and by helping in the dissociation of H(2) to produce the hydrogen necessary for the hydrogenolysis of C-S bonds and the removal of sulfur. H(2) spontaneously dissociates on small two-dimensional clusters of gold in contact with TiC(001). On these systems, the adsorption energy of thiophene is 0.45-0.65 eV larger than that on TiC(001) or Au(111). Thiophene binds in a eta(5) configuration with a large elongation (approximately 0.2 A) of the C-S bonds.

Oxidative Desulfurization of Thiophene Catalyzed by (C4H9)4NBr·2C6H11NO Coordinated Ionic Liquid

Oxidative desulfurization (ODS) of thiophene with hydrogen peroxide/acetic acid using a quaternary ammonium coordinated ionic liquid (IL) (C4H9)4NBr·2C6H11NO as an effective catalyst has been studied. The catalyst of coordinated IL (C4H9)4NBr·2C6H11NO without fluorous anions is environmentally benign and easy prepare from cheap amines. Thiophene can be oxidized in the oil phase to greater polar sulfoxide, sulfone, and SO42−. Most of the oxidation products transfer to the water phase for their higher polar property, resulting in the removal of thiophene from the n-octane phase without additional extraction by solvent. The effect of the amount of catalyst, hydrogen peroxide, and acetic acid, reaction time, and temperature were investigated in detail. Optimal amounts of catalyst, hydrogen peroxide, and acetic acid were obtained at amounts near 0.20 g, 2, and 4 mL/18 mL of model oil, respectively. The catalytic oxidative desulfurization, 98.8% removal rate thiophene in n-octane, and 95.3% sulfur removal rate of actual fluidized catalytic cracking (FCC) gasoline were achieved after 30 min under optimal experimental conditions. Kinetics parameters of the catalytic oxidation of thiophene were measured and calculated. The results show that the kinetics of catalytic oxidation of thiophene is pseudo-first-order, with an apparent rate constant of 1.05 × 10−3 s−1 and half-life of 660 s.

Oxidation Desulfurization of Thiophene Using Phase Transfer Catalyst/H2O2 Systems

In our study, an effective phosphomolybdic acid/hexadecyltrimethyl-ammonium bromide catalyst for oxidative desulfurization of thiophene in a model compound was formed. The oxidation activities of thiophene for a series of heteropoly acids were estimated. The results show that the oxidation activity of thiophene increased with increasing oxidation time, oxidation temperature, and the volume of 30% H2 O2 oxidant. The optimal values are 150 min, 40°C, and 3 mL, and sulfur removal attained 96.3% when phosphotungstic acid/hexadecyltrimethylammonium bromide was used as a catalyst.

Study on photosensitized oxidative desulfurization of thiophene by riboflavin

Photosensitized oxidative desulfurization of thiophene in n-octane/water extraction system with riboflavin as photosensitizer and O 2 in air as oxidant was studied. A 500 W high pressure Hg lamp was used as the light source for irradiation and air was introduced by a gas pump for supplying O 2. The desulfurization yield of thiophene was 85.4% for a 3 h photoirradiation under the conditions with an air flow of 150 mL/min, water/oil ratio of 1:1 and riboflavin concentration of 30 μmol/L. The mechanism of photosensitized oxidation of thiophene is 1O 2 exited from 3O 2 by the addition of riboflavin. Under the above conditions, the photooxidation kinetics of thiophene with O 2/riboflavin is first-order with a rate constant of 0.3277 h −1 and half-time of 1.37 h.

Promotion of Thiophene Hydrodesulfurization by Ammonia over Amorphous-Silica−Alumina-Supported CoMo and NiMo Sulfides

Contrary to the commonly accepted notion that ammonia inhibits the hydrodesulfurization (HDS) of organosulfur compounds, an unexpected promotional effect of ammonia on the hydrodesulfurization of thiophene over amorphous-silica-alumina (ASA)-supported sulfides of CoMo (CoMo/ASA) and NiMo is reported. Addition of ammonia may increase the activity up to a factor of 1.5. The effect is specific to Co-and Ni-promoted MoS 2 supported on an acidic amorphous silica-alumina support. Over CoMo sulfides supported on γ-alumina and carbon, the HDS of thiophene is inhibited by ammonia. The effect is related to the presence of Bronsted acid hydroxyl groups on the amorphous silica-alumina support, as it is found that after ion-exchange with Na + the HDS activity decreases with the NH 3 partial pressure. A comparison of infrared spectra of adsorbed CO over alumina- and ASA-supported CoMo following various pretreatments (H 2 S/H 2 vs H 2 S/NH 3 /H 2 ) points to an electronic effect of the acidic ASA support on the active Co-Mo-S phase. It is speculated that the sulfur bond energy is increased due to this interaction. While the desulfurization of thiophene is sensitive to these changes, sulfur removal from (di)benzothiophene is not, and ammonia acts only as an inhibitor, likely due to the stronger adsorption of these reactants.