Oxidative Desulfurization of Gas Oil Catalyzed by (TBA)4PW11Fe

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Oxidative desulfurization of gas oil catalyzed by (TBA)4PW11Fe@PbO as an efficient and recoverable heterogeneous phase-transfer nanocatalyst Mohammad Ali Rezvani, Sahar Khandan, and Negin Sabahi Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 24 Apr 2017 Downloaded from http://pubs.acs.org on April 27, 2017

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Oxidative desulfurization of gas oil by nanocomposite (TBA)4PW11Fe@PbO as an efficient and recoverable heterogeneous phase-transfer catalyst 846x715mm (96 x 96 DPI)

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Oxidative desulfurization of gas oil catalyzed by (TBA)4PW11Fe@PbO as an efficient and recoverable heterogeneous phase-transfer nanocatalyst Mohammad Ali Rezvani,* Sahar Khandan and Negin Sabahi Department of Chemistry, Faculty of Science, University of Zanjan, Zanjan, Iran *Corresponding author: Fax: +982 415 152 617; E-mail address: [email protected] KEYWORDS:

Transition

metal-substituted

polyoxometalate,

Lead

oxide,

Oxidative

desulfurization, Gas oil

ABSTRACT: In this manuscript, a tetra (n-butyl) ammonium salt of ironIII-substituted phosphotungstate@lead oxide composite, (TBA)4PW11Fe@PbO, was successfully synthesized by the thermal decomposition method as a nanocatalyst for oxidative desulfurization (ODS) of gas oil. The incorporation of the materials was confirmed by FT-IR, UV-vis, XRD, SEM, EDX, and

31

P

NMR

characterization

methods.

To

evaluate

the

catalytic

activity

of

(TBA)4PW11Fe@PbO, ODS process was carried out using CH3COOH:H2O2 oxidizing agent at 60 °C. From the attained results, the total sulfur and mercaptan content of real gas oil were


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reduced with 97% efficiency after 2 hours. Furthermore, the various comparative experiments were performed to investigate the capability of (TBA)4PW11Fe@PbO in ODS of prepared model fuel. Results were indicated that the kinetic of sulfur oxidation fitted to the pseudo-first-order kinetic model. The probable mechanism was proposed via the electrophilic mechanism through the formation of a peroxo-metalate intermediate complex with phase-transfer properties. After five oxidation runs, the heterogeneous nanocatalyst was separated and recovered simplicity.

1. INTRODUCTION

The various types of sulfur compounds present in petroleum products emission SOx gasses during the combustion. These hazardous air pollutants are not only causing corrosion but also contributing to acid rain, photochemical smog, and human diseases.1–3 Also, the strict regulations regarding the environment safety and improvement of transportation fuels quality are the most pressing issues of the world recently. In this respect, lots of substantial research efforts have been conducted to reduce the sulfur levels in refined petroleum products to less than 10 ppmw.4,5 Hydrodesulfurization (HDS) is often used traditional refining process which has been proved as a robust method for lowering thiols, mercaptans, sulfides, and disulfides-containing impurities.6 Nevertheless, it is less effective in the elimination of refractory heterocyclic organosulfur molecules like thiophene (Th), benzothiophene (BT), dibenzothiophene (DBT), and their sterically hindered derivatives. Additionally, the requirement of high temperature and pressure operating conditions with large quantities of hydrogen impose high cost and energy consumption.7 Therefore, some affordable and energy-saving alternative methods have been developed to produce the ultra-clean fuels in many countries. Among them, ODS has been widely recognized as one of the most competitive systems for deep desulfurization under


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moderate condition.7,8 This process has been implemented in two stage: (І) conversion of sulfur compounds to the corresponding sulfoxide or sulfone molecules using an oxidizing agent, and (ІІ) subsequently removal of the oxidized materials from the fuel by means of different methods such as extraction or adsorption.9 Given the importance of choosing oxidant, organic peracids which are produced in situ by reaction of H2O2 and short-chain carboxylic acids (formic acids or acetic acids) employed as an effective oxidizing system in the organic phase.10,11 Polyoxometalates (POMs) as well-known metal-oxygen inorganic compounds have received extensive attention in catalysis area over the past decade.12–14 Among the different varieties of their structures, transition metal-monosubstituted polyoxoanion in the primary Keggin structure, [XM11TMO39]n- (X= P, Si, B; M= W, Mo; TM= transition metal), is favored for the synthesis of POM-based catalysts due to their variable structures, tunable solubility, reversible redox transformations, and high catalytic activity.15–17 The bulk POMs with water-soluble properties have been widely investigated in catalytic homogeneous reactions.15 However, these systems are suffered from difficult separation and regeneration of the catalyst. To overcome these undesirable obstacles, designing heterogeneous catalysts are explored by deposition of POMs onto suitable supports or preparing their insoluble salts.18,19 Nowadays, the incorporation of POMs and metal oxide supports such as TiO2 20, ZrO2 21, and Al2O3 22 have been developed as a promising strategy to enhance the catalytic activity of the polyoxo anion clusters. Lead oxide (PbO) particles are attracted interest for catalyzing the organic reactions 23, graphite oxidation 24, and dye degradation.25 The oxidative properties, simple preparation, and recoverability of PbO particles make it appropriate candidates for supporting POMs in the heterogeneous oxidation reaction of sulfur-containing compounds.


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As a part of our ongoing efforts for developing the application of POMs to promote the quality of fuels

26–29

, we report the designing of phase-transfer-type (TBA)4PW11Fe@PbO nanocatalyst

for ODS of real gas oil and prepared model fuel. In typical oxidation reactions, the mixture of CH3COOH:H2O2 is used as oxidant and CH3CN applied for extracting the polar oxidized sulfur compounds. Moreover, the influence of the main affecting factors on the ODS efficiency, kinetics parameters, and probable reaction mechanism are discussed.

2. EXPERIMENTAL SECTION

2.1. Materials. All chemicals and solvents were commercially available and used as received. Benzothiophene (BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT), 4,6dimethyldibenzothiophene (4,6-DMDBT), n-heptane, hydrogen peroxide (H2O2, 30 vol.%), and acetic acid (CH3COOH, 99.7%), acetonitrile (CH3CN), sodium tungstate dihydrate (Na2WO4.2H2O), disodium hydrogen phosphate (Na2HPO4), Iron(III) nitrate nonahydrate (Fe(NO3)3.9H2O), and tetrabutylammonium bromide (TBAB) were purchased from Sigma– Aldrich company. The lead nitrate (Pb(NO3)2) and citric acid monohydrate (C6H8O7.H2O) were obtained from Merck Chemical Company. Typical real gas oil was used with the following specification: density 0.8256 g/mL at 15 °C, total sulfur content 0.8738 wt.%. 2.2. Synthesis of the ((n-C4H9)4N)4[PW11Fe(H2O)O39]. The tetra (n-butyl) ammonium salt of ironIII-substituted phosphotungstate was synthesized by the following procedure: 3.29 g (10 mmol) Na2WO4·2H2O was dissolved in 20 mL of distilled water. To the solution, 0.13 g (0.91 mmol) Na2HPO4 and 0.49 g (1.2 mmol) Fe(NO3)3.9H2O were added. The pH of the solution was adjusted to 4.5 under stirring, and the mixture was heated to 80–85 °C. After that, an aqueous solution of TBAB 1.45 g (4.5 mmol) in 5 mL distillated water was added drop-wise to the above


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solution. The mixture was magnetically stirred to form a white precipitate. Finally, the precipitate ((n-C4H9)4N)4[PW11Fe(H2O)O39] (hereinafter referred as (TBA)4PW11Fe) was recovered by filtration, washed with ether, and air dried. 2.3. Synthesis of the PbO support. In a typical synthesis, 1.90 g (10 mmol) of C6H8O7.H2O was dissolved in 15 mL of distilled water as a capping agent. After the complete dissolution of the above solid substance, this solution was added drop-wise to the 15 mL of aqueous solution containing 3.90 g (10 mmol) Pb(NO3)2 under magnetic stirring at 70 °C for 45 minutes to form a milky white gel. At last, the obtained gel was aged and dried at 80 °C for 2 hours and then the dried sample was calcined at 600 °C for 2 hours. 2.4. Synthesis of the ((n-C4H9)4N)4[PW11Fe(H2O)O39]@PbO nanocatalyst. The ((nC4H9)4N)4[PW11Fe(H2O)O39]@PbO was prepared as follows: the synthesized (TBA)4PW11Fe (0.10 g) was dissolved in 5 mL boiling distilled water and then added slowly into the Pb(NO3)2 and C6H8O7.H2O solutions during the preparation of the PbO support. The resulted mixture was maintained at 70 °C under stirring for 45 minutes to obtain a uniform and homogeneous solution. The following steps were accomplished as same as the PbO production. After calcination step, the remained orange powder ((n-C4H9)4N)4[PW11Fe(H2O)O39]@PbO was designated as (TBA)4PW11Fe@PbO nanocatalyst. 2.5. ODS process of prepared model fuel. In this investigation, a certain amount of the aromatic sulfur compounds (ASCs) such as BT, DBT, 4-MDBT, and 4,6-DMDBT were dissolved in n-heptane as a model fuel to evaluate the catalytic performance of (TBA)4PW11Fe@PbO nanocatalyst in sulfur oxidation reactions. The sulfur concentration of each ASCs was 500 ppm (by weight). At the first, the water bath was heated up to 25, 40, 50, and 60 °C in separate experiments. Then, 50 mL of prepared fuel sample in a closed round-


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bottom flask which equipped with a magnetic stirrer was heated to the reaction temperature. Afterward, 6 mL of CH3COOH:H2O2 (the volume ratio of 1:1) and 0.1 g of nanocatalyst was added slowly to the reaction vessel, respectively. The ODS process was continued under stirring condition (500 rmp). After the passage of 2 hours, the above mixture was cooled down to room temperature and 10 mL of acetonitrile added to extract the oxidized ASCs. The formed immiscible liquids (n-heptane and water phases) were separated by separation funnel and decantation technique. The synthesized heterogeneous nanocatalyst was separated and regenerated from reaction system using simple filtration. The total sulfur concentration after oxidation treatment was determined using the X-ray fluorescence spectrometer according to American Standard Test Methods (ASTM D-4294 and ASTM D-3227). The ASCs removal efficiency was calculated using Eq. (1), in which Ai is the initial and Af is the final concentration of ASCs after oxidation treatment.

 Af  ASC removal efficiency (%) = 1 −  × 100  Ai 

(1)

2.6. ODS process of gas oil fuel. In the same manner as the ODS of the ASCs, after heating the water bath, 50 mL of real gas oil fuel was added to the round-bottom flask and its temperature maintained constantly at 60°C during the experiment. Subsequently, 6 mL of CH3COOH:H2O2 and 0.1 g of (TBA)4PW11Fe@PbO were added into the vessel. The mixture was vigorously stirred by a magnetic stirrer for 2 hours. When the oxidation process has been completed, the flask was cooled down to room temperature and then 10 mL of polar CH3CN was used to extract the polar oxidized sulfur compounds from gas oil. In the separation step, the oil phase was separated by decantation. The total sulfur and mercaptan content in gas oil before and after ODS test were determined by using X-ray fluorescence. The ODS efficiency was expressed


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by the following Eq. (2), where Si and Sf correspond to the initial and final concentration of total sulfur content in gas oil, respectively.

 Sf ODS efficiency (%) = 1 −  Si

  × 100 

(2)

2.7. Characterization methods. Fourier transform infrared spectroscopy (FT-IR) studies were done on a Thermo-Nicolet-is 10 spectrometer, using KBr disks in the range 400–4000 cm−1. Ultraviolet–visible (UV–vis) spectra were measured with a double beam Thermo-Heylos spectrometer in the range of 200-400 nm. Measurements were performed by using quartz cuvettes. Powder X-ray diffraction (XRD) analysis was collected between 2θ = 5°-80° at room temperature on a Bruker D8 advance powder X-ray diffractometer with a Cu-Kα (λ = 0.154 nm) radiation source. The surface morphologies were examined by scanning electron microscope (SEM) by LEO 1455 VP equipped with an energy dispersive X-ray (EDX) spectroscopy apparatus. 31P NMR spectrums were recorded on Bruker Ultra Shield 250 MHz. The total sulfur and mercaptan content in gas oil before and after treatment were determined using X-ray fluorescence with a TANAKA X-ray fluorescence spectrometer RX-360 SH.

3. RESULTS AND DISCUSSION

3.1. Material characterizations. The identification of specific chemical bands and functional groups of the synthesized samples was characterized using FT-IR spectroscopy to confirm their successful incorporation. FT-IR spectra of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO nanocatalyst are depicted in Figure 1. The clear intense adsorption peak around 470 cm-1 is attributed to the Pb-O stretching vibrations and also the appeared band at 683 cm-1 is assigned to the asymmetric bending vibrations of Pb-O–Pb bands (Figure 1(a)). In the


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spectrum of prepared PbO support using citric acid capping agent, the bands at 1732 and 2922 cm-1 are revealed the stretching vibrations of C=O and antisymmetric stretching vibrations of CH groups, respectively.30 The bending and stretching vibrations of O-H in water molecules are observed at 1417 and 3385 cm-1. According to Figure 1(b), the unique characteristics peaks at 793, 887, 962, and 1068 cm-1 are caused by the stretching modes involving edge-sharing W–Oc– W, corner-sharing W–Ob–W, terminal W=Od, and P−O bond in the Keggin-type [PW11Fe(H2O)O39]4- anions, respectively.18 Furthermore, the peaks at 1383 and 1483 cm-1 are attributed to C–H scissoring vibrations of CH3–N+. The absorption bands at 2873 and 2961 cm-1 are ascribed to the symmetric and asymmetric stretching modes of –CH2 of TBA cation.31 Figure 1(c) indicates the infrared spectra patterns of (TBA)4PW11Fe@PbO. The existence peaks in the region of 700-1000 cm-1 are demonstrated the presence of (TBA)4PW11Fe after supporting on PbO. The broad peak at 3360 cm-1 is corresponded to the water molecule coordinated to the ironIII-substituted phosphotungstate center, which overlapped by the stretching vibrations of –NH functional group. The observed peak shifts in the FT-IR spectra of the synthesized nanocatalyst compared to the pure materials are suggested that the preparation of (TBA)4PW11Fe@PbO composite. The UV-vis absorption spectra of synthesized samples are illustrated in Figure 2. The maximum absorption peak for pure PbO is shown around 200 nm. As can be seen in Figure 2(b), the peak at 257 nm is considered as ligand-to-metal charge transfer transition of O2-→W6+, where W atoms positioned in W–O–W. In both of (TBA)4PW11Fe and (TBA)4PW11Fe@PbO patterns, the absorptions peaks around the wavelengths of 197-200 nm are served as the evidence for πp-πd electronic transitions of terminal W=Od.32


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The XRD patterns of the powder PbO, (TBA)4PW11Fe, and (TBA)4PW11Fe@PbO nanocatalyst are shown in Figure 3. Based on the obtained results, the main reflections of the pure PbO are observed at 2θ values of 28.5°, 29°, 31.7°, 35.6°, 48.5°, 56°, and 59.6°, which associated to the (111), (002), (200), (210), (022), (222), and (311) crystal planes, respectively.23 The unique intense peaks of (TBA)4PW11Fe are displayed at the position of 16°, 19°, 21.5°, 22.7°, 23.8°, 29.7°, 30.5°, and 31.4° in Figure 3(b). The XRD pattern of prepared nanocatalyst is mainly composed of the diffraction peaks of the PbO, while the exaction of peaks in the range of 15°– 30° is reflected the presences of (TBA)4PW11Fe species. It can be concluded that the structures of materials are remained intact after incorporation using introduced producer method. The nanocrystallite size of (TBA)4PW11Fe@PbO is estimated to be about 62 nm by means of the Debye–Scherrer equation (Eq. 3).33 D=

Kλ β cosθ

(3)

where the value of D is the size of the crystal, K is a constant equal to 0.89, λ is the wavelength of X-ray (1.5406°A), β is the full width at half maximum (FWHM), and θ is the half of the diffraction angle. The surface morphology of PbO support and (TBA)4PW11Fe@PbO catalyst was accurately determined by utilizing SEM technique. As depicted in Figure 4(a), the SEM images of pure PbO are presented well-dispersed spherical particles. After deposition of (TBA)4PW11Fe clusters on PbO, the uniform morphology of support is particularly changed to a rugged surface with a large number of cavities (Figure 4(b,c)). It can be suggested that the porous surface of the synthesized catalyst gives unique features to enhance its catalytic activity. Each of the cavities is an appropriate site for scavenging the sulfur-containing compounds.


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The EDX pattern is revealed the existence of elemental C, O, Fe, W, and Pb in the (TBA)4PW11Fe@PbO composite structure (Figure 5). The observed intense peak is represented around 2-3 keV indicated the formation of the catalyst from a high amount of Pb (84.07 wt.%), which is even in good agreement with the results of XRD and SEM studies. The successful preparation of nanocatalyst was further investigated using

31

P NMR

spectroscopy. After the dissolution of (TBA)4PW11Fe and (TBA)4PW11Fe@PbO solids in dimethyl sulfoxide (DMSO), the main single peak was located at −11.55 and −11.35 ppm (Figure 6(a,b)). These peaks were ascribed to the central phosphorus in the tetrahedral PO4 unit of ironIII-substituted phosphotungstate. As can be seen, there was no significant shift in the position of the peaks, which verifies the presence of the identical phosphorus atom in (TBA)4PW11Fe structure before and after supporting on PbO. 3.2. ODS results of real gas oil and prepared model fuel. For investigation the capability of (TBA)4PW11Fe@PbO nanocatalyst, ODS process was performed on typical real gas oil and prepared model fuel under the mentioned condition in the experimental section. The attained results after oxidation treatment were reported in Table 1 and Figure 7. According to the Entry 1, the total sulfur content of gas oil sample was reduced from 0.8738 to 0.0285 wt. %. Also, the mercaptan sulfur compounds were much lowered to 9 ppm (Entry 3). It should be pointed out that the main specifications of gas oil were remained unchanged after ODS. The removal efficiency of BT, DBT, 4-MDBT, and 4,6-DMDBT from model fuel were 93%, 97%, 94%, and 95%, respectively (Figure 7). These results were rendered the success of this catalytic system (TBA)4PW11Fe@PbO/CH3COOH/H2O2 to desulfurize the organosulfur molecules. 3.3. Effect of different catalysts on ODS process. The competitive desulfurization reactions were applied to investigate the effect of catalyst structure on removal efficiency of sulfur


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compounds. For this purpose, typical kinds of heteropolyoxometalate involve Keggin, Wells– Dawson, and Preyssler were tested as a catalyst for the elimination of ASCs and total sulfur content of real gas oil under the same experimental conditions. The results were listed in Table 2. It was observed that each catalyst by itself decreased the concentration of sulfur compounds and their catalytic activity was followed in order of H3PW12O40> H14[NaP5W30O110]> H6P2W18O62> H6P2Mo18O62. As could be concluded, the POMs in the Keggin structure were proved to be the more efficient catalysts in the ODS reactions. Besides, the high catalytic properties of tungsten compared with molybdenum-based catalysts were caused by the strong Brønsted acidity of tungsten atoms.34 In this work, a poor sulfur removal percentage was attributed to PbO support, while, the superior catalytic performance was achieved by the synthesized (TBA)4PFeW11@PbO nanocatalyst. It was reflected that the supporting of (TBA)4PFeW11 on PbO led to an enhancement in the catalytic activity of unsupported (TBA)4PFeW11. 3.4. Effect of different sulfur compounds on ODS process. The reactivity of the ASCs in designed ODS process is also studied using (TBA)4PW11Fe@PbO catalyst. As noted in Figure 7 and Table 2 (Entry 1), among the different used model sulfur compounds, DBT was shown high oxidative reactivity and removed from n-heptane phase with 97% yield. Based on the results, the ASCs reactivity was decreased in the following order: DBT> 4,6-DMDBT> 4-MDBT> BT. According to reported literature, the trend of electron density of sulfur atom in these compounds was 4,6-DMDBT(5.760)> 4-MDBT (5.759) > DBT (5.758)> BT (5.696).35 It could be speculated that the partial electron charge on the sulfur atom had an effect on the reactivity of thiophenic molecules as well as expressed by J. Xiao et al.8 Another concept relevant was attributed to the stereo-hindrance of the CH3 groups, which caused the highest removal


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efficiency for DBT substrate. Due to the high oxidation reactivity DBT, it was selected as a representative compound of ASCs in following ODS runs. 3.5. Effect of nanocatalyst dosage on ODS process. To assess the effect of nanocatalyst dosage on removal efficiency of sulfur compounds, various amount of (TBA)4PW11Fe@PbO catalyst were used. Based on blank experimental results, 20% of the DBT and 17% of the sulfur content of real gas oil were reduced (Table 2, Entry 8). The results are presented in Figure 8. Also, it was found that the removal percentage of DBT and organosulfur compounds increased consecutively with an increased the concentration levels of nanocatalyst in reaction medium due to the abundance of peroxo-metalate intermediate complexes. When the amount of nanocatalyst was further increased to 0.12 g, any noticeable change was not observed. Therefore, the favorable dosage of (TBA)4PW11Fe@PbO was 0.10 g and the sulfur removal efficiency was obtained 97%. 3.6. Effect of reaction temperature and time on ODS process. The influence of reaction temperature on ODS was evaluated in the temperature range 25-60 °C. From Figure 9, the reducing the concentration of DBT and total sulfur content in the model fuel and real gas oil at the temperature of 25 °C was occurred with 63% and 61% removal efficiency, respectively. While increasing the reaction temperature to 60 °C had a remarkable impact. Increasing the reaction time also had the same effect on the catalytic capability of the oxidation system. The highest yield of sulfur removal was 97%, which attained at 60 °C after 2 hours. 3.7. The kinetic studies on ODS process. In order to clarify the kinetics of DBT and sulfur oxidation, the reaction kinetic parameters were examined using pseudo-first-order model at the different temperatures, from 25 °C to 60 °C in 2 hours. The reaction rate constant k was calculated by plotting the ln[S]t /[S]i or [S]t /[S]i against t as follows:


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r=− [S ]t

d [S ] = k [S ] dt

d [S ]

∫ [ ] [S ] S

= ln

i

[S ]t [S ]i

[S ]t = [S ]i e − kt

= −kt

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(4) (5)

(6)

Where, [S]i and [S]t are the initial concentrations and concentrations at time t, respectively. According to Figure 10 and Eq. (6), a linear relationship was observed between [S]t /[S]i and t parameters and the correlation coefficients obtained close to unity (Table 3). It was indicated that the kinetic results fitted to the pseudo-first-order kinetic model. Further, the affiliation of k on the reaction temperature could be express by the well-known Arrhenius equation 29 in which, A is the pre-exponential factor, Ea the apparent activation energy, R and T are the universal gas constant and the reaction temperature, respectively (Eq. 7). The Ea value was calculated using the plot of Ln k versus 1/T (Figure 11). The Ea were 24.83 and 22.62 kJ/mol for oxidation of DBT and total sulfur content of gas oil, respectively.

k = Ae

− Ea RT

(7)

3.8. Proposed mechanism of ODS process. The overall mechanism of sulfide oxidation can be explained by the formation peroxo-metalate intermediate complex in the presence of (TBA)4PW11Fe@PbO nanocatalyst and CH3COOH:H2O2 in a biphasic system (Scheme 1). To commence, H2O2 reacts with CH3COOH quickly to generate the in-situ formation of peracetic acid (CH3COOOH) as a supplier source of active oxygen (step 1). The terminal metal atoms (M= W or Fe) in (TBA)4PW11Fe accept active oxygen form CH3COOOH and then peroxo-metalate complex, including (TBA)4[PO4(MO(O2)2)4], are made (step 2). Also, the water molecules emerge as a by-product. The sulfur oxidation is occurred via the electrophilic mechanism.8 The


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electron pairs on the sulfur atom can be attacked by the electrophilic active oxygen in (TBA)4[PO4(MO(O2)2)4] structure to produce sulfoxide molecules (step 3). The conversion of sulfoxide to their corresponding sulfone can be performed by undergoing further oxidation process (step 4). At the end, an organic extraction solvent CH3CN is used for extraction of the oxidized products. The high polarity of CH3CN makes it as a good candidate for increasing the polarity of the water phase to improve the extraction of polar sulfones compounds. The synthesized (TBA)4PW11Fe@PbO with a quaternary ammonium cantercation can act as a phasetransfer agent to facilitate the transformation of the peroxo-metal anions into the oil phase. The hydrophobic properties of TBA play an important role in affinity of the catalyst to the sulfur compounds. On the other hand, the mass transfer across the interface of the water phase and oil phase is faced with the rate-limitation. Therefore, a phase-transfer catalyst is used to increase the mass transfer in the emulsion systems.12,36 3.9. Regeneration of the nanocatalyst. After following each catalytic run, the heterogeneous nanocatalyst ((TBA)4PW11Fe@PbO) was regenerated by simple filtration, and washed with dichloromethane and dried at 90 °C for 1 hour. Then, the recovered catalyst was used for the subsequent process under similar oxidation conditions. The results of ODS reaction using reused nanocatalyst after the first run are reported in Table 1. It was found that these results were quite close to the results obtained with fresh nanocatalyst. As shown in Figure 12, the DBT removal efficiency was dropped from 97% to 93% after five regeneration cycles, which can be ascribed to cover the active sites of the nanocatalyst with sulfur-containing substrates during ODS period.

4. CONCLUSIONS


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In conclusion, the (TBA)4PW11Fe@PbO nanocatalyst was has been successfully prepared by supporting Keggin-type (TBA)4PW11Fe on PbO particles via the thermal decomposition method. The catalytic activity of nanocatalyst was carried out on prepared model fuel and real gas oil for removing organosulfur compounds. The comparative experimental results were demonstrated that the desulfurization efficiency depended on the structure of the catalyst, nature of the sulfur molecules, reaction temperature, and dosage of the nanocatalyst. Based on catalytic (TBA)4PW11Fe@PbO/CH3COOH/H2O2 system, the oxidation reactivity of ASCs was decreased according to the following order: DBT> 4,6-DMDBT> 4-MDBT> BT. After catalytic oxidation reactions, the total sulfur content of gas oil fuel could be reduced to 0.0285 wt. %. Moreover, the oxidation of sulfur compounds was followed the pseudo-first-order kinetic model. At the end, the heterogeneous nanocatalyst was reused up to five regeneration cycles. This work was introduced as a facile method for the synthesized phase-transfer nanocatalyst (TBA)4PW11Fe@PbO and its application in the ODS treatment to promote the quality of gas oil fuel.

REFERENCES

(1) Kulkarni, P. S.; Afonso, C. A. M. Deep desulfurization of diesel fuel using ionic liquids: current status and future challenges. Green Chem. 2010, 12, 1139–1149. (2) Yang, C.; Zhao, K.; Cheng, Y.; Zeng, G.; Zhang, M.; Shao, J.; Lu, L. Catalytic oxidative desulfurization of BT and DBT from n-octane using cyclohexanone peroxide and catalyst of molybdenum supported on 4A molecular sieve. Sep. Purif. Technol. 2016, 163, 153–161.


15

Page 17 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(3) Ullah, R.; Bai, P.; Wu, P.; Etim, U. J.; Zhang, Z.; Han, D.; Subhan, F.; Ullah, S.; Rood, M. J.; Yan, Z. Superior performance of freeze-dried Ni/ZnO-Al2O3 adsorbent in the ultra-deep desulfurization of high sulfur model gasoline. Fuel Process. Technol. 2017, 156, 505–514. (4) García-Gutiérrez, J. L.; Laredo, G. C.; García-Gutiérrez, P.; Jiménez-Cruz, F. Oxidative desulfurization of diesel using promising heterogeneous tungsten catalysts and hydrogen peroxide. Fuel 2014, 138, 118–125. (5) Ullah, R.; Bai, P.; Wu, P.; Zhang, Z.; Zhong, Z.; Etim, U. J.; Subhan, F.; Yan, Z. Comparison of reactive adsorption desulfurization performance of Ni/ZnO-Al2O3 adsorbents prepared by different methods. Energy Fuels 2016, 30, 2874–2881. (6) Zhang, H.; Gao, J.; Meng, H.; Li, C. X. Removal of thiophenic sulfurs using an extractive oxidative desulfurization process with three new phosphotungstate catalysts. Ind. Eng. Chem. Res. 2012, 51, 6658−6665. (7) Safa, M.; Mokhtarani, B.; Mortaheb, H. R.; Tabar Heidar, K. Oxidative desulfurization of model diesel using ionic liquid 1-octyl-3-methylimidazolium hydrogen sulfate: an investigation of ultrasonic irradiation effect on performance. Energy Fuels 2016, 30, 10909–10916. (8) Xiao, J.; Wu, L.; Wu, Y.; Liu, B.; Dai, L.; Li, Z.; Xia, Q.; Xi, H. Effect of gasoline composition on oxidative desulfurization using a phosphotungstic acid/activated carbon catalyst with hydrogen peroxide. Appl. Energy 2014, 113, 78–85. (9) Bakar, W. A. W. A.; Ali, R.; Kadir, A. A. A.; Mokhtar, W. N. A. W. Effect of transition metal oxides catalysts on oxidative desulfurization of model diesel. Fuel Process. Technol. 2012, 101, 78–84.


16

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 40

(10) Otsuki, S.; Nonaka, T.; Takashima, N.; Qian, W.; Ishihara, A.; Imai T.; Kabe, T. Oxidative desulfurization of light gas oil and vacuum gas oil by oxidation and solvent extraction. Energy Fuels 2000, 14, 1232–1239. (11) Rezvani, M. A.; Oveisi, M.; Alinia Asli, M. Phosphotungestovanadate immobilized on PVA as an efficient andreusable nano catalyst for oxidative desulfurization of gasoline. J. Mol. Catal. A: Chem. 2015, 410, 121–132. (12) Sachdeva, T. O.; Pant, K. K. Deep desulfurization of diesel via peroxide oxidation using phosphotungstic acid as phase transfer catalyst. Fuel Process. Technol. 2010, 91, 1133–1138. (13) Chen, Y.; Wang, S.; Xue, L.; Zhang, Z.; Li, H.; Wu, L.; Wang, Y.; Li, F.; Zhang, F.; Li, Y. Insights into the working mechanism of cathode interlayers in polymer solar cells via [(C8H17)4N]4[SiW12O40]. J. Mater. Chem. A 2016, 4, 19189–19196. (14) Leng, Y.; Zhao, J.; Jiang, P.; Wang, J. Amphiphilic polyoxometalate-paired polymer coated Fe3O4: Magnetically recyclable catalyst for epoxidation of bio-derived olefins with H2O2. ACS Appl. Mater. Interfaces 2014, 6, 5947–5954. (15) Leng, Y.; Wu, J.; Jiang, P.; Wang, J. Amphiphilic phosphotungstate-paired ionic copolymer as a highly efficient catalyst for triphase epoxidation of alkenes with H2O2. Catal. Sci. Technol. 2014, 4, 1293–1300. (16) Wang, S. S.; Yang, G. Y. Recent Advances in Polyoxometalate-Catalyzed Reactions. Chem. Rev. 2015, 115, 4893–4962.


17

Page 19 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(17) Izzet, G.; Ishow, E.; Delaire, J.; Afonso, C.; Tabet, J. C.; Proust, A. Photochemical activation of an azido manganese-monosubstituted Keggin polyoxometalate: On the road to a Mn(V)−nitrido derivative. Inorg. Chem. 2009, 48, 11865–11870. (18) Estrada, A. C.; Santos, I. C. M. S.; Simões, M. M. Q.; Neves, M. G. P. M. S.; Cavaleiro, J. A. S.; Cavaleiro, A. M. V. Silica supported transition metal substituted polyoxotungstates: Novel heterogeneous catalysts in oxidative transformations with hydrogen peroxide. App. Catal. A: Gen. 2011, 392, 28–35. (19) Pathan, S.; Patel, A. Keggin type transition metal substituted phosphomolybdates: heterogeneous catalysts for selective aerobic oxidation of alcohols and alkenes under solvent free condition. Catal. Sci. Technol. 2014, 4, 648–656. (20) Rezvani, M. A.; Fallah Shojaie, A.; Loghmani, M. H. Synthesis and characterization of novel nanocomposite, anatase sandwich type polyoxometalate, as a reusable and green nano catalyst in oxidation desulfurization of simulated gas oil. Catal. Commun. 2012, 25, 36–40. (21) Li, K.; Wang, J.; Zou, Y.; Song, X.; Gao, H.; Zhu, W.; Zhang, W.; Yu, J.; Jia, M. Surfactant-assisted sol–gel synthesis of zirconia supported phosphotungstates or Ti-substituted phosphotungstates for catalytic oxidation of cyclohexene. App. Catal. A: Gen. 2014, 482, 84–91. (22) North, J.; Poole, O.; Alotaibi, A.; Bayahia, H.; Kozhevnikova, E. F.; Alsalme, A.; Siddiqui, M. R. H.; Kozhevnikov, I. V. Efficient hydrodesulfurization catalysts based on Keggin polyoxometalates. App. Catal. A: Gen. 2015, 508, 16–24.


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Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 40

(23) Borhade, A. V.; Uphade, B. K.; Tope, D. R. PbO as an efficient and reusable catalyst for one-pot synthesis of tetrahydro benzo pyrans and benzylidene malonitriles. J. Chem. Sci. 2013, 125, 583–589. (24) Allen, G. C.; Paul, M. Catalytic effect of vanadium, iron and lead oxides on the oxidation of moderator graphite. J. Chem. Soc. Faraday Trans. 1995, 91, 3717–3723. (25) Ghaedi, M.; Ghaedi, A. M.; Mirtamizdoust, B.; Agarwal, S.; Kumar Gupta, V. Simple and facile sonochemical synthesis of lead oxide nanoparticles loaded activated carbon and its application for methyl orange removal from aqueous phase. J. Mol. Liq. 2016, 213, 48–57. (26) Fallah Shojaei, A.; Rezvani, M. A.; Loghmani, M. H. Comparative study on oxidation desulfurization of real gas oil and model sulfur compounds with hydrogen peroxide promoted by formic acid: Synthesis and characterization of vanadium containing polyoxometalate supported on anatase crushed nanoleaf. Fuel Process. Technol. 2014, 118, 1–6. (27) Rezvani, M. A.; Fallah Shojaei, A.; Mohamadi Zonoz, F. Anatase titania–vanadium polyphosphomolybdate as an efficient and reusable nano catalyst for the desulfurization of gas oil. J. Serb. Chem. Soc. 2014, 79, 1099–1110. (28) Rezvani, M. A.; Alinia Asli, M.; Oveisi, M.; babaei, R.; Qasemi, K.; Khandan, S. An organic-inorganic hybrid based on Anderson-type polyoxometalate immobilized on PVA as a reusable and efficient nanocatalyst for oxidative desulfurization of gasoline. RSC Adv. 2016, 6, 53069–53079.


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Page 21 of 40 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(29) Rezvani, M. A.; Alinia Asli, M.; Khandan, S.; Mousavi, H.; Shokri Aghbolagh, Z. Synthesis and characterization of new nanocomposite CTAB-PTA@CS as an efficient heterogeneous catalyst for oxidative desulfurization of gasoline. Chem. Eng. J. 2017, 312, 243–251. (30) Arulmozhi, K. T.; Mythili, N. Studies on the chemical synthesis and characterization of lead oxide nanoparticles with different organic capping agents. AIP Adv. 2013, 3, 122122–122131. (31) Abdalla, Z. E. A.; Li, B. Preparation of MCM-41 supported (Bu4N)4H3(PW11O39) catalyst and its performance in oxidative desulfurization. Chem. Eng. J. 2012, 200–202, 113–121. (32) Grama, L.; Boda, F.; Gaz Florea, A. S.; Curticăpean, A.; Muntean, D. L. The UV and IR comparative spectrophotometric study of some saturated and lacunary polyoxometalates. Acta Medica Marisiensis 2014, 60, 84–88. (33) Kathiraser, Y.; Ashok, J.; Kawi, S. Synthesis and evaluation of highly dispersed SBA-15 supported Ni–Fe bimetallic catalysts for steam reforming of biomass derived tar reaction. Catal. Sci. Technol. 2016, 6, 4327–4336. (34) Chamack, M.; Mahjoub, A. R.; Aghayan, H. Cesium salts of tungsten-substituted molybdophosphoric acid immobilized onto platelet mesoporous silica: Efficient catalysts for oxidative desulfurization of dibenzothiophene. Chem. Eng. J. 2014, 255, 686–694. (35) Lü, H.; Deng, C.; Ren, W.; Yang, X. Oxidative desulfurization of model diesel using [(C4H9)4N]6Mo7O24 as a catalyst in ionic liquids. Fuel Process. Technol. 2014, 119, 87–91.


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(36) Qiu, J.; Wang, G.; Zeng, D.; Tang, Y.; Wang, M.; Li, Y. Oxidative desulfurization of diesel fuel using amphiphilic quaternary ammonium phosphomolybdate catalysts. Fuel Process. Technol. 2009, 90, 1538–1542.

Table captions Table 1. Results of ODS of real gas oil. Table 2. Effect of different catalysts on ODS of different types of sulfur compounds.


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Table 3. Pseudo-first-order rate constants and correlation factors of the ODS of real gas oil and DBT.


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Table 1. Results of ODS of real gas oil. Entry

Properties of gas oil

Before ODS

After ODSa

After ODSb

1

Total sulfur content wt. %

0.8738

0.0285

0.0287

2

Density @ 15 °C

0.8256

0.8255

0.8255

3

Mercaptans ppm

265

9

10

4

Flash point (°F)

139

138

138

5

Water content vol. %

0.025

0.025

0.025

6

Cloud point (°C)

-4

-4

-4

7

Color test

1.5

1.5

1.5

8

Viscosity KIN @ 50 °C. CST.

2.7

2.6

2.6

9

Pour point (°C)

-9

-9

-9

10

Distillation (IBP °C)

157.5

157.3

157.4

11

Distillation (FBP °C)

387.3

387.2

387.1

a

Condition for ODS: 50 mL of gas oil, 0.1 g of (TBA)4PW11Fe@PbO nanocatalyst, 6 ml of oxidant, 10 mL of extraction solvent, time = 2 hours, and temperature = 60 °C. b

ODS of real gas oil using reused nanocatalyst.


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Table 2. Effect of different catalysts on ODS of different types of sulfur compounds a. Conversion % Entry

Catalyst

DBT

4-MDBT

4,6-DMDBT

BT

Real gas oil

1

(TBA)4PFeW11/PbO

97

94

95

93

97

2

(TBA)4PFeW11

70

68

69

66

68

3

H3PW12O40

66

62

63

61

62

4

H14[NaP5W30O110]

62

61

61

60

61

5

H6P2W18O62

58

56

55

52

57

6

H6P2Mo18O62

58

54

55

52

51

7

PbO

58

55

57

53

55

8

None

20

18

19

18

17

a

Condition for ODS: 50 mL of real gas oil or model fuel, 0.1 g of (TBA)4PW11Fe@PbO nanocatalyst, 6 ml of oxidant, 10 mL of extraction solvent, time = 2 hours, and temperature = 60 °C.


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Table 3. Pseudo-first-order rate constants and correlation factors of the ODS of real gas oil and DBT. Rate constant K (min-1)

Correlation factor R2

Temperature (oC)

Real gas oil

DBT

Real gas oil

DBT

25

0.021

0.008

0.919

0.988

40

0.025

0.012

0.889

0.990

50

0.045

0.016

0.917

0.959

60

0.050

0.023

0.948

0.934


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Figure and scheme captions Figure 1. FT-IR of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO. Figure 2. UV-vis spectra of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO. Figure 3. XRD patterns of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO. Figure 4. SEM images of (a) PbO and (b,c) (TBA)4PW11Fe@PbO. Figure 5. EDX pattern of (TBA)4PW11Fe@PbO. Figure 6. 31P NMR spectra of (a) (TBA)4PW11Fe and (b) (TBA)4PW11Fe@PbO nanocatalyst. Figure 7. Effect of different sulfur compounds on ODS efficiency using (TBA)4PW11Fe@PbO nanocatalyst. Figure 8. Effect of nanocatalyst dosage on removal efficiency of DBT and sulfur content of gas oil. Figure 9. Effect of reaction temperature and time on removal efficiency of (a) DBT and (b) sulfur content of gas oil using (TBA)4PW11Fe@PbO nanocatalyst. Figure 10. Plots of St/Si for the oxidation of (a) DBT and (b) sulfur content of gas oil. Figure 11. Arrhenius plots for the oxidation of (a) DBT and (b) sulfur content of gas oil. Figure 12. The removal efficiency of DBT after each regeneration cycle. Scheme 1. The probable mechanism for the formation of peroxo-metal species by using CH3COOH:H2O2 and (TBA)4PW11Fe@PbO phase-transfer nanocatalyst for oxidation sulfur compounds.


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Figure 1. FT-IR of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO.


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Figure 2. UV-vis spectra of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO.


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Figure 3. XRD patterns of (a) PbO, (b) (TBA)4PW11Fe, and (c) (TBA)4PW11Fe@PbO.


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Figure 4. SEM images of (a) PbO and (b,c) (TBA)4PW11Fe@PbO.


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Figure 5. EDX pattern of (TBA)4PW11Fe@PbO.


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Figure 6. 31P NMR spectra of (a) (TBA)4PW11Fe and (b) (TBA)4PW11Fe@PbO nanocatalyst.


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Figure 7. Effect of different sulfur compounds on ODS efficiency using (TBA)4PW11Fe@PbO nanocatalyst.


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Figure 8. Effect of nanocatalyst dosage on removal efficiency of DBT and sulfur content of gas oil.


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Figure 9. Effect of reaction temperature and time on removal efficiency of (a) DBT and (b) sulfur content of gas oil using (TBA)4PW11Fe@PbO nanocatalyst.


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Figure 10. Plots of St/Si for the oxidation of (a) DBT and (b) sulfur content of gas oil.


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Figure 11. Arrhenius plots for the oxidation of (a) DBT and (b) sulfur content of gas oil.


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Figure 12. The removal efficiency of DBT after each regeneration cycle.


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Scheme 1. The probable mechanism for the formation of peroxo-metal species by using CH3COOH:H2O2 and (TBA)4PW11Fe@PbO phase-transfer nanocatalyst for oxidation sulfur compounds.


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Oxidative Desulfurization of Gas Oil Catalyzed by (TBA)4PW11Fe

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