Desulfurization of Fuel by Extraction and Catalytic Oxidation Using a

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Desulfurization of Fuel by Extraction and Catalytic Oxidation Using Vanadium Substituted Dawson-type Emulsion Catalyst Farhad Banisharif, Mohammad Reza Dehghani, MariCarmen Capel-Sanchez, and Jose Miguel Campos-Martin Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b00089 • Publication Date (Web): 24 Mar 2017 Downloaded from http://pubs.acs.org on March 31, 2017

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Industrial & Engineering Chemistry Research

Desulfurization of Fuel by Extraction and Catalytic Oxidation Using Vanadium Substituted Dawson-type Emulsion Catalyst Farhad Banisharif†, Mohammad Reza Dehghani†,* MariCarmen Capel-Sánchez‡, and José M. Campos-Martin‡ †

Chemical Engineering Department, Iran University of Science and Technology, Narmak, Tehran, Iran ‡

Grupo de Energía y Química Sostenibles (EQS) Instituto de Catálisis y Petroleoquímica, CSIC. Marie Curie, 2 Canto Blanco, 28049 Madrid, Spain

ABSTRACT:

A

[cetronium]11P2W13V5O62

vanadium-substituted was

fabricated

to

Dawson-type use

in

polyoxometalate

extractive-catalytic

oxidative

desulfurization (ECODS) of fuels using hydrogen peroxide and ionic liquid (IL), ethylene glycol and deep eutectic solvent. Taguchi robust was utilized to investigate the effects of operation parameters included of H2O2 dosage, type of solvent, solvent to oil volume ratio, temperature and contact time. The results demonstrated that the highest level of desulfurization could be achieved using volume ratio of IL to oil = 1:6, O/(S+N) mole ratio = 4 and temperature = 70 oC after 45 minutes. The state of combining extraction and catalytic oxidation process showed that the step-by-step system (extraction in series with ECODS) was much better than one-pot system (ECODS in one pot), which can remove 90% sulfur from 500-ppmw fuel and 87% sulfur from 1500-ppmw fuel under optimized conditions. The best system could also be reused 7 times in 500-ppmw model fuel desulfurization and 4 times in 1500-ppmw model fuel desulfurization.

* Corresponding author: Tel.: +98 [email protected] (M.R. Dehghani).

2177240496;

1

Fax:

+98

ACS Paragon Plus Environment

2173227772.

E-mail

address:


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Keywords: Desulfurization, Denitrogenation, Oxidation-extraction, Emulsion catalyst, Ionic Liquid 1. INTRODUCTION Sulfur (S-)/nitrogen (N-) containing compounds in hydrocarbon fuels such as diesel oil can be converted to SOx and NOx during combustion, and are the causes of forming some environmental pollution such as smog, sour gases, and acid rain.1 To date, hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) have been applied in refinery industry because of their high efficiency in removing S-/N- containing compounds from fuels. However, removal of aromatic sulfur compounds such as benzothiophene (BT), dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT) and their derivatives, which are the most common refractory S-containing compounds in diesel fuel, is one of challenges in the conventional refinery hydrogenation plants.1,2 Traditional HDS and HDN require severe conditions such as high temperature, high pressure and high active catalysts, increasing the operating cost of the hydrogenation plants, and are not economical. Under such conditions, one of the promising alternative to HDS is oxidative desulfurization (ODS) process, which has been studied intensively. In comparison to HDS, the operating conditions of ODS are more moderate (with atmospheric pressure and temperature lower than 100 oC) and no hydrogen is necessary, whereby S-containing compounds are oxidized to sulfones and sulfoxides, which are eliminated in the subsequent extraction process.3-5 Previous studies showed that the combination of oxidative desulfurization (ODS) and extractive desulfurization (EDS) (extractive-oxidative desulfurization (EODS)) makes desulfurization more efficient than ODS and EDS.3-7 Sulfur compounds in EODS process are oxidized, in presence of a strong oxidizer, to sulfones and sulfoxides, which are removed by an efficient solvent. Several kinds of solvents, such as acetonitrile (MeCN), dimethyl formamide (DMF), dimethyl sulfoxide (DMSO) and ionic 2


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liquid (IL), have been used to remove sulfoxides and sulfones produced by oxidation reactions.3-7 ILs exhibit many desirable properties such as non-volatility, sparing solubility in nonpolar organic solvents and good solvent power in comparison with conventional toxic, volatile and non-environmental-friendly solvents such as MeCN, DMF, and DMSO. Desulfurization by using ILs has been studied extensively.8-17 The two of IL groups include imidazolium-based ILs and pyridinium-based ILs.8-17 The imidazolium-based ILs, such as [BMIM]BF4,8

[BMIM]PF6,9

[EMIM]AlCl4,10

[BMIM][SCN],11

[BMIM]AlCl4,12

[BMIM]DBP13 and Pyridinium-based ILs, including [BPy]BF4,14 [OPy]BF4,15 [EPy]BF416 and [BPy]NO317 have been evaluated in extraction and extractive-oxidative removal of Scontaining compounds, and good results are observed. Chen et al. studied the extractive desulfurization and denitrogenation of model fuel containing thiophene (TS) and DBT as Scontaining compounds and basic pyridine and neutral carbazole as N-containing compounds, using two kinds of Lewis acidic ILs, [Bmim]Cl/ZnCl2, [Bmim]Cl/2ZnCl2, and two kinds of Bronsted acidic ILs, [Bmim]HSO4 and [Hmim]HSO4.18 They found out that 93.8% of TS removal (S-content drops from 500 ppm to 31 ppm) and 95.9% of DBT removal (S-content drops from 516 ppm to 21 ppm) can be achieved using [Bmim]Cl/ZnCl2. Hansmeier et al. studied

the

performance

of

the

pyridinium-based

ILs,

[3-mebupy]N(CN)2,

[4-

mebupy]N(CN)2, [4-mebupy]SCN, as well as the imidazolium based ILs, [Bmim]C(CN)3, [Bmim]N(CN)2 and [Bmim]SCN in extractive removal of S- and N-containing heteroaromatics from petrochemical streams.19 They found out that ILs such as [3-mebupy]N(CN)2, [4-mebupy]N(CN)2, [4-mebupy]SCN and [Bmim]C(CN)3 can remove 20% of thiophene and 53% of DBT.19 In spite of advantages of ILs in desulfurization/ denitrogenation, there are some disadvantages such as the production of corrosive hydrogen fluoride (HF) through decomposition of fluorinated anions. As a new type of solvent, and similar to ILs, deep eutectic solvents (DESs) have attracted great attentions. Although they do not only possess

3



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the advantages of ILs, they share many excellent features including cheap, easily obtained raw materials, and simple synthetic process.20 Although DESs have been widely used in recent years in catalytic processes,21 organic synthesis,22 materials preparation23 and separation24. few studies have focused on desulfurization by DES25-28 in comparison with ILs. Meanwhile, the presence of N-compounds is studied as well as S-compounds in HDS. It has been proved that N-containing compounds have negative effects on HDS1-3 while a few articles have studied the influence of N-containing compounds on EODS process in contrast to the desulfurization aspect.29-31 Various types of oxidizing agent have been used in the EODS, such as hydrogen peroxide (H2O2). H2O2 is an attractive environmentally friendly strong oxidizer in comparison with other kinds of agents.32-36 There are two parallel H2O2-involved reactions in the EODS, including oxidation of sulfur components and H2O2 thermal decomposition.32 The product of H2O2 thermal decomposition is water, which limits the oxidation reaction. Different kinds of catalysts such as polyoxometalates (POMs) have been studied in catalyst containing EODS (extractive-catalytic oxidative desulfurization (ECODS)) to overcome the effect of water.32-40 Among different catalysts, POMs draw more attention to themselves because of their redox properties and being environment friendly.32-45 Keggin-type and Dawson-type are the two famous groups of POMs, which have been used extensively in catalytic reactions.32-45 Furthermore, one of important POM subclasses is the mixed-addenda vanadium (V) substituted POM. Previous works showed that the introduction of vanadium in POMs frames is useful in changing acid-dominated properties of POMs to redox-domination, as seen by oxidation of some organic compounds. It has been proved that increasing vanadium in Keggin-type catalyst such as (n-But4N)3+x[PW12-xVxO40] (x= 0, 1, 2, 3) improves the activity of the catalyst in desulfurization process.45-49 Our literature review shows that the Dawsontype POMs (Cn [X2M18O62]p-, X=P, Si; M=Mo, W) have been considered a little in

4


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comparison with Keggin-type POMs in the desulfurization process.32-49 Dawson-type polyoxometalate catalyst ([P2W18O61(O2)]6- has a good performance in desulfurization of diesel oil.46 Meanwhile vanadium substituted POM (H9P2Mo15V3O62) was used in natural gas desulfurization,47 and our previous researches indicated good performance of [P2W13V5O62]11in desulfurization of diesel oil. Oxidative reaction occurs in biphasic EODS system, polar solvent, and oily nonpolar phase, in the bulk of the polar phase, and the disadvantage of these systems is phase-transfer limitation across the interface. Furthermore, the homogeneous POMs catalyst cannot supply an adaptive reaction environment in hydrophobic ILs with the accumulation of sulfones. Meanwhile, the extraction ability of solvents decreases in the recycling process.50 Therefore, the use of surfactants to form emulsions has been greatly considered in recent years.51-55 A new approach to phase transfer agent is surfactant based catalysts, which combines a POM anion with a quaternary ammonium cation. It is shown that the length of alkyl chain of quaternary ammonium cations of surfactant-type tungstate POM catalyst plays a significant role in the catalytic performance of these catalysts, as catalysts with longer carbon chains have more appropriate activity.57-60 In this study, based on our previous researches and to search for efficient ECODS system to achieve ultra-low sulfur fuel containing more than 1500 ppmw various kinds of sulfur and more than 450 ppm nitrogen compound, we systematically investigated the ECODS composed of various types of solvents (Lewis acid IL ([BMIM]-methyl SO4), ethylene glycol (EG), DES (ChCl/EG with mole ratio ChCl:EG = 1:3)) and synthesized vanadium-substituted Dawson-type emulsion catalyst ([CTA]11P2W13V5O64) for the first time, by means of Taguchi experimental design. The Taguchi method reduces the number of experiments necessary to study the effects of multiple variables simultaneously, while retaining the quality of data collection.61 5



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2. MATERIALS AND METHODS 2.1. Materials Sulfur compounds, BT, DBT, 4, 6-DMDBT, H2O2 (aqueous solution, 50 wt. %) and IL (1butyl-3-methyl imidazolium methyl sulfate (BMIM-methyl sulfate)) were purchased from Sigma-Aldrich. All of other reagents used in this work are available commercially and were used as received. 2.2. Preparation of Emulsion Catalyst The vanadium-substituted Dawson-type heteropoly acid H11P2W13V5O62 was first synthesized by using modified etherate method59 (preparation of protonated POMs in an aqueous solution and are extracted with acidic diethyl ether), to synthesize the emulsion catalyst. Mixed addenda heteropoly acid was produced as follows: 5.8 g of NH4VO3 and 3.28 g of Na3PO4 were dissolved with 100 mL deionized water at 40°C. Subsequently, 3.315 g of Na2WO4 was added. The solution was then heated to 100 °C after adjusting the pH (pH=4.4) of solution by adding a 5 ml of H2SO4 (1 mol/L). After 8-hour refluxing, the solution was allowed to cool slowly to 25 oC. Then, 150 mL diethyl ether was added. The solution was divided into three phases by the fully shaking and standing for 1 hour. An oily red phase at the bottom of decanter containing the mixture of heteropoly acid and diethyl ether was separated. Then, a powdered vanadium substituted heteropoly acid was achieved after the evaporation of diethyl ether at 200 °C. The synthesized acid was then used to produce the emulsion catalyst. The emulsion catalysts were synthesized as follows: 3.6 g of H11P2W13V5O62 was dissolved in 25 mL distilled water, suitably followed by adjusting the pH (pH=4.4) with a solution of HCl (2 mol/L). Then a solution of cetronium (CTAB) (4.05 g) dissolved in ethanol was added in drops. A red

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precipitate [CTA]11P2W13V5O62 was immediately formed. After continuous stirring for 2 hours, the resulting solid was filtered and dried at 70 ˚C in vacuum oven, over the night. 2.3. Preparation of Deep Eutectic Solvent One of the important industrial solvents is ethylene glycol (EG), which has favorable properties such as low vapor pressure, low toxicity, low viscosity, high chemical stability and low melting point. Because of these properties, EG may be used in cleaning of exhaust air and gas streams from industrial production plants. EG presents native hydrogen bonding sites for flue gas desulfurization, so that the potential desorption characters are presented in the regenerative processes of desulfurizing solutions dissolving SO2.62 Hence, EG in this study was chosen as a green solvent, and it was compared with IL. In addition, the DES chloride chlorine (ChCl)/EG was also selected to investigate the effect of changing EG to DES-type solvent using ChCl on ECODS. DES was prepared according to the published procedure, as follows: ChCl (Sigma-Aldrich, 99%) was mixed with EG (Sigma-Aldrich, 99.8%) in mole ratio of ChCl to EG, 1:3.63 The mixture was stirred at 300 rpm and 60 °C for 3 hours until a homogenous transparent liquid was formed. 2.4. Characterization of Emulsion Catalyst In order to drive the fingerprinting and structural interpretation of the emulsion catalyst,

64

Shimadzu-8400S FT-IR spectrometer was used to record Fourier transform infrared (FT-IR) spectrum of emulsion catalyst from 3 wt. % KBr pellets. Renishaw Raman microscope with a 785 nm laser source was also applied to prepare infrared Raman spectrum of emulsion catalyst to obtain additional structural information concerning the presence of Dawson-type unit in the hybrid catalyst. Plasma Spectroscopy ICP (ICPS S7000, Shimadzu) was used to determine the composition of catalyst. ECS 4010 CHNS-O elemental Analyzer, Costech

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Analytical Technologies, Inc., Italy was also applied to determine the amount of C, H, and N in the sample. Ultra-violet diffuse reflectance spectroscopic study (UV-DRS; Shimadzu UV-2101 PC spectrophotometer equipped with a diffuse-reflectance of the center-metal ions by BaSO4 as an internal standard) was run in a wavelength range from 190 nm to 800 nm in a step-scan mode with a step of 2nm to distinguish the electronic properties. The

31

P magic-angle

spinning nuclear magnetic resonance (31P MAS NMR) measurements were made on a NMR spectrometer BRUKER AVANCE II-9, 4 Tesla magnet (400MHz) operating at 162 MHz with a MAS probe-head using 4-mm ZrO2 rotors spun at 10 kHz. Chemical shifts were referenced to 85% H3PO4. X-ray photoelectron spectroscopy (XPS) spectra were recorded by a VG Escalab 200 R with Al/Mg X-ray source. The analyzer was operated in constant pass energy of 20. The C 1s (284.8 eV) binding energy (BE) was used as internal reference. The spectrometer BE scale was initially calibrated against the Ag 3d5/2 (368.2 eV) level. Pressure was in the 1×10-8 Pa range during the experiment. Thermo-gravimetric-differential thermal analysis (TG-DTA; TA-Q500 instrument) of the emulsion catalyst were carried out from room temperature to 600 oC under pure nitrogen environment at a heating rate of 5 oC/min. 2.5. Preparation of Model Fuel In order to study the effect of process factor by means of Taguchi method on the ECODS, the total sulfur concentration was kept approximately 500 ppm by dissolving three kinds of the model S-containing compound (BT (646 ppmw), DBT (1493.8 ppmw), 4, 6-DMDBT (646 ppmw)) with mixture of iso-octane and toluene (volume ratio of toluene to iso-octane, 1:4). In addition to S-containing compounds, the aromatic N-containing compound “quinolone” was also added to model fuel. The concentration of nitrogen was 445 ppmw.

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The effect of initial sulfur content of fuel on the ECODS process was also evaluated using model fuels containing 1500 and 3500 ppmw sulfur as well as 500 ppmw of it under optimum conditions. The 1500 ppmw sulfur containing model fuel (1500-ppmw model fuel) included 2650 ppmw BT, 6150 ppmw DBT, 2650 ppmw 4,6-DMDBT, 1335 ppmw quinoline and 20 v.% toluene in iso-octane. The 3500 ppmw sulfur containing model fuel (3500-ppmw model fuel) included 6072 ppmw BT, 14096 ppmw DBT, 6072 ppmw 4,6-DMDBT, 4178 ppmw quinoline and 20 v.% toluene in iso-octane. 2.6. Extractive-Catalytic Oxidative Desulfurization In a typical run, ECODS was run as follows: A water bath was heated to a desired temperature. The mixture, containing model fuel and solvent was stirred vigorously using a stir bar at reaction temperature for 3 minutes, to reach the desired temperature. Then the emulsion catalyst (concentration, 7.5 g/L) was added to the mixture followed by 50 wt. % H2O2 (in desired O/S mole ratio). The mixture was stirred vigorously for the determined time. The type of solvent, volume ratio of solvent to oil, reaction temperature, mole ratio of oxidant to oxidized agents, and contact time were adjusted according to the different experimental conditions introduced in experimental design table (Table 1). To evaluate the efficiency of ECODS in each trial, introduced by Table 1, the used mixture of IL and emulsion catalyst was separated from oil phase by decantation after each trial. The sampled oil mixture was analyzed by a gas chromatography (Agilent, 7890A) coupled with a FID detector using a capillary column (HP-5, 30m×0.32mm×0.25µm). The inlet temperature was 310 oC. The oven temperature programming of gas chromatography was set with initial 90 oC for 5 min, ramped to 230 oC at 10 oC/min and held for 10 min, to 310 oC at 10 oC/min, and held for 10 min. In order to understand the efficiency of the ECODS after each recycle run, the used mixture of IL and emulsion catalyst was separated by decantation after each recycle trial and

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used again without any further treatments. The separated oil was analyzed by gas chromatography mentioned above and using the same oven temperature programming. 2.7. Taguchi Method Taguchi experimental design approach was followed by an orthogonal array (L18) as shown in Table 1 in order to analyze the effect of various parameters on the ECODS process and optimize them. All operation factors were studied in three level.61 3. RESULTS AND DISCUSSION 3.1. Characterization of Emulsion Catalyst The elemental analysis demonstrates that the element composition of vanadium substituted Dawson-type emulsion catalyst is nearly the same as the calculated value. (Found: C, 36.91; H, 6.46; N, 2.12; P, 0.88; W, 34.94; V, 3.62. Calculated: C, 36.75; H, 6.77; N, 2.26; P, 0.91; W, 35.05; V, 3.74). The FT-IR spectrum of the prepared vanadium-substituted emulsion catalyst has the characteristic peaks in a range of 700-1100 cm-1, indicating that the compounds possess Dawson-type POM structure (Figure 1).65, 66 FT-IR spectrum peak near 1090 cm-1 is related to the anti-symmetric stretching vibration of P=O, and the peaks near 912 and 960 cm-1 in spectrum are associated with the anti-symmetric stretching vibration of W=O and V=O, covered by W=O band. The peaks close to 912 and 780 cm–1 are associated with the antisymmetric stretching vibration of M-O-M (M= W, V) 65, 66 corresponding to the vibration of bridge bond of total octahedral angle; the vibration of the bridge bond of total octahedral edge respectively. In addition, the other peaks in the FT-IR spectrum of catalyst at 1468, 2850 and 2918 cm-1 can be attributed to the vibrations of the CTA cation. The FT-IR spectrum has provided strong evidence for the vanadium substituted Dawson-type emulsion

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catalyst. The strong and broad FT-IR bands around 3442 cm-1 can be attributed to O-H vibrations for the hybrid catalyst. The Raman spectrum of vanadium substituted Dawson-type phosphotungstate hybrid POM are shown in Figure 2. The Raman spectrum shows the main peaks of Dawson-type POM between 860 and 994 cm-1, that indicates the existence of Dawson-type POM in the emulsion catalyst.67 The Raman spectrum presents extremely strong M= O (M= V, W) stretching with a main maximum at 994 cm-1. The M-O-M (M = V, W) stretching modes (no obvious bands observed between 700 and 800 cm-1, which is the region of MO3,) and the P=O stretching are extremely weak in the Raman spectrum. The bands near 1500 and 2800 are related to the presence of organic C-C bonds of ammonium cations (CTA). The UV spectrum of [CTA]11P2W13V5O62 is shown in Figure 3. It presents the Dawson-type structure UV bands at 198 nm, 214 nm, 278 and 378 nm and is consistent with the results reported previously.66, 67 The bands near 198 nm is related to charge transfer from O to P. The bands close to 214nm can be attributed to the charge transfer from O to W. The bands near 278 and 378 nm belong to the incorporation of vanadium into the Dawson-type anion. 31

P MAS NMR spectra of [CTA]11P2W13V5O62 in the solid-state are shown in Figure 4. In

comparison to [P2W18]6- P MAS NMR, which has a line with a resonance at -13.75 ppm, vanadium substitution for tungstate causes the vanadium substituted Dawson-type emulsion catalysts to show a strong peak at δ = -13.5 ppm which is related to polyphosphate. The weak peak around -1.88 ppm is related to pyrophosphate. Meanwhile, the weak peak near 2.84 ppm is related to orthophosphate diester.65-68 All mentioned

31

P MAS NMR peaks is a typical

properties of vanadium substituted Dawson-type POM.65-67 Figure 5 illustrated the XPS signal shapes of V2p and W4f of emulsion catalyst. It shows the binding energies of 37.43 (W4f5/2) and 35.53 eV (W4f7/2) for W4f doublet of W6+ and 517

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(V2p3/2) and 524.9 (V2p1/2) for V2p doublet of V5+. So, it can be concluded that tungstate and vanadium are at the higher oxidation levels in the frame of vanadium-substituted Dawsontype anion [P2W13V5O62]11-.65 The TG curve of the hybrid catalyst (Figure 6) under nitrogen shows that the vanadium substituted Dawson-type emulsion catalyst has no obvious mass loss before 100 oC, which implies the absence of coordinated water. Differential thermal analysis (DTA) curve shows two endothermic peaks around 200 oC accompanied with mas loss, which may be attributed to the decomposition of long-alkyl chain organic cation of cetrimonium cation and vanadiumsubstituted Dawson-type POM anion [P2W13V5O62]11-. There is no more mass loss until about 600 oC.65-67 3.2. Extractive-Catalytic Oxidative Desulfurization and Denitrogenation It is desirable to find out the extractive efficiency of each selected solvent without catalytic oxidation. Therefore, the extraction efficiency of each solvent was determined at 30 minutes intervals under the conditions including the volume ratio of solvent to oil 1:4, T=40 ˚C and atmospheric pressure using 500-ppmw model fuel. The results showed that the amount of extractive denitrogenation is more than the extractive desulfurization. Figure 7 shows that the extractive efficiency of selected solvent is in the order of IL>EG>DES. The results also showed that the EDS using IL is able to remove nearly 100 % of quinoline, 30.48 % of BT, 33.14% of DBT and 15.09% of 4, 6-DMDBT. Desulfurization is so low; and so, the combination of CODS and EDS has been studied in order to achieve ultra-low sulfurcontaining model fuel. Meanwhile, Taguchi robust was used to determine optimum operating conditions. Table 1 presents the studied parameters at their corresponded levels, and the removals of BT, DBT, 4,6 -DMDBT and total sulfur removal as well as quinoline in each experiment are tabulated in the last columns of Table 1. The effects of H2O2 dosage (mole

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ratio of oxidant (O), including total oxidized agent (N+S)), reaction temperature, types of solvent, volume ratio of solvent to oil and contact time on the ECODS of model fuel, were evaluated in this study. The concentration of emulsion catalyst remained constant (7.5 g/L) in all experiments. The results showed that catalytic oxidation improves the desulfurization up to about 90%, and clearly indicates that BT is the most difficult refractory sulfur compound to oxidize among selected S-containing compounds. In fact, the oxidative reactivity order of sulfur compounds are in DBT> 4, 6-DMDBT> BT. This fact is well defined in the previous literatures and is associated to the electronic density (BT) on the sulfur atom and some steric hindrances (4,6DMDBT).69-71 We detected that a small part of nonpolar phase was extracted because an increase in the mass of polar phase was detected (Table 1, column L). The extraction of catalyst would be very small, because catalyst reacts with H2O2 to form a peroxometal and this peroxometal is a highly polar compound and cannot be dissolved in oil phase during desulfurization. The relative significance of each factor on the ECODS of model fuel was determined via analysis of variance (ANOVA). The ANOVA data are tabulated in Table 2, related to total removal of sulfur and nitrogen. The error term contains information about the following variables in the results, including uncontrollable factors, factors that are not considered in the tests, and test error. The error term for ECODS of the model fuel is 3.539. F-ratio is a criterion for distinguishing important factors from those with less importance. Using the Fisher tables61 at a 95% confidence level, error degree of freedom (DOF), equivalent to 7 and each factor of DOF with the rate of 2 for individual factors give an F-value of 4.74. Table 2 shows that the F-values of all factors except for the type of solvent and reaction temperature are lower than the value from the Fischer table. This means that the variance of all factors is not important for variance of error at 95% confidence level for the model fuel without 13



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aromatic hydrocarbon. Consequently, in order to have an efficient desulfurization and denitrogenation, the selection of solvent and control of temperature is important in the desulfurization. PF obtained from the ANOVA table for each response shows that the selected factors are ranked in such a way that type of solvent (90.854%) >> temperature (4.55%) > time (1.057%), and PFs of other factors, volume ratio of solvent to oil and mole ratio of O/(S+N), are zero. The average effect of each parameter, presented in Figure 8 at different levels shows that variation in the reaction conditions affects desulfurization and denitrogenation phenomena. These values have been obtained by Taguchi design experiment. The mean average demonstrates that the performance of EG is better than the DES (ChCl/EG with mole ratio ChCl: EG = 1:3). The mean average also shows that the predicted range for approaching highest level of removal of total sulfur and total nitrogen is IL, volume ratio of solvent to oil = 1:6, O/S molar ratio= 6, temperature = 70 ˚C, and time = 45min. 88.78 % of total sulfur and 100% of total nitrogen can be removed under the predicted efficient conditions. It is necessary to run a validation test under the predicted efficient conditions. The validation test result proved that the result of test was approximately near the values predicted by Taguchi robust (Figure 9). Meanwhile, it showed that the experiments were reputable. Regarding O/S mole ratio, it is clear that there is a direct relation between oxidation efficiency and H2O2 dosage. Meanwhile, addition of more H2O2 causes a larger amount of water to be introduced into the reaction system composed of two phases, namely water and iso-octane, which significantly affects the reaction environment. By increasing the amount of H2O2, the mass transfer efficiency would be decreased to some extent, which might reduce the catalytic activity. Hence, the effect of decreasing the mole ratio of oxidant to the total oxidized agents on optimum conditions was also investigated. The ratio “4” was used instead of “6”. Figure 9 illustrates that the removal is the same as optimum conditions if the reaction 14


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time is changed to 75min in comparison with 45min (optimum time). As shown in Figure 9, denitrogenation rate is quicker than desulfurization rate and can be achieved 100% removal after 15 min. The sulfur removal was increased so slightly from ~87.9% to ~88.3 % after 45min. Therefore, the optimum conditions were considered as follows: the IL as solvent with the volume ratio of solvent to oil = 1:6, O/(S+N) mole ratio= 4 and residence time 45 min. As mentioned before, the concentration of catalyst was set 7.5 g/L. These optimum conditions and amount of catalyst were used for the following experiments. 3.3. Effect of Initial Sulfur Content on ECODS ECODS was conducted under determined optimum conditions for 1500-ppmw and 3500ppmw sulfur containing model fuel in order to determine the effect of initial sulfur content on the performance of the best ECODS system, IL and emulsion catalyst. Figure 10 shows that the efficiency of ECODS system is reduced from 87.9% for 500-ppmw model fuel to 40% for 3500-ppmw model fuel by increasing the amount of initial sulfur content of the feed. This phenomenon can be referred to blockage of catalyst surface via adsorption of S/N-compounds on the catalyst. It is also shown in Figure 10 that the reaction temperature raising from 60 ˚C to 80 ˚C improves the efficiency of ECODS system. The efficiency of 1500-ppmw model fuel desulfurization is improved by 25% by raising the reaction temperature. Meanwhile, the temperature raise increases the efficiency of 3500-ppmw model fuel desulfurization up to ~75%. This phenomenon can be explained as follows: the raise of temperature increases solubility of sulfur compound and reduces the viscosity of solvent and amount of adsorbed S/N- compound on the surface of catalyst which can block the surface of catalyst.2,3 Therefore, efficiency of ECODS can be increase by the increase of temperature. 3.4. Reusability of Emulsion Catalyst and IL

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The reusability of the catalyst was also investigated in order to find out whether the best ECODS system loses its efficiency during the reaction. For this purpose, the ECODS model fuel was evaluated in the presence of fresh and recovered mixture of IL and emulsion catalyst. The used mixture of IL and emulsion catalyst was separated by decantation after each trial and used again without any further treatments. The result is shown in Figure 11. Even after seven runs in 500ppmw model fuel for the reactions, the catalytic activity was slightly decreased. The sulfur removal was reduced to ~77% from ~88%. The result showed that the weight of mixture used IL and emulsion catalyst has been increased ~15 wt. % after 10th recirculation time. That indicates a double effect, a dissolution of the nonpolar solvent, but this phenomenon stops after the first reaction, and the extraction of oxidized sulfones. We ruled out the extraction of catalysts to the nonpolar phase for the peroxometal formation mentioned before. The by-product of H2O2 is water, and then the amount of water will be increased by reusing the untreated mixture of IL and emulsion catalyst. This increase of water concentration can affect to the mass transfer and the catalytic activity. Hence, the effect of water content of the reaction system was studied to find out its role in the deactivation of the ECODS system. The reusing procedure employed in the experiments implies that the formed water during the reaction, remaining in the IL phase, is increased after each recycling. In addition, some water is added with fresh H2O2 (aqueous solution) to the system in each run. The performance of system was studied by adding distilled water in volume ratio water to hydrogen peroxide of 1:1 and 2:1 and compared with first to third run of recycling of ECODS of 500-ppmw model fuel. The decrease in removal of S- and N- containing compounds due to adding water in different volume ratio was the same as the trend of reusing procedure. Thus, it can be concluded that the water can be one of the factors that reduce the efficiency of ECODS

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system within the recycle run. The result also stated that it is better to use the oxidant with the low water content (Figure 12). The reusability of oxidizing system was also examined by using of 1500 ppmw to study the effect of initial sulfur content on reusability (Figure 11 (b)). The results revealed that the activity of catalyst remained approximately constant after 4 recycle runs. Therefore, it can be concluded that the increase the initial sulfur content can reduce the reusability by about 42%. The result demonstrated that the weight of mixture used IL and emulsion catalyst has been increased ~12.5 wt. % after last recirculation time. There are different regeneration techniques such as distillation.72 The ionic liquid was fully regenerated after heating at 100 °C for 180 min under nitrogen. 1H NMR analyses indicated that the ionic liquids maintained its original structures after the regeneration and consistent with literature values73. The result showed that the treated IL and fresh catalyst (all parameters were set the same as optimal conditions) could desulfurized with desulfurization efficiency about 82% from 500-ppmw model oil and with efficiency about 69% from 1500ppmw model oil. Meanwhile, the denitrogenation efficiency of treated IL with fresh catalyst was the same as the fresh IL with fresh catalyst. Dynamic light scattering (DLS) measurements proved that the selected system (IL with emulsion catalyst) can produce water in oil emulsion. DLS indicated that the aggregates have a hydrodynamic radius (Rh) centered at ~94 nm for fresh system and ~48 nm for used system (Figure 13). The used system has lower reaction activity than fresh system despite the emulsion droplets being formed, possibly because the small emulsion droplets cannot supply enough oxidant. 3.5. Concept Process for Extractive-Catalytic Oxidative Desulfurization

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Stricter conditions with higher costs are usually required in traditional HDS process in order to produce the diesel oil with an ultra-low sulfur content. Moreover, it is difficult to completely remove the benzothiophene sulfur compounds, especially DBT, BT, 4,6-DMDBT and their derivatives using traditional HDS. Therefore, a further deep desulfurization is required after HDS process. A concept of desulfurization process for producing ultra-low sulfur diesel oil is shown in scheme 1, where the deep extractive-catalytic oxidative desulfurization is integrated with the HDS process by using vanadium substituted emulsion catalyst and H2O2. Two types of ECODS process can be considered for integration with the HDS unit. As shown in Scheme 1, the first process is one-pot extractive-catalytic oxidative removal process and the second one is extraction process followed by a one-pot extractive-catalytic-oxidative removal reactor. In the latter, HDS treated diesel oil is first sent to an extraction unit with 30minute residence time; then the whole contents of first reactor are sent to the second reactor to start catalytic-oxidative removal. The emulsion catalyst and oxidant (H2O2) are then added to the mixture (fuel and solvent) in this reactor and allowing the reaction to continue for 45 minutes. In order to compare the mentioned concept designed processes, the performances of both processes were determined by using 500 ppmw and 1500 ppmw S-containing model fuel (Figures 14 and 15). There was no significant difference in performances of two processes in desulfurization of 500-ppmw model fuel. The sulfur removal is nearly the same in both processes. In comparison with the one-pot process, the step-by-step process is more efficient to reduce the sulfur content of 1500-ppmw model fuel. The new combination improves the desulfurization efficiency of 1500-ppmw model fuel. The total sulfur removal was achieved ~87% after 30-minute EDS and 45-minute ECODS. This effect can be related to the concentration of hydrogen peroxide and sulfur present in the IL phase. It can be explained 18


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why the increase the initial sulfur content makes the two-step procedure better than one-pot system. When a concentration of 500ppmw of sulfur is employed, the concentration of H2O2 is not so high, as hydrogen peroxide needed for 1500ppmw sulfur content. Thus, the effect of water produced by the thermal decomposition or injection by fresh oxidant is low. Meanwhile, thermal decomposition is independent of the concentration of sulfur in the IL (one-step or two-step process). However, when 1500ppmw or more has to be treated, the concentration of H2O2 is relatively high and then the decomposition rate will be high, unless a large amount of sulfur is present in the IL phase (two-step process), where the sulfur oxidation consumes H2O2 quickly, yielding a lower hydrogen peroxide decomposition. 4. CONCLUSION Extractive- catalytic oxidative desulfurization of fuel has been assessed in this study by using the several types of solvents (ionic liquid (BMIM-methyl sulfate), ethylene glycol and deep eutectic solvent (ChCl/EG: mole ratio ChCl: EG 1:3), and Dawson-type emulsion catalyst ([CTA]11P2W13V5O62). The model fuel was iso-octane, consisting of toluene (20 v- %), BT, DBT and 4,6-DMDBT as S-containing compounds (as representative diesel S-containing compounds) and quinoline as an N-containing compound. The effects of various operating conditions, such as hydrogen peroxide dosage (O/S mole ratio), type of solvent, volume ratio of solvent to oil, reaction temperature, and contact time, were studied using the statistical method “Taguchi design experimental method”. ANOVA demonstrated that the temperature and selection of solvent were the most important parameters in ECODS. The optimum operating conditions were determined as IL, volume ratio of solvent to oil = 1:6, O/(S+N) mole ratio= 4, T = 70 ˚C and time = 45 minute. The total sulfur removal and total nitrogen removal could be achieved by 88.78 % and 100%, respectively. The validation test showed

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that the DEO was good and almost reputable. The activity test showed that the ECODS system could 7 times be recycled well with slightly decrease the activity of system with IL and emulsion catalyst. The results revealed that the increase the initial sulfur content of feed from 500 to 3500 ppmw reduced the efficiency of ECODS and its recycling ability up to 50% of 500-ppmw model fuel’s desulfurization ability. The results also showed that the increase the temperature could be a good solution to solve the reduction of ECODS activity. The way to combine EDS and CODS was also investigated in order to improve the ECODS system. It was shown that step-by-step procedure of EDS and CODS systems was much better than onepot ECODS system, especially when 1500ppmw or more sulfur content was employed for the treatment. The step-by-step procedure of EDS and CODS systems was able to improve the desulfurization efficiency by about ~16%.

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Surfactant‐Enhanced

Emulsification

Microextraction

for

the

Determination of Three Fungicide Residues in Juice Samples. J. Sep. Sci. 2015, 38(1), 93-99. (51) Zhu, W.; Ding, Y.; Li, H.; Qin, J.; Chao, Y.; Xiong, J.; Xu, Y.; Liu, H. Application of a Self-Emulsifiable Task-Specific Ionic Liquid in Oxidative Desulfurization of Fuels. RSC Adv. 2013, 3(12), 3893-3898. (52) Zhu, W.; Zhu, G.; Li, H.; Chao, Y.; Zhang, M.; Du, D.; Wang, Q.; Zhao, Z. Catalytic Kinetics of Oxidative Desulfurization with Surfactant-Type Polyoxometalate-Based Ionic Liquids. Fuel Process. Technol. 2013, 106, 70-76. (53) Ge, J.; Zhou, Y.; Yang, Y.; Xue, M. The Deep Oxidative Desulfurization of Fuels Catalyzed by Surfactant-Type Octamolybdate in Acidic Ionic Liquids. Petrol. Sci. Technol. 2014, 32(1), 116-123.

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(54) Chen, J.; Chen, C.; Zhang, R.; Guo, L.; Hua, L.; Chen, A.; Xiu, Y.; Liu, X.; Hou, Z. Deep Oxidative Desulfurization Catalyzed by an Ionic Liquid-Type Peroxotungsten Catalyst. RSC Adv. 2015, 5(33), 25904-25910. (55) Gu, Q.; Zhu, W.; Xun, S.; Chang, Y.; Xiong, J.; Zhang, M.; Jiang, W.; Zhu, F.; Li, H. Preparation of Highly Dispersed Tungsten Species within Mesoporous Silica by Ionic Liquid and Their Enhanced Catalytic Activity for Oxidative Desulfurization. Fuel 2014, 117, 667673. (57) Imtiaz, A.; Waqas, A.; Muhammad, I. Desulfurization of Liquid Fuels Using AirAssisted Performic Acid Oxidation and Emulsion Catalyst. Chin. J. Catal. 2013, 34(10), 1839-1847. (58) Ribeiro, S.O.; Julião, D.; Cunha-Silva, L.; Domingues, V.F.; Valença, R.; Ribeiro, J.C.; de Castro, B.; Balula, S.S. Catalytic Oxidative/Extractive Desulfurization of Model and Untreated Diesel Using Hybrid Based Zinc-Substituted Polyoxometalates. Fuel 2016, 166, 268-275. (59) Ueda, T.; Yamashita, K.; Onda, A. New Extraction Procedure for Protonated Polyoxometalates Prepared in Aqueous-Organic Solution and Characterization of Their Catalytic Ability. Appl. Catal. A Gen. 2014, 485, 181-187. (60) Lü, H.; Gao, J.; Jiang, Z.; Yang, Y.; Song, B.; Li, C. Oxidative Desulfurization of Dibenzothiophene with Molecular Oxygen Using Emulsion Catalysis. Chem. Commun. 2007, 2, 150-152. (61) Taguchi, G.; Jugulum, R. The Mahalanobis-Taguchi Strategy: a Pattern Technology System; Wiley: New York, 2002.

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(62) Zhang, J.; Zhang, P.; Chen, G.; Han, F.; Wei, X. Gas-Liquid Equilibrium Data for the Mixture Gas of Sulfur Dioxide/Nitrogen with Ethylene Glycol at Temperatures from (298.15 To 313.15) K under Low Pressures. J. Chem. Eng. Data 2008, 53, 1479-1485. (63) Peng, X.; Duan, M-H.; Yao, X-H.; Zhang, Y-H.; Zhao, C-J.; Zu, Y-G.; Fu, Y-J. Green Extraction of Five Target Phenolic Acids from Lonicerae Japonicae Flos with Deep Eutectic Solvent. Sep. Purif. Technol. 2016, 157, 249-257. (64) Ishida, H. Fourier Transform Infrared Characterization of Polymers. Plenum press: New York, 1987. (65) Zhang, P-P.; Peng, J.; Pang, H-J.; Sha, J-Q.; Zhu, M.; Wang, D-D.; Liu, M-G.; Su An, ZM. Interpenetrating Architecture Based on the Wells Dawson Polyoxometalate and Agi 3 3 3 Agi Interactions. Cryst. Growth Des. 2011, 11, 2736-2742. (66)

Khenkin,

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Polyfluorooxometalates: Synthesis, Characterization, and Catalytic Aerobic Oxidation. Inorg. Chem. 2000, 39, 3455-3462. (67) Busca, G. Differentiation of Mono-Oxo and Polyoxo and of Monomeric and Polymeric Vanadate, Molybdate and Tungstate Species in Metal Oxide Catalysts by IR and Raman Spectroscopy. J. Raman Spectrosc. 2002, 33, 348-358. (68) Read, E. K.; Ivancic, M.; Hanson, P.; Cade-Menun, B. J.; McMahon, K. D. Phosphorus speciation in a eutrophic lake by 31 P NMR spectroscopy. Water Res. 2014, 62, 229-240. (69) Kianpour, E.; Azizian, S. Polyethylene Glycol as a Green Solvent for Effective Extractive Desulfurization of Liquid Fuel at Ambient Conditions. Fuel 2014, 137, 36-40.

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(70) Zhang, J.; Wang, A.; Wang, Y.; Wang, H.; Gui, J. Heterogeneous Oxidative Desulfurization of Diesel Oil by Hydrogen Peroxide: Catalysis of an Amphipathic Hybrid Material Supported on SiO2. Chem. Eng. J. 2014, 245, 65-70. (71) Lü, H.; Wang, S.; Deng, C.; Ren, W.; Guo, B. Oxidative Desulfurization of Model fuel via Dual Activation by a Protic Ionic Liquid. J. hazard. Mater. 2014, 279, 220-225. (72) Ferreira, A. R.; Freire, M. G.; Ribeiro, J. C.; Lopes F. M.; Crespo, J. G.; Coutinho, J. A. Ionic liquids for thiols desulfurization: experimental liquid-liquid equilibrium and COSMORS description. Fuel 2014, 128, 314-329. (73) Santamarta, F.; Verdía, P.; Tojo, E. A simple, efficient and green procedure for Knoevenagel reaction in [MMIm][MSO4] ionic liquid. Catal. Commun. 2008, 9(8), 17791781.

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Table 1. L18 orthogonal array experiment designed used for optimization the ECODS. Removal % L No A B C D E 4,6 Q BT DBT Total S DMDBT 1: 1 IL 4 60 15 0.111 100 77.27 75 79.25 75.77 4 1: 2 IL 6 70 30 0.141 100 72.73 94.17 77.36 84.06 6 1: 3 IL 8 80 45 0.187 100 75 95 77.36 85.20 8 1: 4 DES 4 70 30 0.086 69.23 47.73 58.33 62.26 54.57 4 1: 5 DES 6 80 45 0.061 84.62 47.73 60 62.26 55.44 6 1: 6 DES 8 60 15 0.066 29.23 50 57.50 60.38 54.45 8 1: 7 EG 6 60 45 0.073 73.85 54.55 65.83 69.81 62.10 4 1: 8 EG 8 70 15 0.067 95.38 54.55 70 67.92 63.91 6 1: 9 EG 4 80 30 0.021 92.31 52.27 65 66.04 60.21 8 1: 8 80 30 0.106 100 84.09 95.83 81.13 89.18 10 IL 4 1: 11 IL 4 60 45 0.069 100 54.55 95 83.02 80.04 6 1: 12 IL 6 70 15 0.197 100 77.27 93.33 81.13 85.77 8 1: 6 80 15 0.059 38.46 52.27 58.33 66.04 56.71 13 DES 4 1: 14 DES 8 60 30 0.097 32.31 50 55.83 64.15 54.33 6 1: 15 DES 4 70 45 0.096 98.46 52.27 59.17 66.04 57.15 8 1: 16 EG 8 70 45 0.128 98.46 61.36 78.33 69.81 70.76 4 1: 17 EG 4 80 15 0.0315 96.92 52.27 67.50 66.04 61.53 6 1: 18 EG 6 60 30 0.178 70.77 54.55 70 71.70 64.66 8 * A: Solvent, B: volume ratio solvent to oil, C: mole ratio oxidant to sulfur, D: temperature (oC), E: Time (minute), L: increase of polar phase (mg) * Deep Eutectic Solvent (DES): ChCl/EG with the mole ratio of ChCl to EG, 1:3. * Ionic Liquid (IL): 1-butyl-3-methyl imidazolium methyl sulfate. * EG: Ethylene Glycol. * BT: benzothiophene, DBT: dibenzothiophene, 4, 6-DMDBT: 4,6dimethyldibenzothiophene.

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* Q: quinoline.

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Table 2. The results of ANOVA for optimization the ECODS of model fuel. Factor DOF Sum of Square Variance F-Ratio Pure (f) (S) (V) (F) Sum (S’)

Type of Solvent Volume Ratio Solvent to Oil O/S Mole Ratio Temperature Time Other/Error Total



2 2

Total Sulfur 2456.602 1228301 9.137 4.568

2 2 2 7 17

70.966 53.778 13.873 42.036 2646.396

2 2

Total Nitrogen (Quinoline) 5569.867 2784.933 20.25 75.015 37.507 0.272

2 2 2 7 17

1054.218 2164.983 993.238 962.649 10819.974

35.483 26.889 6.936 6.005

204.534 2444.592 0.76 0

92.374 0

5.908 4.477 1.155

58.955 41.767 1.863

2.227 1.578 0.07 3.751 100%

5294.824 0

48.935 0

779.175 1889.94 718.195

7.201 17.467 6.637 19.76 100%

2673.833 0

90.854 0

0 133.912 31.112

0 4.55 1.057 3.539 100%

527.109 3.832 1082.491 7.871 496.619 3.611 137.521

Total Removal of Sulfur and Nitrogen 2 2687.474 1343.737 197.01 2 2.657 1.328 0.194 2 2 2 7 17

12.814 147.553 44.753 47.743 2942.998

6.407 73.776 22.376 6.82

33


Percent P (%)

0.939 10.816 3.28


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Figure and scheme captions: Figure 1. FT-IR spectrum of [CTA]11P2W13V5O62. Figure 2. The Raman spectra of [CTA]11P2W13V5O62. Figure 3. UV-DRS spectrum of [CTA]11P2W13V5O62. Figure 4. 31P NMR sample spectra of vanadium substituted Emulsion Catalyst. Figure 5. X-ray photoelectron deconvoluted profiles of the V2p3/2 and W4f7/2 for emuslion catalyst. Figure 6. Thermal gravimetric analysis of vanadium-substituted hybrid Dawson-type POM. Figure 7. Extraction efficiency of solvent, T= 40 oC, Time= 30 min, 1000 rpm, volume ratio of solvent to oil: 1:4. Figure 8. Mean effect of selected factors on ECODS system. (ionic liquid (IL), deep eutectic solvent (DES): (EG) ChCl/ethylene glycol (EG) with the mole ratio of ChCl (1) to EG (3), EG) Figure 9. The validation test and effect of reduction amount of oxidize on optimum conditions vs. time. Figure 10 Effect of initial sulfur content on the ECODS system. (Solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, Time=45 min, 7.5 g/L emulsion catalyst)

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Figure 11. Recycle of ECODS system in different initial sulfur content. (Solvent: IL, O/(S+N) mole ratio= 4, Volume Ratio of solvent to oil= 1:6, T=70 oC, time=45 minutes, 7.5 g/L emulsion catalyst) Figure 12. Effect of water on deactivation of one-pot ECODS. (IL + emulsion catalyst) (volume ratio of H2O2 to water: 1:1 and 1:2) comparison with several-time recycle run: (Initial Sulfur content: 500 ppmw; Solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, time=45 minutes, 7.5 g/L emulsion catalyst) Figure 13. a) Optical micrographs and b) Dynamic light scattering patterns of water in oil emulsion produced by fresh hybrid catalyst in 7.5 g/mL (20 v.% Toluene in iso-Octane, volume ratio solvent (Ionic Liquid ([Bmim]SO4)) to oil= 1:6, O/S mole ratio=4); c) Optical micrographs d) Dynamic light scattering patterns of water in oil emulsion produced by used emulsion catalyst and IL in the first recirculation trial (volume ratio solvent to oil= 1:6, O/S mole ratio = 4) Figure 14. ECODS in new process design: a) performance of system in different CODS contact time; b) comparison the new process design with one-pot ECODS; 7.5 g/L emulsion catalyst was used (Initial Sulfur content: 500 ppmw; One-pot: solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, time=45 minutes; Step-by-step: solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, time=30 minutes in EDS and 45 minutes in ECODS). Figure 15. Performance of ECODS in new process design: a) performance of system in different CODS contact time; b) comparison the new process design with one-pot ECODS. 7.5 g/L emulsion catalyst (Initial Sulfur content: 1500 ppmw; One-pot: solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T =70 oC, time=45 minutes, step-by-step:

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Solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=60 oC, time=30 minutes in EDS and 45 minutes in ECODS). Scheme 1. Concept processes to produce S-free diesel fuel in a refinery, with a vanadium substituted Dawson emulsion catalyst and IL.

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Figure 1. FT-IR spectrum of [CTA]11P2W13V5O62.

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Figure 2. The Raman spectra of [CTA]11P2W13V5O62.

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Figure 3. UV-DRS spectrum of [CTA]11P2W13V5O62.

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Figure 4. 31P NMR sample spectra of vanadium substituted Emulsion Catalyst.

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Figure 5. X-ray photoelectron deconvoluted profiles of the V2p3/2 and W4f7/2 for emuslion catalyst.

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Figure 6. Thermal gravimetric analysis of vanadium-substituted hybrid Dawson-type POM.

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Figure 7. Extraction efficiency of solvent, T= 40 oC, Time= 30 min, 1000 rpm, volume ratio of solvent to oil: 1:4.

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Figure 8. Mean effect of selected factors on ECODS system. (ionic liquid (IL), deep eutectic solvent (DES): (EG) ChCl/ethylene glycol (EG) with the mole ratio of ChCl (1) to EG (3), EG)

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Figure 9. The validation test and effect of reduction amount of oxidize on optimum conditions vs. time.

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a) ECODS of 1500-ppmw-sulfur model fuel vs. temperature.

b) ECODS of 3500-ppmw-sulfur model fuel vs. temperature.

c) Comparison ECODS in different initial sulfur content feed.

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Figure 10. Effect of initial sulfur content on the ECODS system. (Solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, Time=45 min, 7.5 g/L emulsion catalyst)

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a) 500-ppmw-sulfur model fuel.

b) 1500-ppmw-sulfur model fuel.

Figure 11. Recycle of ECODS system in different initial sulfur content. (Solvent: IL, O/(S+N) mole ratio= 4, Volume Ratio of solvent to oil= 1:6, T=70 oC, time=45 minutes,

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7.5 g/L emulsion catalyst)

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Figure 12. Effect of water on deactivation of one-pot ECODS. (IL + emulsion catalyst) (volume ratio of H2O2 to water: 1:1 and 1:2) comparison with several-time recycle run: (Initial Sulfur content: 500 ppmw; Solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, time=45 minutes, 7.5 g/L emulsion catalyst)

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a)

b)

c) d) Figure 13. a) Optical micrographs and b) Dynamic light scattering patterns of water in oil emulsion produced by fresh hybrid catalyst in 7.5 g/mL (20 v.% Toluene in isoOctane, volume ratio solvent (Ionic Liquid ([Bmim]SO4)) to oil= 1:6, O/S mole ratio=4); c) Optical micrographs d) Dynamic light scattering patterns of water in oil emulsion produced by used emulsion catalyst and IL in the first recirculation trial (volume ratio solvent to oil= 1:6, O/S mole ratio = 4)

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a)

b)

Figure 14. ECODS in new process design: a) performance of system in different CODS contact time; b) comparison the new process design with one-pot ECODS; 7.5 g/L emulsion catalyst was used (Initial Sulfur content: 500 ppmw; One-pot: solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, time=45 minutes; Step-by-step: solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=70 oC, time=30 minutes in EDS and 45 minutes in ECODS)

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a)

b)

Figure 15. Performance of ECODS in new process design: a) performance of system in different CODS contact time; b) comparison the new process design with one-pot ECODS. 7.5 g/L emulsion catalyst (Initial Sulfur content: 1500 ppmw; One-pot: solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T =70 oC, time=45 minutes, step-by-step: Solvent: IL, O/(S+N) mole ratio= 4, volume ratio of solvent to oil= 1:6, T=60 oC, time=30 minutes in EDS and 45 minutes in ECODS)

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a) One-Pot ECODS Process

b) Step-by-step ECODS Process

Scheme 1. Concept processes to produce S-free diesel fuel in a refinery, with a vanadium substituted Dawson emulsion catalyst and IL.

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TOC Table /Graphical Abstract

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246x203mm (96 x 96 DPI)


Desulfurization of Fuel by Extraction and Catalytic Oxidation Using a

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