Oxidative Desulfurization of Diesel Using Vanadium-Substituted

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OXIDATIVE DESULFURIZATION OF DIESEL USING VANADIUMSUBSTITUTED DAWSON-TYPE EMULSION CATALYSTS Farhad Banisharif, Mohammad Reza Dehghani, and Jose Miguel Campos-Martin Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b02791 • Publication Date (Web): 21 Mar 2017 Downloaded from http://pubs.acs.org on March 28, 2017

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OXIDATIVE DESULFURIZATION OF DIESEL USING VANADIUMSUBSTITUTED DAWSON-TYPE EMULSION CATALYSTS F. Banisharifa, M.R. Dehghania,*, J.M. Campos-Martinb a

Chemical engineering department, Iran university of science and technology, Narmak, Tehran, Iran

b

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

ABSTRACT In this study, we aimed at investigating the catalytic oxidative desulfurization (CODS) of the model diesel oil and real diesel oil using the vanadium substituted Dawson-type emulsion catalyst ([cetrimonium]6+xP2W18-xVxO62 (x=1, 3, 5)). Among all prepared samples, [cetrimonium]11P2W13V5O64 showed the best results in CODS of model diesel oil under determined conditions (10 g/L catalyst and O/S mole ratio = 4). Taguchi method was then applied to optimize the catalyst dosage, hydrogen peroxide dosage and the reaction temperature in CODS using the best emulsion catalyst. Then formic acid and acetic acid were used as a co-oxidant to improve the oxidation ability. Under optimum conditions, a mixture of H2O2/formic acid (1:1), in the presence of [cetrimonium]11P2W13V5O62 could remove 98% of dibenzothiophene and 82% of benzothiophene. Finally, under optimum conditions of CODS, 90 % of total sulfur were removed from a real diesel sample. It is worth mentioning that we could recycle [cetrimonium]11P2W13V5O64, 8 times without a significant decrease in catalyst activity. Keywords: Oxidative desulfurization, Diesel fuel, Dawson, Emulsion catalyst, BT, DBT *

Corresponding

author:

Tel.:

+98

2177240496;

Fax:

+98

[email protected] (M.R. Dehghani).

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2173227772.

E-mail

address:

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1. INTRODUCTION Sulfur in fuel is considered as a source of air pollution; in this regard, many governments around the world enact environmental legislations to decrease the sulfur content of fuels to ultralow levels.1 Usually, meeting restricted environmental conditions causes major operational and economical challenges for petroleum refineries.2 Hydrodesulfurization (HDS) is one of the most conventional method for sulfur reduction, unfortunately this process requires severe conditions such as high pressure and temperature, which increase capital expenditure (CAPEX) and operating expenditure (OPEX) of the unit. In this regard during recent years, oxidative desulfurization (CODS) has been considered as an alternative technology for deep desulfurization of fuel.3,4 ODS generally consists of oxidation of organosulfur compounds in fuel using appropriate oxidizing agents in the presence of a suitable catalyst. Different oxidizing agents such as H2O25-7, ozone8 and t-butyl-hydroperoxide9 have been used in ODS. H2O2 is the mostly selected oxidant not only due to oxidizing ability but also because of its environmental compatibility.5 In order to improve the performance of oxidative desulfurization, different combinations of H2O2/acid have also been studied. Previous works showed that organic acids, such as formic acid and acetic acid have higher efficiency compared to inorganic acids, such as H2SO4 in ODS.8-12 In the presence of mixed oxidant (organic acid + hydrogen peroxide, the sulfur content was reduced to 5 ppmw under the mild conditions (temperature lower than 100 oC and atmospheric pressure). Formation of acid such as peroxyacetic acid and peroxyformic acid in the presence of H2O2 and their solubility in oil phase are the main reason of their high ODS performance; 13 while, the high consumption of oxidant is a major limitation for industrialization. In this regard, during last years, scientists have focused on oxidation in the presence of oxidizing agents and catalysts which is named catalytic oxidative desulfurization (CODS).


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Previous

studies

on

CODS

systems

revealed

that

catalysts

like

polyoxometalates(POMs), V2O5/Al2O3, Ni/Al-Si show good activities in the oxidation of DBT and benzothiophene (BT).5, 8-13 Among different catalysts, POMs have received much more attention because of their acidic and redox properties and being environmental friendly.5,10-14 Keggin-type (([XM12O40](3+a)-; X= P, Si; M=W, Mo; a=1,2)) and Dawson-type (([X2M18O64]6-; X= P, Si; M=W, Mo)) are the most common types of POMs15. Previous researches demonstrated that the acidity and catalytic activity of Dawson-type POMs are higher than Keggin-type POMs. The acidity of Dawson-type POMs are in the order of H6P2W18O62 > H6Si2W18O62 > H6P2Mo18O62 > H6Si2Mo18O62.16-18 Furthermore, one of the most significant subclasses of POMs is the vanadium (V) substituted POMs. The introduction of vanadium to POM frame is beneficial to change POM’s reactivity from acid-dominated to redox-dominated, as shown by the oxidation of some organic compounds.18-20. Dawson-type POM contains 12 axial sites and 6 polar sites,15 usually the vanadium is located in a polar site of [P2W18O62]6- which leads to [P2W18-xVxO62](6+x)-.21 The vanadium substituted for tungstate strongly affects the terminal and bridge bonds on the plane formed by WO6 octahedral sharing edges,20 this substitution increases reaction activity. In order to remain the structure of Dawson-type POM unaffected, the maximum number of vanadium substituted for tungstate cannot be more than 5 in the frame of phosphotungstate.21-23 Mass transfer resistance between the aqueous phase, containing the oxidizer and catalyst, and the oil phase is a barrier and limits the overall efficiency of CODS. Using a phase transfer agent can improve the mass transfer between phases. Surfactant based catalysts can be considered as a new approach for phase transfer agent. surfactant based catalyst is a combination of a POM anion and a quaternary ammonium cation.24-26 Recently, Lu et al. utilized

emulsion

catalyst

[(C18H37)2N(CH3)2]3[PW12O40]

and

[(C18H37)2N(CH3)2]3Co(OH)6Mo6O18·3H2O to reduce the sulfur contents of diesel oil from


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500mg/g to less than 30mg/g under mild conditions. They could recycle it with 100% selectivity.24, 25 The most of studies on usage of POM in desulfurization is limited to Keggin-type POM as a homogeneous and heterogeneous catalysts, whereas a few studies paid attention to application of Dawson-type POM for desulfurization.8-28 So, in this work we aim at studying the

capability

of

vanadium

substituted

Dawson-type

emulsion

catalyst,

[cetrimonium]6+xP2W18-xVxO62 (x=1, 3, 5), as an amphiphilic catalyst for the first time. Finally, the operation conditions to achieve ultra-low-sulfur diesel oil are presented using Taguchi method. Taguchi is one of the best robust designs that utilizes an orthogonal array to handle any given system by a set of independent factors over specific levels to reduce test error and to increase reproducibility.29 2. EXPERIMENTAL 2.1. Chemical and Reagent. Benzothiophene (BT), dibenzothiophene (DBT) (representative refractory sulfur compounds in a real diesel oil) and H2O2 (aqueous solution, 30 wt. %) were purchased from Sigma-Aldrich. Other reagents and solvents used in this work are available commercially and were used as received. Typical actual diesel (density = 0.8365 g/mL at 15 °C, total sulfur content ~ 0.01 wt.%) was used and details are shown in Table 1. 2.2. Preparation of Emulsion Catalyst. H6+xP2W18-xVxO62 (x= 1, 3, and 5) heteropoly acids were prepared according to the similar method reported in the literature.30 For example, H11P2W13V5O62 was prepared as follows: 5.8 g of NH4VO3 and 3.28 g of Na3PO4 were dissolved with 100 mL deionized water at 40 °C. Thereafter, 3.315 g of Na2WO4 was added and solution was heated to 96 °C, after adjusting the pH (pH = 4.4) by adding 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 fully shaking


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and standing for 1 h. Then an oily red phase at the bottom of decanter which consists of the mixture of heteropoly acid and diethyl ether was separated. Finally, after evaporation of diethyl ether at 200 °C, a powdered vanadium substituted heteropoly acid was obtained. Emulsion catalysts, [cetrimonium]6+xP2W18-xVxO62 (x= 1, 3, and 5), were synthesized utilizing available procedures for POMs,31 For example, [cetrimonium]11P2W13V5O62 was synthesized as follows: The (3.6 g) H11P2W13V5O62 was dissolved in distilled water (25 ml) appropriately followed by adjusting the pH (pH=4.4) with a solution of HCl (2 mol/L). Then 4.05 g of cetrimonium (CTAB) was dissolved in 40 mL of ethanol and was added drop wise. A red precipitate [CTA]11P2W13V5 O62 was immediately formed. After continuous stirring for 2 h, the resulting solid was filtered by centrifuge and dried at 70 oC in vacuum oven overnight. 2.3. Characterization of Catalyst. Transmission FT-IR spectra of emulsion catalysts were measured as 3% KBr pellets on Shimadzu-8400S FT-IR spectrometer. The chemical analysis (P, V, W) of each sample was determined by inductively coupled plasma spectroscopy (ICP) (ICPS S7000, Shimadzu). Elemental combustion system (ECS), 4010 CHNS-O elemental analyzer Costech Analytical Technologies, Inc., Italy was also used to determine the amount of C, H and N in each sample. UV-vis diffuse reflectance spectroscopy (UV-vis DRS) spectrum was recorded on a Shimadzu UV-2101 PC spectrometer equipped with a diffuse-reflectance to distinguish the electronic properties of the center-metal ions. BaSO4 was used as the internal standard. The scanning patterns were recorded at 190-800 nm in a step-scan mode with a step of 2 nm. In order to determine the crystalline phase, the X-ray diffraction (XRD) experiments were performed on a Philips PW-1800 diffractometer using Cu Kα radiation (λ= 0.15406 nm) at 40 kV and 30mA. The XRD spectrum of catalyst samples were measured over an angular range of 5oV1. In fact, Vn+ which is the most strongly oxidizing element and can be readily reduced to V(n-1)+ with the concomitant oxidation of an organic substrate, improves the catalytic activity of emulsion catalyst. Meanwhile, the substitution of W6+ by V5+ in the POM’s frame results in the generation of more reactive lattice oxygen associated to the W-OV species.19,20 The similar trend was also reported in the literature on aerobic oxidation of tetrahydrothiophene using Keggin-type heteropoly acids H3+x[PW12-xVxO40] catalysts [34] and CODS of DBT using Keggin-type emulsion catalyst, (TBA)3+x[PW12-xVxO40] (x =0, 1, 2, 3).35 3.3. Optimization of CODS Reaction Conditions. In this study, Taguchi method design was used for optimization of the CODS using [CTA]11P2W13V5O62. In this investigation, the effects of various process parameters, catalyst, H2O2 (mole ratio of H2O2 (O): Sulfur(S)) dosage and reaction temperature on the CODS of model fuel (DBT and BT in iso-octane) were investigated. Table 3 presents the studied parameters at their corresponded levels. The oxidative desulfurization percent in each experiment is indicated in the last column of Table 3. The sample was taken after 60 minutes and put into an ice chamber to stop the reaction. The catalyst in the emulsion sample was separated by centrifugation. Average effect of each parameter at different levels showed that variation in the reaction conditions affects the desulfurization of DBT and BT. The relative significance of the


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parameters on catalytic oxidative desulfurization was determined via analysis of variance (ANOVA). ANOVA data, was computed for 95% confidence interval among the studied parameters, the results are illustrated in Table 6. The error term contains information about the following variables for results: uncontrollable factors, factors that are not considered in the tests, and test error (20.84%). F-ratio is criterion for distinguishing important factors from those with less importance. Using the Fisher tables29 at a 95% confidence level, degree of freedom (DOF) of error equal to 6 and DOF of each factor equal to 3, for individual factors give an F-value of 8.94. Table 6 illustrates that the F-values of all factors are greater than the value from the Fischer table. This means that the variance of all factors is important for variance of error at 95% confidence level and shows that experiments are reliable. PF obtained for each factor shows that the significant order of parameters is as follows: hydrogen peroxide dosage (53.506%) > catalyst dosage (15.327%) > temperature (10.327%). This determines that factor hydrogen peroxide dosage (amount of oxidant) has the utmost effect on the CODS. In Figure 5, the average effects of various parameters are presented. These values have been obtained using experiments’ results presented in Table 3. Figure 5 shows that the highest desulfurization level may achieve at O/S mole ratio=8 (Figure 5a), catalyst dosage=7.5 g/L (Figure 5b) and temperature=80 oC (Figure 5c). In order to test these proposed criteria, the CODS experiment was conducted under these conditions. At these conditions, 91% of DBT and 76% of BT were removed. These results are nearly similar to the results obtained by test number 15. So, the designed experiments could be reputational and the predicted optimum conditions was validated. The results also show that temperature increase from 60 oC to 80 oC, has a negligible effect on BT and DBT removal. While we expected an increase in oxidation rate. Following justification can be considered for this matter: there are two parallel H2O2-involved reactions in the CODS, including BT and DBT


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oxidation and H2O2 thermal decomposition. As temperature is raised, the rate of oxidation is increased. This phenomenon is observable in the range of 50-60 oC while after that thermal decomposition of H2O2 becomes dominant reaction, consequently rate of oxidation decreases. In this regard, T=60 oC has been selected as the optimum temperature in the following experiments. In the case of O/S mole ratio, it is obvious that there is a direct relation between oxidation efficiency and H2O2 dosage. Meanwhile addition of more H2O2 introduce more water into the reaction system, composed of two phases of water and iso-octane, which meaningfully affects the reaction environment. When the amount of H2O2 is increased, the mass transfer efficiency is decreased to some extent and consequently the catalytic activity decreases. In next steps, we try to decrease O/S mole ratio. 3.3. Effect of Organic Acid on the Catalytic Oxidative Desulfurization. In order to improve the oxidative desulfurization of DBT and BT, formic acid and acetic acid were also used as a co-oxidant at different mole ratios to hydrogen peroxide. In order to reduce the hydrogen peroxide (30 wt. %) consumption, the mole ratio of H2O2 to total sulfur was set at 4 instead of 8. At this condition sulfur removal was improved nearly 7% and the highest level of desulfurization was achieved at mole ratio of H2O2/formic acid=1 (Table 7). Using the optimum catalyst [CTA]11P2W13V5O62 and under the optimum conditions (T=60 oC, mole ratio O/S= 4, H2O2/formic acid mole ratio= 1, 7.5 g/L catalyst) model fuel was desulfurized. Figure 6 demonstrates that the sulfur removal versus time. The maximum removal of DBT (~98%) and BT (~82%) were achieved approximately after 45 minutes. 3.4. Catalytic Oxidative Desulfurization of Real Diesel. The catalytic oxidation desulfurization of commercial diesel (containing 105 ppmw) was carried out under optimum condition (O/S molar ratio = 4, H2O2/formic acid mole ratio= 1, T = 60 oC, 7.5 g/L catalyst).


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At this state, total sulfur of real diesel oil was decreased from 105 to less than 10 ppmw. This result shows that emulsion catalyst can have high catalytic activity for all kinds of sulfurcontaining compounds which may present in real diesel oil. This result is also interesting, because there is a competition among sulfur compounds, naphthenics, aromatics and nitrogen compounds in CODS. 3.5. The Reusability of Dawson-Type Emulsion Catalyst. The reusability of the catalyst was investigated to distinguish whether the catalyst would lose its catalytic activity during the reaction. For this purpose, the oxidative desulfurization of real and model fuel was repeated several times. The results are presented in Figure 7. The emulsion catalyst was separated by centrifuge after each run and reused without any treatment. It can be seen that in the case of model fuel, after 8 runs the catalytic activity is almost the same as the fresh catalyst. However in the case of real fuel after 4 runs the catalyst activity is declined. This phenomenon can be referred to catalyst loss during recycling and blockage of catalyst surface. 4. CONCLUSION For

the

first

time,

vanadium

substituted

Dawson-type

emulsion

catalysts

([CTA]6+xP2W18-xVxO62 (x=1, 3, 5)) were synthesized and used for the catalytic oxidative desulfurization of the model fuel (500 ppmw DBT and 500 ppmw BT in iso-octane) and real diesel oil. The results showed that the order of catalytic activity was V5>V3>V1. The effects of the catalyst dosage, O/S mole ratio and the reaction temperature on the CODS were investigated. The results showed that the hydrogen peroxide dosage and catalyst dosage were the most effective parameters among selected parameters. Then formic acid and acetic acid were used as a co-oxidant to improve the desulfurization efficiency. The results revealed that H2O2/formic acid was more efficient than H2O2/acetic acid and improved the desulfurization


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efficiency ~7%. Under the optimum conditions (H2O2/formic acid mole ratio = 1, T = 60 oC, O/S mole ratio= 4 and 7.5 g/L of the best emulsion catalyst), ~98% of DBT and ~82% of BT were removed from model fuel at 45 minutes. Finally, the optimum condition of CODS was applied to a real diesel sample; the results revealed that the level of total sulfur of real sample can be lowered to 10 ppmw after 45 min.


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(14) Mirhoseini, H.; Taghdiri, M. Fuel 2016, 167, 60-67. (15) Ammam, M.; Fransaer, J. J. Solid State Chem. 2011, 184, 818-824. (16) Misono, M. Surf. Sci. Catal. 2013, 176, 97-154. (17) Wang, C.; Bu, X.; Ma, J.; Liu, C.; Chou, K.; Wang, X.; Li, Q. Catal. Today 2016, 274, 82-87. (18) Park, D.R.; Kim, H.; Jung, J.C.; Lee, S.H.; Song, I.K. Catal. Commun. 2008, 9, 293-298. (19) Zou, C.; Zhao, P.; Ge, J.; Qin, Y.; Luo, P. Fuel 2013, 104, 635-640. (20) Omwoma, S.; Gore, C.T.; Ji, Y.; Hu, C.; Song, Y-F. Coord. Chem. Rev. 2015, 286, 1729. (21) Ueda, T.; Nishimoto, Y.; Saito, R.; Ohnishi, M.; Nambu, J.-I. Inorganics 2015, 3, 355369. (22) Yuhao, S.; Jingfu, L.; Enbo, W. Inorg. Chim. Acta 1986, 117, 23-26. (23) Yu, F.; Wang, R. Chem. Lett. 2014, 43, 834-836. (24) Lü, H.; Zhang, Y.; Jiang, Z.; Li, C. Green Chem. 2010, 12, 1954-1958. (25) Lü, H.; Ren, W.; Liao, W.; Chen, W.; Li, Y.; Suo, Z. Appl. Catal. B Environ. 2013, 138139, 79-83. (26) Lü, H.; Gao, J.; Jiang, Z.; Jing, F.; Yang, Y.; Wang, G.; Li, C. J. Catal. 2006, 239, 369375. (27) Huang, W.; Zhu, W.; Li, H.; Shi, H.; Zhu, G.; Liu, H.; Chen, G. Ind. Eng. Chem. Res. 2010, 49, 8998-9003.


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(28) Zhu, W.; Huang, W.; Li, H.; Zhang, M.; Jiang, W.; Chen, G.; Han, C. Fuel Process. Technol. 2011, 92, 1842-1848. (29) Taguchi, G. Systems of Experimental Design; UNIPUB/Kraus International Publications: New York, 1987. (30) Wang, E.B.; Gao, L.H.; Liu, J.F.; Liu, Z.X.; Yan, D.H. Acta. Chem. Sinica. 1986, 46, 757-762. (31) Ueda, T.; Komatsu, M.; Hojo, M. Inorg. Chem. Act. 2003, 344, 77-84. (32) Pope, M.T. Heteropoly and Isopoly Oxometalates; Springer: Berlin, 1983; pp 128-141. (33) Dablemont, C.; Hamaker, C.G.; Thouvenot, R.; Sojka, Z.; Che, M.; Maatta, E.A.; Proust, A. Chem. Eur. J. 2006, 12, 9150-9160. (34) Hill, C.L.; Gall, R.D. J. Mol. Catal. A Chem. 1996, 114, 103-111. (35) Ribeiro, S.; Barbosa, A.D.S.; Gomes, A.C.; Pillinger, M.; Gonçalves, I.S.; Cunha-Silva, L.; Balula, S.S. Fuel Process. Technol. 2013, 116, 350-357.


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Table 1. Properties of Diesel Real Sample Entry Properties

Unit

Method

1

Total sulfur

Wt. %

ASTM D4294 0.0107

2

Specific gravity @ 60 oF

[-]

ASTM D1298 0.8365

2

Density @ 15 oC

g/mL

ASTM D1298 0.8361

3

Water content by distillation

Vol. % ASTM D4006 0.025

6

Result

IBP

o

ASTM D86

157.8

10%

o

ASTM D86

194.6

20%

o

ASTM D86

213.6

50%

o

ASTM D86

268.6

90%

o

ASTM D86

353.9

FBP

o

ASTM D86

384.9

C C C

Distilled C C C


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Table 2. Selected factors and assigned levels Level Entry

Factor 1

2

3

4

2

4

6

8

1

O/S mole ratio

4

Catalyst dosage (g/L)

2.5

5

7.5

10

5

Temperature (oC)

50

60

70

80


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Table 3. L16 orthogonal array experiment designed used for optimization the oxidative desulfurization of model fuel Removal (%) O/S mole

Catalyst dosage Temperature (oC)

NO ratio

(g/L)

Total DBT

BT sulfur

1

2

2.5

50

56.56

30.56

41.50

2

2

5

60

65.44

36.00

48.39

3

2

7.5

70

74.25

48.89

59.56

4

2

10

80

69.69

71.58

70.78

5

4

2.5

60

85.94

59.03

70.36

6

4

5

50

69.38

54.44

60.73

7

4

7.5

80

88.75

77.78

82.40

8

4

10

70

84.38

72.22

77.34

9

6

2.5

70

81.13

63.89

71.14

10

6

5

80

78.75

68.61

72.88

11

6

7.5

50

81.25

77.78

79.24

12

6

10

60

82.50

70.50

75.55

13

8

2.5

80

81.13

67.78

73.39

14

8

5

70

88.13

75.00

80.53

15

8

7.5

60

89.06

76.39

81.72

16

8

10

50

78.00

66.67

71.43


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Energy & Fuels

Table 4. FT-IR absorption frequencies (cm-1) of emulsion catalyst (M=W, V) υas (M-O-

υas

M)

(M=O)

Sample

υas (M=O)

υas (P=O)

υas (O-H)

υas (C-H)

1468, [CTA]7P2W17VO62

780

912

960

1091

3442

2850, 2918 1468,

[CTA]9P2W15V3O62

786

908

960

1090

3442

2850, 2918 1468,

[CTA]9P2W13V5O62

778

912

958

1089

3442

2850, 2918


Energy & Fuels

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Table 5. Effect of structure of emulsion catalyst Removal (%) Sample DBT

BT

Total Sulfur

Without Catalyst

45.06

35.75

40.28

[CTA]7P2W17VO62

67.60

57.20

60.42

[CTA]9P2W15V3O62

82.81

61.73

70.16

[CTA]11P2W17V5O62

86.69

72.79

82.22

* oxidation reaction conditions: O/S mole ratio = 4, T= 60 oC, rpm=1000, Catalyst dosage= 10 g/L, Time= 60 min


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Energy & Fuels

Table 6. The results of ANOVA for optimization the catalytic oxidative desulfurization of model fuel using vanadium-substituted emulsion catalyst Factor

DOF

Sum of

Variance

F-Ratio

Pure sum

Percent

(f)

square (S)

(V)

(F)

(S’)

P (%)

O/S mole Ratio

3

1193.745

397.915

13.837

1107.478

53.506

Catalyst dosage

3

403.513

134.504

4.677

317.246

15.327

Temperature

3

300.023

100.007

3.477

213.756

10.327

Others/error

6

172.533

28.755

20.84

Total

15

2069.816

28.755

100.00%


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Table 7. Effect of different oxidant system in oxidation desulphurization of different sulfur compounds. Removal %

Type of Mole ratio of acid to H2O2 acid

Formic acid

Acetic acid

DBT

BT

Total sulfur

1:4

90.65

74.79

81.47

1:2

94.80

78.01

85.08

1:1

97.65

81.80

88.48

1:4

88.70

74.30

80.36

1:2

90.80

76.52

82.53

1:1

96.90

80.23

87.25

* Conditions of desulfurization: 7.5 g/L emulsion catalyst, time= 60 minutes and temperature = 60 oC


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Energy & Fuels

Figure Caption Figure 1. Powder X-ray diffraction patterns of emulsion catalyst. Figure 2. P MAS NMR of emulsion catalysts. Figure 3. UV spectra of emulsion catalysts and their mother sources. Figure 4. XPS spectra for the V2p3/2 and W4f7/2. The spectra for H6+xP2W18-xVxO62 (x=1,3,5) and [CTA]11P2W13V5O62 are the nearly the same. Figure 5. Average removal of DBT and BT correspond to the different levels of the studied parameters: (a) O/S mole ratio, (b) Catalyst dosage (g/L), (c) temperature (oC). Figure 6. Conversion of DBT and BT over [CTA]11P2W13V5O62 (H2O2/formic acid, mole ratio acid:H2O2=1:1, catalyst dosage:7.5 g/L, O/S mole ratio = 4, T=60 oC). Figure 7. Recycle performance of the best catalyst, [CTA]11P2W13V5O62: (a) Model fuel, (b) Real diesel oil (total sulfur); Reaction conditions: H2O2/formic acid, mole ratio of acid: H2O2=1:1, 7.5 g/L catalyst, O/S mole ratio = 4, time = 45 minutes and T= 60 oC.


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

a) [CTA]7P2W17VO62

b) [CTA]9P2W15V3O62

C) [CTA]11P2W13V5O62


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Energy & Fuels

Figure 1. Powder X-ray diffraction patterns of emulsion catalyst (d space of main peak mentioned in each diagram).


Energy & Fuels

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Figure 2. P MAS NMR of emulsion catalysts.


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Energy & Fuels

Figure 3. UV spectra of emulsion catalysts and their mother sources.


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

Figure 4. XPS spectra for the V2p3/2 and W4f7/2. The spectra for H6+xP2W18-xVxO62 (x=1,3,5) and [CTA]11P2W13V5O62 are the nearly the same.


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Energy & Fuels

a) O/S mole ratio

b) Catalyst dosage (g/L)


Energy & Fuels

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c) Temperature (oC)


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Energy & Fuels

Figure 5. Average removal of DBT and BT correspond to the different levels of the studied parameters: (a) O/S mole ratio, (b) Catalyst dosage (g/L), (c) temperature (oC).


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

Figure 6. Conversion of DBT and BT over [CTA]11P2W13V5O62 (H2O2/formic acid, mole ratio acid:H2O2=1:1, catalyst dosage:7.5 g/L, O/S mole ratio = 4, T=60 oC).


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Energy & Fuels

a) Model diesel oil

b) Real diesel oil


Energy & Fuels

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Figure 7. Recycle performance of the best catalyst, [CTA]11P2W13V5O62: (a) Model fuel, (b) Real diesel oil (total sulfur); Reaction conditions: H2O2/formic acid, mole ratio of acid: H2O2=1:1, 7.5 g/L catalyst, O/S mole ratio = 4, time = 45 minutes and T= 60 oC.


Page 36 of 36

Oxidative Desulfurization of Diesel Using Vanadium-Substituted

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