Extractive Desulfurization of Gasoline Using Imidazolium-Based

Energy & Fuels 2006, 20, 2083-2087

2083

Extractive Desulfurization of Gasoline Using Imidazolium-Based Phosphoric Ionic Liquids Yi Nie, Chunxi Li,* Aijun Sun, Hong Meng, and Zihao Wang College of Chemical Engineering, Beijing UniVersity of Chemical Technology, Beijing 100029, People’s Republic of China ReceiVed April 21, 2006. ReVised Manuscript ReceiVed June 19, 2006

Sulfur partition coefficients for sulfur compounds 3-methylthiophene (3-MT), benzothiophene (BT), and dibenzothiophene (DBT) between phosphoric ionic liquids (ILs), namely, N-methyl-N-methylimidazolium dimethyl phosphate ([MMIM][DMP]), N-ethyl-N-methylimidazolium diethyl phosphate ([EMIM][DEP]), and N-butyl-N-methylimidazolium dibutyl phosphate (BMIM][DBP]), and gasoline were determined experimentally at 298.15 K over a wide range of sulfur content and compared with other IL extractants. The solubility of sulfur (as DBT, BT) in ILs aqueous solution at 298.15 K and varying water content was also measured. It was shown that the desulfurization ability of the ILs for each sulfur component (DBT, BT, 3-MT) followed the order of [BMIM][DBP] > [EMIM][DEP] . [MMIM][DMP], and the sulfur removal selectivity for a specified IL followed the order of DBT > BT > 3-MT. The phosphoric ILs are insoluble in gasoline while the fuel solubility in ILs is noticeable and follows the order of [BMIM][DBP] . [EMIM][DEP] > [MMIM][DMP]. Considering the relatively high sulfur removal ability, low fuel dissolvability, and small influence on the gasoline treated, [EMIM][DEP] might be used as a promising solvent for the desulfurization of gasoline via an extractive desulfurization (EDS) process. The sulfur components in the spent ILs could be conveniently separated via a water dilution process.

Introduction Deep desulfurization of gasoline and diesel has attracted much attention in recent years as the environment regulation on the sulfur limit of fuels becomes increasingly stringent. To reduce the sulfur content (hereinafter noted as S-content) to a much lower limit, say 10-20 ppm,1 the traditional hydrodesulfurization (HDS) process is confronted with a great challenge and need a substantial improvement for both reactivity and selectivity of the catalyst used. Otherwise, the HDS process may fail to be effective in terms of fuel quality and cost as the traditional commercial Co/Mo catalyst is less effective for the hydrogenation of benzothiophene (BT) and dibenzothiophene (DBT) series sulfur component (S-component), which however is inevitable in the deep desulfurization process.2,3 To overcome this difficulty, many alternative processes such as adsorption, extraction, selective oxidation, and/or alkylation of S-components have been studied extensively. Among these alternatives, extractive desulfurization (EDS) seems more attractive for the fact that the extraction process is a well-established process that can be carried out at or around ambient temperature and pressure and without the need for hydrogen and catalysts.2 More importantly, some BT and DBT series S-components can be extracted quite efficiently. Therefore, the EDS process can at least be a complementary technology for the HDS process. For the extraction of S-components, some molecular solvents such as polyalkylene glycol, polyalkylene glycol ether, pyrrolidones, imidazolidinones, and pyrimidinones have been patented.3 * Corresponding author. E-mail: [email protected]. Tel.: +86-1064444911. Fax: +86-10-64410308. (1) Song, C. S. Catal. Today 2003, 86, 211-263. (2) Babich, I. V.; Moulijn, J. A. Fuel 2003, 82, 607-631. (3) Horii, Y.; Onuki, H.; Doi, S.; Mori, T.; Takatori, T.; Sato, H.; Ookuro, T.; Sugawara, T. U.S. Patent 5,494,572, 1996.

However, their extraction performance seems mean, and sometimes their solubility in fuel or vice versa is noticeable leading to a cross-contamination. In contrast to the molecular solvents, ionic liquid (IL) seems more competitive considering the facts: (1) It is environmentally benign and designable. (2) It is virtually immiscible with fuels and hence free of cross-contamination. (3) It is nonvolatile and thermal stable over a wide range of temperature, as a result the used IL can be regenerated by distillation. (4) Its conductance makes much room for the selection of regeneration methods for the used IL solvent. (5) Many ILs (e.g., [BMIM]Cl/AlCl3, [BMIM][BF4], [BMIM][PF6], [BMIM][OcSO4], [MMIM][DMP],4-6 [BMIM][Cu2Cl3],7 etc.) show desulfurization ability to a varying degree. For the EDS process, the key to success is to find an effective IL that is nontoxic, chemically stable to moisture and air, and not expensive for commercial application. Considering these requirements, the imidazolium-based phosphoric ILs [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP] are advantageous as they are easy to be manufactured in a commercial scale with very high yield. Feng et al.8 has studied the extraction performance of the above three phosphoric ILs for S-components 3-MT, BT, and DBT from model oil with encouraging results. The objective of this work is to evaluate the feasibility of these phosphoric ILs for the desulfurization of gasoline in terms of the sulfur partition coefficient and to explore the possibility of reclaiming the used ILs via the water dilution method. (4) Esser, J.; Wasserscheid, P.; Jess, A. Green Chem. 2004, 7, 316322. (5) Bo¨smann, A.; Datsevich, L.; Jess, A.; Lauter, A.; Schmitz, C.; Wasserscheid, P. Chem. Commun. 2001, 23, 2494-2495. (6) Schoonover, R. E. U.S. Patent 2,003,085,156, 2003. (7) Huang, C. P.; Chen, B. H.; Zhang, J.; Liu, Z. C.; Li, Y. X. Energy Fuel 2004, 18, 1862-1864. (8) Feng, J.; Li, C. X.; Meng, H.; Wang, Z. H. Petrochem. Technol. 2006, 35, 272-275.

10.1021/ef060170i CCC: $33.50 © 2006 American Chemical Society Published on Web 08/12/2006

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Table 1. Solubility of Gasoline in IL at 298.15 K in Mass Percentage IL

[MMIM][DMP]

[EMIM][DEP]

[BMIM][DBP]

oil solubility in IL, wt %

1.12

4.25

20.6

Experimental Section Preparation of Phosphoric Ionic Liquids. [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP] were prepared by reacting N-methylimidazole and the corresponding trialkyl phosphate at 423 K for 10 h with a yield of 97%.9 The resulting yellowish viscous liquid was washed three times with diethyl ether at room temperature followed by rotary evaporation under reduced pressure for 12 h to remove all volatile residues (e.g., the reactants unreacted and diethyl ether). The purity and structure of these ILs have been analyzed by NMR and electronic spray mass spectrum. Mutual Solubility of Ionic Liquid and Gasoline. The mutual solubility is an important factor to be considered in choosing an extractant because the noticeable solubility of imidazolium-based IL in gasoline may on one hand contaminate the fuel and on the other hand lead to a NOx pollution while we are intending to remove the SOx pollution. By analyzing the IL-saturated gasoline sample with liquid chromatograph10 (SHIMADZU-10AVP equipped with UV-Vis detector under 295 nm wavelength; column, C-18; mobile phase, methanol/water ) 8/2; flow rate, 1.0 mL/min), no IL peak was found. Hence the phosphoric ILs studied here have negligible solubility in gasoline. The solubility of gasoline in IL was measured using gravimetric method by weighing the mass difference of a given amount of IL saturated with gasoline before and after solvent removal by vaporization at high temperature and reduced pressure. The solubility data of gasoline in different phosphoric ILs at 298.15 K are shown in Table 1. Sulfur Partition Coefficient Measurement for Gasoline-Ionic Liquid Systems. A straight-run gasoline was used as purchased from QiLu Oil Field in the whole desulfurization experiment, and its composition was analyzed qualitatively by gas chromatograph3,6 (SHIMADZU GC2010 equipped with a FID-Detector; DB-1 column, 30 m × 0.25 mm i.d. × 5 µm; carrier gas, N2; temperature program: 50 °C-5 °C/min-100 °C-20 °C/min-320 °C) as shown in Figure 1 (curve d). The sulfur content in ppm was determined by the corresponding peak area along with the external standard curve relating the peak area and mass percentage of sulfur component for a specified system. For each sample, GC analysis was repeated three times to obtain the average value of sulfur content. Before experiment, a concentrated IL solution with known S-content (in mg of S‚(kg of IL)-1) was prepared using the gravimetric method by dissolving a definite amount of 3-MT, BT, or DBT in known quantities of IL, which was used as S-source in the following extraction experiment. For example, by dissolving 0.174 g of DBT in 17.734 g of [BMIM]][DBP], a 1689.8 ppm S-content IL sample was obtained. Sulfur partition coefficient (KN), which is defined as the ratio of S-concentration in IL to S-concentration in gasoline, is an important parameter for an EDS process, and the higher the partition coefficient is, the better the desulfurization performance of an IL. In this work, KN was measured as follows. First, a known weight of S-free IL and gasoline was mixed in a conical flask under vigorous magnetic stirring for pre-equilibrium so as to minimize the effect of gasoline dissolution in IL phase on the calculation of sulfur partition coefficient. Second, a known amount of S-concentrated IL was added to the above biphasic mixture, magnetically stirred for 15 min11,12 at room temperature to reach the thermodynamic equilibrium, and then laid aside 10 min for phase splitting and settling. The phase equilibrium time of 15 min was determined through a test run for the distribution of DBT between gasoline and [EMIM][DEP] at room temperature. The S-content in (9) Jiang, X. C.; Yu, C. Y.; Feng, J.; Li, C. X.; Wang, Z. H. J. Beijing UniV. Chem. Technol., Nat. Sci. Ed. 2006, 33, 5-7. (10) Stepnowski, P.; Mller, A.; Behrend, P.; Ranke, J.; Hoffmann, J.; Jastorff, B. J. Chromatogr. A 2003, 993, 173-178.

gasoline phase was measured by liquid chromatograph using the external standard method (SHIMADZU-10AVP equipped with UV-Vis detector; wavelength, 310 nm for DBT, 251 nm for BT, 242 nm for 3-MT; mobile phase, methanol/water ) 9/1 for DBT, methanol/water ) 8/2 for BT and 3-MT; flow rate, 1.0 mL/min), and the S-content in IL phase was calculated via mass balance as such the sulfur partition coefficient was calculated. The second step was repeated several times until the equilibrium S-content in gasoline fell into the sulfur concentration range expected. The experimental data are listed in Tables 2 through 4 and in Figure 2. To investigate the effect of water content in ionic liquid on the extractive desulfurization performance, the sulfur partition coefficients for extraction of DBT, BT, and 3-MT between gasoline and [EMIM][DEP] at room temperature were measured, as listed in Table 5. Solubility of BT and DBT in Phosphoric IL Aqueous Solution. When the used IL is to be regenerated via removal of S-component by water dilution, the saturated solubility data of BT and DBT in IL aqueous solution at varying water content are of vital importance. In this work, the solubility of BT and DBT in an IL aqueous solution was determined by stepwise diluting the S-concentrated IL with water. In the dilution process, the BT or DBT component precipitated or crystallized gradually in the solution, and 12 h was given to each precipitation process to make sure that solubility equilibrium was reached. After the precipitates were removed by centrifugation, the S-content in mother liquid was measured using HPLC with UV-Vis detector at a wavelength of 310 nm for DBT and 251 nm for BT. The solubility data of a specified S-component in an IL aqueous solution at varying water content and 298.15 K are shown in Figure 3.

Results and Discussion Sulfur Removal Performance of Phosphoric ILs for Gasoline. As shown in Tables 2 to 4, the sulfur partition coefficient KN for each phosphoric IL and S-component (namely, 3-MT, BT, and DBT) is virtually a constant irrespective of the S-content in gasoline. That is, the S-content in the IL phase is linearly proportional to the S-content in gasoline at equilibrium in the sulfur concentration range studied (see Figure 2). The independence of KN on sulfur concentration is mainly attributed to the thermodynamic behavior of the dilute solution because the mole fractions of S-component in both phases are extremely low, which makes the nonideality variation of S-component negligible. For each S-component studied, the sulfur partition coefficients between IL and gasoline followed the order of [BMIM][DBP] > [EMIM][DEP] > [MMIM][DMP], and for a specified IL, the sulfur partition coefficient always followed the order of DBT > BT > 3-MT (see Figure 2). The later attribute is of practical significance suggesting that although DBT and BT series S-component cannot be removed efficiently by HDS process they can be extracted easily by ILs. The mechanism for the extraction of S-compounds with imidazolium-based IL is likely relevant to the formation of liquid clathrate due to the π-π interaction between unsaturated bonds of S-compound and the imidazolium ring of ILs.13 As seen in Table 5, the sulfur partition coefficients KN decrease dramatically as the water content in IL increases, and even 1% of water content in IL can give rise to about 20% lowering of extractive ability of [EMIM][DEP] for DBT from gasoline. This suggests that in order to use the IL extractant in a recycle way, the water residue in phosphoric IL must be removed as low as possible. (11) Zhang, S.; Zhang, Q.; Zhang, Z. C. Ind. Eng. Chem. Res. 2004, 43, 614-622. (12) Zhang, S.; Zhang, Z. C. Green Chem. 2002, 4, 376-379. (13) Holbrey, J. D.; Reichert, W. M.; Nieuwenhuyzen, M.; Sheppard, O.; Hardacre, C.; Rogers, R. D. Chem. Commun. 2003, 4, 476-477.

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Energy & Fuels, Vol. 20, No. 5, 2006 2085

Figure 1. GC spectrum of gasoline before and after EDS with [EMIM][DEP] and [BMIM][DBP]. (a) Mixture of gasoline and DBT, (b) gasoline desulfurizeded with [BMIM][DBP], (c) gasoline desulfurized with [EMIM][DEP], (d) gasoline. (1) 2,3-dimethylbutane, (2) 3-methylpentane, (3) hexane, (4) methylcyclopentane, (5) cyclohexane, (6) 3,7-dimethyloctene, (7) 1,3-dimethylcyclopentane, (8) heptane, (9) methylcyclohexane, (10) ethylcyclopentane.

Sulfur removal ability of phosphoric ILs [EMIM][DEP] and [BMIM][DBP] is satisfactory in comparison with other ILs reported in the literature, as can be seen by the sulfur partition coefficients listed in Table 6.4,5 In addition to the high desulfurization ability, [EMIM][DEP] and [BMIM][DBP] also feature good stability, fluidity, nontoxicity, and nonsensitivity to moisture and air, which make them superior to ILs such as [BMIM]Cl/AlCl3 and [BMIM][Cu2Cl3].7 Influence of Extractive Desulfurization on the Composition of Gasoline. The EDS process has two potential influences

on the fuel. On one hand, the mutual solubility of the imidazolium-based IL in fuel can give rise to a NOx pollution; on the other hand, the fuel composition is likely to be changed due to the selective extraction of IL for some specified components of fuel. In effect, the variation of fuel composition and quality can be reflected by the fuel solubility in the ILs involved, and the lower the solubility is, the smaller the variation of fuel quality should be. As an extreme case, the fuel quality and composition will remain unchanged when it is immiscible with the IL solvent. Hence the cross contamination of EDS

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Table 2. Sulfur (as DBT) Partition between IL and Gasoline and the Corresponding Partition Coefficients of Sulfur,a KN [BMIM][DBP]/ gasoline system S-content in gasoline (ppm), x

S-content in IL (ppm), y

128.1 232.0 223.6 371.9 303.6 490.4 383.3 604.9 453.6 702.1 516.9 806.5 568.1 900.8 611.1 980.6 y ) 1.587x (R2 ) 0.998) a

[EMIM][DEP]/ gasoline system

KN 1.81 1.66 1.62 1.58 1.55 1.56 1.59 1.60

S-content in gasoline (ppm), x


KN

191.6 394.5 543.2 673.5 800.4 889.0 929.0

278.4 487.9 697.0 818.1 1000.0 1129.0 1221.3

1.45 1.24 1.28 1.21 1.25 1.27 1.31

y ) 1.272x (R2 ) 0.996)

Experimental conditions: 298.15 K, vigorous stirring 15 min.

Table 3. Sulfur (as BT) Partition between IL and Gasoline and the Corresponding Partition Coefficients of Sulfur,a KN [BMIM][DBP]/ gasoline system S-content in gasoline (ppm), x


128.6 193.2 250.9 401.3 370.6 537.7 464.4 651.6 542.2 731.5 615.2 837.3 698.6 928.9 741.6 1008.4 y ) 1.370x (R2 ) 0.994) a


KN 1.50 1.60 1.45 1.40 1.35 1.36 1.33 1.36



180.1 209.7 359.8 372.5 517.0 479.8 602.0 604.5 703.8 642.5 789.9 715.5 846.4 808.6 922.0 863.5 y ) 0.944x (R2 ) 0.992)

KN 1.16 1.04 0.93 1.00 0.91 0.91 0.96 0.94


Table 4. Sulfur (as 3-MT) Partition between IL and Gasoline and the Corresponding Partition Coefficients of Sulfur,a KN [BMIM][DBP]/ gasoline system S-content in gasoline (ppm), x


282.2 181.4 535.9 375.3 892.8 567.4 1083.4 588.6 1215.9 697.3 y ) 0.588x (R2 ) 0.98) a


KN 0.64 0.70 0.64 0.54 0.57



150.5 65.1 281.0 115.2 446.2 192.4 628.6 285.6 766.4 392.1 y ) 0.474x (R2 ) 0.98)

KN 0.43 0.41 0.43 0.45 0.51


process is closely related to the mutual solubility of fuel and IL related. As the imidazolium-based phosphoric ILs studied here have negligible solubility in gasoline, the fuel will be free of NOx contamination. However, the solubility of fuel in the phosphoric ILs varies to a large extent for different IL species and follows the order of [MMIM][DMP] < [EMIM][DEP] , [BMIM][DBP] with the maximum solubility being 20.6 wt % for [BMIM][DBP]. The fuel solubility order was largely attributed to hydrophobic increase from [MMIM][DMP] to [BMIM][DBP] as the alkyl substitutes in the ILs increase from methyl to butyl. Considering the noticeable solubility of fuel in [EMIM][DEP] and [BMIM][DBP] as well as the selective extraction of ILs for aromatics and olefins in gasoline, fuel composition may be changed by [EMIM][DEP] and [BMIM][DBP] after an EDS process. From our previous study on EDS with phosphoric ILs for model oil,8 a mixture of 24.7% n-hexene + 24.7% xylene

Figure 2. Sulfur partition between phosphoric IL and gasoline at 298.15 K. Table 5. Effect of Water Content in IL on Sulfur Partition Coefficients between [EMIM][DEP] and Gasolinea DBT water content in IL (wt %) 0 1.04 3.00 5.42 a

BT KN

water content in IL (wt %)

1.28 1.05 0.75 0.53

0 1.07 3.00 4.99

3-MT KN

water content in IL (wt %)

KN

0.99 0.84 0.59 0.43

0 0.93 3.02 5.17

0.49 0.48 0.38 0.31


+ 50.6% n-hexane, it was found that [MMIM][DMP] and [BMIM][DBP] had a preferential extraction for n-hexene and that [EMIM][DEP] had a selective extraction on xylene. To investigate the influence of the EDS process on the composition of real gasoline, GC analysis was conducted for the following samples: a mixture of gasoline and DBT with S-content of 558 ppm (curve a), gasoline extracted three times by [BMIM][DBP] with mass ratio of IL/oil being unity and the

Desulfurization of Gasoline

Energy & Fuels, Vol. 20, No. 5, 2006 2087

Figure 3. Solubility of BT and DBT in [EMIM][DEP] and [BMIM][DBP] solution at varying water content and 298.15 K. Table 6. Sulfur Partition Coefficients KN for Extraction of DBT with IL

IL

KN [mg of S‚(kg of IL)-1/mg of S‚(kg of oil)-1]

IL

KN [mg of S‚(kg of IL)-1/mg of S‚(kg of oil)-1]

[BMIM]Cl/AlCl3a [BMIM][BF4]a [BMIM][PF6]a [EMIM][EtSO4]a [BMIM][OcSO4]a [BMIM][MeSO4]a

4.0 0.7 0.9 0.8 1.9 1.1

[BMIM][MeSO3]b [BMIM][CF3SO3]b [MMIM][Me2PO4]a [BMIM][DBP]c [EMIM][DEP]c [MMIM][DMP]c

1.1 0.8 0.7 1.59 1.27 0.46

b

a Model oil:4 500 ppm sulfur as DBT in n-dodecane, room temperature. 60 °C. c Real gasoline: sulfur as DBT, 298.15 K.

[BMIM][DBP], which was largely attributed to its lower solubility for gasoline as shown in Table 1. Regeneration of Sulfur-Loaded Phosphoric ILs. For the technical application of an IL extraction, the regeneration and subsequent recycling of IL is of vital importance. Removal of S-compounds from an IL can be conducted by a variety of techniques that are well-known to those skilled in the art. Such techniques can be selected from heating the IL to vaporize the S-compounds at temperatures within the IL stability range,6,11 back extraction of the S-compounds from the IL with another solvent,3,4 removing the aromatic S-component by electrolysis,8,14 or precipitating the S-components by dilution with water, etc.12,15 Among these approaches, the vaporization method is less effective for the long chain alkyl substituted BTs and DBTs as their boiling temperature may exceed the stable range of ILs, back extraction generally suffers from lack of efficient solvent and cross-contamination of fuel, electrolysis is limited by its efficiency due to the low conductance of ILs, while the precipitating method features ease of operation and convenience of separation of IL and water. Variation of solubility of BT and DBT with water content in an IL as shown in Figure 3 indicates that the solubility of S-components decreases drastically with water added and that the higher the water content in IL the lower the solubility of S-component. For both BT and DBT at specified water content, precipitation of S-component from [EMIM][DEP] is much easier than from [BMIM][DBP] since the former is more hydrophilic than the later as a result that the S-component around [EMIM][DEP] can be easily repelled by water and precipitated due to the stronger electrostatic interaction between water and [EMIM][DEP]. As a whole, S-compounds in an IL can be conveniently separated out by water dilution, and the IL can be reclaimed after vaporization of water at higher temperature. Regeneration of IL via water dilution although technically possible does not seem economically feasible considering the intense energy expenses for the subsequent water removal by evaporation. Therefore, other efficient techniques for separating water and IL need further investigation.

Table 7. Peak Area of Gasoline before and after Extraction with Phosphoric IL peak no. curve

1

2

3

4

5

6

7

8

9

10

a b c d avg of a and d

15.70 10.83 12.99 16.58 16.14

2.49 2.45 2.45 2.38 2.44

7.86 8.15 7.93 7.94 7.90

26.52 21.58 24.97 26.73 26.62

10.86 9.71 10.66 10.89 10.87

2.18 2.54 2.34 2.18 2.18

6.61 7.27 7.02 6.45 6.53

3.57 5.05 4.14 3.50 3.53

8.25 9.07 8.83 8.04 8.14

3.46 3.86 3.70 3.37 3.41

resulting S-content being 10 ppm (curve b), and gasoline extracted four times by [EMIM][DEP] with mass ratio of IL/oil being unity and the resulting S-content being ca. 3 ppm (curve c). The corresponding GC spectrum of gasoline as well as the peak areas are shown in Figure 1 and listed in Table 7 for convenience of comparison. Peaks 1-10 were identified by GC-MS (SHIMADZU QP2010; ion energy, 70 eV; scan range, 20-600 m/z; other conditions same as conditions of gas chromatograph.). The results showed that among the complicated components of gasoline only two components noted as peak 1 (2,3-dimethylbutane) and peak 4 (methylcyclopentane) in Figure 1 were selectively extracted by the ILs used, as can be seen by the decrease of normalized area percentage shown in Table 7. The results also indicated that [EMIM][DEP] had a lower influence on the composition of gasoline as compared to

Conclusion Extractive performance of three phosphoric ILs for the sulfur compounds 3-MT, BT, and DBT from gasoline was investigated experimentally. It was shown that the desulfurization ability of the ILs followed the order of [BMIM][DBP] > [EMIM][DEP] . [MMIM][DMP] and that the sulfur removal selectivity for S-compounds followed the order of DBT > BT > 3-MT. The phosphoric ILs studied are insoluble in gasoline; however, the gasoline is partially soluble to the ILs with the lowest solubility of 1.12% for [MMIM][DMP] and the highest solubility of 20.6% for [BMIM][DBP]. Considering the relatively high sulfur removal ability, immiscibility with gasoline, low oil solubility, and hence small influence on the gasoline composition as well as the ease of being reclaimed by dilution with water, the phosphoric IL [EMIM][DEP] may be used as a promising solvent and is worth recommendation for practical uses. Acknowledgment. The authors are grateful for the financial support from the National Natural Science Foundation of China (20376004) and the Fundamental Research Foundation of Sinopec. EF060170I (14) Shi, J. H.; Yang, C. H.; Gao, Q. Y.; Li, Y. F. Chin. J. Chem. Phys. 2004, 17, 503-507. (15) Lo, W. H.; Yang, H. Y.; Wei, G. T. Green Chem. 2003, 5, 639642.

Extractive Desulfurization of Gasoline Using Imidazolium-Based

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