Extractive Desulfurization of Fuel Oil Using Alkylimidazole and Its Mixture withDialkylphosphate Ionic Liquids

Yi Nie, Chun-Xi Li,* and Zi-Hao Wang

State Key Laboratory of Chemical Resource Engineering and College of Chemical Engineering, BeijingUniVersity of Chemical Technology, Beijing 100029, People’s Republic of China

The sulfur partition coefficientKN is usually used to characterize the ability of extractive desulfurization(EDS). In this work, severalKN values are measured at 298.15 K, which are between straight-run fuel oil andN-ethylimidazole (EIM),N-methylimidazole (MIM), and its mixture with a dialkylphosphate ionic liquid(IL), viz. N-ethyl-N-methylimidazolium diethylphosphate ([EMIM][DEP]) orN-butyl-N-methylimidazoliumdibutylphosphate ([BMIM][DBP]).KN values between the oil and solvent at varying water content are alsomeasured at 298.15 K. The results indicate that both EIM and MIM have excellent EDS performance withKN above 3.1 for dibenzothiophene. They have some solubility in fuel oil, but their solubility decreases withaddition of IL. The EDS ability of the solvents for a specified sulfur compound followed the orderalkylimidazole (EIM> MIM) > mixed solvent (MIM+ IL) > IL ([BMIM][DBP] > [EMIM][DEP]); theextractive selectivity of sulfur for a specified solvent followed the order dibenzothiophene (DBT)>benzothiophene (BT)> 3-methylthiophene (3-MT). The used sulfur-containing solvent can be regeneratedvia a water diluting process followed by a simple distillation process; therefore, the solvent can be reclaimedin a cost-effective way. This work shows that the alkylimidazole solvent and/or its mixture with an IL can beused as a potential extractant for the EDS of fuel oils.

Introduction

Fuel combustion may cause pollution to the environment dueto the sulfur in fuel oils, which forms SOx during combustion.In order to minimize SOx emission, increasingly stringentregulations are being imposed on oil refineries to reduce thesulfur content (S content) to a very low limit, around 10-20ppm.1 However, the present hydrodesulfurization (HDS) processencounters a great challenge to meet this requirement costeffectively as hydrogenation of aromatic sulfur compounds (Scompounds), e.g., benzothiophene (BT), dibenzothiophene(DBT), and their alkyl derivatives, is quite difficult by theavailable catalyst. In addition to the HDS process, alternativedesulfurization processes based on adsorption, extraction, oxida-tion, alkylation, and complexation of aromatic S compoundshave been studied extensively. Among them, extractive de-sulfurization (EDS) is an attractive one, which can be performedunder mild conditions at low energy consumption and withouthydrogen consumption.

Regarding the EDS process some molecular solvents,2-3 e.g.,polyalkylene glycol, imidazolidinone, pyrimidinone, and di-methyl sulfoxide, have been patented. However, their abilitiesof EDS are not sufficient and solubility in fuel is noticeable,which may cause cross contamination; more efficient molecularextractants are expected. Compared to molecular solvents, someionic liquids (ILs), e.g., [EMIM][DEP], [BMIM][DBP],4 [BMIM]-[Cl/AlCl 3], and [BMIM][BF4],5-8 show high extractability forsulfur component (S component), which indicates that ILs mightbe a novel and competitive extractive solvent if their shortcom-ings on high cost and viscosity can be somehow overcome.

The objective of this paper is to explore some new andefficient molecular solvents for the EDS of fuel oil and use themtogether with ionic liquid so as to (1) adjust the viscosity ofthe ILs to a suitable range for extraction operation and mass

transfer, (2) reduce the cost of the extractant since the molecularsolvent is generally cheaper than ILs, and (3) decrease thesolubility of the molecular solvent in the fuel oil. In this paper,the excellent EDS ability ofN-ethylimidazole (EIM) andN-methylimidazole (MIM) from fuel is reported for the firsttime. Meanwhile, the sulfur partition coefficients for 3-MT, BT,and DBT between fuel oil and EIM, MIM, or its mixture withan IL ([EMIM][DEP] or [BMIM][DBP]) are measured, and thereclaiming method for the used extractant is studied briefly.

Experimental Section

Chemical Materials. MIM and EIM of A.R grade used inthis work are from the Zhejiang Kaiyue Chemical plant. Thestraight-run gasoline is provided by the Qilu refinery of Sinopec,and its composition is analyzed by GC-MS (Shimadzu QP2010).Commercial 97# gasoline was purchased from a gas station ofSinopec Corporation.

Ionic liquids [EMIM][DEP] and [BMIM][DBP] are preparedby reacting equal moles of MIM and the corresponding trialkylphosphate at 423.2 K for 10 h with a yield of 97%.9 Theresulting yellowish viscous liquid has been washed three timeswith diethyl ether at room temperature followed by rotaryevaporation under reduced pressure of 1 kPa for 12 h to removeall volatile residues. The purity and structure of these ILs havebeen analyzed by1H NMR and electronic spray mass spectros-copy.

Mutual Solubility of Solvent and Fuel Oil. Mutual solubilityis an important factor to be considered in choosing an extractantbecause a noticeable solubility of a nitrogen-bearing solvent infuel may contaminate the fuel and lead to NOx pollution and anoticeable solubility of oil in solvents can increase the separationcost. The solubility of fuel oil in solvent and solubility of solventin fuel oil are measured using gravimetric methods, gaschromatography (Shimadzu GC-2010 equipped with a FIDdetector; DB-1 column, 30 m× 0.25 mm i.d.× 5 µm; carriergas N2; temperature program 50-5 °C/min-100-20 °C/min-

* To whom correspondence should be addressed. Tel.: 86-10-64444911, Fax: 86-10-64410308. E-mail: licx@mail.buct.edu.cn.

5108 Ind. Eng. Chem. Res.2007,46, 5108-5112

10.1021/ie070385v CCC: $37.00 © 2007 American Chemical SocietyPublished on Web 06/23/2007

320 °C; area unitary method and calibration curve), or liquidchromatography.10 It should be pointed out that the solubilityof the mixed solvent, MIM+ IL, in fuel oil refers to that ofMIM since the IL component is insoluble in fuel oil.4-5

Sulfur Partition Coefficients Measurement for Fuel Oil/Solvent System.The sulfur partition coefficient (KN), which isdefined as the ratio of S concentration (on weight basis) insolvent to S concentration in gasoline, is an important parameterfor an EDS process, and the higher theKN the better thedesulfurization performance of a solvent.

In this work, KN is measured as described below. First, anextracting solvent with known S content in ppm, i.e.,mg(S)‚kg(IL)-1, is prepared by gravimetric method. A definiteamount of 3-MT, BT, or DBT is dissolved in known quantitiesof solvent, which is used as a S source in the followingextraction experiment. For example, by dissolving 0.714 g ofDBT in 19.994 g of MIM, a 5996 ppm S content MIM sampleis obtained. Second, a known weight of S-free solvent and fueloil is mixed in a 100 mL conical flask under vigorous magneticstirring for pre-equilibrium so as to minimize the effect of oildissolution in solvent phase on calculation of the sulfur partitioncoefficient. Third, a known amount of S-concentrated solventis added to the above biphasic mixture, magnetically stirred for15 min at room temperature to reach thermodynamic equili-brium,6-7 and then laid aside for 10 min for phase splitting andsettling. The S content in the oil phase is measured by liquidchromatography using the external standard method (Shimadzu-10AVP equipped with UV-vis detector and a C-18 column;mobile phase methanol/water) 9/1 for DBT, methanol/water) 8/2 for BT and 3-MT; wavelength 310 nm for DBT, 251 nmfor BT, 242 nm for 3-MT; flow rate 1.0 mL/min), and the Scontent in the solvent phase is calculated via mass balance assuch the sulfur partition coefficient is calculated. The third stepis repeated several times until the equilibrium S content in oilfalls into the S concentration range expected.

In order to investigate the effect of water content in solventon the EDS performance, theKN values for DBT, BT, and 3-MTbetween MIM+ 40%(wt %)[EMIM][DEP] aqueous solutionand fuel oil at room temperature are also measured.

Recovery of Used Solvents.The oil-saturated S-containingsolvents are regenerated by successive dissolution with waterfollowed by a simple distillation for the aqueous solution at373.15 K under reduced pressure of about 1 kPa for 12 h.

Results and Discussion

EDS Performance of EIM, MIM, and Its Mixture with aDialkylphosphate IL for Straight-Run Gasoline. The EDSperformance of MIM and EIM is investigated for the first timein terms of the sulfur partition coefficientsKN for typical S

component DBT, BT, and 3-MT between fuel and solventaccording to the experimental procedure described above. Table1 shows the equilibrium S content in MIM and oil phases andthe correspondingKN values for DBT, BT, and 3-MT at 298.15K. As shown in Table 1, theKN value for a specified Scomponent (namely, DBT, BT, and 3-MT) is virtually constantregardless of the S content in fuel oil, which means the S contentin solvent is linearly proportional to the S content in fuel oil atequilibrium in the S concentration range studied (see the secondline from the top in Figure 1). A similar behavior is observedfor EIM, phosphate ILs, and the mixtures thereof. The inde-pendence ofKN on S concentration is mainly attributed to thethermodynamic behavior of the dilute solution since the molefractions of S component in both phases are extremely low,and hence, the nonideality of S component is negligible.

Although EIM and MIM have high partition coefficients forS compounds, their mutual solubility with fuel oil is quite high,as shown in Table 2, which may cause fuel contamination.Compared to the molecular solvents, IL is virtually insolublein fuel oil and shows good EDS ability but has the drawbackof high viscosity. Considering these factors a ‘solvent cocktail’,i.e., a mixture of MIM and a dialkylphosphate IL, combiningthe merits of both is prepared, and its EDS performance ismeasured in terms of sulfur partition coefficients. The presenceof ionic liquid can slightly decrease the solubility of solvent infuel oil, while the solubility of fuel oil in a mixed solventdepends on the solvent composition and solubility of fuel inthe corresponding pure solvents.

As shown in Table 3 the sulfur partition coefficient for aspecified S compound follows the order EIM> MIM > MIM+ 20%(wt %) IL > MIM + 40%(wt %) IL > IL, the EDS

Table 1. Equilibrium Distribution of DBT, BT, and 3-MT between MIM and Straight-Run Gasoline and the Corresponding Sulfur PartitionCoefficients KN at 298.15 K

DBT BT 3-MT

S content inoil (ppm),x

S content inMIM (ppm), y KN

S content inoil (ppm),x

S content inMIM (ppm), y KN

S content inoil (ppm),x

S content inMIM (ppm), y KN

151.4 512.2 3.38 81.3 151.8 1.87 133.9 111.6 0.83332.6 1030.9 3.10 137.0 372.8 2.72 259.7 229.1 0.88457.4 1387.5 3.03 196.0 542.5 2.77 332.5 290.5 0.87619.1 1866.8 3.02 246.1 678.4 2.76 411.4 358.0 0.87684.0 2130.8 3.12 317.3 832.0 2.62 490.3 427.4 0.87755.0 2324.6 3.08 363.9 923.8 2.54 573.5 546.0 0.95820.5 2529.9 3.08 418.2 1039.4 2.49 653.6 659.7 1.01869.0 2723.9 3.13 458.7 1169.2 2.55 728.1 730.5 1.00923.1 2916.8 3.16 526.7 1308.7 2.48 854.3 832.9 0.97977.4 3005.3 3.07 545.4 1397.2 2.56

y ) 3.10x (R2 ) 0.999) y ) 2.55x (R2 ) 0.995) y ) 0.96x (R2 ) 0.990)

Figure 1. Sulfur partition between different solvent and straight-rungasoline at 298.15 K.

Ind. Eng. Chem. Res., Vol. 46, No. 15, 20075109

ability of MIM + [EMIM][DEP] is always between MIM andIL and depends on the mass fraction of MIM. This trend isalso valid for other solvent mixtures studied herein. For aspecified solvent, the sulfur partition coefficient always followsthe order DBT> BT > 3-MT.

The extractive sulfur removal ability of MIM and EIM issuperior to any extractant reported except ionic liquid [BMIM]-[Cl/AlCl 3],2,4,5,8 as can be seen from theKN values for DBTlisted in Table 4. Considering the fact that [BMIM][Cl/AlCl3]is very viscous and sensitive to water and thus incompatiblewith a water environment, the solvent EIM, MIM, and itsmixture with a phosphate IL is more competitive and feasiblefor EDS applications. The most likely mechanism for extractionof S compounds with EIM, MIM, and its mixture with animidazolium-based phosphate IL is formation of liquid clathratedue to theπ-π interaction between aromatic structures of theextraction target sulfur compounds and the imidazole ringsystem.11

EDS Performance of MIM for Commercial 97# Gasoline.In all experiments the “simulated oil” is prepared by dissolvinga specified S component, e.g., 3-MT, BT, or DBT, to straight-run oil obtained from an oil refinery of Sinopec. In order toshow the difference of EDS performance of MIM betweenstraight-run oil and real oil, a complementary experiment isconducted using commercial 97# gasoline purchased from a gasstation of Sinopec Corporation. The sulfur (as DBT) partitioncoefficient between MIM and 97# gasoline is measured andlisted in Table 5. As shown in Table 5, the sulfur partitioncoefficient drops from 3.10 between MIM and straight-rungasoline to 2.61 between MIM and 97# gasoline. This suggeststhat sulfur removal from real gasoline is a little harder thandesulfurization of straight-run gasoline.

Influence of EDS on the Composition of Fuel Oil.The EDSprocess has two potential influences on fuel. On one hand, thesolubility of EIM, MIM, and the imidazolium-based phosphateILs in fuel can cause NOx pollution; on the other hand, the fuelcomposition is likely to be changed due to the selective

extraction of solvent for some specified components of fuel. Ineffect the loss of fuel and variation of fuel composition can bereflected by the fuel solubility in the solvent, and the lower thesolubility, the smaller the variation of fuel quality should be.As an extreme case, the fuel quality and composition will remainunchanged when it is immiscible with the solvent. Hence, thecross contamination of the EDS process is closely related tothe mutual solubility of fuel and solvent involved.

As shown in Table 2, the solubility of fuel oil in pure solventfollows the order [BMIM][DBP] ) EIM > MIM > [EMIM]-[DEP]; the solubility of molecular solvents EIM and MIM infuel oil is relatively low, while ILs are insoluble in fuel oil.The mutual solubility of a solvent mixture and fuel oil isbasically proportional to the solvent composition and mutualsolubility of the corresponding pure solvent/fuel systems, e.g.,the solubility of fuel oil in solvent follows the order of [BMIM]-[DBP] > MIM + 40%[BMIM][DBP] > MIM + 20%[BMIM]-[DBP] > MIM. The solubility of molecular solvent in fuel oildecreases slightly by addition of IL component.

In order to investigate the influence of the EDS process onthe composition of fuel oil, GC analysis is conducted for thefollowing four samples: straight-run gasoline (sample A); amixture of sample A and DBT with S content of 558 ppm(sample B); sample B extracted three times by solvent MIM+40%[EMIM][DEP] with a mass ratio of solvent/oil being 2:1and the resulting S content being 61 ppm (sample C); sampleB extracted three times by solvent MIM with a mass ratio ofsolvent/oil being 2:1 and the resulting S content being ca. 11ppm (sample D). On the basis of the GC spectrum measured,the area percentage for peaks 1-10 is listed in Table 6, and thepeaks are identified by GC-MS (Shimadzu QP2010; ion energy70 eV; scan range 20-600 m/z; other conditions are the sameas the conditions for gas chromatography) as shown in Figure2.

The results show that 2,3-dimethylbutane and methylcyclo-pentane among the components of fuel oil are selectivelyextracted by the solvent used, which can be seen by the decreaseof normalized area percentage as shown in Table 6. However,the overall influence of an EDS process on the composition offuel is limited.

Regeneration of the Used Extractant.Considering the factthat all extractants used here are hydrophilic while all Scomponents are hydrophobic, separation of solvent and Scomponents can be carried out by diluting the solvent withwater,6-7 as the S component in the vicinity of solvent moleculesis repelled by water. For this purpose, sulfur partition coefficientsbetween MIM aqueous solution and oil are measured andgraphically shown in Figure 3. When about 50% water (massratio, water:MIM ) 1:1) is added into the oil-saturated MIMaqueous solution, the sulfur partition coefficient reaches null.This indicates that 50% water is enough to make sulfur transferfrom MIM aqueous solution phase into the oil phase completely.

Table 2. Mutual Solubility of Solvent and Straight-Run Gasoline at 298.15 K

system solubility, g of solvent/100 g of oil solubility, g of oil/100 g of solvent

EIM/fuel oil 1.71a 20.6a

MIM/fuel oil 1.51a 15.22a

MIM +20%[EMIM][DEP]/fuel oil 1.21a,d 11.87a

MIM +40%[EMIM][DEP]/fuel oil 0.99a,d 9.76a

MIM +20%[BMIM][DBP]/fuel oil 1.26a,d 18.95a

MIM +40%[BMIM][DBP]/fuel oil 1.21a,d 20.2a

[EMIM][DEP]/fuel oil 4 0b 4.25c

[BMIM][DBP]/fuel oil 4 0b 20.6c

a The solubility data was measured using gas chromatography.b The solubility data was measured using liquid chromatography.c The solubility data wasmeasured using the gravimetric method.d Solubility of MIM in fuel oil.

Table 3. Sulfur Partition Coefficients KN at 298.15K in DifferentSolvent/Straight-Run Gasoline Systemsa

DBT BT 3-MT

solvent KN R2 KN R2 KN R2

EIM 3.28 0.997 2.67 0.996 1.17 0.980MIM 3.10 0.999 2.55 0.995 1.03 0.987[BMIM][DBP] 4 1.59 0.998 1.37 0.994 0.59 0.977[EMIM][DEP] 4 1.27 0.999 0.94 0.992 0.47 0.984MIM + 20 %[BMIM][DBP] 2.63 0.999 2.20 0.987 0.95 0.985MIM + 40 %[BMIM][DBP] 2.28 0.999 2.03 0.995 0.92 0.994MIM + 20 %[EMIM][DEP] 2.28 0.997 2.02 0.992 0.85 0.991MIM + 40 %[EMIM][DEP] 1.73 0.999 1.47 0.981 0.69 0.988

a KN was obtained by fitting the experimental S content in both phaseswith a least-square method using the equationy ) KNx, wherey and xrepresent S content (ppm) in solvent and fuel, respectively.R2 is the squaredcorrelation coefficient.

5110 Ind. Eng. Chem. Res., Vol. 46, No. 15, 2007

In the dilution process, when about 50% water is added intothe used oil-saturated MIM, two phases are formed, viz. a MIMaqueous phase being free of S compounds and oil and a solvent-free oil phase containing all the S compounds precipitated duringwater dilution process. The composition of MIM aqueous phaseand oil phase is identified using GC and Karl Fischer-Titration(CBS-1A), respectively. The solvent aqueous phase is distilledat 373.15 K to remove the water component and get theextractant at the bottom, while the sulfur-rich oil phase couldbe collected for further treatment. An extractive desulfurizationprocess is proposed as shown in Figure 4.

When the solvent is regenerated via distillation, water residuein the reclaimed extractant is inevitable. In order to assess theinfluence of water content on the EDS performance, the sulfurpartition coefficientsKN for DBT, BT, and 3-MT between fueloil and MIM + 40%[EMIM][DEP] at varying water contentare measured and listed in Table 7. It is seen that theKN valuesdecrease dramatically with the increase of water content insolvent, and even 1.42% of water can give rise to about 20%lowering of the extractive ability of the solvent for DBT,suggesting that the water residue in the reclaimed solvent shouldbe removed as low as possible.

The operation cost can be evaluated as following steps.Assume that (1) initial S content as DBT in fuel is 2000 ppm,(2) the required S content of fuel product is 10 ppm, and (3)mass ratio of solvent/fuel in an extraction column is 1:2; then

Table 4. Sulfur Partition Coefficients KN for Extraction of DBT with Different Solvent

solvent KN, mg(S) kg(IL)p-1/mg(s) kg(oil)-1 solvent KN, mg(S) kg(IL)p-1/mg(s) kg(oil)-1

[BMIM][AlCl 4]a 4.0 [BMIM][MeSO3]b 1.1EIMc 3.22 [BMIM][PF6]b 0.9MIM c 3.10 [EMIM][EtSO4]a 0.8[BMIM][OcSO4]a 1.9 [BMIM][CF3SO3]b 0.8MIM + 40%[EMIM][DEP]c 1.73 DMFd 0.72[BMIM][DBP] c 1.59 [MMIM][Me 2PO4]a 0.7NMPd 1.59 [BMIM][BF4]a 0.7DMId 1.50 [MMIM][DMP] c 0.46[EMIM][DEP] c 1.27 TMPId 0.38[BMIM][MeSO4]b 1.1 TMPBd 0.26

a Model oil:5 500 ppm sulfur as DBT inN-dodecane, room temperature.b Model oil:5 500 ppm sulfur as DBT inN-dodecane, 60°C. c Straight-rungasoline:4 sulfur as DBT, 298.15 K.d Light oil:2 450 ppm sulfur as 4-MeDBT, 4, 6-Me2DBT.

Table 5. Equilibrium Sulfur Partition between MIM andCommercial 97# Gasoline at 298.15 K

S content in 97# gasoline (ppm),x S content in MIM (ppm),y

108. 6 371.5288.2 749.5423.1 1072.1490.8 1286.4y ) 2.61x, R2 ) 0.992

Table 6. Peak Area Percentage of the Corresponding Component ofStraight-run Gasoline before and after Extraction with MIM andMIM +40%(wt%)[EMIM][DEP]

peak no.a

sampleb 1 2 3 4 5 6 7 8 9 10

A 16.58 2.38 7.94 26.73 10.89 2.18 6.45 3.50 8.04 3.37B 15.70 2.49 7.86 26.52 10.86 2.18 6.61 3.57 8.25 3.46C 13.38 2.75 8.25 25.18 10.78 2.51 7.02 4.50 8.49 3.72D 14.23 2.64 7.84 25.92 10.83 2.27 6.87 3.82 8.60 3.61av. of A and B 16.14 2.44 7.90 26.62 10.87 2.18 6.53 3.53 8.14 3.41

a Components identified: (1) 2, 3-dimethylbutane; (2) 3-methylpentane;(3) hexane; (4) methylcyclopentane; (5) cyclohexane; (6) 3,7-dimethyl-octene; (7) 1,3-dimethylcyclopentane; (8) heptane; (9) methylcyclohexane;(10) ethylcyclopentane.b See the description in text.

Figure 2. GC-MS chromatogram of straight-run 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.

Figure 3. Sulfur partition coefficients between MIM aqueous solution andstraight-run gasoline at 298.15 K.

Figure 4. Schematic flowchart for a combined EDS and solvent regenera-tion process.

Ind. Eng. Chem. Res., Vol. 46, No. 15, 20075111

the extraction stage number required can be estimated as about10 and the extracting solvent required per ton of fuel is 0.5 tonof MIM. To regenerate such an amount of solvent at least 0.5ton of low-pressure steam is required, and the resulting steamcost is about USD5. Since the energy cost is the main expenseof regeneration, the operation cost of such EDS process isexpected within USD10 per ton of fuel. From this verypreliminary assessment it is seen that the cost of the EDS processis relatively low in comparison with the commercial HDSprocess. Therefore, the EDS process with alkylimidazole or itsmixture with a dialkylphosphate ionic liquid from fuel oils isquite promising for cost-efficient practical application.

Possible NOx contamination of fuel due to the solubility ofnitrogen-bearing solvent in the fuel oil can be overcome by backextraction with water,2 as shown in Figure 4. Since the solventMIM is highly hydrophilic, its partition coefficient betweenwater and fuel oil at 298.15 K is as high as 10.18; thus, MIMand its mixture MIM+ [EMIM][DEP] dissolved in the fuelcan be removed conveniently and easily by a back extractionprocess.

In summary, the desulfurization ability of EIM and MIM ormixtures of MIM with a dialkylphosphate IL is very attractive.The used S-containing solvent can be regenerated by a waterdiluting process followed by simple distillation. The EDSprocess with alkylimidazole or its mixture with a dialkylphos-phate ionic liquid may be used for the deep desulfurization offuel oil efficiently.

Acknowledgment

The work was supported by the National Natural ScienceFoundation of China (under Grant No. 20376004) and theFundamental Research Foundation of Sinopec (Grant No.X505015).

Literature Cited

(1) Song, C. S. An overview of approaches to deep desulfurization forultra-clean gasoline, diesel fuel and jet fuel.Catal. Today2003, 86, 211.

(2) Horii, Y.; Onuki, H.; Doi, S. Desulfurization and denitration of lightoil by extraction. U.S. Patent 5494572, 1996.

(3) Paulino, F.; Yonkers, N. Y. Process for the removal of sulfur frompetroleum fractions. U.S. Patent 5582714, 1996.

(4) Nie, Y.; Li, C. X.; Sun, A. J.; Meng, H.; Wang, Z. H. Extractivedesulfurization of gasoline using imidazolium-based phosphoric ionicliquids. Energy Fuels2006, 20, 2083.

(5) Esser, J.; Wasserscheid, P.; Jess, A. Deep desulfurization of oilrefinery streams by extraction with ionic liquids.Green Chem. 2004, 6,316.

(6) Zhang, S. G.; Zhang, Q. L.; Zhang, Z. C. Extractive desulfurizationand denitrogenation of fuels using ionic liquids.Ind. Eng. Chem. Res. 2004,43, 614.

(7) Zhang, S.; Zhang, Z. C. Novel properties of ionic liquids in selectivesulfur removal from fuels at room temperature.Green Chem.2002, 4, 376.

(8) Bosmann, A.; Datsevich, L.; Jess, A.; Lauter, A.; Schmitz, C.;Wasserscheid, P. Deep desulfurization of diesel fuel by extraction with ionicliquids. Chem. Commun.2001, 23, 2494.

(9) Jiang, X. C.; Yu, C. Y.; Li, C. X.; Wang, Z. H. Synthesis andapplication of ionic liquid 1-butyl-3-methyl imidazolium dibutyl phosphate.J. Beijing UniV. Chem. Technol. (Nat. Sci. Ed.)2006, 33, 5.

(10) Stepnowski, P.; Mu¨ller, A.; Behrend, P.; Ranke, J.; Hoffmann, J.;Jastorff, B. Reverse phase liquid chromatographic method for the deter-mination of selected room temperature ionic liquids cations.J. Chromatogr.A 2003, 993, 173.

(11) Holbrey, J. D.; Reichert, W. M.; Nieuwenhuyzen, M.; Sheppard,O.; Hardacre, C.; Rogers, R. D. Liquid clathrate formation in ionic liquid-aromatic mixtures.Chem. Commun.2003, 3, 476.

ReceiVed for reView March 14, 2007ReVised manuscript receiVed April 19, 2007

AcceptedApril 23, 2007

IE070385V

Table 7. Effect of Water Content in Solvent on the Sulfur PartitionCoefficients KN between MIM + 40%(wt %)[EMIM][DEP] andStraight-Run Gasoline

DBT BT 3-MT

water content insolvent (wt %) KN

water content insolvent (wt %) KN

water content insolvent (wt %) KN

0 1.72 0 1.47 0 0.671.42 1.37 0.94 1.35 1.20 0.543.10 1.20 3.13 1.12 3.30 0.475.15 0.92 5.02 0.85 5.09 0.34

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