Extraction of Thiophene

Published: January 20, 2011

r 2011 American Chemical Society 2296 dx.doi.org/10.1021/ie101834m | Ind. Eng. Chem. Res. 2011, 50, 2296–2306

ARTICLE

pubs.acs.org/IECR

Extraction of Thiophene or Pyridine from n-Heptane Using IonicLiquids. Gasoline and Diesel DesulfurizationKarolina Ke-dra-Kr�olik, Mutelet Fabrice,* and Jean-No€el Jaubert

Laboratoire R�eactions et G�enie des Proc�ed�es, Nancy-Universit�e, 1 rue Grandville, BP 20451 54001 Nancy, France

ABSTRACT: The aim of this study is to investigate the possible use of ILs as solvents for two separation problems frequentlyencountered in petroleum industry: {aromatic sulfur compound þ aliphatic hydrocarbon} or {nitrogen compound þ aliphatichydrocarbon}. This work is focused on three ILs: 1-ethyl-3-methylimidazolium thiocyanate, 1,3-dimethylimidazolium methylpho-sphonate, and tris-(2-hydroxyethyl)-methylammonium-methylsulfate. In the first part of this article, a study of new three ternarysystems is studied in view of defining the capacity of proposed ILs as solvents for extraction of sulfur and nitrogen containing organiccompounds from aliphatic hydrocarbons. Therefore, LLE measurements of ternary mixtures for five systems were measured at298.15 K and at atmospheric pressure: {thiophene þ n-heptane þ1-ethyl-3-methylimidazolium thiocyanate}, {thiophene þn-heptaneþ 1,3-dimethylimidazoliummethylphosphonate}, {thiopheneþ n-heptaneþ tris-(2-hydroxyethyl)-methylammonium-methylsulfate}, {pyridine þ n-heptane þ1-ethyl-3-methylimidazolium thiocyanate}, {pyridine þ n-heptane þ1,3-dimethylimida-zoliummethylphosphonate}. The second section of this article presents results of extraction of synthetic fuels-model gasoline andmodel diesel by the use of selected ILs. The influence of extraction time or temperature as well as three stepped procedure using eachtime a fresh portion of ILs on the final fuel contamination was investigated.

’ INTRODUCTION

The separation of mixtures by liquid-liquid extraction is oftenapplied by many industrial procedures due to simplistic opera-tion option, mild processes conditions, and economical advan-tages of this method. High efficiency of this technique dependslargely on precisely selected the most suitable solvent for specificseparation process. However, conventional solvents commonlyused for extraction are highly volatile, flammable, and often toxic.The environmental regulations all over the world aremore stringentso applications of green solvents in classical methods or neweconomically and environmentally friendly technologies are in greatdemand. Someof industrially important extraction processes are stilla challenge e.g. separations of aliphatic and aromatic hydrocarbonsor alcohols and aliphatic hydrocarbons. The components of suchsystems have very narrow range of boiling points and severalcombinations form azeotropes. This makes them also impracticableto be separated by distillation.

In recent years considerable attention has been given to deepdesulfurization of gasoline and diesel due to the higher restric-tions concerning sulfur-compounds content level in fuels. Sulfuroxides that form in gasoil combustion process contribute to acidrains, global warming effect, and air pollution. Those affect urbanas well as industrial areas and are harmful for human health due tosecondary inorganic aerosol gases formation. The EuropeanUnion gradually reduced the maximum sulfur concentration infuels to avoid high emission of gases resulting from combustionof heavy fuels. Since 2010 the total sulfur content cannot behigher than 10 ppm. Deep desulfurization of gasoline and dieselis a very complex problem for petroleum industry and has to besolved to minimize the pollutions from fuel oils exhaust gas.Indeed, many research groups carry out deep investigations ofenvironmentally benign, energy saving, and effective methods.1

The conventional method applied by refineries is hydrodesulfur-ization (HDS) and consists of catalytic hydrotreating withCo-Mo/Al2O3, Ni-Mo/Al2O3, or Ni-W/Al2O3 catalysts.2

HDS is highly efficient for removal of aliphatic hydrocarbonscontaining sulfur. However, the challenging task arises withelimination of aromatic sulfur compounds such as thiopheneor dibenzothiophene and their alkyl derivatives such as 4-methyl-dibenzothiophene by use of the HDS method.3 Moreover, HDSprocesses have to be conducted under elevated temperatures(300-400 �C) as well as elevated pressures (20-100 atm of H2)which makes the method cost and energy consumptive. To facethese problems with the purpose of regard sulfur contaminationwithin the required levels, researchers have been making severalefforts to elaborate new catalysts or to enhance existing catalystactivity and change HDS operation conditions. On the otherhand, many investigations have been directed toward expandingon new original approaches to deep desulfurization of fuels, suchas processes based on distillation, adsorption, extraction, reac-tive alkylation, complexation, precipitation, photochemical de-sulfurization, selective oxidation, biodesulfurization, ultrasoundsaccompanied extraction, and combinations of mentionedmethods.4

The use of ionic liquids (ILs) for liquid-liquid extractionshows a great potential in comparison with conventional organicsolvents, due to their unique physicochemical properties. Neg-ligible vapor pressure, high chemical and thermal stability,nonflammability, or recyclability makes them environmentallyfriendly solvents. Moreover they are able to dissolve a wide rangeof organic or inorganic substances, and it is possible to adjust

Received: September 1, 2010Accepted: December 6, 2010

2297 dx.doi.org/10.1021/ie101834m |Ind. Eng. Chem. Res. 2011, 50, 2296–2306

Industrial & Engineering Chemistry Research ARTICLE

some of their properties such as polarity or miscibility for certainsystem requirements. They also have high ionic conductivity andwide electrochemical window. These properties make ILs verygood solvents for liquid-liquid extractions as well as for anumber of applications e.g. catalysis, synthesis, gas separationswhich was proved by some thermodynamic methods concerningdetermination of activity coefficients at infinite dilution.5-7 Theuse of ILs usually causes higher values of selectivities at infinitedilution for a specific separation process comparing to classicalsolvents. This is generally caused by the high solubility of polarcompounds in ionic liquids and the low miscibility of aliphaticcompounds.

The interactions between aromatic sulfur compounds andionic liquids were conducted by many research groups.8-10

Revelli and co-workers demonstrated using Nuclear MagneticResonance (NMR) that thiophenemolecules are accommodatedinto the ionic pair structure of the ionic liquids enabling theselective and extractive removal of aromatic sulfur compoundsfrom fuels.8 A unique feature of ionic liquids as salts is theirmobility and flexibility, which allow for a facile restructuring ofthe ionic liquids in the process of thiophene dissolution. Therestructuring process is primarily driven by the interaction ofthiophene with the imidazolium cations of the ionic liquids, andthe maximum absorption capacity of thiophene by ionic liquids isprimarily determined by the size and structure of both cationsand anions.8

The first investigations of fuels extractive desulfurization usingionic liquids has been reported by B€ossman et al. in 2001.11

These authors studied the dialkylimidazolium chlorides mixedwith AlCl3 as an extracting solvent and showed that the stericfactors of specific ionic liquids are responsible for S-containingcompounds extraction rather than chemical interactions in-volving the acid proton, as they supposed before. Amongmany types of studied ionic liquids, those based on imidazo-lium cations and BF4

- or PF6- anions showed high efficiency

for organic sulfur as well as organic nitrogen compoundsextraction.12,13 It was proved that these ionic liquids interactby coulombian forces with π electrons of aromatic ring.However, several liquid-liquid equilibrium data showed thatunwanted effect of aromatic hydrocarbons extraction pro-ceeds parallel to desulfurization and decreases of fuel octanenumber.14 Due to the stability and corrosion problems as wellas the total costs of deep fuel desulfurization the choice ofthe most suitable ionic liquid is still a challenging task forresearchers. Among many investigated ionic liquids, theimidazolium thiocyanate ones, e.g. [BMIM][SCN], [EMIM]-[SCN] were proved to show very small interactions betweenalkanes and cycloalkanes and high selectivity with respect tothiophene separation from such solvents, and they were highlyuseful for the fuel desulfurization process.8,14,15 A less expen-sive alternative is the use of imidazolium-based phosphoricionic liquid which showed encouraging results.16-18 Thereported desulfurization facility of this type of ILs may beordered as follows: [BMIM][DBP] > [EMIM][DEP] .[MMIM][DMP]. Additionally the selectivity for sulfur re-moval decreases from dibenzothiophene through benzothio-phene up to 3-methylthiophene.17 On the other hand the fuelsolubility increases in the same way, so the compromise isnecessary to choose the most effective one which was provedby Nie et al.18 The authors showed that partition coefficientsvalues increases for ionic liquids containing longer alkylsubstitute of the anion or cation. Holbrey and co-workers19

have investigated {dibenzothiophene þ dodecane þ IL} ter-nary systems for a range of ionic liquids with different cationtype (imidazolium, pyridinium, and pyrrolidinium) and arange of anion types. The partition coefficient of dibenzothio-phene to the ionic liquids varies following the order withcation class (dimethylpyridinium > methylpyridinium > pyr-idinium ≈ imidazolium ≈ pyrrolidinium). The anion typeinfluence is much less important.

The aim of this study is to investigate the possible use of ILs assolvents for two separation problems frequently encountered inpetroleum industry: {aromatic sulfur compoundþ aliphatic hydro-carbon} or {nitrogen compound þ aliphatic hydrocarbon}. Thiswork is focused on three ILs: 1-ethyl-3-methylimidazolium thiocya-nate, 1,3-dimethylimidazolium methylphosphonate, and tris-(2-hy-droxyethyl)-methylammonium-methylsulfate.

The first part of presented work consists on a study of newternary systems to acquire information about application ofproposed ILs as solvents for extraction of sulfur and nitrogencontaining organic compounds from aliphatic hydrocarbons.Therefore, LLE measurements of ternary mixtures for fivesystems were measured at 298.15 K and atmospheric pressure:{thiophene þ n-heptaneþ1-ethyl-3-methylimidazolium thiocy-anate}, {thiophene þ n-heptane þ1,3-dimethylimidazoliummethylphosphonate}, {thiophene þ n-heptane þ tris-(2-hydro-xyethyl)-methylammonium-methylsulfate}, {pyridine þ n-hep-tane þ1-ethyl-3-methylimidazolium thiocyanate}, {pyridine þn-heptane þ1,3-dimethylimidazolium methylphosphonate}.Moreover the temperature influence for the best one of usedILs and LLEmeasurement at 303.15 K and atmospheric pressurefor {thiophene þ n-heptane þ1-ethyl-3-methylimidazoliumthiocyanate} system is shown. Experimental data were correlatedusing the NRTL and UNIQUAC activity coefficient models. Thesecond section of this article presents results of extraction ofsynthetic fuels - model gasoline and model diesel by the use ofselected ILs. The influence of extraction time or temperature andthree-step extraction using each time a fresh portion of ILs on thefinal fuel contamination were investigated.

’EXPERIMENTAL SECTION

Thiophene and pyridine were supplied by Sigma-Aldrich withpurity of 99% and 99.8%, respectively. N-Heptane was purchasedfrom Fisher Scientific, with purity of 99%. 2,2,4-Trimethylpentanewas 99% pure from Merck. Toluene, dibenzothiophene, and n-hex-ane were supplied by Across Organics with a quoted purity of 99%and 99% and 95%, respectively.N-Dodecane and n-hexadecaneweretaken from Fluka and were over 98% pure. All those chemicals wereused for experiments without any further purification. The investi-gated ionic liquids: 1-ethyl-3-methylimidazolium thiocyanate,[EMIM][SCN], and tris-(2-hydroxyethyl)-methylammonium-methylsulfate, [TEMA][MeSO4], were purchased from Fluka andwere over 95% pure. 1,3-Dimethylimidazolium methylphosphonate,[DMIM][MP], was obtained from Solvionic with reported purity of98%. Before measurements, the ionic liquids were purified undervacuum for approximately 12 h to remove possible traces of solventsand moisture. The water content of the ionic liquids determinedusing the Karl Fischer technique was from 300 to 700 ppm.

’DETERMINATION OF TIE LINES OF TERNARY MIX-TURES

The LLE measurements of ternary mixtures have beenperformed in jacketed glass cells. The experimental set up



consists of a cell with an internal volume of about 30 cm3 kept atconstant temperature of 298.15 K using a thermostated bath.The temperature inside the cell is measured by a platinumresistance thermometer PT-100 with an accuracy of (0.1 K.The ternary mixtures, with compositions inside the immiscibleregion of the system, are weighed using a METTLER analyticalbalance with a precision of (0.0001 g. All the mixtures werevigorously mixed using a Teflon coated magnetic stirrer for 2 h toreach a good contact between both phases and kept overnight inorder to settle down. Then, samples of both layers were takenfrom the cell using a syringe. The compositions of organiccompounds such as n-heptane, thiophene, or pyridine weredetermined by gas chromatography. The GC operating condi-tions are given in Table 1. All GC analysis were repeated threetimes to check reproducibility. For determination of the ionicliquid composition, density measurements of both phases wereperformed at 298.15 or 302.15 K with a vibrating tube densi-meter (Anton Paar, model DMA601). The uncertainty in themeasurements is (10-5 g 3 cm

-3. The estimated uncertainty inthe determination of mole fraction compositions is (10-4.

’MODELED FUELS DESULFURIZATION EXPERIMENTS

The commercial gasoline was modeled by the mixture of26 wt % hexane, 26 wt % heptane, 26 wt % iso-octane, 10 wt %toluene, 6 wt % thiophene, and 6 wt % pyridine. Commercialdiesel was represented by model mixture containing 26 wt %heptane, 26 wt % dodecane, 26 wt % hexadecane, 10 wt %toluene, 3 wt % thiophene, 3 wt % dibenzothiophene, and 6 wt %pyridine. The influence of time of extraction on the model-fuelcomposition was investigated by introduction of equal volumesof model gasoline and IL into thermostated, 30 cm3 cells. Themixture was vigorously stirred to achieve good contact of bothphases and stopped after 15 min to separate the phases. Thegasoline phase samples were taken using syringe with needle after0.5 h, 1 h, 2 h, and 6 h after stopping the stirring and theircompositions were analyzed by GC. The extraction in steps wasconducted three times by using new portion of IL and gasoline ordiesel as a feed in following extraction stages. The fuel composi-tion after each step was determined by GC.

’RESULTS AND DISCUSSION

Thermodynamic Study of the Ternary Systems {Thio-phene or Pyridine/n-Heptane/IL}. The investigations of pos-sible use of selected ionic liquids for sulfur or nitrogen containingorganic compounds extraction in fuel industry have been per-formed. For this purpose, LLE of five ternary systems weredetermined: {thiopheneþ n-heptaneþ [EMIM][SCN]}, {pyri-dineþ n-heptaneþ [EMIM][SCN]}, {thiopheneþ n-heptaneþ[DMIM][MP]}, {pyridine þ n-heptane þ [DMIM][MP]},

{thiopheneþ n-heptaneþ [TEMA][MeSO4]}. The influenceof water contents of 2 and 5 wt % on the desulfurizationselectivity and capacity of [EMIM][SCN] at 298.15 and303.15 K have been studied. Moreover, synthetic gasolineand diesel were prepared, and their desulfurizations by the useof selected ILs have been conducted.Table 2 shows the compositions of the experimental tie lines

for the five investigated ternary systems at 298.15 K. Theequilateral triangular diagrams with LLE representation of thesesystems are presented in Figures 1- 5. All equilateral triangulardiagrams show a behavior that corresponds to the Type 2 withtwo of their binary systems exhibiting partial immiscibility andwith only one immiscibility region. Values of solute distributionratio β and selectivity S reported in Table 2 are calculated fromexperimental data according to equations

β ¼ xIL1xHC1

ð1Þ

S ¼ xIL1 3 xHC2

xHC1 3 xIL2

ð2Þ

where x is the mole fraction, subscripts 1 and 2 refer to solute(pyridine, thiophene) and to hydrocarbon (n-heptane), respec-tively, and superscripts HC and IL indicate the hydrocarbon-richphase and the IL-rich phase, respectively.In these ternary phase diagrams, the low thiophene or pyridine

concentration part should be considered in order to investigatedeep desulfurization of fuels using ionic liquids. Among investi-gated ionic liquids, [EMIM][SCN] shows the highest selectivityfor thiophene and pyridine (see Table 2). [DMIM][MP] is alsohighly selective for thiophene, but the solute distribution ratio istwice smaller than with [EMIM][SCN]. At low molar fractionof thiophene, the selectivity with [EMIM][SCN] is about 1600at 298.15 K. This high selectivity is mainly due to the immiscibi-lity of n-heptane in this ionic liquid. The capacity of [EMIM]-[SCN] for thiophene extraction from hydrocarbon solventdecreases with increment of temperature. Selectivity of numer-ous ternary systems {thiophene þ heptane þ ionic liquid} hasbeen reported in the literature. Our previous investigation on[BMIM][SCN] showed lower values of selectivity ranging from19 up to 284 than with [EMIM][SCN].8 Nevertheless, thesolute distribution ratio increases when the alkyl chain lengthgrafted on the cation increases. Arce and co-workers have alsoinvestigated some other ionic liquids for the extraction ofthiophene from n-heptane: [HMMpy][Ntf2], [OMIM][Ntf2],[OMIM][BF4], and [EMIM][EtSO4].

20-24 For these ternarysystems, the highest selectivity was found for [EMIM][EtSO4],and the capacity was ranging from 0.7 to 1.68. Compared to[EMIM][SCN], [EMIM][EtSO4] has a lower selectivity but asolute distribution ratio twice higher.Figures 6 and 7 show the evolution of the solute distribution

ratio as a function of thiophene or pyridine mole fraction. Thethiophene distribution coefficients are relatively low in all ternarysystems containing thiophene. Values of β are below the unit forall three investigated ionic liquids. In case of ternary systemscontaining pyridine, β values are over the unit for [DMIM][MP]and [EMIM][SCN] in the whole range of concentration. Thehighest β values are obtained for [EMIM][SCN] indicating thatthis ionic liquid would be the most advantageous as a solvent forhydrocarbon fuels denitrification. Figure 8 shows the influence ofwater content of 2 or 5 wt % in ionic liquid for the ternary system

Table 1. GCOperating Conditions for Composition Analysis

injector temperature 250 �Ccarrier gas helium

capillary column WCOT Ulti-Metal coated with HT-SIMDIST-CB

(10 m � 0.53 mm � 0.53 μm) with

an empty precolumn

flow rate 2 mL.min-1

column oven 70 �Cf125 �C (5 �C/min), 5 mindetector type FID

detector temperature 250 �C



Table 2. Compositions of Experimental Tie Lines, Solute Distribution Ratios β, and Selectivity S for All Ternary Systems

hydrocarbon-rich phase IL-rich phase

x1HC x2

HC x3HC x1

IL x2IL x3

IL β S

Thiophene (1) þ Heptane (2) þ [EMIM][SCN] (3) at T = 298.15 K

0.0824 0.9176 0 0.0523 0.0004 0.9473 0.64 1598.5

0.1561 0.8439 0 0.1082 0 0.8918 0.69 -

0.2045 0.7955 0 0.1287 0.0020 0.8694 0.63 252.5

0.3088 0.6596 0.0317 0.2311 0 0.7689 0.75 -

0.3701 0.6159 0.0140 0.2660 0 0.7340 0.72 -

0.4486 0.5514 0 0.3396 0 0.6604 0.76 -

0.5702 0.4298 0 0.4030 0 0.5970 0.71 -

0.7361 0.2639 0 0.5153 0.0017 0.4830 0.70 106.5

Thiophene (1) þ Heptane (2) þ [EMIM][SCN] (3) at T = 303.15 K

0.1133 0.8867 0 0.0683 0.0015 0.9302 0.60 346.8

0.2451 0.7549 0 0.1695 0.0010 0.8295 0.69 497.3

0.3482 0.6061 0.0457 0.2370 0 0.7630 0.68

0.3945 0.5750 0.0305 0.2575 0 0.7425 0.65

0.4386 0.5036 0.0578 0.3237 0.0019 0.6744 0.74 193.4

0.6035 0.3846 0.0119 0.4363 0.0017 0.5620 0.72 165.2

0.6884 0.3116 0 0.4790 0.0018 0.5192 0.70 119.0

0.7874 0.2126 0 0.5390 0 0.4610 0.68

0.1133 0.8867 0 0.0683 0.0015 0.9302 0.60 346.8

Thiophene (1) þ Heptane (2) þ [DMIM][MP] (3) at T = 298.15 K

0.2200 0.7555 0.0245 0.0923 0.0002 0.9075 0.42 1756.2

0.2700 0.7300 0 0.1155 0.0002 0.8842 0.43 1261.2

0.3589 0.6411 0 0.1574 0.0013 0.8413 0.44 217.1

0.4777 0.5223 0 0.1927 0.0007 0.8067 0.40 303.7

0.5618 0.4305 0.0078 0.2039 0 0.7961 0.36

0.6154 0.3846 0 0.2003 0.0026 0.7971 0.33 48.8

0.6917 0.3083 0 0.2254 0.0008 0.7739 0.33 133.8

0.9273 0.0727 0 0.2402 0.0010 0.7588 0.26 18.9

Thiophene (1) þ Heptane (2) þ [TEMA][MeSO4] (3) at T = 298.15 K

0.1079 0.8873 0.0047 0.0087 0.0026 0.9887 0.08 27.5

0.2942 0.7058 0 0.0175 0.0024 0.9801 0.06 17.6

0.4443 0.5557 0 0.0227 0.0031 0.9742 0.05 9.3

0.4952 0.5048 0 0.0400 0.0007 0.9593 0.08 56.3

0.6279 0.3721 0 0.0453 0.0014 0.9534 0.07 19.7

0.6667 0.3310 0.0022 0.0525 0.0011 0.9465 0.08 24.5

0.7905 0.2095 0 0.0641 0.0002 0.9358 0.08 102.0

0.8321 0.1679 0 0.0733 0.0013 0.9254 0.09 11.1

Pyridine (1) þ Heptane (2) þ [EMIM][SCN] (3) at T = 298.15 K

0.0719 0.9155 0.0126 0.2769 0.0064 0.7167 3.85 549.3

0.1940 0.8060 0.0000 0.5485 0.0133 0.4382 2.83 170.7

0.0346 0.9654 0.0000 0.1670 0.0040 0.8290 4.82 1156.4

0.1104 0.8896 0.0000 0.4363 0.0133 0.5504 3.95 264.0

0.1542 0.8458 0.0000 0.5078 0.0187 0.4734 3.29 148.7

0.5110 0.4890 0.0000 0.7201 0.0202 0.2597 1.41 34.2

0.7164 0.2836 0.0000 0.8783 0.0507 0.1616 1.12 6.8

0.0263 0.9604 0.0133 0.0992 0.0030 0.8978 3.77 1208.9

Pyridine (1) þ Heptane (2) þ [DMIM][MP] (3) at T = 298.15 K

0.0731 0.9269 0 0.0450 0.0115 0.9436 0.61 49.6

0.1408 0.8592 0 0.0924 0.0322 0.8754 0.66 17.5

0.1936 0.8064 0 0.2298 0.0393 0.7310 1.19 24.4



{thiophene þ heptane þ [EMIM][SCN]}. The solute distribu-tion ratio is about three times higher for low thiophene con-centration in the case of presence of water. An increase oftemperature decreases the solute distribution ratio.

The LLE data of the investigated ternary systems werecorrelated using the Non-Random Two-Liquid equation(NTRL) proposed by Renon and Prausnitz25 and the UNI-versal QUAsi-Chemical (UNIQUAC) theory developed byAbrams and Prausnitz.26

Table 2. Continued

hydrocarbon-rich phase IL-rich phase

x1HC x2

HC x3HC x1

IL x2IL x3

IL β S

0.2924 0.7076 0 0.2976 0.0417 0.6607 1.02 17.3

0.3529 0.6471 0 0.3499 0.0355 0.6146 0.99 18.1

0.4254 0.5746 0 0.3729 0.0292 0.5979 0.88 17.2

0.4555 0.5445 0 0.4104 0.0469 0.5428 0.90 10.5

0.5043 0.4957 0 0.4404 0.0382 0.5214 0.87 11.3

0.6740 0.3260 0 0.4947 0.0380 0.4674 0.73 6.3

Figure 2. Tie lines for ternary mixture {Thiophene þ Heptane þ[DMIM][MP]} at 298.15 K. Experimental data: þ and ;. NRTLCorrelation � (red) and ---- (red). UNIQUAC Correlation 0 (green)and -- (green).

Figure 3. Tie lines for ternary mixture {Thiophene þ Heptane þ[TEMA][MeSO4] } at 298.15 K. Experimental data: þ and ;. NRTLCorrelation � (red) and ---- (red).

Figure 4. Tie lines for ternary mixture {Pyridine þ Heptane þ[EMIM][SCN]} at 298.15 K. Experimental data: þ and ;. NRTLCorrelation and � (red) and ---- (red). UNIQUAC Correlation 0(blue) and -- (blue).

Figure 1. Tie lines for ternary mixture {Thiophene þ Heptane þ[EMIM][SCN]} at 298.15 K. Experimental data: þ and ;. NRTLCorrelation � (red) and ---- (red). UNIQUAC Correlation 0 (green)and -- (green).



NRTL Model. For the NRTLModel, the activity coefficient γi,for any component i of the ternary system, is given by

ln γi ¼

Pmj¼ 1

τjiGjixj

Pml¼ 1

Glixl

þXmj¼ 1

xjGij

Pml¼ 1

Gljxlτij -

Pmr¼ 1

xrτrjGrj

Pml¼ 1

Gljxl

0BBB@

1CCCA ð3Þ

with Gji = exp(-Rjiτji), τji = (gji-gii)/(RT) = (Δgji)/(RT), andRji = Rij = R where g is an energy parameter characterizing theinteraction of species i and j, xi is the mole fraction of componenti, R is the nonrandomness parameter. Although R can be treatedas an adjustable parameter, in this study it was set equal to 0.3.27

UNIQUAC Model. For the UNIQUAC Model, the activitycoefficient γi, for any component i of the ternary system, is given by

ln γi ¼ lnΦi

xiþ z2qiln

θiΦi

þ li -Φi

xi

Xmj¼ 1

xjlj - qilnðθjτjiÞ

þ qi - qiXmj¼ 1

θjτjiPmk¼ 1

θkτkj

ð4Þ

where Φi = (rixi)/(P

j=1m rjxj), θi = (qixi)/(

Pj=1m qjxj), lj = z/

2(rj-qj)-(rj-1), and τji = exp((-Δuij)/(RT)). Here, the lattice

Figure 6. Solute distribution ratio β as function of mole fraction ofthiophene in the hydrocarbon-rich phase for the three systems at298.15 K.

Figure 7. Solute distribution ratio β as function of mole fraction ofpyridine in the hydrocarbon-rich phase for two systems at 298.15 K.

Figure 8. Water influence on solute distribution ratioβ as function ofmolefraction of thiophene in the hydrocarbon-rich phase for [EMIM][SCN] at298.15 K.

Figure 5. Tie lines for ternary mixture {Pyridine þ Heptane þ[DMIM][MP]} at 298.15 K. Experimental data: þ and ;. NRTLCorrelation � (red) and ---- (red). UNIQUAC Correlation and 0(green) and -- (green).



coordination number z is assumed to be equal to 10, and ri and qi arerespectively a relative volume and surface area of the pure compo-nent i. Parameters ri and qi are respectively relative to molecular vander Waals volumes and molecular surface areas. They are calculatedas the sumof the group volume and group area parametersRk andQk

ri ¼Xk

υikRk and qi ¼Xk

υikQk ð5Þ

where υki is the number of groups of type k in molecule i. The group

parameters Rk and Qk are obtained from van der Waals groupvolumes and surface areas, andVk andAk are taken from theUNIFACgroup contributions28

Rk ¼ Vk

15:17and Qk ¼ Ak

2:5� 109ð6Þ

The values of 15.17 and 2.5 � 109 are respectively the standardsegment volume and standard segment area of a methylene group.28

This means that a total of two adjustable parameters per binaryΔgji or Δuji have to be fitted for both models. Interactionparameters for binary systems {thiophene þ n-heptane} and{pyridine þ n-heptane} are not available in the literature at298 K. These parameters are then fitted using the three ternarymixture data.

Binary interaction parameters for bothNRTL andUNIQUACequations are those which minimize the difference between the

Table 3. Values of Binary Parameters for the NRTL Equation for the Ternary Mixtures

system ij Δgij (J.mol-1) Δgji (J.mol-1) R rmsd

Thiophene (1) þ Heptane (2) þ [DMIM][MP] (3) 12 5622.87 1771.01 0.3 0.0321

13 24275.07 6054.1

23 9001.6 20975.87

Thiophene (1) þ Heptane (2) þ [BMIM][SCN] (3) 12 19100.2 5400.98 0.3 0.0056

13 18505.7 5836.4

23 9466.4 20557.2

Pyridine (1) þ Heptane (2) þ [DMIM][MP] (3) 12 12351.06 9629.64 0.3 0.0005

13 7913.05 9420.3

23 15198.1 5861.5

Pyridine (1) þ Heptane (2) þ [BMIM][SCN] (3) 12 4521.7 1465.4 0.3 0.0338

13 12560.4 -3810

23 12602.3 19510.5

Thiophene (1) þ Heptane (2) þ [TEMA][MeSO4] 12 4605.5 -2679.5 0.3 0.0024

13 18003 5526.6

23 12058 12393

Table 4. Values of the Binary Parameters for the UNIQUAC Equation

system ij Δuij (J.mol-1) Δuji (J.mol-1) rmsd

Thiophene (1) þ Heptane (2) þ [DMIM][MP] (3) 12 1386 64 0.0055

13 2720 524

23 1072 3300

Thiophene (1) þ Heptane (2) þ [BMIM][SCN] (3) 12 6400 -810 0.0112

13 2600 450

23 -150 3960

Pyridine (1) þ Heptane (2) þ [DMIM][MP] (3) 12 -340 2298 0.0058

13 -212 2498

23 6929 -172

Pyridine (1) þ Heptane (2) þ [BMIM][SCN] (3) 12 510 2330 0.0117

13 4910 -860

23 4900 150

Figure 9. Evolution of model gasoline components weight % changesduring extractive desulfurization using [EMIM][SCN] as a solvent at298.15 and 303.15 K.



experimental and calculated mole fractions

Fobj: ¼XNk¼ 1

X3i¼ 1

fðxI, expi, k - xI, calci, k Þ2 þðxII, expi, k - xII, calci, k Þ2g ð7Þ

whereN is the number of tie lines in the data set, xi,kI,exp and xi,k

I,calc arethe experimental and calculated mole fractions of one phase, andxi,kII,exp and xi,k

II,calc are the experimental and calculatedmole fractions ofthe second phase.The binary parameters and root mean-square deviation (rmsd),

calculated using the procedure above, of the NRTL andUNIQUACequations are given in Tables 3 and 4, respectively. The rmsd values,which provide a measure of the accuracy of the correlations, werecalculated according to the following equation:

rmsd ¼PNk¼ 1

P3i¼ 1

fðxI, expi, k - xI, calci, k Þ2 þðxII, expi, k - xII, calci, k Þ2g6N

0BBB@

1CCCA

1=2

ð8Þ

For the ternary system {Thiophene þ Heptane þ [TEMA]-[MeSO4] }, the UNIQUAC model was not applied due to the lackof volume, Rk, and area, Qk, parameters of van der Waals groups forthis ionic liquid. As can be inferred from the rmsd values, fairly goodcorrelation of the experimental values with NTRL and UNIQUACmodels was obtained.In the case of ternary systems {Thiophene þ n-heptane þ

[DMIM][MP]} and {Pyridineþ n-heptaneþ [BMIM][SCN]},the UNIQUACmodel fits much better than the NRTL equation.

’MODEL FUELS EXTRACTION

The weight percentage of model gasoline components changes asa function of extraction time using [EMIM][SCN] and [DMIM]-[MP] as an extractive solvent are shown at Figures 9 and 10, respec-tively. In both experiments, the concentration of sulfur and nitrogen-containing compounds reached the minimum after 2 h. Thus, theextraction period applied in all fuel desulfurization stages was 2 h.The higher temperature of extraction process causes the higher

Figure 10. Evolution of model gasoline components weight % changesduring extractive desulfurization using [DMIM][MP] as solvent, 298.15 Kand 303.15.

Figure 11. Evolution of model gasoline components weight % changes inthree-steps extraction process using [EMIM][SCN] as solvent at 298.15 K.

Figure 12. Evolution of model gasoline components weight % changes inthree-steps extraction process using [DMIM][MP] as solvent at 298.15 K.

Figure 13. Evolution of model diesel components weight % changes inthree-steps extraction process using [EMIM][SCN] as solvent at 298.15 K.



equilibrium content of thiophene as well as pyridine in refinedgasoline (Figures 9 and 10). Thus desulfurization conducted at298.15 K for both examined [EMIM][SCN] and [DMIM][MP] ismore efficient, and this temperature was applied in all furtherexperiments presented in this work.

Model gasoline has been desulfurized in three steps at298.15 K using [EMIM][SCN] and [DMIM][MP] as solvent.Figures 11 and 12 show the composition of model gasolinemixture and changes of weight percent of each component afterone, two, and three extraction steps. The same experiments havebeen performed for simulated diesel oil. Desulfurization wereconducted with [EMIM][SCN], [DMIM][MP], and [TEMA]-[MeSO4] as an extractive solvents. Results are presented atFigures 13-15. Sulfur and nitrogen containing compounds areextracted from hydrocarbon fuels by all free investigated ionic

liquids. The best results have been obtained for [EMIM][SCN]where after the third stage most of the thiophene and all of thepyridine have been extracted. These results are in agreement withobtained LLE data of ternary systems. However, deep desulfur-ization is also accompanied with unwanted reduction of aromatichydrocarbon concentration, which causes lower octane numberof the fuels. Comparison of investigated ionic liquids for gaso-line and diesel desulfurization is presented in Figures 16-18.[EMIM][SCN] ensures 94% of thiophene content reduction inmodel gasoline and 88% in model diesel oil, while dibenzothio-phene is completely extracted from diesel after three processstages. This ionic liquid [TEMA][MeSO4] chosen due to itsrelatively low price presents the lowest capacity for fuels desul-furization. The use of [TEMA][MeSO4] allows for extraction ofabout 10% of thiophene and 20% of dibenzothiophene fromsimulated diesel. It shows that this IL is useless for fuel desul-furization purpose. The third investigated ionic liquid [DMIM]-[MP] allows for more than 50% of sulfur containing compounds

Figure 14. Evolution of model diesel components weight % changesin three-steps extraction process using [DMIM][MP] as solvent at298.15 K.

Figure 15. Evolution of model diesel components weight % changesin three-steps extraction process using [TEMA][MeSO4] as solvent at298.15 K.

Figure 16. Evolution of thiophene content (wt%) in simulated gasolinefor investigated ionic liquids in three-step desulfurization process.

Figure 17. Evolution of thiophene content (wt%) in simulated dieselfor investigated ionic liquids in three-step desulfurization process.



extraction, effective denitrogenation without fuel dearoma-tization.

’CONCLUSIONS

(Liquidþ liquid) equilibrium data for the five ternary systems{thiophene þ n-heptane þ [EMIM][SCN]}, {pyridine þn-heptane þ [EMIM][SCN]}, {thiophene þ n-heptane þ[DMIM][MP]}, {pyridine þ n-heptane þ [DMIM][MP]},and {thiophene þ n-heptane þ [TEMA][MeSO4]} at T =298.15 K were determined. All ternary systems correspond to theType 2 category, with partial or total immiscibility of the IL withthe thiophene and the hydrocarbons. The NRTL and UNIQUACmodels were used to correlate the experimental LLE results.In general, the LLE data of the ternary systems studiedare better correlated with the UNIQUAC model than withthe NRTL model. Then, it was found that [EMIM][SCN]has a good capacity for fuels desulfurization. Indeed,[EMIM][SCN] ensures 94% of thiophene content reductionin model gasoline and 88% in model diesel oil, while diben-zothiophene is completely extracted from diesel in the thirdprocess stage. This ionic liquid [TEMA][MeSO4] chosen due toits relatively low price presents the lowest capacity for fuelsdesulfurization.

’AUTHOR INFORMATION

Corresponding Author*Phone: þ33 3 83 17 51 31. Fax: þ33 3 83 17 53 95. E-mail:[email protected].

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Extraction of Thiophene

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