Extraction of Butylbenzene from Dodecane Using ... - ACS Publications

Oct 8, 2012 - Chemical Engineering Department, College of Technological Studies, PAAET, P.O. Box 42325, Shuwaikh, 70654 Kuwait. J. Chem. Eng. Data ...
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Extraction of Butylbenzene from Dodecane Using Hexafluorophosphate-Based Ionic Liquids: Effect of Cation Change Mohsen H. Al-Rashed,* Khaled H. A. E. Alkhaldi, Mohammad S. Al-Tuwaim, Mohamed S. Fandary, and Adel S. Al-Jimaz Chemical Engineering Department, College of Technological Studies, PAAET, P.O. Box 42325, Shuwaikh, 70654 Kuwait ABSTRACT: Three ternary liquid systems, {dodecane + butylbenzene + [bmim]PF6, [hmim]PF6, or [omim]PF6}, were studied at 313 K and 333 K and atmospheric pressure. Equilibrium tie-line data were measured and plotted for all systems. The effects of the alkyl group in 1-alkyl-3-methylimidazolium hexafluorophosphate, temperature, and solvent-to-feed ratio upon solubility, selectivity (S), and distribution coefficient (K) were investigated. The liquid− liquid equilibrium (LLE) data were correlated sufficiently with both universal quasichemical activity coefficient (UNIQUAC) and nonrandom two-liquid (NRTL) models, and the interaction parameters between each of the three pairs of components for the UNIQUAC and the NRTL models were estimated as a function of temperature. The root-mean-square deviations between the correlated results and experimental data were calculated and found to be satisfactory.

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INTRODUCTION Liquid−liquid extraction has been widely used to separate aromatics from aliphatic hydrocarbons. It has proven to be more feasible than distillation for hydrocarbons containing 20 wt % to 65 wt % aromatic content, as it does not require hydrogen and is carried out at atmospheric pressure and comparatively low temperatures.1 This process aims to enhance middle distillate properties such as the smoke point of kerosene, the cetane number of diesel, or the viscosity index of mineral oil. Appreciable research has been devoted to examine the properties of ionic liquids (ILs). They are considered “green solvents” because of their negligible vapor pressure which implies no significant contamination to the atmosphere. On the other hand, ILs demonstrate high thermal/chemical stability, and they are not flammable nor explosive. They also exhibit a wide liquid temperature range. Another key feature of ILs is tailorability of their physicochemical properties by designing different cation−anion combinations to meet specific needs.2−5 Recent research has shown that a large number of ionic liquids have better selectivity and capacity in the extraction of aromatics from aromatic/aliphatic mixtures than typical solvents such as sulfolane6,7 and NMP.8 Meindersma et al.9 found that [bmim]BF4, [mebupy]BF4, [mebupy]CH3SO4, and [emim]C7H7SO3 gave higher distribution coefficients of toluene and toluene/heptane selectivities than with sulfolane. They also studied the effect of alkyl chain length in the cation of [emim]BF4 and [bmim]BF4 ionic solvents. Arce et al.10 investigated the effect of alkyl-chain length in the cation of the 1-alkyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide on the extraction of benzene from hexane. Poole and Poole11 reviewed several systems and stated that the cation plays a dominant role in establishing selectivity. © XXXX American Chemical Society

This work is a continuation of our research on the extraction of aromatic compounds from alkane/aromatic mixtures in the middle distillate range using ILs as solvents.12−14 Dodecane and butylbenzene were selected as representatives of the aliphatic and aromatic groups of Kuwait middle distillates. In this paper the effect of IL cation change on the extraction process was studied. 1-Butyl-3-methylimidazolium hexafluorophosphate {[bmim]PF6}, 1-hexyl-3-methylimidazolium hexafluorophosphate {[hmim]PF6}, and 1-octyl-3-methylimidazolium hexafluorophosphate {[omim]PF6} were used to extract butylbenzene from dodecane at atmospheric pressure and two different temperatures, 313 K and 333 K. These ionic liquids were selected because of their high capacity and percentage aromatic removal. They are also stable at low to moderate temperatures, as studied by Freire et al.15 Many researchers have investigated these ionic liquids in recent years. For example, Santiago et al.16 and Banerjee et al.17 studied systems involving [bmim][PF6] and [hmim][PF6]; Sahandzhieva et al.18 and Simoni et al.19 modeled ternary systems involving [bmim][PF6]; Pereiro and Rodriguez20 investigated ternary systems involving [hmim][PF6] and [omim][PF6]. The extracting distribution coefficients as well as the selectivity were calculated for all systems under consideration. The experimental results were regressed to estimate the interaction parameters between each of the three pairs of components for the universal quasichemical activity coefficient (UNIQUAC)21 and the nonrandom two-liquid (NRTL)22 models as a function of temperature. Received: January 12, 2012 Accepted: September 24, 2012

A

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Table 1. Details of the Chemicals, Purities, UNIQUAC Structural Parameters, and Refractive Indices (nD) purity

a

nD20

UNIQUAC structural parameter

compound

supplier

(mole %)

r

q

exp

lit.

[bmim][PF6] [hmim][PF6] [omim][PF6] dodecane butylbenzene

Fluka Fluka Fluka Aldrich Aldrich

>98 >98 >98 >99 >99

8.4606 9.6811 14.230 8.5462 5.4983

6.808 7.845 8.935 7.096 4.356

1.4101 1.4176 1.4231 1.4221 1.4894

1.4095a 1.41787b 1.42302b 1.4216c 1.4898c

Reference 27. bReference 28. cReference 29.

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EXPERIMENTAL SECTION The ionic liquids [bmim]PF6, [hmim]PF6, and [omim]PF6 were obtained from Fluka with stated mass fraction purity of 98 %. Dodecane and butylbenzene were supplied by Sigma-Aldrich with stated mass fraction purity of 99 %. Gas chromatography was used to determine the purity of dodecane and butylbenzene. No further purification was made. The ILs and butylbenzene were stored under 4 nm molecular sieve. Karl Fischer titration method was performed to measure the water content and showed that the mass fraction of water was < 6·10−4. This method was regularly employed on the IL, and no increase of water content could be detected. Table 1 shows the purities and refractive indices of all chemicals used in this work. [bmim]PF6, [hmim]PF6, or [omim]PF6 were mixed with dodecane and butylbenzene. A glass cell of 60 mL was used with a water jacket to maintain a constant temperature with an accuracy of ± 0.2 K. The cell was attached to a water bath (Haake K15) fitted with a thermostat (Haake DC1). Mixtures consisting of 12 mL of dodecane, 8 mL of [bmim]PF6, 8 mL of [hmim]PF6, or 6.5 mL of [omim]PF6 and varying amounts of butylbenzene were mixed vigorously in the extraction vessel for 1 h at 293 K, followed by settling for 4 h. The experiments were performed under two temperatures, 313 K and 333 K. Samples were carefully taken by a syringe from both the upper and lower layers. To avoid phase splitting and to maintain a homogeneous mixture, 1-butanol (0.5 mL) was added to each sample. Then, the samples were analyzed using a Varian 450 gas chromatography equipped with an autosampler (Varian CP-8400), an on-column injector, flame ionization detector (FID), and a data processing system. Varian VF-5 ms CP8944 column was used with a 30 m length, 0.25 mm inner diameter (i.d.), and 0.25 μm film thickness. Since the ILs have negligible vapor pressure, they cannot be analyzed by gas chromatography (GC). Therefore, two components could be analyzed, whereas the IL was estimated by a mass balance of the measured mass fractions of dodecane and butylbenzene. A fixed amount of ethylbenzene was added to each sample as an internal standard. A precolumn was utilized to protect the column and collect the ionic solvent. The GC column temperature was programmed for an initial temperature of 363 K maintained for 2 min and a final temperature of 673 K maintained for 5 min. The heating rate was 35 K·min−1, and helium was the carrier gas with a flow rate of 3·10−5 m3·min−1. The injection temperature was 523 K, and the detector temperature was 573 K. The temperature was controlled with a precision of ± 0.03 K. Each mole fraction was measured repeatedly four times to reduce experimental uncertainty associated with random errors, and the average value was recorded. The compositions in mole fractions were measured with an experimental uncertainty of ± 5·10−4.14

RESULTS AND DISCUSSION Tables 2 to 4 present the measured equilibrium mole fractions of the three systems for two temperatures 313 K and 333 K at Table 2. Experimental Dataa for the Ternary System I {Dodecane (1) + Butylbenzene (2) + [bmim][PF6] (3)} at T = 313 K and 333 K and P = 101.3 kPa dodecane-rich phase

solvent-rich phase

T/K

x1

x2

x1

x2

K

S

313

0.8924 0.8044 0.7309 0.6698 0.618 0.5738 0.5348 0.5006 0.4705 0.4439 0.4197 0.3597 0.2912 0.2070 0.1602 0.1093 0.0696 0.8941 0.8074 0.7349 0.6741 0.6221 0.577 0.538 0.5037 0.4733 0.4463 0.4222 0.3621 0.2930 0.2082 0.1617 0.1102 0.0700

0.1076 0.1956 0.2691 0.3302 0.382 0.4262 0.4652 0.4994 0.5295 0.5561 0.5803 0.6403 0.7088 0.7930 0.8398 0.8907 0.9304 0.1059 0.1926 0.2651 0.3259 0.3779 0.423 0.462 0.4963 0.5267 0.5537 0.5778 0.6379 0.7070 0.7918 0.8383 0.8898 0.9300

0.0180 0.0183 0.0186 0.0189 0.0192 0.0195 0.0198 0.0201 0.0204 0.0207 0.0210 0.0213 0.0216 0.0219 0.0230 0.0233 0.0236 0.0201 0.0205 0.0211 0.0215 0.0216 0.0218 0.0220 0.0223 0.0226 0.0226 0.0229 0.0232 0.0235 0.0238 0.0241 0.0244 0.0247

0.0352 0.0660 0.0923 0.1176 0.1412 0.1641 0.1840 0.2026 0.2204 0.2377 0.2528 0.2892 0.3487 0.4045 0.4518 0.5009 0.5408 0.0379 0.0715 0.1008 0.128 0.1523 0.174 0.1948 0.2139 0.2316 0.2483 0.2644 0.3033 0.3623 0.4212 0.4783 0.5333 0.5817

0.33 0.34 0.34 0.36 0.37 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.49 0.51 0.54 0.56 0.58 0.36 0.37 0.38 0.39 0.40 0.41 0.42 0.43 0.44 0.45 0.46 0.48 0.51 0.53 0.57 0.60 0.63

16.24 14.84 13.48 12.62 11.90 11.33 10.68 10.11 9.60 9.17 8.71 7.63 6.63 4.82 3.75 2.64 1.71 15.93 14.62 13.24 12.32 11.60 10.89 10.31 9.73 9.21 8.85 8.44 7.42 6.39 4.65 3.83 2.71 1.77

333

Temperature controlled with an uncertainty of ± 0.2 K. Composition in mole fraction with an uncertainty of ± 0.0005.

a

atmospheric pressure; where system I is {dodecane + butylbenzene + [bmim]PF6}, system II is {dodecane + butylbenzene + [hmim]PF6}, and system III is {dodecane + butylbenzene + [omim]PF6}. Neither temperature nor concentration of butylbenzene in the feed B

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Table 3. Experimental Dataa for the Ternary System II {Dodecane (1) + Butylbenzene (2) + [hmim][PF6] (3)} at T = 313 K and 333 K and P = 101.3 kPa dodecane-rich phase

Table 4. Experimental Dataa for the Ternary System III {Dodecane (1) + Butylbenzene (2) + [omim][PF6] (3)} at T = 313 K and 333 K and P = 101.3 kPa

solvent-rich phase

dodecane-rich phase

solvent-rich phase

T/K

x1

x2

x1

x2

K

S

T/K

x1

x2

x1

x2

K

S

313

0.8966 0.8109 0.7392 0.6785 0.6279 0.5824 0.5430 0.5083 0.4782 0.4507 0.4263 0.3658 0.3088 0.2336 0.1725 0.1174 0.0853 0.8971 0.8127 0.7415 0.6813 0.6292 0.5842 0.5454 0.5105 0.4804 0.4527 0.4282 0.3685 0.3116 0.2356 0.1749 0.1191 0.0862

0.1034 0.1891 0.2608 0.3215 0.3721 0.4176 0.4570 0.4917 0.5218 0.5493 0.5737 0.6342 0.6912 0.7664 0.8275 0.8826 0.9147 0.1029 0.1873 0.2585 0.3187 0.3708 0.4158 0.4546 0.4895 0.5196 0.5473 0.5718 0.6315 0.6884 0.7644 0.8251 0.8809 0.9138

0.0190 0.0193 0.0196 0.0199 0.0202 0.0205 0.0208 0.0211 0.0214 0.0217 0.0220 0.0223 0.0226 0.0229 0.0230 0.0233 0.0236 0.0211 0.0215 0.0221 0.0225 0.0226 0.0228 0.0230 0.0233 0.0236 0.0236 0.0239 0.0242 0.0245 0.0248 0.0230 0.0233 0.0236

0.0443 0.0820 0.1151 0.1444 0.1743 0.1972 0.2187 0.2387 0.2590 0.2755 0.2920 0.3330 0.3885 0.4643 0.5200 0.5728 0.6137 0.0453 0.0854 0.1200 0.1513 0.1782 0.2028 0.2268 0.2465 0.2674 0.2839 0.3004 0.3467 0.4053 0.4817 0.5447 0.6037 0.6415

0.43 0.43 0.44 0.45 0.47 0.47 0.48 0.49 0.50 0.50 0.51 0.53 0.56 0.61 0.63 0.65 0.67 0.44 0.46 0.46 0.47 0.48 0.49 0.50 0.50 0.51 0.52 0.53 0.55 0.59 0.63 0.66 0.69 0.70

20.21 18.21 16.64 15.31 14.56 13.41 12.49 11.70 11.10 10.42 9.870 8.62 7.68 6.18 4.71 3.27 2.42 18.72 17.24 15.57 14.37 13.38 12.50 11.83 11.04 10.48 9.95 9.41 8.36 7.49 5.99 5.02 3.50 2.56

313

0.8985 0.8154 0.7458 0.6867 0.6362 0.5928 0.5547 0.5209 0.4915 0.4645 0.4405 0.3816 0.3249 0.2484 0.1861 0.1292 0.0947 0.8994 0.8164 0.7472 0.6882 0.6378 0.5941 0.5559 0.5222 0.4932 0.4664 0.4426 0.3850 0.3293 0.2539 0.1935 0.1358 0.1029

0.1015 0.1846 0.2542 0.3133 0.3638 0.4072 0.4453 0.4791 0.5085 0.5355 0.5595 0.6184 0.6751 0.7516 0.8139 0.8708 0.9053 0.1006 0.1836 0.2528 0.3118 0.3622 0.4059 0.4441 0.4778 0.5068 0.5336 0.5574 0.6150 0.6707 0.7461 0.8065 0.8642 0.8971

0.0250 0.0253 0.0256 0.0259 0.0262 0.0265 0.0268 0.0271 0.0274 0.0277 0.0280 0.0283 0.0286 0.0289 0.0292 0.0295 0.0298 0.0271 0.0275 0.0281 0.0285 0.0286 0.0288 0.0290 0.0293 0.0296 0.0296 0.0299 0.0302 0.0305 0.0308 0.0311 0.0314 0.0317

0.0703 0.1307 0.1824 0.2273 0.2674 0.3040 0.3368 0.3654 0.3938 0.4170 0.4395 0.4984 0.5647 0.6486 0.7174 0.7887 0.8372 0.0723 0.1334 0.1864 0.2317 0.2721 0.3083 0.3407 0.3700 0.3997 0.4238 0.4469 0.5108 0.5810 0.6698 0.7472 0.8175 0.8698

0.69 0.71 0.72 0.73 0.73 0.75 0.76 0.76 0.77 0.78 0.79 0.81 0.84 0.86 0.88 0.91 0.92 0.72 0.73 0.74 0.74 0.75 0.76 0.77 0.77 0.79 0.79 0.80 0.83 0.87 0.90 0.93 0.95 0.97

24.89 22.83 20.91 19.24 17.85 16.70 15.66 14.66 13.89 13.06 12.36 10.86 9.50 7.42 5.62 3.97 2.94 23.85 21.57 19.61 17.94 16.75 15.67 14.70 13.80 13.14 12.51 11.87 10.59 9.36 7.40 5.76 4.09 3.15

333

333

a

Temperature controlled with an uncertainty of ± 0.2 K. Composition in mole fraction with an uncertainty of ± 0.0005.

a

has any effect on the solubility of ionic liquids in the dodecanerich phase that presented by the upper layer, whereas both temperature and concentration of butylbenzene in the feed has little effect on the solubility of dodecane in the solvent-rich phase. The ternary phase diagrams and the tie lines of the studied systems are given in Figures 1 to 3. These figures show that butylbenzene is partially soluble in the ionic liquid and that the dodecane and butylbenzene compounds are completely soluble in all proportions. Also, no detectable concentrations of the ionic solvents were found in the dodecane-rich phase.13 The solvent power or capacity can be presented by the distribution coefficient (K) of butylbenzene:

where xI1 and xI2 are the mole fractions of dodecane and butylbenzene, respectively, in dodecane-rich phase, xII1 and xII2 are the mole fractions of dodecane and butylbenzene, respectively, in the IL-rich phase. K and S values of the three systems are presented in Tables 2 to 4. As the butylbenzene concentration in the raffinate phase increases, the distribution coefficient (K) shows an increase. However, the selectivity (S) displays a decrease as demonstrated in the same tables. This sort of behavior is also observed in a previous study.23 The studied ionic liquids proved to be suitable alternative solvents for the extraction of aromatic compounds from alkanes/aromatic mixtures in the middle distillate range because the selectivity values were greater than unity in all studied systems. The distribution coefficients (K) is plotted against the solvent-to-feed ratio (αstf) for all studied systems at 313 K as shown in Figure 4. The selectivity (S) is similarly plotted against the solvent-to-feed ratio (αstf) at the same temperature, in Figure 5. As the temperature increases and/or the solvent-tofeed ratio (αstf) decreases, a slightly increase is observed in the distribution coefficient values while an increase is noticed with

K = x 2II/x 2I

Temperature controlled with an uncertainty of ± 0.2 K. Composition in mole fraction with an uncertainty of ± 0.0005.

(1)

The capability of the IL to separate butylbenzene from dodecane can be represented by the selectivity (S): S = x 2IIx1I/x 2Ix1II

(2) C

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Figure 1. Experimental and calculated LLE of the ternary system I {dodecane (1) + butylbenzene (2) + [(bmim)(PF6)] (3)}; (a) T = 313 K; (b) T = 333 K.

also included data of a previous study13 which used [mebupy][BF4] to extract butylbenzene from dodecane under same operating conditions. Both K and S were higher for [mebupy][BF4] than the other systems. In addition, aromatic percentage removal is plotted against αstf in Figure 6 to compare the three systems under consideration with the same previous study. This figure illustrates that hexafluorophosphatebased ILs give a better aromatic percentage removal than [mebupy][BF4].

the selectivity values as the temperature decreases and/or the solvent-to-feed ratio (αstf) increases. The effect of the cation change on distribution coefficient (K) and selectivity (S) is also observed in Figures 4 and 5. It is evident that the distribution coefficient (K) of butylbenzene changes significantly with the cation change ([omim]+ > [hmim]+ > [bmim]+) for the same anion and at a certain temperature. This illustrates that the effect of the cation change has a more prominent influence than the temperature change examined in this study. Figures 4 and 5 D

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Figure 2. Experimental and calculated LLE of the ternary system II {dodecane (1) + butylbenzene (2) + [(hmim)(PF6)] (3)}; (a) T = 313 K; (b) T = 333 K.

The UNIQUAC and NRTL thermodynamic models were implemented effectively to correlate the experimental (liquid + liquid) equilibrium data in several ILs in which an iterative computer program is utilized, based on flash calculation method as presented in literature.24,25 The parameters, ri and qi, of the UNIQUAC model were predicted by Magnussen et al.26 and Santiago et al.,16 as in Table 1. For each pair of components, the NRTL model employed constant values of the third nonrandomness parameter, αij. Minimizing the differences between

the experimental and calculated mole fractions for each component determined the constituent binary parameters of both models over all of the measured LLE data of the ternary systems. The objective function (OF) was used as follows: exp cal 2 OF = min ∑ ∑ ∑ (xijk − xijk ) k exp

j

i

(3)

cal

where x and x are the experimental and calculated mole fractions, respectively. The subscripts i, j, and k denote E

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Figure 3. Experimental and calculated LLE of the ternary system III {dodecane (1) + butylbenzene (2) + [(omim)(PF6)] (3)}; (a) T = 313 K; (b) T = 333 K.

exp cal 2 rmsd = 100{∑ ∑ ∑ (xijk − xijk ) /6n}1/2

the component, phase, and tie line, respectively. The quality of the binary parameters can be evaluated according to the mean deviation in the compositions of coexisting phase.13 The optimized binary parameters of the two implemented models (UNIQUAC and NRTL) for the ternary systems are presented in Tables 5 and 6, respectively. The rmsd values between experimental and calculated data, given as:

k

j

i

(4)

where n is the number of tie lines, the number 6 refers to the three component pairs in the two phases. The LLE tie lines for all studied systems were calculated by employing the interaction parameters for the UNIQUAC and the NRTL models as a function of temperature. The NRTL model was F

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Table 5. UNIQUAC Interaction Parameters and Root-MeanSquare Deviation (rmsd) of the Ternary Systems under Study at T = 313 K and 333 K and P = 101.3 kPa UNIQUAC T/K

i

j

aij

aji

313

dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene

butylbenzene bmim(PF6) bmim(PF6) butylbenzene bmim(PF6) bmim(PF6) butylbenzene hmim(PF6) hmim(PF6) butylbenzene hmim(PF6) hmim(PF6) butylbenzene omim(PF6) omim(PF6) butylbenzene omim(PF6) omim(PF6)

423.96 686.2 434.36 −230.58 911.67 418.81 −106.8 276.8 445.49 −122.78 285.47 493.83 −221.26 895.28 414.72 −233.27 947.82 423.98

−274.25 −104.59 −177.07 289.37 −143.65 −180.42 68.802 −21.193 −200.48 76.236 −22.91 −226.3 277.26 −191.06 −250.26 243.41 −206.96 −280.8

333

313

333

Figure 4. Aromatic distribution coefficient (K) as a function of solvent-to-feed ratio (αstf) at T = 313 K. ●, system I; ○, system II; ▼, system III; △, ref 13.

313

333

rmsd

0.3916

0.4771

0.4812

0.4974

0.2943

0.3625

Table 6. NRTL Interaction Parameters and Root-MeanSquare Deviation (rmsd) of the Ternary Systems under Study at T = 313 K and 333 K and P = 101.3 kPa NRTL (αij = 0.3) T/K

i

j

aij

aji

313

dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene dodecane dodecane butylbenzene

butylbenzene bmim(PFs6) bmim(PF6) butylbenzene bmim(PF6) bmim(PF6) butylbenzene hmim(PF6) hmim(PF6) butylbenzene hmim(PF6) hmim(PF6) butylbenzene omim(PF6) omim(PF6) butylbenzene omim(PF6) omim(PF6)

−564.39 1713.2 1538.4 −636.39 1881.1 1563.1 −689.15 1682.9 1626.2 −786.11 1721.9 1802.9 −1072.7 1677.5 1685.5 −1640.2 1823.3 1801.4

382.02 1004.3 −203.7 474.72 1025.2 −262.04 514.12 965.58 −354.75 533.39 988.05 −441.66 494.83 977.25 −976.95 541.55 999.58 −1541

333

313

Figure 5. Selectivity (S) as a function of solvent-to-feed ratio (αstf) at T = 313 K. ●, system I; ○, system II; ▼, system III; △, ref 13.

333

313

333

rmsd

0.418

0.4814

0.4522

0.4506

0.3549

0.3457

fitted with αij = 0.2 or 0.3. The correlation with αij = 0.3 produced more accurate results according to rmsd values. Both models produced adequate results to correlate the LLE experimental data for the systems under consideration (the average rmsd values were 0.4174 for UNIQUAC and 0.41713 for NRTL).

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CONCLUSIONS The equilibrium behavior of (liquid + liquid) systems was investigated experimentally over two temperatures 313 K and 333 K and atmospheric pressure. Three ternary systems were studied, {dodecane + butylbenzene + [bmim]PF6, [hmim]PF6, or [omim]PF6}. The distribution coefficient (K) and the

Figure 6. Percentage removal of aromatics as a function of solvent-tofeed ratio (αstf) at T = 313 K. ●, system I; ○, system II; ▼, system III; △, ref 13. G

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selectivity (S) both increased as the chain length of the alkyl group in the cation increased, that is, [omim]+ > [hmim]+ > [bmim]+ for the same anion hexafluorophosphate [PF6] at a certain temperature. This result underlined the prominent influence of the cation change, whereas temperature change demonstrated no effect on the solubility of IL in the dodecane rich phase and limited effect on the solubility of dodecane in the IL-rich phase. The UNIQUAC and the NRTL models reasonably correlated the LLE experimental data. The studied ionic liquids ([bmim]PF6, [hmim]PF6, or [omim]PF6) proved to be suitable alternative solvents for the extraction of aromatic compounds from alkanes/aromatic mixtures in the middle distillate range because the selectivity values were greater than unity in all systems.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: (965) 55559500. Fax: (965) 24811568. Funding

The authors thank the Public Authority for Applied Education and Training (PAAET-TS-06-03) for financial support of this work. Notes

The authors declare no competing financial interest.

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REFERENCES

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dx.doi.org/10.1021/je3002305 | J. Chem. Eng. Data XXXX, XXX, XXX−XXX