Dialkylphosphate-Based Ionic Liquids as Solvents to Extract Toluene

May 13, 2015 - The toluene solute distribution ratios and toluene/heptane selectivities, derived from the experimental LLE data, were compiled and ana...
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Dialkylphosphate-Based Ionic Liquids as Solvents to Extract Toluene from Heptane Fufeng Cai, Wei Zhu, Yanbin Wang, Tongzhen Wang, and Guomin Xiao* School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China ABSTRACT: In this work, the ability of ionic liquids (ILs) 1,3-dimethylimidazolium dimethylphosphate ([MMIM][DMP]), 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][DBP]) as alternative solvents used in liquid removal of toluene from its combination with heptane was studied. The liquid−liquid equilibrium (LLE) data in relation to ternary systems {toluene + heptane + [MMIM][DMP], [EMIM][DEP], or [BMIM][DBP]} calibrated at T = 298.2 K and atmospheric pressure. The LLE results studied in relation to ternary systems were fitted by the thermodynamic nonrandom two-liquid (NRTL) model. The toluene solute distribution ratios and toluene/heptane selectivities, derived from the experimental LLE data, were compiled and analyzed to determine the extraction capacity of the studied ILs.

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298.2 K and atmospheric pressure. The NRTL10 model was used to fit the experimental results for the ternary systems studied. The capacity of the investigated ILs as solvents in the extraction process was analyzed by applying the toluene solute distribution ratios and toluene/heptane selectivities.

INTRODUCTION The separation of toluene and heptane is a difficult and complicated process because of the formation of azeotrope. For the toluene and heptane system, liquid−liquid extraction is a common industrial separation process in which conventional organic compounds such as sulfolane, N-methyl pyrrolidone, or dimethyl sulfoxide1,2 are used as solvents. However, the disadvantage of these solvents is that they are not environmentally friendly. Over the past decade, ionic liquids (ILs) have received considerable attention for their use as possible replacements for the conventional organic solvents in liquid−liquid extraction because of their notable properties. 3−5 Currently, few publications in relation to the liquid−liquid extraction of toluene from heptane using ILs as solvents have been investigated. Meindersma et al.6 evaluated the separation of toluene from heptane using sulfolane and 1-alkyl-3-methylimidazolium methylsulfate ([AMIM][MeSO4]) ILs. Larriba et al.7 investigated the effect of the length of alkyl substituent chain of 1-alkyl-3-methylimidazolium thiocyanate and 1-alkyl-3methylimidazolium dicyanamide ([AMIM][DCA]) ILs, in the separation of toluene and heptane. Corderi ́ et al.8 investigated the separation of toluene from heptane using the IL 1-ethyl-3methylimidazolium acetate ([EMIM][OAc]). Ebrahimi et al.9 studied the LLE data in relation to the ternary system containing bis(trifluoromethylsulfonyl)imide-based ILs with toluene + heptane. In this work, three dialkylphosphate-based ILs, [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP], were studied as solvents for the liquid removal of toluene from heptane. Subsequently, the experimental LLE data generated were measured for the ternary systems {toluene + heptane + [MMIM][DMP], [EMIM][DEP], or [BMIM][DBP]} at T = © 2015 American Chemical Society

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EXPERIMENTAL SECTION Materials. Toluene with purity of 99.5 % (mass; Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), heptane with purity of 99.0 % (mass; Aladdin Industrial Corporation, Shanghai, China), and 1-propanol with purity of 99.9 % (mass; Aladdin Industrial Corporation, Shanghai, China), were used in this work. The studied ILs, [MMIM][DMP], [EMIM][DEP], and [BMIM][DBP], were synthesized in accordance with the procedures described in the literature.11 Prior to use, the ILs were dried at T = 393 K under high vacuum for 48 h. The water in IL mass fraction measured by the Karl Fischer titration (AKF-2010, China), was found to be less than 5·10−4. The IL structure was verified using 1H NMR spectrum (Bruker AV-600 NMR spectrometer) with purity of 98.0 % (mass). The specifications of the chemicals used in this work are listed in Table 1. Additionally, the structure formulas of the ILs studied are shown in Figure 1. All chemicals were stored in a drying oven under an inert nitrogen atmosphere to avoid moisture contamination. Procedure and Analysis. The determination of experimental LLE data was carried out in a 50 mL glass cell containing a magnetic stirrer, thermostatically controlled at T = Received: December 27, 2014 Accepted: May 5, 2015 Published: May 13, 2015 1776

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were prepared by mass and were analyzed by the GC. The compositions from GC analysis were compared with those obtained by mass. The standard uncertainties of the mole fractions of toluene and heptane in the specimens were ± 0.001. Because ILs have minimal vapor pressure, analysis by GC is not possible. The whole of the ILs were retained by an empty precolumn situated between the injector and the capillary column during the GC analysis. The empty precolumn was cleaned occasionally to prevent the ILs from flowing into the capillary column. The 1H NMR spectrum determination was used to show that the IL was not present in the upper layer (i.e., heptane-rich phase) so that the IL in this phase could be assumed as zero. This assumption has also been shown by various researchers in reviewing the LLE data of ternary systems of toluene and heptane containing different ILs.7,12 The IL concentration in the lower layer (i.e., IL-rich phase) was measured gravimetrically by determining the mass difference of the specimen (≈ 3.5 g) before and after vaporization of the solvents at T = 393 K and under high vacuum until reaching a constant mass.13−16 The standard uncertainty of the concentration of IL in the specimens was found to be ± 0.002. Using 1 H NMR spectrum, the purity of the IL after vaporization was determined.

Table 1. Sources, Purities, Purification Methods, and Water Contents by Mass ww of the Chemicals Used in This Work chemical name toluene

heptane 1-propanol [MMIM] [DMP]b [EMIM] [DEP]e [BMIM] [DBP]f

source Sinopharm Chemical Reagent Co., Ltd. Aladdin Industrial Corporation Aladdin Industrial Corporation prepared in the laboratory prepared in the laboratory prepared in the laboratory

mass fraction purity

purification method

≥ 0.995

none

GC

≥ 0.990

none

GC

≥ 0.999

none

GC

≥ 0.980

vacuum desiccation vacuum desiccation vacuum desiccation

≥ 0.980 ≥ 0.980

ww· 10−6

< 500 < 500 < 500

analysis methoda

KF, NMR KF, NMR KF, NMR

a

GC, gas chromatography; KF, Karl Fischer titration. b[MMIM][DMP] = 1,3-dimethylimidazolium dimethylphosphate. e[EMIM][DEP] = 1-ethyl-3-methylimidazolium diethylphosphate. f[BMIM][DBP] = 1-butyl-3-methylimidazolium dibutylphosphate.

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RESULTS AND DISCUSSION Experimental LLE Data. The experimental LLE data of the ternary systems {toluene (1) + heptane (2) + [MMIM][DMP] (3)}, {toluene (1) + heptane (2) + [EMIM][DEP] (4)}, and {toluene (1) + heptane (2) + [BMIM][DBP] (5)} at T = 298.2 K and atmospheric pressure are tabulated in Table 2, where xi was the concentration of component i in the liquid phase. The triangular diagrams for the studied ternary systems are displayed in Figure 2, where the differences in the slopes of the experimental tie-lines and the size of the immiscibility region are shown. As can be seen from Figure 2, the upper layers (i.e., heptane-rich phase) for the studied systems are free of ILs, which has been discussed in the Experimental Section. It can be noted that comparatively ILs as solvents are more advantageous than sulfolane because this behavior could minimize the number of purification procedures in the extraction process, thus minimizing the running costs. The quantity of the heptane dissolved in the ILs is minimal, and its solubility in the studied ILs decreases as follows: [BMIM][DBP] > [EMIM][DEP] > [MMIM][DMP]. Finally, the negative slopes of the tie-lines in Figure 2 indicate that toluene has a higher affinity for heptane than toward the ILs. LLE Data Correlation. The NRTL10 model was used to fit the experimental LLE data in this study. It has proven its correlating capabilities in relation to ternary LLE data for systems involving ILs. For the investigated systems, the parameters of the NRTL model (i.e., Δgij, Δgji, and αij) were obtained by reduction of the objective function (OF) shown in eq 1, using the SOLVER tool.17,18

Figure 1. Structure formulas of the ionic liquids studied in this work.

298.2 K. For the measurements of LLE data, 30 mL of an immiscible emulsion of known composition was put into the glass cell and stirred using the magnetic stirrer. The temperature in the glass cell was measured by an thermometer with a standard uncertainty ± 0.1 K. The sample mixture was stirred vigorously for 1 h with a speed of 800 rpm (time dependency experiments showed that equilibrium for the system is reached within 1 h) to ensure an intimate connection between both phases in the glass cell. Then, the final two-phase solution was left to settle for 4 h to ensure a complete separation between the equilibrium phases. Next, samples were obtained from the upper and lower layers using a syringe, and compositional analysis was carried out. The concentrations of toluene and heptane in the sample were verified by using the gas chromatography. The gas chromatograph (GC-6890, China) was equipped with a flame ionization detector, and the capillary column was SE-54 (50 m × 0.32 mm). The carrier gas was high-purity nitrogen (Nanjing Special Gas Factory Co., Ltd., Nanjing, China, ≥ 99.999 %), and the following operating situations were noted: the oven temperature was 343 K, the injector temperature was 423 K, and the detector temperature was 473 K. 1-Propanol was included in the sample as an internal standard substance for the GC analysis. A calibration curve was determined from a set of gravimetrically prepared standard solutions, which allowed for the determination of toluene and heptane in the solution. All the calibrations were carried out in duplicate to exclude exceptions in the composition analysis. Each sample was analyzed five times. An appropriate balance with a standard uncertainty of ± 0.0001 g was used to determine the weight of the sample. Some specimens with a well-known concentration

OF =

∑ [(x1I − x1I(calc))2 + (x2I − x2I(calc))2 + (x1II − x1I(calc))2 + (x 2II − x 2II(calc))2 ]

(1)

where xI1, xI2, xII1 , xII2 and xI1(calc), xI2(calc), xII1 (calc), and xII2 (calc) are the experimental and calculated values, respectively, superscripts I and II represent the upper and lower layers, respectively, subscripts 1 and 2 represent the components 1777

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Table 2. Experimental Liquid−Liquid Equilibrium Data on Mole Fraction x, the Toluene Solute Distribution Ratios β, and Toluene/Heptane Selectivities S for the Studied Ternary Systems at T = 298.2 K and p = 101.3 kPaa upper layer xI1

lower layer xI2

xII1

xII2

β

toluene (1) + heptane (2) + [MMIM][DMP] (3) 1.000 0.000 0.006 0.952 0.022 0.006 0.46 0.835 0.068 0.005 0.41 0.738 0.107 0.005 0.41 0.616 0.143 0.004 0.37 0.557 0.165 0.004 0.37 0.465 0.199 0.004 0.37 0.315 0.238 0.003 0.35 0.199 0.268 0.003 0.33 toluene (1) + heptane (2) + [EMIM][DEP] (4) 1.000 0.000 0.009 0.941 0.031 0.009 0.53 0.857 0.072 0.008 0.50 0.763 0.117 0.008 0.49 0.646 0.170 0.007 0.48 0.564 0.194 0.006 0.44 0.431 0.249 0.006 0.44 0.316 0.295 0.006 0.43 0.218 0.331 0.005 0.42 toluene (1) + heptane (2) + [BMIM][DBP] (5) 1.000 0.000 0.025 0.953 0.029 0.024 0.62 0.874 0.074 0.023 0.59 0.758 0.138 0.023 0.57 0.644 0.197 0.023 0.55 0.571 0.230 0.022 0.54 0.485 0.265 0.021 0.51 0.376 0.319 0.019 0.51 0.253 0.378 0.019 0.51

0.000 0.048 0.165 0.262 0.384 0.443 0.535 0.685 0.801 0.000 0.059 0.143 0.237 0.354 0.436 0.569 0.684 0.782 0.000 0.047 0.126 0.242 0.356 0.429 0.515 0.624 0.747

S

72.72 68.82 60.28 57.35 51.87 43.24 36.48 22.19

54.94 53.94 47.08 44.32 41.83 31.43 22.71 18.45

24.50 22.32 18.79 15.49 13.92 11.88 10.12 6.74

a

Standard uncertainties u are u(T) = 0.1 K, u(p) = 1 kPa, u(x1) = 0.001, and u(x2) = 0.001.

toluene and heptane, respectively, and the summations are extended to the whole range of data points. During the parameters regression, each component in both phase activity was assumed to be equal. Assuming equilibrium in the liquid phase, the referring equation is xiI =

γi II γi I

xiII

(2)

where xIi and xIIi are the concentrations of component i in the upper and lower layers, respectively, and γIi and γIIi are the activity coefficients of component i in the upper and lower layers, respectively. The fitting parameters and root-mean-square deviations, σ, are given in Table 3. The root-mean-square deviation was calculated by using the equation ⎛ ∑ (x exptl − x calc)2 ⎞1/2 ilm ilm ⎟⎟ σ = 100⎜⎜ 6 k ⎝ ⎠

Figure 2. Experimental and calculated LLE data in mole fraction for the ternary systems at T = 298.2 K and atmospheric pressure: (a) toluene (1) + heptane (2) + [MMIM][DMP] (3), (b) toluene (1) + heptane (2) + [EMIM][DEP] (4), and (c) toluene (1) + heptane (2) + [BMIM][DBP] (5). Solid lines and full points represent experimental tie-lines, and dashed lines and empty squares represent calculated data by the NRTL model.

respectively, and superscripts exptl and calc represent the experimental and calculated values, respectively. From the low values of σ presented in Table 3, it can be inferred that the NRTL model can fit the experimental result with a high degree of accuracy. In addition, for a visual confirmation, the

(3)

where x is the concentration (i.e., mole fraction), k represents the number of experimental tie-lines, subscripts i, l, and m represent the component, the phase, and the tie-lines, 1778

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Table 3. Binary Interaction Parameters Δgij and Δgji, Nonrandomness Factor αij, and Root-Mean-Square Deviations σ Obtained from the Correlation of the Experimental Liquid−Liquid Equilibrium Data of the Studied Ternary Systems by the NRTL Model at T = 298.2 K and p = 101.3 kPa i−j

Δgij

Δgji

J·mol−1

J·mol−1

αij

toluene (1) + heptane (2) + [MMIM][DMP] (3) 28342.8 2453.1 0.254 84666.6 3898.1 0.111 −6949.5 28334.6 0.210 toluene (1) + heptane (2) + [EMIM][DEP] (4) 44867.9 3269.8 0.176 72457.8 4507.5 0.123 −12920.3 38395.4 0.116 toluene (1) + heptane (2) + [BMIM][DBP] (5) 9965.1 2642.6 0.457 8379.3 2621.0 0.348 743.8 11532.7 0.391

1−2 1−3 2−3 1−2 1−3 2−3 1−2 1−3 2−3

σ 0.190

0.212

0.179

experimental result and those calculated by means of the NRTL model are shown in Figure 2, where the fitness of the correlations can also be confirmed. Solute Distribution Ratio and Selectivity. To assess the extraction capability of the studied ILs as solvents, toluene/ solute distribution ratios and toluene/heptane selectivities are also listed in Table 2. The solute distribution ratio parameter provides an insight into the amount of IL that is required for an extraction process. The selectivity is also an important parameter that is widely used to assess the possibility of using IL in liquid−liquid extraction. Obtaining high values of both parameters ensures that an IL is a good candidate for an extraction process. The toluene solute distribution ratios β and toluene/heptane selectivities S are defined as

β=

S=

Figure 3. (a) Toluene solute distribution ratios β and (b) toluene/ heptane selectivities S a function of the mole fraction of toluene in the upper layer xI1 for the ternary system {toluene (1) + heptane (2) + solvent (3)} at T = 298.2 K and atmospheric pressure. Solvents: ■, [MMIM][DMP]; ●, [EMIM][DEP]; ▲, [BMIM][DBP]; ◊, sulfolane from ref 6 at T = 313.2 K; □, [MMIM][MeSO4] from ref 6 at T = 313.2 K; ⊕, [EMIM][OAc] from ref 8 at T = 298.15 K; ○, [EMIM][DCA] from ref 7 at T = 313.2 K; and Δ, [BMIM][DCA] from ref at T = 313.2 K.

x1II x1I

(4)

x1IIx 2I x1Ix 2II

xI1

(5)

3a, the values of β for the ILs with the same cation but different anion followed this order: [MMIM][DMP] > [MMIM][MeSO4], [EMIM][DEP] > [EMIM][DCA] > [EMIM][OAc], [BMIM][DBP] > [BMIM][DCA]. However, the toluene/ solute distribution ratios for the studied systems were always less than unity, which meant that large amounts of IL are needed for the extraction of toluene from heptane. The capacities of the ILs to separate toluene and heptane in the extraction process are likely related to the Kamlet−Taft solvent parameters.19 For the system of toluene and heptane, the extraction capabilities of ILs are probably mainly dependent on the polarity/polarizability (π*).20,21 The values of π* for imidazolium-based ILs with the same cation but different anion decreased in the order [BMIM][DCA] (1.052) > [BMIM][MeSO4] (1.046) > [BMIM][DMP] (0.976) > [BMIM][OAc] (0.971).19,22 As shown in Figure 3b, comparing the systems {toluene (1) + heptane (2) + solvent (3)}, it is interesting to notice that the values of S decrease in the following order: [EMIM][DCA] ≥ [MMIM][DMP] ≥ [MMIM][MeSO4] > [EMIM][DEP] > [BMIM][DCA] > [EMIM][OAc] > [BMIM][DBP] ≥ sulfolane. This order shows that the alkyl

xI2

where and are the concentrations of toluene and heptane in the upper layer (i.e., heptane-rich phase), respectively, and xII1 and xII2 are the concentrations of toluene and heptane in the lower layer (i.e., IL-rich phase), respectively. The toluene/solute distribution ratios and toluene/heptane selectivities for the studied systems as a function of the mole fraction of toluene in the upper layer are plotted in Figure 3. In addition, comparisons with published data for sulfolane and other ILs with a similar cation but varying anion are also displayed.6−8 As observed in Figure 3a, the values of β for the studied ternary systems decreased as the concentration of toluene in the upper layer increased, and the values of β for the studied ILs decreased as follows: [BMIM][DBP] > [EMIM][DEP] > [MMIM][DMP], which showed that the increase of the alkyl length chain for the ILs studied would lead to an increase of toluene solubility in the lower layer. This result is in agreement with the trend observed in imidazolium-based ILs formed by dicyanamide anion.7 Additionally, the studied ILs showed higher values of β than those of sulfolane with lower toluene composition. Finally, as it can be observed from Figure 1779

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the Unique, Doubly Dual Nature of Ionic Liquids from a Molecular Thermodynamic and Modeling Standpoint. Acc. Chem. Res. 2007, 40, 1114−1121. (5) Han, X.; Armstrong, D. W. Ionic Liquids in Separations. Acc. Chem. Res. 2007, 40, 1079−1086. (6) Meindersma, G. W.; Podt, A.; de Haan, A. B. Ternary Liquid− Liquid Equilibria for Mixtures of Toluene + n-Heptane + an Ionic Liquid. Fluid Phase Equilib. 2006, 247, 158−168. (7) Larriba, M.; Navarro, P.; García, J.; Rodríguez, F. Liquid−Liquid Extraction of Toluene from Heptane Using [emim][DCA], [bmim][DCA], and [emim][TCM] Ionic Liquids. Ind. Eng. Chem. Res. 2013, 52, 2714−2720. (8) Corderí, S.; Gómez, E.; Calvar, N.; Domínguez, Á . Measurement and Correlation of Liquid−Liquid Equilibria for Ternary and Quaternary Systems of Heptane, Cyclohexane, Toluene, and [EMim][OAc] at 298.15 K. Ind. Eng. Chem. Res. 2014, 53, 9471−9477. (9) Ebrahimi, M.; Ahmadi, A. N.; Safekordi, A. A.; Fateminasab, F.; Mehdizadeh, A. Liquid−Liquid Equilibrium Data for {Heptane + Aromatic + 1-(2-Hydroxyethyl)-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide ([hemim][NTf2])} Ternary Systems. J. Chem. Eng. Data 2014, 59, 197−204. (10) Renon, H.; Prausnitz, J. M. Local Compositions in Thermodynamic Excess Functions for Liquid Mixtures. AIChE J. 1968, 14, 136−144. (11) Zhou, Y.; Robertson, A. J.; Hillhouse, J. H.; Baumann, D. U.S. Patent No. 20060264645 A1, 2006. (12) Mirkhani, S. A.; Vossoughi, M.; Pazuki, G. R.; Safekordi, A. A.; Heydari, A.; Akbari, J.; Yavari, M. Liquid + Liquid) Equilibrium for Ternary Mixtures of {Heptane + Aromatic Compounds + [EMpy][ESO4]} at T = 298.15 K. J. Chem. Thermodyn. 2011, 43, 1530−1534. (13) Orchillés, A. V.; Miguel, P. J.; Vercher, E.; Martínez-Andreu, A. Isobaric Vapor−Liquid Equilibria for 1-Propanol + Water + 1-Ethyl-3methylimidazolium Trifluoromethanesulfonate at 100 kPa. J. Chem. Eng. Data 2008, 53, 2426−2431. (14) Orchillés, A. V.; Miguel, P. J.; Vercher, E.; Martínez-Andreu, A. Using 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate as an Entrainer for the Extractive Distillation of Ethanol + Water Mixtures. J. Chem. Eng. Data 2010, 55, 1669−1674. (15) Orchillés, A. V.; Miguel, P. J.; González-Alfaro, V.; Vercher, E.; Martínez-Andreu, A. Isobaric Vapor−Liquid Equilibria of 1-Propanol + Water + Trifluoromethanesulfonate-Based Ionic Liquid Ternary Systems at 100 kPa. J. Chem. Eng. Data 2011, 56, 4454−4460. (16) Orchillés, A. V.; Miguel, P. J.; González-Alfaro, V.; Vercher, E.; Martínez-Andreu, A. 1-Ethyl-3-methylimidazolium Dicyanamide as a Very Efficient Entrainer for the Extractive Distillation of the Acetone + Methanol System. J. Chem. Eng. Data 2012, 57, 394−399. (17) Vercher, E.; Rojo, F. J.; Martínez-Andreu, A. Isobaric Vapor− Liquid Equilibria for 1-Propanol + Water + Calcium Nitrate. J. Chem. Eng. Data 1999, 44, 1216−1221. (18) Pereiro, A. B.; Rodríguez, A. Phase Equilibria of the Azeotropic Mixture Hexane + Ethyl Acetate with Ionic Liquids at 298.15 K. J. Chem. Eng. Data 2008, 53, 1360−1366. (19) Palgunadi, J.; Hong, S. Y.; Lee, J. K.; Lee, H.; Lee, S. D.; Cheong, M.; Kim, H. S. Correlation between Hydrogen Bond Basicity and Acetylene Solubility in Room Temperature Ionic Liquids. J. Phys. Chem. B 2011, 115, 1067−1074. (20) García, J.; García, S.; Torrecilla, J. S.; Oliet, M.; Rodríguez, F. Separation of Toluene and Heptane by Liquid−Liquid Extraction Using z-Methyl-N-butylpyridinium Tetrafluoroborate Isomers (z = 2, 3, or 4) at T = 313.2 K. J. Chem. Thermodyn. 2010, 42, 1004−1008. (21) Dukhande, V. A.; Choksi, T. S.; Sabnis, S. U.; Patwardhan, A. W.; Patwardhan, A. V. Separation of Toluene from n-Heptane Using Monocationic and Dicationic Ionic Liquids. Fluid Phase Equilib. 2013, 342, 75−81. (22) Brandt, A.; Hallett, J. P.; Leak, D. J.; Murphy, R. J.; Welton, T. The Effect of the Ionic Liquid Anion in the Pretreatment of Pine Wood Chips. Green Chem. 2010, 12, 672−679.

chain length of the imidazolium-based ILs negatively affects the capacity of the ILs as solvents to separate toluene and heptane. This is similar to the effect of the alkyl chain length of ILs on the extractive capacity for the system of toluene and heptane in the literature.6,7 In any case, taken into consideration the values of S, it can be inferred that the IL [MMIM][DMP] could be considered the best choice among the ILs studied to act as a solvent for the extraction of toluene from heptane.

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CONCLUSIONS In this study, the feasibility of using three dialkylphosphatebased ILs as toluene extraction solvents was analyzed. For this purpose, the experimental LLE data for the systems, {toluene (1) + heptane (2) + [MMIM][DMP] (3)}, {toluene (1) + heptane (2) + [EMIM][DEP] (4)}, and {toluene (1) + heptane (2) + [BMIM][DBP] (5)} were determined at T = 298.2 K and atmospheric pressure. The NRTL model showed satisfactory results in the correlation of the experimental LLE data for the studied ternary systems. From the experimental LLE data, the toluene/solute distribution ratios β and selectivities S of toluene/heptane were calculated and compared with those of other solvents obtained from literature. Both parameters for the studied ternary systems studied decreased with an increase of the mole fraction of toluene in the upper layer. Because of the low values of β (i.e., β < 1) for the studied ILs, large quantities of the ILs would be required for the extraction process, but that should not be considered a disadvantage because of the recyclability of the ILs. In addition, the values of S for the studied ILs decreased in the order [MMIM][DMP] > [EMIM][DEP] > [BMIM][DBP]. Finally, the values of S were found to be greater than unity for the studied ternary systems, which confirmed that the ILs investigated could be used as possible solvents for the extraction separation of toluene and heptane.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-25-5209-0612. Fax: +86-25-5209-0612. E-mail: [email protected]. Funding

This work was financially supported by the Scientific Research Foundation of Graduate School of Southeast University (YBJJ1530) and the National Natural Science Foundation of China (nos. 21276050 and 21076044). The authors gratefully acknowledge these grants. Notes

The authors declare no competing financial interest.

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REFERENCES

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DOI: 10.1021/je501170h J. Chem. Eng. Data 2015, 60, 1776−1780