Liquid–liquid extraction of toluene from heptane by {[4bmpy][Tf2N] + [emim][CHF2CF2SO3]} ionic liquid mixed solvents

Fluid Phase Equilibria 337 (2013) 47–52

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Liquid–liquid extraction of toluene from heptane by {[4bmpy][Tf2 N] + [emim][CHF2 CF2 SO3 ]} ionic liquid mixed solvents Silvia García, Julián García ∗ , Marcos Larriba, Ana Casas, Francisco Rodríguez Department of Chemical Engineering, Complutense University of Madrid, E-28040 Madrid, Spain

a r t i c l e

i n f o

Article history: Received 18 May 2012 Received in revised form 5 September 2012 Accepted 10 September 2012 Available online 18 September 2012 Keywords: Aromatic/aliphatic separation Liquid–liquid equilibria Ionic liquids Mixed solvents

a b s t r a c t Extraction of toluene from heptane at T = 313.2 K and atmospheric pressure using a mixed solvent composed of the ionic liquids 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2 N]) and 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate ([emim][CHF2 CF2 SO3 ]) has been considered in this study. The results show that for a mole fraction of 0.3 for [4bmpy][Tf2 N] the values of the capacity of extraction of toluene and the selectivity of the mixed solvent are higher than those of sulfolane for the whole range of compositions, taken this organic solvent as a benchmark. Therefore, this mixture of ILs could be an alternative to sulfolane in the liquid–liquid extraction of toluene from heptane. © 2012 Elsevier B.V. All rights reserved.

1. Introduction During recent years, there have been a great variety of studies focused on the use of ionic liquids (ILs) as solvent for the liquid–liquid extraction process of aromatic hydrocarbons from aliphatics [1]. These studies have been carried out in an attempt to find out alternatives to the current organic compounds used as solvents such as sulfolane, and thus improve both the economy and the environmental aspects of the process [2,3]. An IL could be a good solvent to substitute sulfolane if it shows selectivity and capacity of extraction higher than those of this organic solvent. However, among the ILs thus far investigated, only a few meet these two requisites [1]. In this context, our research group has recently proposed the use of binary mixtures of ILs for the liquid–liquid extraction of aromatics from aliphatics [4,5]. Our previous results showed that mixed ILs solvent could be used to balance between selectivity and capacity of extraction. In particular, mixing an IL with high capacity of extraction of aromatics with another IL with high selectivity could be achieve an intermediate situation in which both extractive properties were higher than those of sulfolane. Moreover, mixing ILs could optimize other designer properties such as density and viscosity [6]. Bearing these aspects in mind, and as a continuation of our previous work, the aim of this paper was to study the liquid–liquid

∗ Corresponding author. Tel.: +34 91 394 51 19; fax: +34 91 394 42 43. E-mail address: [email protected] (J. García). 0378-3812/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fluid.2012.09.008

extraction of toluene from heptane at 313.2 K and atmospheric pressure using a mixed solvent composed of the 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2 N]) IL and the 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate ([emim][CHF2 CF2 SO3 ]) IL. These ILs have been selected because of the low selectivity and the high extractive capacity showed by the [4bmpy][Tf2 N] IL [7], and the opposite occurred for the [emim][CHF2 CF2 SO3 ] IL [8]. Firstly, we have explored the influence of solvent composition on selectivity and capacity of extraction of toluene for a toluene/heptane feed containing 10.5% molar of toluene. Based on these results, we have determined the liquid–liquid equilibria (LLE) for the pseudoternary system {heptane + toluene + ([4bmpy][Tf2 N] + [emim][CHF2 CF2 SO3 ])} with a fixed solvent molar composition of 0.3 for the [4bmpy][Tf2 N] IL. The selectivity and the capacity of extraction were calculated from the LLE data. The quality of the experimental LLE data was ascertained using the Othmer–Tobias correlation. In addition, the phase diagram was plotted and the LLE data were correlated by the nonrandom two-liquid (NRTL) model.

2. Experimental 2.1. Chemicals Toluene and heptane over molecular sieves were supplied by Sigma–Aldrich with mass fraction purity greater than 0.995 and 0.997, respectively. Their water mass fractions were less than 0.00005. The ILs 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2 N]) and 1-ethyl-3-methylimidazolium

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S. García et al. / Fluid Phase Equilibria 337 (2013) 47–52

Table 1 Sample description. Chemical name

Source

Mass fraction purity

Analysis method

Toluene Heptane [4bmpy][Tf2 N]a [emim][CHF2 CF2 SO3 ]b

Sigma–Aldrich Sigma–Aldrich Iolitec GmbH Iolitec GmbH

0.995 0.997 0.99 0.99

GCc GCc NMRd and ICe NMRd and ICe

a b c d e

[4bmpy][Tf2 N] = 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide. [emim][CHF2 CF2 SO3 ] = 1-ethyl-3-methylimidazolium 1,1,2,2-tetrafluoroethanesulfonate. Gas chromatography. Nuclear magnetic resonance. Ion chromatography.

1,1,2,2-tetrafluoroethanesulfonate ([emim][CHF2 CF2 SO3 ]) were provided by Iolitec GmbH with quoted mass fraction purities greater than 0.99, and halides and water mass fractions less than 1 × 10−4 . Water content and purity of the reagents were given by the manufacturer. All chemicals were used as received without further purification. Specifications of the chemicals used in this work are gathered in Table 1. To prevent water hydration, they were kept in their original tightly closed bottles in a desiccator. When any chemicals were used, they were always manipulated inside a glove box under a dry nitrogen atmosphere.

through weighing with an electronic balance having a precision of ±0.0001 g. Toluene in the mixture was chosen as the standard, and its response factor was set to 1.0. The response factor for heptane was then calculated using the renormalization method before every run of samples to ensure measurement accuracy. Samples were taken in triplicate and each of them injected six times in the GC. The average compositions are the ones reported here. The maximum estimated uncertainties in the compositions, calculated by the standard deviation of the measurements or the propagation of uncertainty, are shown in Tables 2 and 3. 3. Results and discussion

2.2. Experimental procedure and analysis

3.1. Screening LLE experiments with mixed {[4bmpy][Tf2 N] + [emim][CHF2 CF2 SO3 ]} ILs

The LLE experiments were performed in 8 mL vials with screw caps providing hermetic sealing. Mixtures of known masses of toluene/heptane feed were transferred to tared vials. After the vials were reweighed the pure or mixed IL was gravimetrically added to the feed. The vials were then placed in a shaking incubator at 313.2 K with a shaking speed of 800 rpm for 5 h and then settled overnight. This was carried out according to the procedure previously reported [9]. The estimated error in the mole fraction in the prepared feed mixture was less than 0.001. Samples from the n-heptane-rich phase were analyzed by 1 H NMR. The spectra showed no detectable signals arising from the mixture of ILs, so the ILs mole fractions in the heptane-rich phases appear to be negligible. Thus, gas chromatographic analyses of each layer plus an overall mass balance on hydrocarbons in the mixture were done to determine the phase compositions. Because of the nonvolatile nature of the ILs, a precolumn was needed in the gas chromatograph to collect the pure or mixed ILs present in the lower layer in order not to disrupt the analysis. A detailed description of the equipments and the analysis conditions can be found elsewhere [9]. An area normalization method with response factors was carried out to determine the hydrocarbon molar ratio in each layer. The gas chromatography response factors for the hydrocarbons were calculated by using standard mixture samples of pure heptane and toluene. The compositions of these standard samples were obtained

The LLE data for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at 313.2 K, atmospheric pressure, and several [4bmpy][Tf2 N] mole fractions in the mixed IL solvent (˚3 ) are shown in Table 2. The influence of the IL binary mixture composition on capacity of extraction of heptane and toluene, and selectivity was evaluated by the distribution ratio of heptane and toluene, D1 and D2 , respectively, and the separation factor, ˛2,1 . The values of D1 , D2 , and ˛2,1 are also shown in Table 2, and they were calculated from the experimental LLE data as follows: D1 =

D2 =

x1II

(1)

x1I x2II

(2)

x2I

˛2,1 =

x2II x1I x2I x1II

=

D2 D1

(3)

where x is the mole fraction, superscripts I and II refer to the heptane-rich and IL-rich phases, respectively, and subscripts 1 and 2 to heptane and toluene, respectively.

Table 2 Experimental LLE data on mole fraction (x), distribution ratios (Di ), and separation factors (˛2,1 ) as a function of [4bmpy][Tf2 N] mole fraction in the mixed IL solvent (˚3 ) for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 (4)]} at T = 313.2 K, and atmospheric pressure (10.5% molar of toluene in feed and solvent-to-feed ratio of 0.9).a [4bmpy][Tf2 N] in solvent

Heptane-rich phase (upper layer)

IL-rich phase (low layer)

˚3

x1I

x2I

x1II

x2II

x3II

x4II

0.00 0.20 0.40 0.60 0.80 1.00

0.9141 0.9248 0.9343 0.9425 0.9506 0.9559

0.0859 0.0752 0.0657 0.0575 0.0494 0.0441

0.0051 0.0103 0.0201 0.0334 0.0500 0.0571

0.0248 0.0309 0.0414 0.0496 0.0571 0.0615

0.0000 0.1918 0.3765 0.5506 0.7159 0.8814

0.9701 0.7670 0.5621 0.3664 0.1770 0.0000

a

Standard uncertainties (u) are: u(T) = 0.1 K; u(xiI ) = 0.0016; u(x1II ) = 0.0023; u(x2II ) = 0.0034.

D1

D2

˛2,1

0.006 0.011 0.021 0.035 0.053 0.060

0.288 0.411 0.631 0.863 1.155 1.394

51.8 36.9 29.4 24.4 22.0 23.3

S. García et al. / Fluid Phase Equilibria 337 (2013) 47–52

49

Table 3 Experimental LLE data in mole fraction (x), distribution ratios (Di ), and separation factors (˛2,1 ), for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ]} at ˚3 = 0.3, T = 313.2 K, and atmospheric pressure.a Feed (global composition)

Heptane-rich phase (upper layer)

IL-rich phase (lower layer)

x10

x20

x1I

x2I

x1II

x2II

0.5014 0.4883 0.4745 0.4439 0.4062 0.3514 0.3102 0.2767 0.2303 0.1753 0.1221 0.0000

0.0000 0.0263 0.0534 0.1151 0.1902 0.2984 0.3835 0.4483 0.5419 0.6502 0.7564 0.8510

1.0000 0.9655 0.9281 0.8493 0.7545 0.6263 0.5242 0.4518 0.3565 0.2439 0.1522 0.0000

0.0000 0.0345 0.0719 0.1507 0.2455 0.3737 0.4758 0.5482 0.6435 0.7561 0.8478 1.0000

0.0178 0.0150 0.0136 0.0145 0.0159 0.0143 0.0155 0.0152 0.0164 0.0119 0.0087 0.0000

0.0000 0.0181 0.0346 0.0774 0.1281 0.2060 0.2563 0.2991 0.3696 0.3980 0.4114 0.4969

a

D1

0.018 0.016 0.015 0.017 0.021 0.023 0.030 0.034 0.046 0.049 0.057

D2

˛2,1

0.525 0.481 0.514 0.522 0.551 0.539 0.546 0.574 0.526 0.485 0.497

33.8 32.8 30.1 24.8 24.1 18.2 16.2 12.5 10.8 8.5

Standard uncertainties (u) are: u(T) = 0.1 K, u(xiI ) = 0.0023; u(x1II ) = 0.0012; u(x2II ) = 0.0098.

As can be seen in Table 2, no IL was detected in the heptanerich phase. This behavior is the same as previously reported for the pure ILs [7,8]. Thus, no extra operation will be needed to purify the raffinate phase for recovering the solvent if a binary mixture of these ILs is used for industrial aromatic extraction purposes. The values of distribution ratio of toluene (D2 ) and the separation factor (˛2,1 ) are plotted in Fig. 1 versus the [4bmpy][Tf2 N] mole fraction in the mixed IL solvent (˚3 ). These results were compared with those of sulfolane [10] and also with those obtained from the toluene and heptane solubilities in ideal mixed IL solutions calculated as follows: I or II = ln xi,ideal



I or II ˚j · ln xi,j

(4)

j

where x is the mole fraction, ˚ is the mixed IL composition in mole fraction, superscripts I and II refer to the heptane-rich and IL-rich phases, subscript i to heptane or toluene, and subscript j to the pure ILs. Thus, the ideal solubility of heptane or toluene in a mixed IL solvent is calculated from the solubility of heptane or toluene in the pure ILs and the mole fraction of each IL in the mixed solvent. The logarithmic-linear model from Eq. (4) was derived from the equilibrium conditions of a solute dissolved in two phases and the expression for the chemical potential of a solute in a

mixture of solvents [11]. As Maitra and Bagchi suggested [12], an ideal model is usually suitable when the values of solubility versus solvent composition show no maximum. This fact can be observed in the experimental LLE data in Table 2. On the other hand, as the toluene and heptane are dissolved in the mixed IL, compositions of toluene and heptane are modified in the heptane-rich phase because both phases are conjugate. This justifies the application of the logarithmic-linear model for the compositions of heptane and toluene in the heptane-rich phase for calculating the ideal compositions. As can be observed in Fig. 1, the experimental values of D2 and ˛2,1 for all the compositions for the binary mixture {[4bmpy][Tf2 N] + [emim][CHF2 CF2 SO3 ]} follow the same trend as those calculated by the logarithmic-linear model. Hence, the solubility of heptane and toluene in the binary mixture of ILs {[4bmpy][Tf2 N] + [emim][CHF2 CF2 SO3 ]} could be consider ideal. In addition, it can be observed in Fig. 1 that for a [4bmpy][Tf2 N] mole fraction in the mixed IL solvent around 0.3 the values of D2 and ˛2,1 are higher than those of sulfolane. Consequently, this IL mixed solvent can simultaneously reach better results for the two extractives properties than those of sulfolane for a particular molar composition of the mixed ILs. Thus, we have chosen ˚3 = 0.3 as an intermediate composition to study the LLE for all the toluene/heptane compositions.

120.0

1.54

105.0

1.32

90.0

1.10

75.0

0.88

D2

60.0 0.66

45.0

0.44

30.0

0.22

15.0 0.0 0.00

0.20

0.40

0.60

0.80

0.00 1.00

Fig. 1. Separation factors () and distribution ratios of toluene (♦) versus [4bmpy][Tf2 N] mole fraction in the mixed IL solvent (˚3 ) for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at T = 313.2 K, and atmospheric pressure (10.5% molar of toluene in feed and solvent-to-feed ratio of 0.9). The dashed line represents the separation factor and distribution ratio of sulfolane at the same conditions [10]. The solid lines represent the separation factors and distribution ratios for the mixed IL solvents following the ideal behavior defined by Eq. (4).

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S. García et al. / Fluid Phase Equilibria 337 (2013) 47–52

0.00 1.00

0.15

0.25

0.75

0.50

D1

ne

He

l ue

pta

To

ne

0.10

0.50

0.75

0.05

0.25

0.00 0.00

0.20

0.40

0.60

0.80

1.00

x2I 1.00 0.00

0.25

0.50

0.00 1.00

0.75

[4bmpy][Tf2N] + [emim][CHF2CF2SO3] Fig. 2. Experimental and calculated LLE data in mole fraction (x) of pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] the (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3, T = 313.2 K, and atmospheric pressure. Solid lines and full points indicate experimental tie lines, and dashed lines and empty squares indicate calculated data by the NRTL model.

3.2. LLE of the pseudoternary system {heptane (1) + toluene (2) + [4bpmy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3 3.2.1. Experimental LLE data The experimental LLE data for the pseudoternary {heptane (1) + toluene (2) + [4bmpy][Tf2 N] system (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3 at 313.2 K and atmospheric pressure are given in Table 3 and plotted on a triangular diagram in Fig. 2. As can be seen, the upper layer (heptane-rich phase) is totally free of ILs for all the toluene/heptane compositions. On the other hand, it can be observed that toluene has a higher affinity toward heptane than toward the binary mixture of ILs, as shown the negative slopes of the tie lines on the triangular diagram. The reliability of the experimentally measured LLE data can be ascertained by applying the Othmer–Tobias correlation [13]:



ln

II 1 − w(3+4) II w(3+4)



 = a + b ln

1 − w1I

 (5)

w1I

Fig. 4. Distribution ratio of heptane at T = 313.2 K and atmospheric pressure for the systems: () {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)}, ˚3 = 0.3; (䊉) {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3)} [7]; () {heptane ) {n-heptane (1) + toluene (1) + toluene (2) + [emim][CHF2 CF2 SO3 ] (3)} [8]; ( (2) + sulfolane (3)} [10].

II where w(3+4) is the mass fraction of the mixed IL (3 + 4) in the

lower layer (IL-rich phase), considered as a pseudo-component, w1I is the mass fraction of heptane (1) in the upper layer (heptane-rich phase), and a and b are the fitting parameters of the Othmer–Tobias correlation. The linearity of the plot, shown in Fig. 3, the regression coefficients close to unity (R2 = 0.9665), and the small values of the standard deviation ( = 0.3213) indicate the degree of quality of the experimental LLE data. The parameters of the Othmer–Tobias correlation are a = −2.3001 and b = 0.6669. 3.2.2. Distribution ratios and separation factor The comparison of the distribution ratios of heptane and toluene and the separation factors of the binary mixture of ILs {[4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3 with those of sulfolane [10] let evaluate the potential of this binary mixture of ILs as solvent in the liquid–liquid extraction of toluene from heptane. D1 , D2 , and ˛2,1 have been calculated from the experimental LLE data with Eqs. (1)–(3). Their values are shown in Table 3 together with the LLE data. The distribution ratios of toluene and heptane, and the separation factor versus the toluene mole fraction in the heptane-rich phase (x2I ) are plotted in Figs. 4–6, together with the distribution

ln [(1-w(3+4)II)/w(3+4)II]

-5.00

-4.00

-3.00

-2.00

-1.00

0.00 2.00

1.00

0.00

-1.00

-2.00

-3.00

-4.00

ln [(1-w1I)/w1I] Fig. 3. Othmer–Tobias plot for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3, T = 313.2 K, and atmospheric pressure. Solid lines represent the linear Othmer–Tobias fit.

S. García et al. / Fluid Phase Equilibria 337 (2013) 47–52

2.00

51

Table 4 Values of the NRTL parameters regressed from LLE data for the pseudoternary system {n-heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3, T = 313.2 K, and atmospheric pressure.

1.60

x

NRTL parameters

i−j

(gij /R)/K

(gji /R)/K

˛ij

0.80

1−2 1 − (3 + 4) 2 − (3 + 4)

231.65 −555.90 2037.9

448.46 910.02 −920.80

0.2229 0.4772 0.0607

D2

Component

1.20

0.40 0.00 0.00

0.20

0.40

x2I

0.60

0.80

1.00

Fig. 5. Distribution ratio of toluene at T = 313.2 K and atmospheric pressure for the systems: () {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)}, ˚3 = 0.3; (䊉) {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3)} [7]; () {heptane ) {n-heptane (1) + toluene (1) + toluene (2) + [emim][CHF2 CF2 SO3 ] (3)} [8]; ( (2) + sulfolane (3)} [10].

ratios and separation factor of sulfolane [10] and also those for the pure ILs [4bmpy][Tf2 N] and [emim][CHF2 CF2 SO3 ] [7,8]. As can be seen in Figs. 4–6, the distribution ratios and separation factor for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3 show values between those corresponding to the pure ILs on the whole range of compositions. This is in consistency with the idea that mixing two ILs could lead to values of capacity of extraction and selectivity between those shown by the ILs individually. In addition, the values of D2 and ˛2,1 are higher than those of sulfolane in the whole range of compositions (Figs. 5 and 6). Thus, the binary mixture of ILs {[4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)} at ˚3 = 0.3 could be considered an alternative to this organic solvent for the liquid–liquid extraction of toluene from heptane. 3.2.3. Correlation of LLE data The NRTL model [14] was used to correlate the LLE data in the present work, as it has proven an adequate correlating capability with respect to ternary LLE data for systems containing ILs [15]. The binary mixture of solvents has been considered as a pseudocomponent. In this model, the two binary interaction parameters gij /R and gji /R were calculated using an ASPEN Plus simulator. The method used in the ASPEN simulator was the generalized 80.0

60.0

method based on maximum likelihood principles. The Britt–Luecke algorithm [16] was employed to obtain the model parameters with the Deming initialization method. The convergence tolerance was set to 0.0001. The value of the third nonrandomness parameter, ˛ij , in the NRTL model was subject to optimization between 0 and 1. Table 4 shows the values of the fitting parameters obtained using the NRTL model to correlate the experimental LLE data for the pseudoternary system. The calculated tie lines from the correlation based on the NRTL model are plotted in Fig. 2. The values of the root mean square deviation ( x ) for the pseudoternary system are listed also in Table 4. The  x is defined as follows:

   x =

i

l

exp tl

(x m ilm 6k

calc ) − xilm

2

1/2 (6)

where x is the mole fraction and the subscripts i, l and m provide a designation for the component, phase, and the tie lines, respectively. The value k designates the number of tie lines. It can be conclude from Fig. 2 and  x that the NRTL model correlates satisfactorily the experimental results for the LLE of the pseudoternary system. 4. Conclusions This work has been focused on the liquid–liquid extraction of toluene from heptane using binary mixtures of {[4bmpy][Tf2 N] + [emim][CHF2 CF2 SO3 ]} ILs at T = 313.2 K and atmospheric pressure. This mixture has been chosen to combine an IL with high capacity of extraction of toluene and another IL with high selectivity to achieve an intermediate situation in which both extractive properties were better than those of sulfolane. For a fixed composition of 10.5% molar of toluene in the toluene/heptane feed, we observed higher values of both extractive properties than those of sulfolane for a [4bmpy][Tf2 N] mole fraction around 0.3. Hence, this composition has been selected for studying the LLE for all toluene/heptane compositions. The results may us consider this binary mixture of ILs a potential substitute to sulfolane because of the higher capacity of extraction of toluene and separation factor comparing to those of the organic solvent. Acknowledgements

40.0

20.0

0.0 0.00

0.0037

0.20

0.40

0.60

0.80

1.00

x2I Fig. 6. Separation factors at T = 313.2 K and atmospheric pressure for the systems: () {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3) + [emim][CHF2 CF2 SO3 ] (4)}, ˚3 = 0.3; (䊉) {heptane (1) + toluene (2) + [4bmpy][Tf2 N] (3)} [7]; () {heptane ) {n-heptane (1) + toluene (1) + toluene (2) + [emim][CHF2 CF2 SO3 ] (3)} [8]; ( (2) + sulfolane (3)} [10].

The authors are grateful to the Ministerio de Economía y Competitividad of Spain (MINECO) and the Comunidad Autónoma de Madrid (CAM) for financial support of Projects CTQ2011-23533 and S2009/PPQ-1545, respectively. Silvia García also thanks MINECO for awarding her an FPI Grant (Reference BES-2009-014703) under the project CTQ2008-01591, and Marcos Larriba thanks Ministerio de Educación, Cultura y Deporte for awarding him an FPU grant (Reference AP-2010-0318). References [1] G.W. Meindersma, A.R. Hansmeier, A.B. de Haan, Ind. Eng. Chem. Res. 49 (2010) 7530–7540.

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