Separation of Toluene and Heptane by LiquidâLiquid Extraction Using

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Separation of Toluene and Heptane by Liquid−Liquid Extraction Using Binary Mixtures of the Ionic Liquids 1‑Butyl-4methylpyridinium Bis(trifluoromethylsulfonyl)imide and 1‑Ethyl-3methylimidazolium Ethylsulfate Silvia García, Marcos Larriba, Ana Casas, Julián García,* and Francisco Rodríguez Department of Chemical Engineering, Complutense University of Madrid, E-28040 Madrid, Spain ABSTRACT: The feasibility of the binary mixture of 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide and 1-ethyl-3-methylimidazolium ethylsulfate ({[4bmpy][Tf2N] + [emim][C2H5SO4]}) ionic liquids (ILs)) in the liquid−liquid extraction of toluene from heptane has been investigated at 313.2 K and atmospheric pressure. Toluene and heptane distribution ratios and toluene selectivity were obtained from the liquid−liquid equilibrium data for the pseudoternary system {heptane + toluene + ([4bmpy][Tf2N] + [emim][C2H5SO4])} and compared to those of sulfolane, the conventional organic solvent used in industry. Our results have revealed that an equimolar binary mixture of these ILs could be an environmentally friendly alternative to sulfolane.

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INTRODUCTION Aromatic hydrocarbons are important raw materials in the chemical and petrochemical industry for the manufacturing of a great variety of products, such as detergents or plastics.1 Liquid−liquid extraction is the most commonly employed process in the industry for isolating these aromatics compounds from aromatic/aliphatic mixtures. However, this process presents some problems from an environmental point of view and some economic disadvantages due to the volatility of the conventional organic solvents.2 To optimize this industrial process, the use of new solvents that can replace the current ones is being studied. Ionic liquids (ILs) combine some special properties to be studied as alternative solvents, such as an extremely low vapor pressure and a very low solubility in hydrocarbons.3 The requirements for an IL to be appropriate for use are a higher selectivity and a higher aromatic distribution ratio than those of sulfolane,4 taken this organic solvent as a benchmark. However, among the ILs investigated to date5−48 only a small number of them have shown higher values of both extractive properties than the sulfolane values.49 In a previous work, we proposed the use of binary mixtures of ILs to solve this problem.50 Our results showed that the combination of an IL with a high selectivity with an IL with a high extractive capacity in a specific composition could provide a solvent with both the selectivity and the aromatic distribution ratio better than those of sulfolane. In this paper, we have studied the separation of heptane and toluene by liquid−liquid extraction using a binary mixture of the ILs 1-butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2N]) and 1-ethyl3-methylimidazolium ethylsulfate ([emim][C2H5SO4]), which have previously shown a high toluene distribution ratio and a high selectivity, respectively.37,45 First, we have analyzed the © 2012 American Chemical Society

effect of the composition of the {[4bmpy][Tf2N] + [emim][C2H5SO4]} IL mixture on selectivity and distribution ratios for the extraction of toluene from toluene/heptane mixtures with 10.5 % of toluene in molar basis at 313.2 K. These conditions have chosen taking into account the limitations of organic solvents for extracting aromatics from petroleum streams when the composition is below 20 wt %.2 Starting from these results, liquid−liquid equilibrium (LLE) were obtained for the system {heptane + toluene + ([4bmpy][Tf2N] + [emim][C2H5SO4])} at 313.2 K with a molar composition of the mixed ILs of 0.5. The selectivity and the distribution ratios were calculated from the experimental LLE. The reliability of the experimental LLE data was checked using the Othmer−Tobias correlation. Moreover, the ternary phase diagram was plotted, and the LLE was adjusted to the nonrandom two-liquid (NRTL) model.

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EXPERIMENTAL SECTION Heptane and toluene over molecular sieves were purchased from Sigma-Aldrich with a mass fraction purity higher than 0.995 and 0.997, respectively. Their water content in mass fractions was less than 0.00005. 1-Butyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([4bmpy][Tf2N]) and 1ethyl-3-methylimidazolium ethylsulfate ([emim][C2H5SO4]) ILs were purchased from Iolitec GmbH with mass fraction purities higher than 0.99 and halides and water mass fractions less than 0.0001. The water content and purity of the ILs were measured by Iolitec GmbH. All chemicals were used as received without further purification. To avoid water absorption, they were stored in their original tightly closed vessels in a Received: April 16, 2012 Accepted: August 1, 2012 Published: August 9, 2012 2472

dx.doi.org/10.1021/je300635c | J. Chem. Eng. Data 2012, 57, 2472−2478

Journal of Chemical & Engineering Data

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Table 1. Experimental LLE Data on Mole Fraction (x), Distribution Ratios (Di), and Separation Factors (α2,1), as a Function of [4bmpy][Tf2N] Mole Fraction in the Mixed IL Solvent (Φ3) for the Pseudoternary System {Heptane (1) + Toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at 313.2 K (10.5 mol % of Toluene in Feed and Solvent-to-Feed Ratio of 0.9)a [4bmpy][Tf2N] in solvent

a

heptane-rich phase (upper layer)

IL-rich phase (lower layer)

Φ3

x1I

x2I

x1II

x2II

x3II

x4II

D1

D2

α2,1

0.00 0.20 0.40 0.60 0.80 1.00

0.9136 0.9208 0.9303 0.9389 0.9471 0.9562

0.0864 0.0792 0.0697 0.0611 0.0529 0.0438

0.0032 0.0094 0.0198 0.0348 0.0477 0.0655

0.0180 0.0267 0.0372 0.0462 0.0538 0.0616

0.0000 0.1935 0.3777 0.5542 0.7195 0.8729

0.9788 0.7705 0.5653 0.3647 0.1790 0.0000

0.004 0.010 0.021 0.037 0.050 0.068

0.208 0.337 0.534 0.757 1.016 1.408

59.0 33.1 25.1 20.4 20.1 20.6

Standard uncertainties (u) are: u(T) = 0.1 K, u(xiI) = 0.0008, u(x1II) = 0.0023, and u(x2II) = 0.0041.

Table 2. Experimental LLE Data in Mole Fraction (x), Distribution Ratios (Di), and Separation Factors (α2,1), for the Pseudoternary System {Heptane (1) + Toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5 and 313.2 Ka feed (global composition)

a

x10

0

x2

0.5015 0.4884 0.4748 0.4438 0.4134 0.3655 0.3144 0.2793 0.2401 0.1770 0.1235 0.0000

0.0000 0.0283 0.0534 0.1151 0.1755 0.2723 0.3692 0.4431 0.5214 0.6489 0.7526 0.8509

heptane-rich phase (upper layer)

ILs-rich phase (lower layer)

x1I

x2I

x1II

x2II

D1

1.0000 0.9676 0.9371 0.8640 0.7934 0.6748 0.5535 0.4698 0.3676 0.2414 0.1573 0.0000

0.0000 0.0324 0.0629 0.1360 0.2066 0.3252 0.4465 0.5302 0.6324 0.7586 0.8427 1.0000

0.0358 0.0286 0.0304 0.0297 0.0295 0.0271 0.0269 0.0259 0.0196 0.0158 0.0135 0.0000

0.0000 0.0243 0.0443 0.0944 0.1440 0.2144 0.2762 0.3272 0.3295 0.3742 0.4590 0.5682

0.036 0.029 0.032 0.034 0.037 0.040 0.049 0.055 0.053 0.066 0.086

D2

α2,1

0.750 0.704 0.694 0.697 0.659 0.619 0.617 0.521 0.493 0.545 0.568

25.4 21.7 20.2 18.7 16.4 12.7 11.2 9.8 7.5 6.4

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

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.50 A detailed description of the equipments and the analysis conditions can be found elsewhere.38 The mean 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 1 and 2.

desiccator. The handling of the chemicals was made in a glovebox filled with dry nitrogen. 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. The estimated error in the mole fraction in the prepared feed mixture was less than 0.001. Samples from the heptane-rich phase were analyzed by 1H NMR. The spectra showed no detectable signals arising from the ILs, so the IL 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 is needed in the gas chromatograph to collect the pure or mixed ILs present in the lower layer in order not to disrupt the analysis. 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 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

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RESULTS AND DISCUSSION

LLE Experiments with Mixed {[4bmpy][Tf2 N] + [emim][C2H5SO4]} ILs. The experimental LLE for the system {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at 313.2 K is presented in Table 1. For all tested mixed IL compositions a complete miscibility was found between the two ILs. To evaluate the extractive capacity and the selectivity of mixed {[4bmpy][Tf2N] + [emim][C2H5SO4]} ILs, the heptane and toluene distribution ratios (D1 and D2) and the separation factor (α2,1) were calculated. The values of D1, D2, and α2,1 are also shown in Table 1, and they were determined from the LLE with the following expressions:

D1 = 2473

x1II x1I

(1) dx.doi.org/10.1021/je300635c | J. Chem. Eng. Data 2012, 57, 2472−2478

Journal of Chemical & Engineering Data D2 =

α2,1 =

Article

x 2II x 2I

As toluene and heptane are dissolved in the binary IL mixture, compositions of toluene and heptane are modified in the hydrocarbon-rich phase. Therefore, the use of the logarithmic−linear model for the compositions of toluene and heptane in the hydrocarbon-rich phase is valid because both phases are conjugate. As can be seen in Figure 1, toluene distribution ratios over the whole range of composition of the {[4bmpy][Tf2N] + [emim][C2H5SO4]} IL are very closed to the values estimated from the logarithmic−linear model for an ideal IL mixture. However, the negative deviation from the ideality observed in the separation factor, around 30 %, may highlight deviations in the behavior of this binary IL mixture from the ideality. As observed also in Figure 1, the values of D2 and α2,1 are not simultaneously higher than those of sulfolane for neither of the compositions of the ILs mixture. We have chosen Φ3 = 0.5 to study the LLE over the whole range of toluene/heptane compositions because of that composition of the ILs mixture shows intermediate values of both extractive properties between the pure ILs. Moreover, for that composition of the binary mixture of the ILs, the value of D2 are higher than that of sulfolane, and the separation factor became similar to that of this organic solvent. Thus, we have also selected the equimolar composition of the mixture considering that an increase in the distribution ratio of toluene is more significant to the economy of the process than in the selectivity due to the high molecular weight of the ILs that form the binary mixture. However, it could have chosen another composition of the IL mixture depending on the selectivity or the capacity of extraction of interest. Hence, mixing ILs can be considered as a new way of obtaining IL-based solvents with the desired properties for a specific application. LLE of the Pseudoternary System {Heptane (1) + Toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5. The experimental LLE for the pseudoternary {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} system for Φ3 = 0.5 at 313.2 K are shown in Table 2 and represented in a ternary diagram in Figure 2. As can be observed, the presence of ILs was not

(2)

x 2IIx1I x 2Ix1II

(3)

where x is the mole fraction, superscripts I and II denote the heptane-rich and IL-rich phases, respectively, and subscripts 1 and 2 refer to heptane and toluene, respectively. As observed in Table 1, the presence of ILs was not detected in the hydrocarbon-rich phase. This behavior was previously observed for the pure ILs.37,45 Therefore, an industrial process which will use this binary IL mixture as a solvent would not require an additional operation for recovering the solvent from the raffinate phase. The values of toluene distribution ratio (D2) and the separation factor (α2,1) are graphically shown in Figure 1 versus

Figure 1. Separation factors (□) and distribution ratios of toluene (◊) vs [4bmpy][Tf2N] mole fraction in the mixed IL solvent (Φ3) for the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at 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 (from ref 9). The solid lines represent the separation factors and distribution ratios for the mixed IL solvents following the ideal behavior defined by eq 4.

the [4bmpy][Tf2N] mole fraction in the mixed IL solvent (Φ3). These extractive properties have been compared with those of sulfolane9 and also with those predicted from the heptane and toluene solubilities using the following logarithmic−linear model: ln xiIorII ,ideal =

∑ Φj ·ln xiIorII ,j j

(4)

where x denotes the mole fraction, Φ is the IL mole fraction in the mixed IL, 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. The logarithmic−linear model was derived from the equilibrium conditions of a solute dissolved in two phases and the equation of the chemical potential of a solute in a mixture of solvents.51 This model was previously applied for describing the solubility of gas solutes and poor solids in mixtures of solvents.51−58 As Maitra and Bagchi suggested,57 the use of the ideal model is adequate when there is not a maximum in the plot of solubility of a solute against solvent composition. As can be observed in Table 1, the solubilities of toluene and heptane as a function of [4bmpy][Tf2N] mole fraction in the mixed IL do not present a maximum.

Figure 2. Experimental and calculated LLE data in mole fraction (x) of the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5 and 313.2 K. Solid lines and full points indicate experimental tie lines, and dashed lines and empty squares indicate calculated data by the NRTL model. 2474



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In Table 4 the values of the adjusted parameters of the NRTL model for the pseudoternary system {heptane (1) +

detected in the hydrocarbon-rich phase in the whole range of toluene/heptane compositions. Furthermore, toluene has a higher affinity toward heptane than toward the binary IL mixture, as evidenced by the negative slopes of the tie lines on the ternary diagram. The reliability of the experimental LLE can be proved by using the Othmer−Tobias correlation:59 ⎛ 1 − w II ⎞ ⎛ 1 − wI ⎞ (3 + 4) 1 ⎟⎟ = a + b ln⎜ ⎟ ln⎜⎜ II I ⎝ w1 ⎠ ⎝ w(3 + 4) ⎠

Table 4. Values of the NRTL Parameters Regressed from LLE Data for the Pseudoternary System {Heptane (1) + Toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5 and 313.2 K component

(5)

where wII(3+4) denotes the mass fraction of the mixed ILs (3 + 4) in the IL-rich phase, considered as a pseudo-component, wI1 indicates the mass fraction of heptane (1) in the heptane-rich phase, and a and b are the adjusted parameters of the Othmer− Tobias correlation. As shown in Figure 3, the linearity of the

NRTL parameters

i−j

(Δgij /R)/K

(Δgji/R)/K

αij

σx

1−2 1−(3 + 4) 2−(3 + 4)

1075.3 −496.05 1977.4

2221.4 444.84 −1002.2

0.2806 0.3666 0.0127

0.0224

toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} are listed at Φ3 = 0.5. The predicted tie lines by the NRTL model are represented in Figure 2 along with the experimental data. The root-mean-square deviation (σx) is also shown in Table 4. The σx was determined with the following equation: exptl calc 2 ⎫1/2 ⎧ ) ⎪ − xilm ⎪ ∑ ∑ ∑ (x i l m ilm ⎬ σx = ⎨ ⎪ ⎪ 6k ⎩ ⎭

where x denotes the mole fraction and the subscripts i, l, and m refer to the component, phase, and the tie lines, respectively. The parameter k is the number of tie lines in the ternary diagram. As can be observed in Figure 2, the experimental LLE of the pseudoternary system {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5 was satisfactorily correlated to the NRTL model. The suitability of using the {[4bmpy][Tf2N] + [emim][C2H5SO4]} equimolar binary IL mixture as an alternative solvent for the liquid−liquid extraction of aromatic hydrocarbons was studied by the analysis of the toluene and heptane distribution ratios (Di) and the separation factor (α2,1). These extractive properties were determined from the experimental LLE with eqs 1 to 3. The values of D1, D2, and α2,1 are shown in Table 2 together with the experimental LLE results. Toluene and heptane distribution ratios and the separation factor against the mole fraction of toluene in the hydrocarbonrich phase (x2I) are graphically shown in Figures 4 to 6, along with the extractive properties of sulfolane.9 In the same figures,

Figure 3. Othmer−Tobias plot for the pseudoternary system {heptane (1) + toluene (2) + [4bmbpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5, 313.2 K, and atmospheric pressure. Solid lines represent the linear Othmer−Tobias fit.

plot, the regression coefficients (R2) are close to unity, and the small values of the standard deviation (σ) presented in Table 3 indicate the quality of the experimental LLE. The fitting parameters of the Othmer−Tobias equation are also given in Table 3. Table 3. Fitting Parameters of the Othmer−Tobias Correlation (a, b), Regression Coefficients (R2), and Standard Deviations (σ) for the Pseudoternary System {Heptane (1) + Toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)} at Φ3 = 0.5 and 313.2 K a

b

R2

σ

−2.1228

0.5588

0.9723

0.1861

(6)

The NRTL model60 was employed to fit the experimental LLE gathered in this work. This model has been able to reproduce the LLE data of mixtures containing ILs.61 Due to the total miscibility of the ILs, the {[4bmpy][Tf2N] + [emim][C2H5SO4]} IL mixture has been treated as a pseudocomponent. The two binary interaction parameters Δgij/R and Δgji/R were obtained using the ASPEN Plus simulation software. The regression method employed was the leastsquares method based on maximum likelihood principle. The Britt−Luecke algorithm62 was used to calculate the fitting parameters with the Deming initialization method. The value of the third nonrandomness parameter, αij, in the NRTL model was restricted to optimization between 0 and 1. The convergence of the iterative method was set to 0.0001.

Figure 4. Distribution ratio of heptane for the systems: ◆, {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)}, Φ3 = 0.5; ●, {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3)} (from ref 37); ▲, {heptane (1) + toluene (2) + [emim][C2H5SO4] (3)} (from ref 45); ∗, {heptane (1) + toluene (2) + sulfolane (3)} (from ref 9). 2475



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could be considered as an alternative solvent to sulfolane in the liquid−liquid extraction of toluene from heptane, although using the pure IL [4bmpy][Tf2N] achieved a better capacity of extraction. The study of other parameters such as density or viscosity would be interesting to finally consider the IL mixtures as a solvent for the extraction process.

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CONCLUSIONS The objective of this paper was to study the separation of toluene from heptane employing binary mixtures of {[4bmpy][Tf2N] + [emim][C2H5SO4]} ILs as solvents by liquid−liquid extraction. First, we have analyzed the effect of the composition of the binary IL mixtures on the toluene distribution ratio and selectivity for heptane/toluene mixtures with 10.5 % of toluene in molar basis at 313.2 K and atmospheric pressure. The results obtained show that the IL mixtures achieve certain values of extractive properties depending on its composition, and thus, mixing ILs can be a viable alternative to design new processes using IL-based solvents with specific properties. In addition, the equimolar composition of the binary mixture of ILs has been chosen to determine the LLE equilibrium and the extractive properties for heptane/toluene mixtures on the whole range of compositions, observing that the binary mixture of {[4bmpy][Tf2N] + [emim][C2H5SO4]} ILs could be a potential solvent for the separation of toluene from heptane for showing a higher capacity of extraction of toluene than that of sulfolane and similar separation factors to those of this organic solvent.

Figure 5. Distribution ratio of toluene for the systems: ◆, {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)}, Φ3 = 0.5; ●, {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3)} (from ref 37); ▲, {heptane (1) + toluene (2) + [emim][C2H5SO4] (3)} (from ref 45); ∗, {heptane (1) + toluene (2) + sulfolane (3)} (from ref 9).

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +34 91 394 51 19. Fax: +34 91 394 42 43. E-mail ́ address: [email protected] (Julián Garcia).

Figure 6. Separation factor for the systems: ◆, {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3) + [emim][C2H5SO4] (4)}, Φ3 = 0.5; ●, {heptane (1) + toluene (2) + [4bmpy][Tf2N] (3)} (from ref 37); ▲, {heptane (1) + toluene (2) + [emim][C2H5SO4] (3)} (from ref 45); ∗, {heptane (1) + toluene (2) + sulfolane (3)} (from ref 9).

Funding

The authors are grateful to the Ministerio de Economiá y Competitividad of Spain and the Comunidad Autónoma de Madrid for financial support of Projects CTQ2011-23533 and S2009/PPQ-1545, respectively. S.G. also thanks Ministerio de Ciencia e Innovación for awarding her an FPI Grant (Reference BES-2009-014703) under the project CTQ2008-01591, and M.L. thanks Ministerio de Educación, Cultura y Deporte for awarding him an FPU grant (Reference AP-2010-0318).

distribution ratios and separation factors of the [4bmpy][Tf2N] and [emim][C2H5SO4] pure ILs are also represented.37,45 The values of the heptane distribution ratios (D1) for the {heptane (1) + toluene (2) + [4bmpy][ Tf2N] (3) + [emim][C2H5SO4] (4)} system with Φ3 = 0.5, plotted in Figure 4, are higher than those of sulfolane, except at higher toluene mole fractions in the hydrocarbon-rich phase (xI2). Similarly, as seen in Figure 5, the values of D2 are higher than the sulfolane values at xI2 < 0.6 and are almost coincident for higher toluene mole fractions in the heptane-rich phase. On the other hand, the separation factors (α2,1) are slightly lower than those of sulfolane at the lower toluene mole fractions in the heptane-rich phase and become slightly higher than the values for the sulfolane at xI2 < 0.4. As shown in Figures 4 and 5, the toluene and heptane distribution ratios for the binary IL mixture present intermediate values between the values of the pure ILs over the whole range of compositions. Thus, the capacity of extraction of toluene for the ILs mixture would improve with respect to the [emim][C2H5SO4] IL, but not for the [4bmpy][Tf2N] IL. Moreover, the separation factors are similar as those of the [4bmpy][Tf2N] ILs, as Figure 6 shows. Therefore, the binary mixture of ILs {[4bmpy][Tf2N] + [emim][C2H5SO4]} with a molar fraction composition of 0.5

Notes

The authors declare no competing financial interest.

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REFERENCES

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