Article pubs.acs.org/jced
Liquid−Liquid Equilibrium Studies on the Removal of Thiophene and Pyridine from Pentane Using Imidazolium-Based Ionic Liquids Ramalingam Anantharaj† and Tamal Banerjee*,‡ †
Department of Chemical Engineering, University of Malaya, Kuala Lampur, Malaysia 50603 Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati - 781039, Assam, India
‡
ABSTRACT: 1-Ethyl-3-methylimidazolium-based ionic liquid with acetate [OAc], ethylsulfate [EtSO4], and methyl sulfonate [MeSO3] anions was used to generate the liquid−liquid equilibrium (LLE) data for the quaternary mixture of IL (1)−thiophene (2)−pyridine (3)−pentane (4). The selectivity and distribution coefficient values were calculated to evaluate the effectiveness of the simultaneous extraction of thiophene and pyridine from pentane at ambient conditions. The experimental tie-line data were successfully validated by the nonrandom two liquid (NRTL) and universal quasi-chemical (UNIQUAC) models, giving root mean square deviation (RMSD) values less than 1 % for all the systems. The novelty of the work was that a conductor like screening model for real solvents (COSMO-RS) model was used to predict compositions of quaternary systems. However, it failed to reproduce the slope of the tie-lines at high solute concentration, especially for the ionic liquid rich phase. The COSMO-RS predictions gave a RMSD of 4.62 % ([EMIM][OAc]), 5.3 % ([EMIM][EtSO4]), and 6.07 % ([EMIM][MeSO3]).
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anions of the salt.12−16 In our earlier work, we have reviewed and discussed the ability of the ionic liquid to remove aromatic sulfur and nitrogen compounds via conductor like screening model for real solvent (COSMO-RS) predictions. The model can be used to predict the infinite dilution of activity coefficient (IDAC) where solvent selection parameters such as selectivity, capacity, and performance index can be predicted. With respect to the COSMO-RS predictions (i.e., the selectivity and capacity), the ILs 1-ethyl-3-methylimidazolium acetate [EMIM][OAc], 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4], and 1-ethyl-3-methylimidazolium methylsulfonate [EMIM][MeSO3] have been chosen for the current experimental work. The aim of this work is to investigate the feasibility of separating thiophene and pyridine from a diesel compound (pentane) at ambient temperature using 1-ethyl-3-methylimidazolium acetate [EMIM][OAc], 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtSO4], and 1-ethyl-3-methylimidazolium methylsulfonate [EMIM][MeSO3]. Further, the ability of these selected ILs will be evaluated in terms of quaternary LLE data by generating a triangular diagram using thiophene + pyridine as a pseudocomponent. Here we have chosen the simplest aromatic and sulfur and nitrogen deriviative, i.e., thiophene and sulfur. However, it should be noted that the compounds such as polysubstituted thiophene (benzothiophene, dibenzothiophene), indoline, and carbozole are the most difficult to remove because of the presence of two or more aromatic rings. This increases the steric hindrance toward solvents such as ionic
INTRODUCTION The removal of nitrogen and sulfur containing compounds from diesel oil is currently achieved by hydrodenitrification (HDN) and hydrodesulfurization (HDS) using a metal oxide/sulfide based catalyst and zeolites. The current HDN and HDS technology can denitrify and desulfurize saturated compounds on an industrial scale. However, unsaturated aromatic compounds such as pyrrole (PYR), indole (INDO), indoline (INDOL), and carbazole (CAR) and sulfur-based compounds such as thiophene (TS), benzothiophene (BT), dibenzothiophene (DBT), and its alkylated compounds are difficult to convert on the catalyst surface because of its sterical hindrance. For this reason, the removal of these compounds by HDN and HDS requires: (i) high temperature, (ii) bigger reactor size, and (iii) an active catalyst. From an emission, economic, and efficiency point of view, it is thus important to develop an alternative methodology for the production of virtually nitrogen and sulfur free diesel oil.1−11 Liquid−liquid extraction (LLE) is an efficient process as compared to distillation, absorption, and other chemical processes for the removal of aromatic compounds of nitrogen and sulfur from diesel oil. Ionice liquids (ILs) are a mixture of salts with wide liquid range from −98 to 99.5 % from Merck, Germany. Deuterated chloroform (Sigma Aldrich, Germany) having purity greater than 99.8 % was used in the 1H NMR analysis of the extract and raffinate phase. The chemical structures of the ionic liquids and the solute molecules are given in Table 1. For reducing the water content and volatile compounds, vacuum (0.1 Pa) for at least 48 h was applied to all the IL samples prior to the measurements. Equal mole fractions of ionic liquid and pentane were first prepared. Thereafter, desired compositions of thiophene and pyridine were added in the mixture such that the combined mole fraction varied from (5 to 80) %. The total volume of the whole mixture was kept constant at 8 mL. They were then transferred into 15 mL stoppered bottles which were sealed by parafilm to prevent loss of any hydrocarbon phase. A thermostatic shaker bath (Dailhan Lab, China) within the temperature uncertainty of ± 0.01 K was used for shaking the 830
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Table 1. List of Ionic Liquids and Solutes Used in This Study
Table 2. Experimental Tie-Lines, Selectivity (S), and Distribution Ratio for [EMIM][OAc] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) at 298.15 K IL-rich phase
pentane-rich phase
selection parameter
S no.
xI1
xI2
xI3
xI23a
xI4
xII1
xII2
xII3
xII23a
xII4
S23
β23
1 2 3 4 5 6 7 8
0.9056 0.8772 0.7555 0.6902 0.6593 0.5589 0.5409 0.4949
0.0572 0.0781 0.1882 0.2150 0.1585 0.2952 0.3407 0.3143
0.0297 0.0411 0.0504 0.0864 0.1755 0.1390 0.1145 0.1898
0.0870 0.1193 0.2387 0.3013 0.3339 0.4342 0.4552 0.5041
0.0074 0.0036 0.0058 0.0085 0.0068 0.0069 0.0039 0.0010
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.0079 0.0650 0.1235 0.2433 0.3511 0.4088 0.4599 0.5439
0.0245 0.0208 0.0387 0.0937 0.0881 0.1368 0.1221 0.1951
0.0324 0.0858 0.1622 0.3370 0.4393 0.5456 0.5819 0.7390
0.9676 0.9142 0.8378 0.6630 0.5607 0.4544 0.4181 0.2610
349.3081 357.9476 212.0952 69.7392 62.5698 52.7368 84.0743 174.4802
2.6827 1.3907 1.4714 0.8942 0.7602 0.7958 0.7822 0.6821
a I x23
= xI2 + xI3; xII23 = xII2 + xIi3 .
Table 3. Experimental Tie-Lines, Selectivity (S), and Distribution Ratio for [EMIM][ EtSO4] (1) + Thiophene (2) + Pyridine (3) + Pentane(4) at 298.15 K IL-rich phase
pentane-rich phase
selection parameter
S no.
xI1
xI2
xI3
xI23a
xI4
xII1
xII2
xII3
xII23a
xII4
S23
β23
1 2 3 4 5 6 7 8
0.9176 0.8563 0.8073 0.7684 0.7442 0.7231 0.6330 0.4972
0.0346 0.0674 0.0878 0.0945 0.0975 0.1060 0.1087 0.1642
0.0376 0.0553 0.0623 0.0694 0.0887 0.0917 0.1678 0.1913
0.0722 0.1227 0.1501 0.1639 0.1863 0.1977 0.2766 0.3555
0.0101 0.0210 0.0427 0.0678 0.0695 0.0791 0.0904 0.1473
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.0093 0.0100 0.1038 0.1848 0.2197 0.3222 0.4409 0.4488
0.0184 0.0314 0.0329 0.0419 0.0566 0.0590 0.0753 0.1437
0.0278 0.0414 0.1367 0.2268 0.2764 0.3812 0.5163 0.5926
0.9722 0.9586 0.8633 0.7732 0.7236 0.6188 0.4837 0.4074
249.3191 135.6543 22.2157 8.2408 7.0149 4.0577 2.8665 1.6591
2.6002 2.9664 1.0980 0.7225 0.6740 0.5188 0.5357 0.5999
a I x23
= xI2 + xI3; xII23 = xII2 + xIi3 .
mixture. The bottles were kept inside the shaker bath by setting the speed and temperature of the shaker bath to 100 rpm and 298.15 K, respectively. The mixture was kept in the shaker bath for 6 h. Thereafter, an equilibration time of 12 h was given for both the phases to settle down. In recent times NMR spectra have been used in determining the unknown mole fractions involving ionic liquids.27−29Samples dissolved in 0.5 mL of CDCl3 from both the extract and raffinate phase were then taken for analysis. An NMR spectrometer of 11.74 T (20 MHz response of 1H) was used for the determination of experimental
mole fractions. The details of the compositional analysis can be found from our earlier work on ionic liquid systems.16
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RESULTS AND DISCUSSION The experimental liquid−liquid equilibrium data for the quaternary systems are given in Tables 2 to 4. Further, the tielines are compared with UNIQUAC model in Figures 1 to 3. In all the triangular diagrams, thiophene and pyridine have been taken together as a pseudocomponent. It is interesting to note that in all the plots the tie-lines consist of different slopes. 831
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Table 4. Experimental Tie-Lines, Selectivity (S), and Distribution Ratio for [EMIM][MeSO3] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) at 298.15 K IL-rich phase
pentane-rich phase
selection parameter
S no.
xI1
xI2
xI3
xI23a
xI4
xII1
xII2
xII3
xII23a
xII4
S23
β23
1 2 3 4 5 6 7 8
0.9389 0.8964 0.8690 0.7629 0.6650 0.5550 0.3687 0.2787
0.0132 0.0084 0.0016 0.0563 0.0678 0.0898 0.4135 0.4899
0.0474 0.0930 0.1257 0.1688 0.2033 0.2693 0.0996 0.1159
0.0606 0.1014 0.1273 0.2251 0.2710 0.3590 0.5131 0.6057
0.0005 0.0022 0.0038 0.0120 0.0640 0.0860 0.1182 0.1156
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.0205 0.1051 0.1897 0.2815 0.3688 0.4120 0.5420 0.5394
0.0616 0.0306 0.0328 0.1497 0.1650 0.1830 0.1350 0.1896
0.0821 0.1357 0.2225 0.4312 0.5338 0.5950 0.677 0.729
0.9179 0.8643 0.7775 0.5688 0.4662 0.4050 0.323 0.271
1352.0069 296.2162 117.7196 12.2390 5.6596 5.5199 3.5041 2.5315
0.7372 0.7472 0.5719 0.5292 0.8406 0.6280 0.9274 0.8984
a I x23
= xI2 + xI3; xII23 = xII2 + xIi3 .
Figure 1. Experimental and UNIQUAC predicted tie-lines for the quaternary system: [EMIM][OAc] (1) + thiophene (2) + pyridine (3) + pentane (4) at T = 298.15 K.
Figure 2. Experimental and UNIQUAC predicted tie-lines for the quaternary system: [EMIM][EtSO4] (1) + thiophene (2) + pyridine (3) + pentane (4) at T = 298.15 K.
the lower part and a negative slope at the upper part of the triangular diagram. This behavior is in accordance with previous
The tie-lines for [EMIM][OAc] (Figure 1) and [EMIM][EtSO4] (Figure 2) show two different slopes: a positive slope at 832
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Figure 3. Experimental and UNIQUAC predicted tie-lines for the quaternary system: [EMIM][MeSO3] (1) + thiophene (2) + pyridine (3) + pentane (4) systems at T = 298.15 K.
UNIQUAC models are shown in Tables 6 to 8. RMSDs close to 1 % indicate that they closely match the experimental values. The experimental LLE data were then predicted via the COSMO-RS model via triangular diagram (Figures 4 to 6). The tie-lines agree with each other quantitatively and qualitatively for [EMIM][OAc] (Figure 4) in both the phases. However, for [EMIM][EtSO4] (Figure 5) and [EMIM][EtSO4] (Figure 6), the length and shape of the immiscible region have a high deviation, particularly in the extract (IL) rich phase. The deviations are quite high in the upper phase of the phase diagram where the predicted and experimental slopes are in opposite direction. Thus, COSMO-RS was not able to predict the change of sign of the tie-line in these systems. It should be noted that this was the first time the COSMO-RS approach has been applied to predict the tie-lines of a quaternary system containing ILs. There was no attempt to change the COSMORS parameters that were used from our earlier work.24 This deviation may be due to the several possible interactions between IL and thiophene/pyridine molecules in the mixture where the hydrogen bond interaction plays a major role. Being a multicomponent mixture, the deviations are higher as the cross hydrogen bonding term is absent in the COSMO modeling. We have not attempted to correct this inadequacy of the COSMO-RS model in this current version. To get a more
work on the LLE of IL containing systems such as hexane + pyridine + [EMIM][EtSO4],30,31 hexane + thiophene + [HMIM][NTf2], dodecane + thiophene + [HMIM][NTf2], and hexadecane + thiophene + [HMIM][NTf2], where both positive and negative slopes are visible in the ternary plot.32,33 However, the opposite is seen with [EMIM][MeSO3] (Figure 3). The NRTL and UNIQUAC models were thereafter used to validate the experimental LLE data. Table 5 reports the r and q Table 5. UNIQUAC Structural Parameters18 in the LLE System component
r
q
1-ethyl-3-methylimidazolium acetate 1-ethyl-3-methylimidazolium ethyl sulfate 1-ethyl-3-methylimidazolium methylsulfonate thiophene pyridine pentane
8.7500 8.3927 8.14 2.8569 2.9993 3.8254
5.5600 6.6260 6.08 2.140 2.113 3.316
parameters that were derived via PCM calculations.33 Both NRTL and UNIQUAC models (Tables 6 to 8) were able to correlate the experimental data with high consistency. The binary interaction parameters obtained using the NRTL and
Table 6. NRTL and UNIQUAC Interaction Parameters for [EMIM][OAc] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) at T = 298.15 K NRTL model parameters
a
−1
i−j
τij/J·mol
1−2 1−3 1−4 2−3 2−4 3−4
4901.2 1468.6 4903.8 1852.5 1217.4 2814.9
−1
τij/J·mol
F
a
UNIQUAC model parameters RMSD
b
−1
Aij/J·mol
Aij/J·mol−1
System: [EMIM][OAc] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) 4149.1 −3.4 × 10−3 0.0073 197.55 994.31 −59.601 −632.88 −37.805 4129.8 232.31 669.61 1421.2 366.55 208.06 4567.5 −159.76 86.708 1612.8 961.13 −671.03
Fa
RMSDb
−1.82 × 10−3
0.0169
Calculated using eq 1. bCalculated using eq 2. 833
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Table 7. NRTL and UNIQUAC Interaction Parameters for the [EMIM][EtSO4] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) at T = 298.15 K NRTL model parameters
a
i−j
τij/J·mol−1
1−2 1−3 1−4 2−3 2−4 3−4
2695 4477.7 5548.6 6681.9 5904 3925
τij/J·mol−1
Fa
UNIQUAC model parameters RMSDb
Aij/J·mol−1
Aij/J·mol−1
System: [EMIM][ EtSO4] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) 1101 −6.7 × 10−3 0.0102 −35.853 335.64 −378.4 444.14 999.67 3743 139.34 631.97 6034.8 998.26 154.34 4367.6 457.36 −149.83 2641.5 373.74 451.28
Fa
RMSDb
−3.705 × 10−2
0.02106
Calculated using eq 1. bCalculated using eq 2.
Table 8. NRTL and UNIQUAC Interaction Parameters for [EMIM][MeSO3] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) at T = 298.15 K NRTL model parameters
a
−1
i−j
τij/J·mol
1−2 1−3 1−4 2−3 2−4 3−4
664.04 697.94 704.64 507.05 716.49 309.01
τij/J·mol
−1
F
a
UNIQUAC model parameters RMSD
b
−1
Aij/J·mol
Aij/J·mol−1
System: [EMIM][ MeSO3] (1) + Thiophene (2) + Pyridine (3) + Pentane (4) 692.46 −14.25 × 10−3 0.014923 2005.4 −18.062 842.87 2600.8 49.031 350 330.81 722.95 1999.8 49.132 34.142 418.34 567.31 1367.5 967.29 645.45 777.07
Fa
RMSDb
−16.51 × 10−3
0.016061
Calculated using eq 1. bCalculated using eq 2.
Figure 4. Experimental and COSMO-RS predicted tie-lines for the quaternary system: [EMIM][OAc] (1) + thiophene (2) + pyridine (3) + pentane (4) at T = 298.15 K.
thereby preventing cross-contamination in the hydrocarbon streams. Further, the solvents were screened by calculating the selectivity (Figure 7) and distribution coefficient (Figure 8). The mathematical expression can be written as (eqs 4 and 5)
accurate composition in the extract phase, the hydrogen bonding parameter needs to be reparameterized,34 and a specific value (i.e., hydrogen bonding constant or cutoff for hydrogen bonding) needs to be adopted for particular bonds which occur between thiophene/pyridine and the IL. For example, Hsieh et al.35 have adopted a bond-specific hydrogen bonding energy constant or use of Gaussian type probability for the hydrogen bonding sigma profile. However such an approach may lead to parameters for specific systems leading to loss of universal applicability. The values of RMSD were 4.62 % for [EMIM][OAc], 5.3 % for [EMIM][EtSO4,] and 6.07 % for [EMIM][MeSO3], respectively. In all the systems, the predicted composition of IL in the raffinate phase is zero,
selectivity (S) =
E R (xthiophene + pyridine) · (x pentane) R E (xthiophene + pyridine) · (x pentane)
distribution coefficient (β) = 834
(4)
E (xthiophene + pyridine) R (xthiophene + pyridine)
(5)
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Figure 5. Experimental and COSMO-RS predicted tie-lines for the quaternary system: [EMIM][EtSO4] (1) + thiophene (2) + pyridine (3) + pentane (4) at T = 298.15 K.
Figure 6. Experimental and COSMO-RS predicted tie-lines for the quaternary system: [EMIM][MeSO3] (1) + thiophene (2) + pyridine (3) + pentane (4) at T = 298.15 K.
However, in a recent work,36 it was found that the regeneration of ionic liquid poses a problem for systems involving nitrogen species. In their work, toluene was used as a regenerative solvent to remove indole and DBT from 1-ethyl-3-methylimidazolium chloride. The results indicated that the extent of removal was 46 % (from initial concentration 2993 mg·kg−1 of IL) after two regenerative cycles for indole and nearly 85 % (from initial concentration 4532 mg·kg−1 of IL) for DBT. Thus, in this work [EMIM][OAc], [EMIM][EtSO4], and [EMIM][MeSO3] ionic liquid could be considered as solvents for the simultaneous desulfurization and denitrification of paraffinic diesel oil especially when the aromatic sulfur and nitrogen concentration in the diesel oil is low, i.e., parts per million level. However, it is easier to extract thiophene from a paraffinic oil than from an aromatic oil or from higher molecular weight hydrocarbon such as dodecane and hexadecane. Further, the
Here x is the thiophene/pyridine/pentane mole fraction in the extract (E) and raffinate (R) phases. The selectivities of the studied quaternary systems are plotted in Figure 7. It is seen that the selectivity is highest at low concentration of solute in feed. At all other concentrations it decreases with concentration. This agrees well with the previous work on heptane−toluene separation using the ILs: n-butylpyridinium tetrafluoroborate33 and n-ethylpyridinium bis(trifluoromethylsulfonyl)imide,32 respectively. The distribution values are higher than unity for all the systems at higher solute concentrations (Figure 8). This confirms that [EMIM][OAc], [EMIM][EtSO4], and [EMIM][MeSO3] would be required in higher quantities as most of the solutes (thiophene/pyridine) have low concentrations in commercial diesel. By their inherent property, ILs are immiscible in the pentane-rich phase. This could make their recovery and reuse easier and cheaper when multiple extraction steps are carried out. 835
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[EMIM][EtSO4], and 6.07 % for [EMIM][MeSO3] based systems.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +91.361.2582266. Fax: +91.361.2690762. Funding
The authors are grateful to the Department of Science and Technology (DST), Government of India, for the financial support through project SR/FTP/08-08 under the Fast Track Scheme. Notes
The authors declare no competing financial interest.
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Figure 7. Selectivity for the quaternary systems at T = 298.15 K as a function of mole fraction of the solute in the pentane-rich phase.
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Figure 8. Distribution ratios for the quaternary systems at T = 298.15 K as a function of mole fraction of solute in the pentane-rich phase.
solubility of an aromatic hydrocarbon in an ionic liquid is larger than that of a paraffinic hydrocarbon. It will be interesting to study extraction of thiophene and pyridine from a heavy aromatic oil. The difficulty in using heavy aromatic oil is that it will lead to an overlapping of 1H NMR of aromatic oil with thiophene for aromatic hydrogen protons. Aromatic oil along with polysubstituited compounds will be attempted in our future work.
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LATIN SYMBOLS [EMIM], Cation: 1-ethyl-3-methylimidazolium [HMIM], Cation: 1-hexyl-3-methylimidazolium [OAc], Anion: acetate [EtSO4], Anion: ethyl sulfate [MeSO3], Anion: methylsulfonate [NTf2], Anion: bis(trifluoromethanesulfonyl)amide S, selectivity F, objective function RMSD, root mean square deviation T, temperature, K m, number of tie-lines c, number of components in the LLE system xi, mole fraction of component i of either phase in the LLE system r, pure component volume parameter q, pure component surface area parameter GREEK SYMBOLS β, distribution coefficient τ, NRTL interaction parameter α, NRTL nonrandomness parameter REFERENCES
(1) Wiwel, P.; Knudsen, K.; Zeuthen, P.; Whitehurst, D. Assessing compositional changes of nitrogen compounds during hydrotreating of typical diesel range gas oils using a novel preconcentration technique coupled with gas chromatography and atomic emission detection. Ind. Eng. Chem. Res. 2000, 39, 533−540. (2) Yang, H.; Chen, J.; Briker, Y.; Szynkarczuk, R.; Ring, Z. Effect of nitrogen removal from light cycle oil on the hydrodesulfurization of dibenzothiophene, 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene. Catal. Today 2005, 109, 16−23. (3) Hernandez-Maldonado, A. J.; Ralph, T.; Yang, Y. Desulfurization of commercial liquid fuels by selective adsorption via π-complexation with Cu(I)-Y zeolite. Ind. Eng. Chem. Res. 2003, 42, 3103−3110. (4) Zhang, Z.; Zhou, Z.; Zhang, S.; Xu, C. Hydrodesulfurization of resid fluid catalytic cracking diesel oil over TiO2-SiO2 supported catalysts. Energy Fuels 2006, 20, 293−2298. (5) Trakarnpruk, W.; Seentrakoon, B.; Porntangjitlikit, S. Hydrodesulphurization of diesel oils by MoS2 catalyst prepared by in situ decomposition of ammonium thiomolybdate. Silpakorn Univ. Sci. Technol. J. 2008, 2, 7−13. (6) Li, W.; Liu, Q.; Xing, J.; Gao, H.; Xiong, X.; Li, Y.; Li, X. X.; Liu, H. High-efficiency desulfurization by adsorption with mesoporous aluminosilicates. AlChE J. 2003, 53, 3263−3268. (7) Shifu, C.; Yueming, L.; Jinbao, G.; Lingling, W.; Xiuli, L.; Guohua, G.; Peng, W.; Mingyuan, H. Catalytic oxidation of
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CONCLUSION In this work, the following quaternary systems, namely, [EMIM][OAc] (1) + thiophene (2) + pyridine (3) + pentane (4), [EMIM][EtSO4] (1) + thiophene (2) + pyridine (3) + pentane (4), and [EMIM][MeSO3] (1) + thiophene (2) + pyridine (3) + pentane (4), were studied and experimental tielines generated. In general, the tie-lines show a positive slope at the bottom of the triangular diagram and a negative slope elsewhere. The tie-lines for [EMIM][OAc] and [EMIM][EtSO4] show two different slopes: a positive slope at the lower part and a negative slope at the upper part of the triangular diagram. The selectivity values were found to increase and then decrease with an increase in mole fraction of solute. The distribution values are higher than unity for all the systems at low solute concentrations. NRTL and UNIQUAC models gave RMSDs less than 1 % for all the systems. Finally, the experimental data were predicted with the COSMO-RS model by giving a RMSD of 4.62 % for [EMIM][OAc], 5.3 % for 836
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dx.doi.org/10.1021/je301188p | J. Chem. Eng. Data 2013, 58, 829−837
