Separation of ethyl acetate and ethanol by room temperature ionic liquids with the tetrafluoroborate anion

Article abstract of DOI:10.1021/je700516t

Liquid-liquid equilibrium data are presented for mixtures of 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim]BF₄) or 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([C₂OHmim] BF₄) or 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate ([edmim]BF₄) or 1-(2-hydroxyethyl)-2,3-dimethylimidazolium tetrafluoroborate ([C₂OHdmim]BF₄) + ethanol + ethyl acetate at 298.15 K. The distribution ratio and selectivity values, derived from the tie line data, show that [C₂OHmim]BF₄ has better extraction capacity than other studied ionic liquids and that a hydroxyl group on the cation and a CH₃ group at the 2-position can obviously affect the interaction between the ionic liquid and ethanol. The experimental results show that [C₂OHmim]BF₄ is potentially a candidate to separate ethyl acetate and ethanol by liquid-liquid extraction. The experimental tie lines were correlated with the NRTL equation.

Full text of DOI:10.1021/je700516t

J. Chem. Eng. Data 2008, 53, 427–433
427
Separation of Ethyl Acetate and Ethanol by Room Temperature Ionic Liquids
with the Tetrafluoroborate Anion
Xuesheng Hu, Yingxia Li,* Dannan Cui, and Biaohua Chen
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, 100029, China
Liquid–liquid equilibrium data are presented for mixtures of 1-ethyl-3-methylimidazolium tetrafluoroborate
([emim]BF4) or 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([C2OHmim]BF4) or 1-ethyl-
2,3-dimethylimidazolium tetrafluoroborate ([edmim]BF4) or 1-(2-hydroxyethyl)-2,3-dimethylimidazolium
tetrafluoroborate ([C2OHdmim]BF4) + ethanol + ethyl acetate at 298.15 K. The distribution ratio and
selectivity values, derived from the tie line data, show that [C2OHmim]BF4 has better extraction capacity
than other studied ionic liquids and that a hydroxyl group on the cation and a CH3 group at the 2-position
can obviously affect the interaction between the ionic liquid and ethanol. The experimental results show
that [C2OHmim]BF4 is potentially a candidate to separate ethyl acetate and ethanol by liquid–liquid extraction.
The experimental tie lines were correlated with the NRTL equation.
adjusted by changing the substituting group H or CH3 at the C2
position. This work continues to aim to elucidate the suitability
of different ionic liquids as extraction solvents for liquid–liquid
extraction. Four ionic liquids with the tetrafluoroborate anion
are studied in this paper.
The ternary liquid–liquid equilibria of the system 1-ethyl-3-
methylimidazolium tetrafluoroborate ([emim]BF4) or 1-(2-
hydroxyethyl)-3-methylimidazoliumtetrafluoroborate([C2OHmim]-
BF4) or 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate
([edmim]BF4) or 1-(2-hydroxyethyl)-2,3-dimethylimidazolium
tetrafluoroborate ([C2OHdmim]BF4) + ethanol + ethyl acetate
at 298.15 K is presented. The abilities of the four ionic liquids
for separation of the ethyl acetate and ethanol system are
discussed.
Introduction
Due to their measurable but relatively low vapor pressure,
room-temperature ionic liquids have been applied to separate
some organic mixtures.1,2 Alrt et al.3,4 reported that 1-ethyl-3-
methylimidazolium tetrafluoroborate ([emim]BF4) and 1-butyl-
3-methylimidazolium tetrafluoroborate ([bmim]BF4) can change
the liquid–liquid equilibria of THF and water. Meindersma et
al.5 used 1-ethyl-3-methylimidazolium ethylsulfate ([emim]-
C2H5SO4), 1,3-dimethylimidazolium methylsulfate ([mmim]-
CH3SO4), and 1-butyl-3-methylimidazolium methylsulfate
([bmim]CH3SO4) to separate toluene and n-heptane. Arce et
al.6 separated the hexane and benzene mixture by 1-eth-
yl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}amide
([C2mim]NTf2). All ionic liquids used above have good extrac-
tion efficiency according to the results, which shows that they
are potentially candidates to separate organic mixtures by
liquid–liquid extraction.
Experimental
Materials. Ethyl acetate, ethanol, 2-chloroethanol, ethyl
bromide, and NaBF4 were all analytical grade reagents (purity
g 99 %) supplied by Beijing Chemical Reagents Corporation.
1-Methylimidazole and 1,2-dimethylimidazole (purity g 99 %)
were purchased from Suzhou Meihua Daily Use Perfume
Company (Suzhou, Jiangsu, China) and distilled before use.
1-Ethyl-3-methylimidazolium tetrafluoroborate ([emim]BF4)
was synthesized by the traditional method.11,12 First, ethyl
bromide (1.1 mol) and 1-methylimidazole (1.0 mol) were added
to a round-bottomed flask fitted with a reflux condenser for 24 h
at room temperature with stirring. Then, the temperature was
allowed to rise to 343.15 K to remove unreacted ethyl bromide.
The product was washed by ethyl ether three times and then
was under a vacuum at 343.15 K for 8 h. The product, 1-ethyl-
3-methylimidazolium bromide ([emim]Br), was solid at room
temperature (90 % yield). Second, [emim]Br (0.5 mol) and
NaBF4 (0.55 mol) were mixed in 500 mL of acetone. The
mixture was stirred at room temperature for 24 h. The resulting
mixture was then filtered. The solvents were removed under a
vacuum at 343.15 K for 12 h to give the crude product, and
over 95 % yield was obtained. Third, the crude ionic liquid
including bromide impurity was diluted by a small amount of
dichloromethane to lower the viscosity and filtered a couple of
In many chemical processes, ester-alkanol systems need be
separated to obtain pure ester and pure alkanol. For example,
during acetic acid/ethanol esterification, about 9 % by mass of
ethanol in the crude ethyl acetate product needs to be removed
by a high-energy-consuming process such as extractive distil-
lation.7 Liquid–liquid extraction of ester-alkanol systems by
ionic liquids, which may be a high selectivity process with low-
energy consumption, was reported recently. Pereiro et al.8
reported liquid–liquid equilibria of 2-propanol + ethyl acetate
+ 1,3-dimethylimidazolium methylsulfate ([mmim]CH3SO4) or
1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF6)
or 1-hexyl-3-methylimidazolium hexafluorophosphate ([hmim]-
PF6), which showed that [mmim]CH3SO4 obtained higher values
than [Rmim]PF6 for the proposed process according to the
selectivity values.
Recently, ionic liquids with functional hydroxyl groups have
been studied to separate alcohols from other solvents.9,10 In our
previous work,9 ionic liquids with a hydroxyl group were tried
to separate 1-butanol and water, which also showed that the
mutual solubility between alkanol and ionic liquids can be
* Corresponding author. E-mail: liyx@mail.buct.edu.cn.
10.1021/je700516t CCC: $40.75
2008 American Chemical Society
Published on Web 01/01/2008

428 Journal of Chemical & Engineering Data, Vol. 53, No. 2, 2008
Table 1. Physical Properties of the Pure Components at T ) 298.15
K: Mole Mass M, Density G, and Water Mass Fraction w
Table 2. Solubility Data for [emim]BF4 (1) + Ethanol (2) + Ethyl
Acetate (3) at T ) 298.15 K
M
F(exptl)
F(lit.)
(g·cm-3
1.240a
w
(106)
x1
x2
x3
F/g·cm-3
(g·mol-1
)
(g·cm-3
)
)
0.655
0.536
0.465
0.401
0.351
0.312
0.267
0.255
0.239
0.209
0.182
0.155
0.127
0.110
0.091
0.077
0.064
0.047
0.039
0.028
0.017
0.013
0.006
0.002
0.000
0.102
0.155
0.219
0.249
0.276
0.300
0.307
0.314
0.327
0.336
0.337
0.337
0.331
0.324
0.315
0.301
0.265
0.241
0.230
0.208
0.165
0.111
0.056
0.345
0.361
0.379
0.380
0.400
0.411
0.434
0.438
0.447
0.464
0.481
0.508
0.536
0.559
0.584
0.608
0.636
0.688
0.721
0.742
0.775
0.823
0.882
0.942
1.112
1.080
1.071
1.058
1.021
1.006
0.999
0.997
0.984
0.968
0.954
0.932
0.896
0.894
0.892
0.890
0.888
0.886
0.885
0.882
0.870
0.864
0.828
0.819
[emim]BF4
[edmim]BF4
[C2OHmim]BF4
[C2OHdmim]BF4
197.97
212.00
213.97
228.00
1.242
1.250
1.332
1.368
55
60
80
89
b
-
1.33c
1.36d
a Ref 1. b No literature reported. c Ref 11. d Ref 9.
times by being passed through a silica column to remove the
bromide impurity analogous to the methods previously
reported.13,14 The ionic liquid phase obtained from the filtration
method was tested for the residual bromide salt through the
concentrated AgNO3 solution, and no clear precipitation of AgBr
was detected by the naked eye, which means that bromide
impurity was almost adsorbed by the silica. The dichloromethane
was then removed under vacuum to give the 1-ethyl-3-
methylimidazolium tetrafluoroborate ([emim]BF4) as a colorless
liquid (purity > 99.0 % mass fraction, water content < 1.0 %
mass fraction). Thus, the filtration method using a silica column
appears to be very effective in removing the residual bromide
ion. However, when purified, some loss of product will occur,
resulting in an overall yield of about 80 %.
other two from a value of 1; e.g., after measuring the densities
of the upper and lower phases at equilibrium point, we can
calculate the actual compositions of w1 and w2 by the interpola-
tion method according to the standard curve determined by
cloud-point titration and get w3 with 1-w1-w2.
The densities were measured through the use of a calibrated
Anton Paar DMA 5000 density meter with an uncertainty of
1·10-4 g·cm-3 in the measurement.
The ternary liquid–liquid equilibrium [emim]BF4 (1) or
[edmim]BF4 (1) or [C2OHmim]BF4 (1) or [C2OHdmim]BF4 (1)
+ ethanol (2) + ethyl acetate (3) at 298.15 K was measured by
the shake-flask method. The three materials were added into a
jacketed glass vessel containing a magnetic stirrer connected
to a temperature-controlled circulating bath (501A Super
Constant Temp Bath, Shanghai Hengping Instrument Company,
( 0.1 K). The mixture was stirred and then put into a jacketed
funnel connected to the same temperature-controlled circulating
bath to settle for 24 h to achieve phase equilibrium. All the
temperatures were controlled to (298.15 ( 0.1) K.
Similarly, the other three ionic liquids, 1-ethyl-2,3-dimethyl-
imidazolium terafluoroborate ([edmim]BF4, purity > 99.0 % mass
fraction, water content < 1.0 % mass fraction), 1-(2-hydroxyethyl)-
3-methylimidazolium terafluoroborate ([C2OHmim]BF4, purity >
99.0 % mass fraction, water content < 1.0 % mass fraction), and
1-(2-hydroxyethyl)-2,3-dimethylimidazolium tetrafluoroborate
([C2OHdmim]BF4, purity > 99.0 % mass fraction, water content
< 1.0 % mass fraction) were synthesized by using 1,2-dimethyl-
imidazole instead of 1-methylimidazole or 2-chloroethanol instead
of ethyl bromide. The four ionic liquids used in this work have
a purity of more than 99 % mass fraction and a water content
less than 1 % mass fraction determined by the Karl Fischer
method (SC-6 mini-amount Water Detective Instrument,
Shangdong Zhonghui Instrument Company,
5 mg of
H2O · cm-3).
Before use, every sample of ionic liquid was heated at 333.15
K for 24 h under reduced pressure to remove residual water.
The physical properties of these ionic liquids at T ) 298.15 K
and water content before use were listed in Table 1.
Procedure. The binodal curves were determined at T )
298.15 K and 101.325 kPa through the use of the cloud-point
titration technique described by Letcher and Siswana.15 All
mixtures were prepared and “titrated” in screwcap glass vials
with septa to allow for careful sampling with glass syringes.
The glass vial has a diameter of 2 cm, a height of 10 cm, and
a total capacity of about 10 cm3. There was negligible mass
loss from the glass vials.
The determination of the tie line compositions was carried
out by correlating the densities of the two immiscible liquid
phases of the conjugate solutions with that of standard curves
of density versus composition for the three components. The
standard curve was obtained by measuring the densities of binary
mixtures of ethyl acetate and ethanol and equilibrium ternary
mixtures of the components, i.e., at the cloud-point, throughout
the composition range of the ternary system. The density values
of each conjugate phase, i.e., two phases, in the ternary mixture
were then correlated with the standard curve to obtain the
compositions of the components in each of the phases. Only
two of the three component compositions are required for each
phase, as the third is obtained by subtracting the sum of the
Every tie line has been reproduced at least once. The mole
fraction of each component can be determined with an uncer-
tainty of E 0.2 %.
Results and Discussion
The compositions of the solubility curve data for [emim]BF4
(1) + ethanol (2) + ethyl acetate (3), [C2OHmim]BF4 (1) +
ethanol (2) + ethyl acetate (3), [edmim]BF4 (1) + ethanol (2)
+ ethyl acetate (3), and [C2OHdmim]BF4 (1) + ethanol (2) +
ethyl acetate (3) are presented in Tables 2 to 5, respectively,
and the corresponding solubility curve diagrams are also shown
as Figures 1 to 4, respectively. As shown in Figures 1 to 4, all
the studied ILs have low solubility in ethyl acetate (< 1 % mole
fraction), except [edmim]BF4 which has about 6 % mole
fraction. The solubility of ethyl acetate is (35, 21, 40, and 30)
% mole fraction, respectively, in [emim]BF4, [C2OHmim]BF4,
[edmim]BF4, and [C2OHdmim]BF4.
The compositions of the tie line data for [emim]BF4 (1) +
ethanol (2) + ethyl acetate (3), [C2OHmim]BF4 (1) + ethanol
(2) + ethyl acetate (3), [edmim]BF4 (1) + ethanol (2) + ethyl
acetate (3), and [C2OHdmim]BF4 (1) + ethanol (2) + ethyl

Journal of Chemical & Engineering Data, Vol. 53, No. 2, 2008 429
Table 3. Solubility Data for [C2OHmim]BF4 (1) + Ethanol (2) +
Ethyl Acetate (3) at T ) 298.15 K
Table 5. Solubility Data for [C2OHdmim]BF4 (1) + Ethanol (2) +
Ethyl Acetate (3) at T ) 298.15 K
x1
x2
x3
F/g·cm-3
x1
x2
x3
F/g·cm-3
0.784
0.637
0.493
0.409
0.332
0.284
0.258
0.217
0.185
0.154
0.131
0.108
0.085
0.064
0.052
0.039
0.036
0.028
0.022
0.015
0.011
0.011
0.010
0.009
0.008
0.007
0.005
0.004
0.002
0.000
0.157
0.302
0.397
0.468
0.512
0.534
0.570
0.591
0.600
0.608
0.609
0.601
0.577
0.556
0.530
0.499
0.475
0.444
0.404
0.381
0.350
0.325
0.291
0.264
0.224
0.152
0.116
0.063
0.216
0.206
0.205
0.194
0.200
0.204
0.208
0.213
0.225
0.246
0.261
0.283
0.314
0.359
0.391
0.431
0.466
0.497
0.534
0.581
0.608
0.638
0.665
0.701
0.727
0.769
0.844
0.880
0.935
1.205
1.172
1.154
1.133
1.102
1.050
1.028
1.019
1.011
1.008
0.997
0.953
0.899
0.873
0.870
0.865
0.855
0.850
0.849
0.845
0.842
0.837
0.830
0.828
0.824
0.821
0.817
0.811
0.805
0.700
0.547
0.475
0.402
0.351
0.306
0.247
0.204
0.161
0.136
0.110
0.088
0.075
0.065
0.053
0.040
0.030
0.023
0.017
0.013
0.009
0.007
0.006
0.005
0.005
0.005
0.004
0.004
0.002
0.002
0.000
0.160
0.228
0.299
0.349
0.386
0.437
0.469
0.501
0.514
0.521
0.527
0.524
0.513
0.514
0.495
0.477
0.455
0.433
0.401
0.373
0.345
0.312
0.270
0.231
0.204
0.175
0.130
0.100
0.060
0.300
0.294
0.297
0.299
0.300
0.308
0.317
0.327
0.338
0.350
0.369
0.385
0.402
0.423
0.433
0.465
0.493
0.522
0.550
0.587
0.618
0.648
0.682
0.725
0.764
0.791
0.821
0.866
0.898
0.939
1.070
1.046
1.037
1.030
1.016
1.005
0.998
0.976
0.958
0.938
0.908
0.882
0.874
0.868
0.865
0.862
0.860
0.869
0.862
0.859
0.858
0.855
0.852
0.848
0.845
0.841
0.837
0.831
0.825
0.817
Table 4. Solubility Data for [edmim]BF4 (1) + Ethanol (2) + Ethyl
Acetate (3) at T ) 298.15 K
On the basis of the four figures above, the four ionic liquids
[emim]BF4, [C2OHmim]BF4, [edmim]BF4, and [C2OHdmim]-
BF4 can be used for ethyl acetate and ethanol separation by
solvent extraction. The addition of a 25 % mole fraction
[emim]BF4 or [C2OHmim]BF4 or [edmim]BF4 or [C2OHdmim]-
BF4 to a preconcentrated binary ethyl acetate + ethanol solution
(such as 32 % mole fraction of ethyl acetate) causes a phase
split. For [emim]BF4, the upper phase contains about 70.5 %
mole fraction of ethyl acetate, 25.3 % mole fraction of ethanol,
and 4.2 % mole fraction of [emim]BF4, and the lower phase
consists of 43.5 % mole fraction of ethyl acetate, 26.5 % mole
fraction of ethanol, and 30.0 % mole fraction of [emim]BF4. In
the upper phase, the ethyl acetate-ethanol preliminary composi-
tion has been changed.
x1
x2
x3
F/g·cm-3
0.602
0.510
0.477
0.442
0.411
0.385
0.360
0.316
0.291
0.267
0.247
0.226
0.212
0.194
0.178
0.161
0.151
0.137
0.126
0.115
0.104
0.094
0.080
0.066
0.062
0.057
0.057
0.055
0.055
0.054
0.057
0.055
0.057
0.058
0.000
0.077
0.108
0.133
0.162
0.180
0.208
0.249
0.268
0.292
0.306
0.325
0.336
0.348
0.356
0.363
0.367
0.375
0.376
0.376
0.376
0.370
0.358
0.349
0.329
0.300
0.267
0.244
0.202
0.164
0.083
0.132
0.056
0.000
0.398
0.414
0.415
0.424
0.427
0.435
0.432
0.435
0.441
0.442
0.447
0.448
0.452
0.459
0.466
0.476
0.482
0.488
0.498
0.509
0.520
0.537
0.562
0.585
0.609
0.643
0.676
0.701
0.743
0.782
0.860
0.814
0.887
0.942
1.070
1.066
1.016
1.032
1.030
1.028
1.015
1.004
0.985
0.966
0.954
0.951
0.944
0.927
0.915
0.898
0.884
0.881
0.878
0.875
0.872
0.867
0.858
0.855
0.852
0.851
0.849
0.847
0.846
0.845
0.843
0.842
0.834
0.822
acetate (3) are presented in Tables 6 to 9, respectively, and the
corresponding tie line diagrams are shown as Figure 5 to 8.
The sloping of tie lines to the ethyl acetate vertex in Figures 5
and 6 is very clear.
Figure 1. Solubility curve for [emim]BF4 (1) + ethanol (2) + ethyl acetate
(3) at T ) 298.15 K.

430 Journal of Chemical & Engineering Data, Vol. 53, No. 2, 2008
Table 6. Tie Line Data for [emim]BF4 (1) + Ethanol (2) + Ethyl
Acetate (3) at T ) 298.15 K
EA-rich phase
IL-rich phase
x1
x2
x3
x1
x2
x3
ꢀ
S
0.004
0.005
0.007
0.009
0.012
0.016
0.029
0.054
0.071
0.077
0.096
0.117
0.137
0.158
0.201
0.226
0.280
0.303
0.919
0.898
0.876
0.853
0.831
0.783
0.745
0.666
0.627
0.621
0.608
0.557
0.472
0.406
0.360
0.329
0.269
0.236
0.042
0.056
0.085
0.137
0.177
0.216
0.240
0.293
0.315
0.337
0.335
0.359
0.391
0.417
0.424
0.431
0.438
0.449
0.546
0.584
0.722
0.996
1.123
1.075
1.062
1.045
1.040
1.490
1.563
1.763
2.170
2.238
1.985
1.836
1.588
1.452
Table 7. Tie Line Data for [C2OHmim]BF4 (1) + Ethanol (2) +
Ethyl Acetate (3) at T ) 298.15 K
EA-rich phase
IL-rich phase
x1
x2
x3
x1
x2
x3
ꢀ
S
0.003
0.004
0.005
0.008
0.009
0.011
0.016
0.025
0.063
0.138
0.197
0.264
0.309
0.353
0.408
0.451
0.933
0.858
0.797
0.728
0.682
0.637
0.576
0.524
0.781
0.695
0.575
0.468
0.372
0.318
0.267
0.209
0.032
0.092
0.184
0.291
0.368
0.428
0.482
0.520
0.187
0.213
0.241
0.242
0.260
0.255
0.252
0.272
0.503
0.668
0.934
1.101
1.191
1.212
1.180
1.152
2.505
2.698
3.090
3.314
3.122
3.029
2.698
2.222
Figure 2. Solubility curve for [C2OHmim]BF4 (1) + ethanol (2) + ethyl
acetate (3) at T ) 298.15 K.
Table 8. Tie Line Data for [edmim]BF4 (1) + Ethanol (2) + Ethyl
Acetate (3) at T ) 298.15 K
EA-rich phase
IL-rich phase
x1
x2
x3
x1
x2
x3
ꢀ
S
0.057
0.058
0.058
0.058
0.059
0.063
0.070
0.080
0.062
0.104
0.147
0.203
0.252
0.303
0.336
0.350
0.881
0.838
0.795
0.739
0.689
0.634
0.594
0.569
0.564
0.506
0.459
0.420
0.381
0.334
0.286
0.244
0.037
0.080
0.138
0.177
0.218
0.263
0.306
0.334
0.399
0.414
0.403
0.403
0.401
0.403
0.409
0.422
0.597
0.762
0.940
0.873
0.863
0.868
0.909
0.953
1.317
1.540
1.853
1.603
1.481
1.364
1.320
1.285
Table 9. Tie Line Data for [C2OHdmim]BF4 (1) + Ethanol (2) +
Ethyl Acetate (3) at T ) 298.15 K
Figure 3. Solubility curve for [edmim]BF4 (1) + ethanol (2) + ethyl acetate
(3) at T ) 298.15 K.
EA-rich phase
IL-rich phase
x1
x2
x3
x1
x2
x3
ꢀ
S
0.003
0.004
0.006
0.008
0.012
0.018
0.019
0.022
0.126
0.163
0.238
0.285
0.341
0.392
0.433
0.445
0.871
0.833
0.756
0.707
0.647
0.590
0.548
0.533
0.616
0.520
0.428
0.357
0.310
0.260
0.212
0.165
0.084
0.153
0.238
0.290
0.346
0.423
0.437
0.453
0.301
0.327
0.335
0.352
0.345
0.317
0.351
0.382
0.664
0.939
0.999
1.019
1.014
1.079
1.008
1.018
1.926
2.390
2.259
2.046
1.903
2.006
1.574
1.420
The selectivity (S) and distribution ratio (ꢀ) are important
parameters in assessing the feasibility of utilizing the solvent
in liquid–liquid extraction. With regard to the ethanol + ethyl
acetate mixture studied, the selectivity (S) of extracting ethanol
from the mixture and the distribution ratio (ꢀ) of ethanol in
two phases are given in terms of mole fraction as:
(x2 ⁄ x3) ionic liquid rich phase
S )
(x2 ⁄ x3) ethyl acetate rich phase
(x2) ionic liquid rich phase
Figure 4. Solubility curve for [C2OHdmim]BF4 (1) + ethanol (2) + ethyl
acetate (3) at T ) 298.15 K.
ꢀ )
(x2) ethyl acetate rich phase
Similarly for the other three ionic liquids, the ethyl
acetate-ethanol mixture all divided into the ethyl acetate rich
phase and the ionic liquid rich phase, which result in the
distribution of ethanol in the two new phases.
As Figure 9 shows, the relationship between the distribution
ratio and the ethanol content in the ethyl acetate rich phase of
the four ionic liquids is complicated and intercrossed at different
districts of ethanol content. When the ethanol content in the

Journal of Chemical & Engineering Data, Vol. 53, No. 2, 2008 431
Figure 5. Tie lines for [emim]BF4 (1) + ethanol (2) + ethyl acetate (3) at
T ) 298.15 K.
Figure 8. Tie lines for [C2OHdmim]BF4 (1) + ethanol (2) + ethyl acetate
(3) at T ) 298.15 K.
Figure 9. Comparison of distribution ratio. 2, [C2OHmim]BF4; b,
[C2OHdmim]BF4; 4, [emim]BF4; O, [edmim]BF4. x2 refers to the mole
fraction of ethanol.
Figure 6. Tie lines for [C2OHmim]BF4 (1) + ethanol (2) + ethyl acetate
(3) at T ) 298.15 K.
content was about 0.3 mole fraction, the order changed into
[C2OHmim]BF4 > [emim]BF4 > [C2OHdmim]BF4 > [ed-
mim]BF4.
As Figure 10 shows, the selectivity of the four ionic liquids
is alike. When the ethanol content in the ethyl acetate rich phase
rises, the selectivity of ionic liquids goes up and then decreases.
When the ethanol content in the ethyl acetate rich phase arrives
at about 0.25 mole fraction, the selectivity of [C2OHmim]BF4
reaches the maximum, while the ethanol content is about 0.15
mole fraction for [emim]BF4, [edmim]BF4, and [C2OHdmim]-
BF4. The order of the selectivity is [C2OHmim]BF4
>
[C2OHdmim]BF4 > [emim]BF4 > [edmim]BF4. In the four
ionic liquids studied, [edmim]BF4 had an overall ꢀ less than
1.0, which means more ethanol was restrained in the EA phase
than extracted into the IL phase. This may be a handicap in the
separation of ethanol and ethyl acetate.
The selectivity of [emim]BF4 is clearly larger than [ed-
mim]BF4, and the selectivity of [C2OHmim]BF4 is clearly large
than [C2OHdmim]BF4. The difference between the selectivity
values may results from [C2OHdmim]BF4 and [edmim]BF4
having a C2 position CH3 instead of a C2 position H. The
hydrogen at the C2 position of the imidazolium ring is known
to be the most acidic hydrogen on the ring. Therefore, the cation
Figure 7. Tie lines for [edmim]BF4 (1) + ethanol (2) + ethyl acetate (3)
at T ) 298.15 K.
ethyl acetate rich phase arrives at about 0.13 mole fraction, the
distribution ratio’s order was [emim]BF4 > [edmim]BF4
>
[C2OHdmim]BF4 > [C2OHmim]BF4, whereas when the ethanol

432 Journal of Chemical & Engineering Data, Vol. 53, No. 2, 2008
VOCs, the use of ionic liquids to separate ethyl acetate and
ethanol takes advantage of their low vapor pressure and their
ability to be easily transported and reused.
Ionic liquids have been regarded as “designed” solvents by
a combination of different anions and cations. We believe that
this art of controlling the mutual solubility between ionic liquids
and other solvents by adjusting groups at different positions of
the cation should regarded as “further design” of ionic liquids.
Tie Line Correlation. The nonrandom two-liquid equation
(NRTL) by Renon and Prausnitz17 was employed to correlate
the experimental tie line data for the ternary systems investi-
gated. Despite the fact that it is intended for nonelectrolyte
solutions, a proper model for ionic liquids has not yet been
developed for correlation and prediction purposes. Previous
works used the NRTL equation to satisfactorily correlate LLE
data.18–23
In the conjugated solutions:
Figure 10. Comparison of selectivity. 2, [C2OHmim]BF4; b,
[C2OHdmim]BF4; 4, [emim]BF4; O, [edmim]BF4. x2 refers to the mole
fraction of ethanol.
ꢁiγi ) ꢁ/ γ/
i
i
The objective function (OF) is defined as shown:
Table 10. Values of Parameters for the NRTL Equation for the
Ternary Mixtures { [emim]BF4 (1) or [C2OHmim]BF4 (1) or
[edmim]BF4 (1) or [C2OHdmim]BF4 (1) + Ethanol (2) + Ethyl
Acetate (3)}
OF ) ln(x/i ⁄ xi) ) ln γi - ln γ/i
where xi ) the mole fraction of the EA-rich phase; x*i ) the
mole fraction of the IL-rich phase; γi ) the activity coefficient
of the EA-rich phase; γ*i ) the activity coefficient of the IL-
rich phase; and i ) the component indices.
component (i-j)
τij
R
rmsd
[emim]BF4 (1), Ethanol (2), Ethyl Acetate (3)
1–2
1–3
2–3
6.799
-2.327
-1.891
2.509
10.390
3.952
0.20
0.001
The experimental values of OF were acquired by ln(x*i /xi),
while the calculated values of OF were obtained by ln γi - ln
γ*i through the NRTL equation.
[C2OHmim]BF4 (1), Ethanol (2), Ethyl Acetate (3)
1–2
1–3
2–3
9.041
-1.438
-1.894
3.262
7.829
3.956
0.20
0.008
0.001
0.001
The R (the nonrandomness parameter) value of 0.2 is
commonly used.24 τ (the interaction parameters) calculated
values are not very different for [C2OHmim]BF4 and
[C2OHdmim]BF4 because the two ionic liquids have a similar
structure and physical properties. The only slight difference
between the interaction parameter values may results from
[C2OHdmim]BF4 having a C2 position CH3 instead of a C2
position H as discussed above.
The interaction parameters τ calculated are quite different
for [C2OHmim]BF4 and [emim]BF4, and [C2OHmim]BF4 has
better extraction capacity than [emim]BF4 because the hydroxyl
group has the strong ability to form a hydrogen bond with
ethanol as discussed above.
The τ23 and τ32 calculated by the NRTL equation approach
Arce’s results,24 which means these values are credible. The
rmsd values from Table 10 provide a measure of the accuracy
of the correlation. As can be inferred from the rmsd values,
fairly good correlation of the experimental values with the
NRTL model was obtained.
[edmim]BF4 (1), Ethanol (2), Ethyl Acetate (3)
1–2
1–3
2–3
1.326
-1.138
-1.893
2.218
4.947
3.954
0.20
[C2OHdmim]BF4 (1), Ethanol (2), Ethyl Acetate (3)
1–2
1–3
2–3
7.881
-1.982
-1.895
3.174
9.749
3.955
0.20
can presumably form a hydrogen bond with the alcohol at this
hydrogen.16 By replacing the hydrogen of the [emim] or
[C2OHmim] cation with a methyl group (forming [edmim] or
[C2OHdmim]), the ability of the cation to form a hydrogen bond
with ethanol is diminished, indirectly resulting in an increase
in the mutual solubility of the ionic liquid [edmim]BF4 or
[C2OHdmim]BF4 and ethyl acetate, which explains why
[emim]BF4 has better extraction capacity than [edmim]BF4 and
[C2OHmim]BF4 is better than [C2OHdmim]BF4.
The selectivity of [C2OHmim]BF4 is clearly larger than
[emim]BF4, and the selectivity of [C2OHdmim]BF4 is clearly
larger than [edmim]BF4. The difference between the selectivity
values may result from [C2OHmim]BF4 and [C2OHdmim]BF4
having a hydroxyl group. The hydroxyl group obviously
enhances the interaction between the ionic liquid and ethanol.
The order of the selectivity in the four ionic liquids shows that
the hydroxyl group should have a stronger ability to affect the
interaction between the ionic liquid and ethanol than the C2
position H.
Conclusions
Liquid–liquid equilibrium data were obtained for the ternary
mixtures of [emim]BF4 or [C2OHmim]BF4 or [edmim]BF4 or
[C2OHdmim]BF4 + ethanol + ethyl acetate at 298.15 K. The
extraction efficiencies of the four ionic liquids for the ethyl
acetate + ethanol mixture were examined. The distribution ratio
and selectivity values show that the hydroxyl group on cation
can obviously enhance the interaction between the ionic liquid
and ethanol, while the CH3 group at the 2-position weakens
these interactions. [C2OHmim]BF4 has better extraction capacity
than the other studied ionic liquids, which can be the potential
solvent for the separation of ester acetic and ethanol by
liquid–liquid extraction.
On the basis of the discussion above, [C2OHmim]BF4 has
better extraction capacity than other studied ionic liquids, which
can be the potential solvent for the separation of ester acetic
and ethanol by liquid–liquid extraction. Compared with using

Journal of Chemical & Engineering Data, Vol. 53, No. 2, 2008 433
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Received for review September 07, 2007. Accepted November 26, 2007.
We would like to thank the financial support from the National Natural
Science Foundation of China (Grant No. 20490209 and 20625621).
JE700516T