Activity coefficients at infinite dilution of organic compounds in 1-butyl-3-methylimidazolium tetrafluoroborate using inverse gas chromatography

Article abstract of DOI:10.1021/je800658v

Activity coefficients at infinite dilution (γ^∞) of organic compounds in the room-temperature ionic liquid 1-butyl-3- methylimidazolium tetrafluoroborate were determined using inverse gas chromatography from (303.35 to 332.55) K. Retention data

Full text of DOI:10.1021/je800658v

9
0
J. Chem. Eng. Data 2009, 54, 90–101
Activity Coefficients at Infinite Dilution of Organic Compounds in
-Butyl-3-methylimidazolium Tetrafluoroborate Using Inverse Gas
1
Chromatography
†
,†
‡
†
†
Anne-Laure Revelli, Fabrice Mutelet,* Mireille Turmine, Roland Solimando, and Jean-No e¨ l Jaubert
Laboratoire de Thermodynamique des Milieux Polyphas e´ s, Nancy-Universit e´ , 1 rue Grandville, BP 20451 54001 Nancy, France,
and Laboratoire d’Electrochimie et Chimie Analytique (UMR7575) Energ e´ tique et R e´ activit e´ aux Interfaces, Universit e´ Pierre et
Marie Curie-PARIS6, case 39, 4 place Jussieu, 75252 Paris Cedex 05, France
∞
Activity coefficients at infinite dilution (γ ) of organic compounds in the room-temperature ionic liquid
1
-butyl-3-methylimidazolium tetrafluoroborate were determined using inverse gas chromatography from
(
303.35 to 332.55) K. Retention data were used to estimate the influence of gas-liquid and gas-solid
interfacial adsorption on the value of activity coefficients at infinite dilution of solutes in this ionic liquid.
Most of the polar solutes were retained largely by partition, while n-alkanes were retained predominantly
by interfacial adsorption on the ionic liquid studied. The solvation characteristics of the ionic liquid were
evaluated using the Abraham solvation parameter model.
Introduction
This study is a continuation of our investigations on ther-
modynamic properties of imidazolium-based ionic liquids.
16-20
Development of safer and environmentally friendly processes
and products is needed to achieve sustainable production and
consumption patterns. New chemical products, such as ionic
liquids, which are of great interest to the chemical and related
industries because of their attractive properties as solvents,
should be considered. Ionic liquids (ILs) are low-melting organic
salts built with an unsymmetrical organic cation and an anion
that is mostly inorganic. Physical and chemical properties of
ILs are influenced not only by the nature of the cation and the
nature of cation substituents but also by the polarity and the
size of the anion. Interactions between IL cations and anions
are the consequence of energetic and geometric factors leading
to a variety of strongly organized and oriented structures. These
Our aim is to focus on the influence of a polar moiety on the
thermodynamic properties of the ionic liquid. More precisely,
we try to define the best structure of the ionic liquids for a given
industrial application. In previous works, we have shown that
introduction of a polar chain in ionic liquids also strongly affects
the behavior of organic compounds in mixtures with the ionic
liquids. A short polar chain in imidazolium-based ionic liquids
increased their selectivity toward mixtures containing {alcohol
2
0
+
aliphatic} or {aromatic + aliphatic}.
Nevertheless, there is a lack of data for ionic liquids used as
a reference in various studies. Moreover, it can be found that
there are two literature sources for the thermodynamic properties
of organic compounds in the extensively studied 1-butyl-3-
methylimidazolium tetrafluoroborate ionic liquid. These data
present a large discrepancy (of about 30 %).
1-8
features infer to ILs numerous applications.
As environmen-
tally benign “green” solvents, ionic liquids have been used in
industrial processes for more than a decade, and their applica-
tions continue to expand. Recently, it was shown that imida-
zolium-based ionic liquids could be used in the liquid-liquid
This work presents activity coefficients at infinite dilution
for a series of organic compounds dissolved in 1-butyl-3-
1
0-15
methylimidazolium tetrafluoroborate [BMIM][BF
using the inverse gas chromatography technique.
] measured
4
extraction of thiophene from aliphatic hydrocarbons
and
of methanol from aliphatic hydrocarbons. It is then clear that
ionic liquids may play an important role since regulations
regarding liquid hydrocarbon fuels are continuously requiring
sulfur content to be reduced to lower levels. The current
specification in Europe and in the USA has defined the
It must be pointed out that the retention in gas chromatog-
raphy is a complex process involving partition between the gas
and the liquid phase but also the adsorption at solid-liquid and
gas-liquid interfaces. Therefore, the comprehensive retention
model should consider not only the contribution resulting from
the gas-liquid partitioning but also the adsorption occurring at
the interface between the bulk liquid and the solid support and
-6
maximum sulfur mass fraction as less than 50 ·10 in gasoline
-6
starting from 2005. This level will be reduced to 10 ·10 by
9
the year 2010. Ionic liquids may also be used for the extraction
2
1-24
at the interface between the gas phase and the bulk liquid.
of methanol from crude oil. Indeed, large amounts of methanol
are used to prevent the hydrate plugs from forming in oil
pipelines, but the presence of high concentrations of methanol
in crude oils can lead to costly problems during refinery
operations.
The classical equation taking into account partition and inter-
facial adsorption contributions in the GC mechanism can be
2
5-27
written as follows
V ) V K + A K + A K
LS GLS
(1)
where V , V , AGL, and ALS are the net retention volume per
N
L
L
GL GL
*
Author to whom correspondence should be addressed. E-mail: mutelet@
ensic.inpl-nancy.fr. Telephone number: +33 3 83 17 51 31. Fax number:
33 3 83 17 51 52.
Nancy-Universit e´ .
Universit e´ Pierre et Marie Curie-PARIS6.
N
L
gram of packing, the volume of liquid phase per gram of
packing, the liquid surface area per gram of column packing,
and the liquid-solid interfacial surface area per gram of column
+
†
‡
1
0.1021/je800658v CCC: $40.75

2009 American Chemical Society
Published on Web 12/04/2008

Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009 91
packing, respectively. K , KGL, and KGLS represent the gas-liquid
five solvent coefficients (e, s, a, b, l) as a summation of their
respective cation and anion
L
partition coefficient, the adsorption coefficient at the gas-liquid
interface, and the coefficient for adsorption at the support
surface, respectively. Performing a series of measurements with
increasing loading of the liquid phase makes it possible to
extrapolate the V /V ratio against 1/V toward 1/V ) 0 and
log SP ) c + (ecation + eanion)E + (scation + sanion)S + (acation
+
aanion)A + (bcation + banion)B + (lcation + lanion)L (3)
Cation-specific and anion-specific equation coefficients of eight
cations and four anions were established to estimate the
logarithm of the gas-to-IL partition coefficients. The major
advantage of this method is that we can make predictions for
more ILs by combining the set of ion coefficients.
N
L
L
L
to obtain the value of the gas-liquid partition coefficient, KL,
independent of adsorption contributions. This approach was
successfully used to obtain gas-liquid partition coefficients of
24,28
polar probes.
Several studies on the influence of concurrent
retention mechanisms on the determination of stationary phase
In this work, activity coefficients at infinite dilution of 44
polar and nonpolar compounds (alkanes, alkenes, alkynes,
cycloalkanes, aromatics, alcohols) have been determined in the
ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate at
(303.35, 312.55, 322.55, and 332.55) K. Experimental results
were analyzed using the LSER approach.
selectivity showed that the n-alkanes were retained predomi-
1
7,19,23
nantly by interfacial adsorption on RTILs.
This can be
explained because of the immiscibility of n-alkanes with polar
salts. Ionic liquids can easily adsorb on solid surfaces and may
form a strongly structured interface at the surface of the support.
2
9
Lynden-Bell et al. used simulation to investigate the surface
structure in models of 1-butyl-3-methylimidazolium ionic liquids
with a number of inorganic anions. The authors found that the
cations are preferentially aligned with their rings perpendicular
to the phase surface and their NN axes parallel to the surface
normal. The [BMIM] cation shows a strong preference for the
butyl group to put away from the bulk of the liquid. Computer
simulation predicted that pure ionic liquids of the 1-alkyl-3-
methylimidazolium family show structuring of their liquid
phases in a manner that is analogous to microphase separation
between polar and nonpolar domains. Polar domain has the
structure of a tridimensional network of ionic channels, whereas
the structure of a nonpolar domain depends on the chain length
Experimental Section
Materials or Chemicals. Sodium tetrafluoroborate (98 %),
1
-methylimidazole (99 %), 1-bromobutane (99 %), and aceto-
nitrile (99 %) were purchased from Acros Organics. Acetone
Normapur) was obtained from Prolabo, and ethyl acetate (purex
(
for analysis) and dichloromethane were from Solvants Docu-
mentation Synth e` ses. All mixtures were prepared in ultrapure
water (all water used was distilled and then filtered with an
ELGA UHQ II system, κ ) 18 MΩ). Imidazolium salt was
3
6
synthesized according to standard methods. An excess of
1
1
-bromobutane was slowly added to a stirred solution of
-methylimidazole in ethyl acetate. The mixture was then heated
3
0
at reflux for 24 h. The reaction was stopped when two phases
were formed. The bottom phase contained the 1-butyl-3-
methylimidazolium bromide [BMIM][Br]. This was washed
three times with ethyl acetate to remove any unreacted reagents.
Residual ethyl acetate was removed by heating (70 °C) under
vacuum (12 h). [BMIM][Br] was obtained as a colorless
of an alkyl chain. This interface may induce the adsorption
of polar solutes. For this reason, it was decided to use the above-
described experimental procedure that allows the separation of
the adsorption contribution.
To quantify intermolecular solute-IL interactions, we have
used the linear solvation energy relationship (LSER) developed
3
1-34
by Abraham et al.
This method allows us to correlate
hygroscopic solid. A solution of NaBF in acetone was added
4
thermodynamic properties of phase transfer processes. The most
recent representation of the LSER model is given by eq 2
slowly to a rapidly stirring solution of [BMIM][Br]. The mixture
was then stirred at room temperature for four days and filtered
through celite, and the acetone was removed with a rotary
evaporator. The resultant viscous liquid was dissolved in
dichloromethane (CH Cl ) and washed with small volumes of
log SP ) c + eE + sS + aA + bB + lL
(2)
where SP is a solute property related with the free energy change
such as gas-liquid partition coefficient, specific retention
volume, or adjusted retention time at a given temperature. The
capital letters represent the solute properties and the lower case
letters the complementary properties of the ionic liquids. The
solute descriptors are the excess molar refraction E, dipolarity/
polarizability S, hydrogen bond acidity basicity A and B,
respectively, and the gas-liquid partition coefficient on n-
hexadecane at 298 K, L. The coefficients c, e, s, a, b, and l are
not simply fitting coefficients, but they reflect complementary
properties of the solvent phase.
The system constants are identified as the opposing contribu-
tions of cavity formation and dispersion interactions, l, the
contribution from interactions with lone pair electrons, e, the
contribution from dipole-type interactions, s, the contribution
from the hydrogen-bond basicity of the stationary phase (because
a basic phase will interact with an acid solute), a, and b the
contribution from the hydrogen-bond acidity of the stationary
phase. The system constants are determined by multiple linear
2
2
distilled water (3:1 v/v) until there was no precipitation of AgBr
in the aqueous phase on addition of a concentrated AgNO3
solution. The CH Cl was then evaporated. Traces of water and
2
2
other volatile solvents were removed by freeze-drying im-
mediately before the experiment. [BMIM][BF ] was thereby
4
obtained as colorless, very viscous, and hydrophilic liquids. The
1
13
structure was confirmed by H and C NMR spectroscopies
3
7,57
and mass spectrometry.
The residual water in the freshly
prepared molten salt was titrated using a Karl Fisher apparatus
(684KF Coulometer, Metrohm): [BMIM][BF ] contained about
4
-4
7.2·10 g of water.
Apparatus and Experimental Procedure. Inverse chroma-
tography experiments were carried out using a Varian CP-3800
gas chromatograph equipped with a heated on-column injector
and a flame ionization detector. The injector and detector
temperatures were kept at 523 K during all experiments. Helium
flow rate was adjusted to obtain adequate retention times.
Methane was used to determine the column hold-up time. Exit
gas flow rates were measured with an Alltech Digital Flow
Check Mass Flowmeter. The temperature of the oven was
measured with a Pt 100 probe and controlled to within 0.1 K.
A personal computer directly recorded detector signals, and
corresponding chromatograms were obtained using Galaxie
software.
regression analysis of experimental log SP (log K in this work)
L
values for a group of solutes of sufficient number and variety
to establish the statistical and chemical validity of the model.
3
5
Recently, Sprunger et al. proposed to separate the anion
and cation contributions in the LSER model. The authors have
modified the LSER equation, eq 3, by rewriting each of the

9
2
Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009
Figure 1. Plot of the net retention volume per gram of packing as a function of mass fraction loading w of 1-butyl-3-methylimidazolium tetrafluoroborate
for n-alkanes.
Figure 2. Plot of the net retention volume per gram of packing as a function of mass fraction loading w of 1-butyl-3-methylimidazolium tetrafluoroborate
bromide for aromatics, alkenes, and alkynes.
Column packing of 1 m length containing a mass fraction of
IL from (10 to 25) % on Chromosorb WHP (60 to 80 mesh)
was prepared using the rotary evaporator technique. After
evaporation of the chloroform under vacuum, the support was
equilibrated at 323 K during 6 h. The mass of the packing
material was calculated from the mass of the packed and empty
column and was checked during experiments. The masses of
the stationary phase were determined with an uncertainty of (
by the helium stream, the measurements of retention times were
repeated systematically every day for three selected solutes. No
changes in the retention times were observed during this study.
Theoretical Basis. The retention data determined with inverse
chromatography experiments were used to calculate activity
coefficients at infinite dilution of the solute in the ionic liquid
3
8
with the following expression
0
1
∞
1
n2RT
B11 - V
2B - V
13
0
5
.0003 g. A volume of the headspace vapor of samples of (1 to
∞
,2
0
1
ln γ1 ) ln
- P
+
JP0 (4)
) µL were introduced to be in infinite dilution conditions. Each
0
1
(
)
RT
RT
V P
N
experiment was repeated at least twice to check the reproduc-
ibility. Retention times were generally reproducible to within
n is the mole number of the stationary phase component
inside the column; R is the ideal gas constant; T is the
temperature of the oven; B11 is the second virial coefficient
2
(
0.01 to 0.03) min. To check the stability of the experimental
conditions, such as the possible elution of the stationary phase

Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009 93
Figure 3. Plot of the net retention volume per gram of packing as a function of mass fraction loading w of 1-butyl-3-methylimidazolium tetrafluoroborate
for some polar probes.
Figure 4. Plot of the net retention volume per gram of packing as a function of mass fraction loading w of 1-butyl-3-methylimidazolium tetrafluoroborate
for some polar probes.
of the solute in the gaseous state at temperature T; B13 is the
However, in the case where gas-liquid adsorption takes place
in the column, eq 4 when the last two terms are neglected can
be rewritten as follows
mutual virial coefficient between the solute 1 and the carrier
0
gas gelium 3; P1 is the probe vapor pressure at temperature
T; P is the pressure at the column outlet. V denotes the
0
N
RTF2
∞
,2
standardized retention volume calculated using the classical
γ1
)
(5)
0
3
8
P M K
2 L
equation described in the literature. The factor J corrects
1
3
9
for the influence of the pressure drop along the column.
where F is the density of the solvent; M is the molecular weight
2
2
0
The values of P and B11 have been taken from the
literature. The molar volume of the solute V was deter-
1
of the stationary phase; and K is the bulk solution partition
L
4
0
0
1
coefficient. The best method of determining K in the presence
of interfering adsorption effects is to plot V /V against 1/V .
Then according to eq 1, K is obtained from the intercept.
L
mined from experimental densities, and the partial molar
N
L
L
∞
volumes of the solutes at infinite dilution V were assumed
1
L
0
to be equal to V . Values of B were estimated using
1
13
4
1-43
Results and Discussion
Tsonopolous’s method.
Critical parameters and acentric
factors used for the calculations were taken from the
literature.
Influence of Concurrent Retention Mechanisms. To correct
for gas-liquid adsorption, the net retention volume VN was
4
0,44

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4
Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009
Figure 5. Relative percent contribution of gas-liquid partitioning and gas-liquid interfacial adsorption to retention on 1-butyl-3-methylimidazolium
tetrafluoroborate (15.30 % w/w) at 322.55 K.
Figure 6. Plot of V /V against 1/VL for aromatics, alkenes, and alkynes on 1-butyl-3-methylimidazolium tetrafluoroborate.
N
L
calculated for all the solutes at different solvent liquid loading
The activity coefficients at infinite dilution not corrected from
interfacial adsorption are calculated using eq 4. The errors in
the γ values may be obtained from the law of propagation of
V . Then, the graphs of V /V versus 1/V were drawn for each
L
N
L
L
∞
solute, and the partition bulk coefficient K was obtained from
L
the intercept. A horizontal line is expected for a pure partitioning
system and a line with a slope and positive intercept on the
V /V axis for a mixed retention mechanism. The K value is
errors. The following measured parameters exhibit errors which
must be taken into account in the error calculations with their
corresponding standard deviations: the adjusted retention time
N
L
L
then used in eq 5 to calculate the activity coefficient at infinite
dilution for bulk solvent loading, i.e., assuming that no
adsorption of the solute at the gas-liquid interface occurs.
Nevertheless, special attention has to be paid when a retention
model is used. From our experience, we observed that reduced
retention times have to be higher than 1 min. Indeed, short
retention times induce high uncertainties on the infinite dilution
t ′, ( 0.01 min; the flow rate of the carrier gas, ( 0.1
R
3
-1
cm ·min ; mass of the stationary phase, 2 %; the inlet and
outlet pressures, ( 0.002 bar; the temperature of the oven, (
0.1 K. The main source of uncertainty in the calculation of the
net retention volume is the determination of the mass of the
stationary phase. The estimated uncertainty in determining
the net retention volume V is about 2 %. Taking into account
N
∞
activity coefficient. In this case, values of corrected γ values
may be ten times higher than uncorrected values.
that thermodynamic parameters are also subject to an uncer-
∞
tainty, the resulting uncertainty in the γ values is about 3 %.

Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009 95
Figure 7. Plot of V /V against 1/VL for alcohols, ketones, 1,4-dioxane, and ether on 1-butyl-3-methylimidazolium tetrafluoroborate.
N
L
Figure 8. Plot of V /V against 1/VL for some test probes on 1-butyl-3-methylimidazolium tetrafluoroborate.
N
L
In Figures 1 to 4, the net retention volume per gram of
gas-liquid partition coefficients with their uncertainty and
activity coefficients at infinite dilution uncorrected and corrected
from interfacial adsorption are listed in Tables 1 and 2. Activity
coefficients at infinite dilution of n-alkanes are multiplied by
two when corrected from interfacial adsorption. As expected,
adsorption effects decrease with temperature.
packing V as a function of the percent phase loading is plotted
N
for nonpolar and polar solutes. In [BMIM][BF ], the polar
4
solutes are retained by partitioning with a small contribution
from adsorption while the n-alkanes are retained predominantly
by adsorption. Indeed, n-alkanes are almost immiscible in ionic
liquids, and gas-liquid interfacial adsorption is then predomi-
nant. Figure 1 indicates that the retention of the n-alkanes with
the ionic liquid stationary phase does not follow the pattern
observed with polar solutes. Probably, at low loading of the
stationary, the support is not completely coated, and results do
not follow the initial straight line. Relative percent contribution
of gas-liquid partitioning and gas-liquid interfacial adsorption
to retention on 1-butyl-3-methylimidazolium tetrafluoroborate
with w ) 15.30 % at 322.55 K is represented in Figure 5. The
average contribution of gas-liquid partitioning and gas-liquid
interfacial adsorption for polar solutes to retention is 95 % and
The magnitude of the activity coefficient values obtained in
this study is significantly higher than the corresponding values
1
6-20,45-53
∞
for other ionic liquids.
As an example, the γ value
for hexane in 1-butyl-3-methylimidazolium tetrafluoroborate is
132.86 (this work), while in 1-butyl-3-methylimidazolium octyl
1
7
sulfate, it is 4.75; in 1-hexyl-3-methylimidazolium tetrafluo-
4
5
roborate it is 22.1; and in 1-ethyl-3-methylimidazolium
5
2
thiocyanate it is about 300 (the highest value found in the
literature). The high values of activity coefficients at infinite
dilution of n-alkanes indicate their low solubility in ionic liquids.
This trend is in good agreement with the data obtained in the
1
6-20,45-49
50,51
5
%, respectively.
The gas-liquid partition coefficients were calculated from
Figures 6 to 8, and activity coefficients at infinite dilution were
imidazolium
and pyridinium
ionic liquids. The
∞
γ values for the n-alkanes increase with an increase in carbon
number. The γ values of n-alkanes are higher than the values
∞
determined from values of KL constants. Values for the
obtained with cyclohexane, alkenes, alkynes, and aromatics.

9
6
Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009
Table 1. Experimental Activity Coefficients at Infinite Dilution of 44 Organic Compounds in the 1-Butyl-3-methylimidazolium
Tetrafluoroborate at (303.35 and 312.55) K as a Function of Loading w
T ) 303.35 K
T ) 312.55 K
∞
∞
uncorrected values of γ
uncorrected values of γ
100 w
1
00 w
20.00
corrected data
corrected data
∞
∞
solutes
10.10
15.30
25.29
KL
γ
10.10
15.30
20.00
25.29
KL
γ
hexane
-methylpentane
heptane
94.31
63.86
91.43
75.22
94.92
79.77
97.27
83.22
3.6 ( 0.1
3.1 ( 0.2
132.86
126.11
53.98
50.49
81.01
58.14
81.63
66.88
88.05
72.27
2.6 ( 0.1
2.9 ( 0.2
130.45
94.30
250.01
231.46
368.37
792.80
53.50
48.41
82.69
98.21
2.17
3.96
6.73
7.40
6.68
5.55
39.33
7.53
12.54
1.48
2.60
2.57
1.24
1.22
1.91
2.70
2.76
3.99
3.82
0.33
9.39
33.47
1.04
0.72
5.44
0.63
0.56
1.46
3
120.31 153.58 158.75 163.29
,2,4-trimethylpentane 131.90 157.46 164.29 173.75
6.0 ( 0.7
259.08 104.58 109.00 140.75 145.15
321.18 106.39 119.42 146.13 154.18
424.91 159.46 180.85 219.51 237.48
955.62 262.08 297.41 366.37 417.22
4.1 ( 1.0
2
4.5 ( 0.3
4.2 ( 0.3
octane
nonane
methylcyclopentane
cyclohexane
methylcyclohexane
cycloheptane
benzene
toluene
ethylbenzene
m-xylene
p-xylene
o-xylene
188.44 244.70 256.17 273.12
305.91 419.55 450.19 484.31
11.5 ( 0.3
17.5 ( 0.6
8.5 ( 0.1
8.4 ( 0.1
12.6 ( 1.2
7.0 ( 0.3
43.92
44.97
66.93
63.26
2.51
4.23
7.41
7.77
7.05
6.21
36.41
7.77
12.74
1.61
2.80
2.81
1.35
1.32
2.33
3.34
3.23
4.83
5.38
0.37
8.46
26.90
1.03
0.70
5.37
0.66
0.58
1.56
14.91
1.00
1.62
0.22
1.36
2.22
50.33
49.18
75.49
67.67
2.56
4.31
7.62
7.78
7.18
6.34
37.40
7.45
12.43
1.64
2.85
2.89
1.39
1.32
2.28
3.33
3.24
4.80
5.21
0.37
8.99
27.69
1.05
0.71
5.51
0.66
0.59
1.55
25.62
1.01
1.62
0.22
1.37
2.21
51.84
46.28
77.65
68.04
2.53
4.24
7.49
7.82
7.20
6.37
38.11
7.47
12.57
1.65
2.87
2.90
1.38
1.33
2.29
3.39
3.30
4.78
5.33
0.33
8.93
26.58
1.07
0.71
5.54
0.67
0.56
1.56
25.24
0.95
1.64
0.23
1.41
2.27
52.73
51.62
79.54
70.26
2.46
4.16
7.35
62.19
62.53
98.30
78.71
2.20
4.37
7.25
7.81
7.36
6.53
48.02
8.29
13.22
1.50
2.60
2.63
1.26
1.22
2.15
3.12
3.20
4.17
4.74
0.36
10.15
30.70
1.04
0.69
5.53
0.65
0.59
1.54
9.44
1.00
1.56
0.22
1.38
2.19
40.53
40.89
60.39
82.31
2.50
4.20
7.44
7.23
7.06
5.53
30.82
7.17
12.35
1.63
2.82
2.84
1.38
1.19
2.12
3.06
2.93
4.22
4.63
0.37
8.38
23.86
1.09
0.76
5.38
0.65
0.60
1.53
16.43
1.01
1.63
0.23
1.33
2.21
41.03
39.86
60.76
80.45
2.32
3.89
6.95
6.98
6.49
5.74
32.96
6.90
11.55
1.50
2.64
2.62
1.27
1.06
1.75
2.79
2.72
3.79
4.09
0.32
8.26
24.19
1.03
0.69
5.11
0.61
0.55
1.40
25.42
0.94
1.52
0.45
1.29
2.09
46.62
45.00
68.33
89.34
2.44
4.09
7.39
7.48
6.95
6.09
35.26
7.32
12.28
1.61
2.78
2.80
1.36
1.21
2.00
2.98
2.87
4.14
4.37
0.34
8.72
26.60
1.07
0.75
5.52
0.64
0.58
1.50
22.14
1.00
1.60
0.24
1.35
2.19
47.20
44.88
71.27
93.24
2.35
4.03
7.15
11.9 ( 0.1
15.7 ( 0.1
37.6 ( 0.8
344.2 ( 4.2
555.7 ( 15.9
928.5 ( 59.1
10.6 ( 0.3
12.6 ( 0.3
29.3 ( 0.2
240.6 ( 7.5
402.2 ( 7.2
636.2 ( 21.1
683.0 ( 29.8
720.5 ( 12.8
7.48 1041.4 ( 10.1
6.93 1037.0 ( 14.6
6.11 1553.3 ( 27.5
40.34
7.65
12.73
1.58
2.75
2.77
7.18
6.76
5.90 1122.9 ( 68.9
1
1
1
2
2
3
1
-hexene
-hexyne
-heptyne
-butanone
-pentanone
-pentanone
,4-dioxane
8.2 ( 0.7
68.0 ( 0.9
128.6 ( 3.8
493.4 ( 17.2
764.5 ( 32.5
691.1 ( 33.0
37.23
7.51
12.53
1.56
2.71
2.71
7.1 ( 0.4
52.1 ( 1.1
90.9 ( 1.4
342.4 ( 7.1
507.5 ( 10.0
466.0 ( 10.3
1.29 1556.3 ( 59.4
1.31 1023.2 ( 23.4
methanol
ethanol
1.22
2.23
3.11
3.18
452.2 ( 25.8
535.5 ( 6.4
974.4 ( 53.0
479.9 ( 12.0
1.22
1.98
2.75
2.79
4.07
293.9 ( 16.3
374.0 ( 4.1
672.1 ( 34.6
333.9 ( 7.8
792.0 ( 13.7
1
2
2
1
2
-propanol
-propanol
-methyl-1-propanol
-butanol
,2,2-trifluoroethanol
4.20 1356.5 ( 119.5
4.73 2035.8 ( 103.9
0.36 2579.2 ( 84.9
9.44
30.17
1.02
3.99 1375.4 ( 71.9
0.35 1786.3 ( 39.2
diethylether
diisopropylether
chloroform
dichloromethane
tetrachloromethane
acetonitrile
13.8 ( 0.1
15.9 ( 1.3
359.8 ( 13.3
175.0 ( 5.3
115.5 ( 2.9
9.05
28.77
1.06
0.73
5.33
0.63
11.0 ( 0.3
10.2 ( 1.2
253.3 ( 6.7
130.7 ( 3.0
81.9 ( 2.7
887.2 ( 14.2
0.69
5.40
0.66 1241.7 ( 18.2
-
-
nitromethane
3274.4 ( 41.2
4385.4 ( 58.5
112.5 ( 46.3
0.57 2268.6 ( 49.5
-
14.66
0.99 2141.8 ( 32.2
1.54
0.23
1.31
2.14
1
-nitropropane
2845.7 ( 3.9
81.8 ( 18.8
triethylamine
pyridine
thiophene
formaldehyde
propionaldehyde
butyraldehyde
14.00
8.90
0.99
1.52
0.23
1.33
2.13
0.97 3318.2 ( 102.4
1.53
0.22
1.36
2.19
573.9 ( 19.2
91.8 ( 2.7
171.4 ( 5.6
301.9 ( 7.3
402.7 ( 14.1
66.6 ( 3.6
125.7 ( 5.8
214.1 ( 6.7
Introduction of a double or triple bond in the n-alkanes decreases
In Table 3, our results are compared with other activity
∞
45
53
the γ values. Cyclization of the alkane skeleton reduces the
coefficients measured by Foco et al. and Zhou et al. The
deviations between our uncorrected data and the results by Foco
∞
value of γ in comparison to that of the corresponding linear
4
5
∞
alkanes (e.g., hexane). Aromatics with their π-delocalized
et al. at 303.15 K amount on average to 7.5 %. γ values
∞
electrons have smaller γ values, presumably because of the
obtained follow the same trend as those measured in this work.
∞
53
interaction with the cation species. Using computer simulation,
As can be seen from Table 3, the γ data by Zhou et al. are
2
9
Lynden and co-workers showed that the cations are found to
interact predominantly with the ring of the benzene, while the
anions interact with the ring hydrogens to a first approximation.
about 32 % lower than our uncorrected values and those
4
5
obtained by Foco et al. If we plot γ values obtained in this
5
3
study as a function of the data set of Zhou et al., there is a
linear relationship. This observation indicates that the differences
are not due to the thermodynamic properties of pure compounds
used in the γ calculation but to the determination of the mass
of the stationary phase or to the measurement of the flow rate
∞
In the series of chloromethanes, it was observed that γ values
strongly increase from dichloromethane to tetrachloromethane.
1
7,19
This behavior already observed with different ionic liquids
indicates that polar compounds have better solubility in the
RTILs when attractive interaction between polar molecules and
or to the purity of the ionic liquid.
∞
∞
2
the charged ions of the solvent is possible. The γ values for the
The selectivity value S1 gives the suitability of a solvent as
alcohols are relatively small (ranging between 1.2 and 4.6). The
lone pair of electrons on the oxygen atom could interact with
the ionic liquid cation, and the acidic proton is attracted by
an entrainer in extractive distillation. It is defined as
∞
γ
∞
1⁄RTIL
∞
S )
(6)
oxygen atoms in the cation. γ values of the branched alkanol
12
∞
γ
∞
2⁄RTIL
skeleton are smaller than γ values of the corresponding linear
∞
∞
2
alcohol. γ values of n-alkanols increase with increasing chain
Table 4 shows selectivities S1 for four separation problems:
∞
length. γ values of ethers and amine are higher in comparison
hexane/benzene, hexane/methanol, hexane/thiophene, cyclohex-
ane/thiophene for ionic liquids based on the 1-alkyl-3-meth-
with those of the alcohols.

Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009 97
Table 2. Experimental Activity Coefficients at Infinite Dilution of 44 Organic Compounds in the 1-Butyl-3-methylimidazolium
Tetrafluoroborate at (322.55 and 332.55) K as a Function of Loading w
T ) 322.55 K
T ) 332.55 K
∞
∞
uncorrected values of γ
uncorrected values of γ
100 w
1
00 w
20.00
corrected data
corrected data
∞
∞
solutes
10.10
15.30
25.29
KL
γ
10.10
15.30
20.00
25.29
KL
γ
hexane
-methylpentane
heptane
,2,4-trimethylpentane
octane
nonane
methylcyclopentane
cyclohexane
methylcyclohexane
cycloheptane
benzene
toluene
ethylbenzene
m-xylene
75.62
72.80
91.44
65.91
51.28
73.76
62.44
79.93
67.25
2.5 ( 0.2
2.4 ( 0.1
97.36
82.92
216.04 109.80
197.53 89.22
333.47 144.03 128.62 164.43 182.29
612.49 218.55 201.34 295.55 312.07
42.76
42.66
64.23
56.43
44.60
49.08
43.06
66.68
56.13
68.58
66.47
2.4 ( 0.1
-
3.3 ( 0.4
-
74.19
152.01
142.31
271.78
297.93
463.75
55.40
35.28
57.10
166.53
2.16
3.84
6.51
6.56
6.26
4.77
38.84
6.82
11.74
1.25
2.53
2.52
1.22
1.18
1.53
2.14
2.15
2.84
2.69
0.30
7.42
24.26
1.09
0.79
5.20
0.61
0.56
1.50
3
96.72 116.67 130.64
3.2 ( 0.3
88.48 109.94 113.65
80.85 124.64 122.71
2
92.42 106.06 116.92 139.91
140.45 170.35 198.02 211.10
232.94 270.08 334.94 370.58
37.09
35.98
54.35
3.4 ( 1.2
5.8 ( 0.4
4.2 ( 0.5
9.7 ( 0.3
7.8 ( 0.7
40.33
37.17
56.08
40.71
39.02
61.47
44.00
41.51
61.76
6.1 ( 1.1
36.55
36.05
53.95
32.07
34.29
51.12
37.32
35.08
52.69
42.25
37.79
58.22
3.4 ( 0.5
8.3 ( 1.0
7.2 ( 1.6
10.9 ( 0.1
21.4 ( 0.4
158.9 ( 5.9
262.3 ( 5.6
394.6 ( 7.3
453.6 ( 14.0
447.0 ( 6.6
655.2 ( 9.9
5.5 ( 0.3
8.5 ( 2.2
111.60 108.82 120.74 122.27
131.04 154.93 139.01 147.95 161.56
16.4 ( 0.1
116.5 ( 11.8
183.3 ( 5.1
270.3 ( 12.7
304.8 ( 15.0
307.7 ( 17.4
511.9 ( 39.8
3.7 ( 0.2
2.48
4.17
7.39
7.39
7.01
6.08
29.67
7.35
12.41
1.55
2.85
2.85
1.40
0.96
1.92
2.80
2.65
3.74
4.12
0.36
8.11
21.55
1.13
0.80
5.33
0.63
0.61
1.53
11.45
1.04
1.65
0.25
1.30
2.11
2.32
3.85
6.80
6.78
6.44
5.62
29.20
6.84
11.45
1.42
2.61
2.62
1.28
0.92
1.80
2.48
2.36
3.36
3.67
0.32
8.05
24.96
1.07
0.76
5.06
0.58
0.55
1.39
23.36
0.93
1.50
0.24
1.23
2.03
2.36
3.95
7.00
6.98
6.64
5.76
30.95
7.22
12.20
1.47
2.71
2.71
1.32
0.99
1.82
2.62
2.50
3.56
3.87
0.34
8.45
25.70
1.07
0.77
5.27
0.62
0.57
1.43
24.68
0.98
1.55
0.25
1.26
2.07
2.39
4.00
7.10
6.96
6.77
5.89
33.64
7.46
12.19
1.49
2.74
2.74
1.33
1.14
1.83
2.49
2.54
3.31
3.39
2.25
3.97
6.85
6.89
6.71
5.83
36.27
7.47
11.94
1.44
2.66
2.66
1.28
1.22
1.70
2.43
2.50
3.28
3.33
0.32
8.18
26.92
1.09
0.79
5.38
0.64
0.56
1.46
35.28
0.97
1.54
0.26
1.29
2.15
2.50
4.21
7.40
7.35
6.99
6.14
28.11
7.53
12.75
1.42
2.86
2.87
1.42
1.04
1.78
2.57
2.42
3.44
3.73
0.36
8.69
22.28
1.20
0.88
5.52
0.66
0.62
1.54
13.13
1.06
1.66
0.27
1.31
2.19
2.16
3.63
6.41
6.36
6.08
5.30
26.18
6.58
10.91
1.23
2.48
2.49
1.22
0.86
1.03
2.18
2.09
2.92
3.15
0.30
7.75
22.23
1.05
0.76
4.88
0.55
0.52
1.30
17.92
0.90
1.42
0.24
1.15
1.90
2.31
3.85
6.81
6.75
6.39
5.62
30.08
6.89
11.62
1.30
2.64
2.65
1.29
0.93
1.61
2.30
2.20
3.10
3.31
0.31
8.57
24.30
1.11
0.80
5.18
0.60
0.56
1.36
25.93
0.96
1.52
0.26
1.23
2.01
2.35
3.96
7.01
6.95
6.64
5.08
32.92
7.27
12.22
1.35
2.71
2.72
1.33
1.05
1.28
2.31
2.29
3.06
2.93
0.33
8.28
25.04
1.15
0.84
5.42
0.61
0.57
-
p-xylene
o-xylene
1
1
1
2
2
3
1
-hexene
-hexyne
-heptyne
-butanone
-pentanone
-pentanone
,4-dioxane
36.2 ( 0.9
63.3 ( 0.3
225.2 ( 4.6
324.6 ( 6.4
296.0 ( 5.8
640.7 ( 13.6
190.5 ( 15.7
258.8 ( 9.2
439.6 ( 25.9
220.3 ( 6.4
541.0 ( 39.6
861.8 ( 92.5
28.0 ( 1.8
43.8 ( 2.5
164.9 ( 8.2
229.9 ( 4.6
211.2 ( 10.0
448.1 ( 22.7
132.1 ( 16.8
183.6 ( 60.2
304.3 ( 13.1
159.8 ( 9.2
367.3 ( 14.7
613.4 ( 51.0
767.8 ( 41.4
7.6 ( 0.3
methanol
ethanol
1
2
2
1
2
-propanol
-propanol
-methyl-1-propanol
-butanol
,2,2-trifluoroethanol
0.33 1130.6 ( 52.0
diethylether
diisopropylether
chloroform
dichloromethane
tetrachloromethane
acetonitrile
7.92
27.28
1.10
0.78
5.37
0.63
9.2 ( 0.7
8.9 ( 1.2
170.2 ( 5.9
91.1 ( 3.0
57.6 ( 1.0
591.7 ( 20.5
7.1 ( 0.4
123.8 ( 6.2
70.6 ( 3.7
42.6 ( 2.3
435.0 ( 16.9
992.0 ( 52.6
1081.7 ( 4.9
5.8 (
nitromethane
0.57 1470.7 ( 42.0
-
28.67
0.99 1390.2 ( 35.6
1.57
0.25
1.29
2.10
1
-nitropropane
1741.8 ( 26.3
14.0 ( 2.4
triethylamine
pyridine
thiophene
formaldehyde
propionaldehyde
butyraldehyde
27.21
1.01
1.59
0.27
1.26
2.09
59.39
0.94
1.49
0.25
1.21
948.9 ( 46.1
194.6 ( 9.8
37.3 ( 1.8
70.2 ( 3.3
105.5 ( 2.7
268.8 ( 5.6
47.1 ( 1.4
91.2 ( 1.8
144.8 ( 4.8
2.06
∞
∞
Table 3. Comparison of γ Values Obtained in This Work with γ
4
5
53
separation of thiophene from alkanes. This value is eight times
higher than for most ionic liquids. The selectivity of
Values Measured by Foco et al. and Zhou et al. at T ) 303.15 K
∞
γ
[
BMIM][BF ] for the {hexane + benzene} mixture at 313.15
4
ref 45 ref 53
this work
K is very large compared to the value for classical solvents such
as dimethylsulfoxide (S1 ) 22.7) or sulfolane (S ) 30.5).
solutes
uncorrected data corrected data
∞
∞
12
2
hexane
heptane
93.41 60.80
134.05 92.45
91.43
153.58
157.46
49.18
2.56
4.31
7.62
37.40
1.32
2.28
3.33
3.24
132.86
259.08
321.18
62.53
2.2
4.09
7.25
48.02
1.10
2.15
2.82
3.03
The selectivity decreases with increasing length of the alkyl
chain. It is obvious that the chemical nature of the cation and
the anion plays an important role in separation of mixtures
containing polar and aliphatic compounds. Table 4 shows that
selectivity decreases when [BF ] is changed by [OcSO ] or
2
,2,4-trimethylpentane 144.82 92.69
cyclohexane
benzene
toluene
44.94 32.41
2.39 1.74
2.91
4
4
ethylbenzene
5.61
[
Tf N].
2
1
-hexene
35.37
methanol
ethanol
1.32 0.83
1.59
From these results and our previous works, some observation
can be made. It is clear that decreasing alkyl chain length of
imidazolium-based ionic liquids tends to increase solubility of
most organic compounds in ionic liquids. Introduction of a polar
chain in ionic liquids also strongly affects the behavior of
organic compounds in mixtures with the ionic liquids.
1
2
-propanol
-propanol
2.80
2.63
chloroform
tetrachloromethane
1.11
5.73
1.05
5.51
0.95
5.21
ylimidazolium cation at T ) 313.15 K. The selectivity for
investigated ILs is high. The value of 85.8 shows the possibility
LSER Characterization. The ionic liquid studied in this work
was analyzed using the LSER approach. Coefficients c, e, s, a,
of using [BMIM][BF ] as an extractive medium for the
b, and l of [BMIM][BF ] were obtained by multiple linear
4
4

9
8
Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009
∞
2
Table 4. Selectivity Values S1 for Different Separation Problems at 313.15 K
∞
S
1
2
solvent
hexane/benzene hexane/methanol hexane/thiophene cyclohexane/thiophene
ref
1
1
1
1
1
1
1
1
1
1
-ethyl-3-methylimidazolium tetrafluoroborate
-butyl-3-methylimidazolium tetrafluoroborate
-hexyl-3-methylimidazolium tetrafluoroborate
-octyl-3-methylimidazolium tetrafluoroborate
-hexadecyl-3-methylimidazolium tetrafluoroborate
-ethyl-3-methylimidazolium ethylsulfate
61.6
60.1
22.3
10.5
2.8
41.4
5.5
21.6
37.5
16.7
27.6
50.4
7
290.4
106.9
29.2
12.1
2.2
-
4.4
10.2
19.5
-
551.6
820
139.3
52.3
455.7
109
116.3
-
-
85.8
-
-
2.2
-
6.5
-
-
-
31.8
-
-
2.0
-
3.9
-
-
45
this work
45
45
19
56
17
46
56
56
20
20
18
18
18
18
18
-butyl-3-methylimidazolium octylsulfate
-hexyl-3-methylimidazolium hexafluorophosphate
-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
-
-
n-acryloyloxypropyl-N-methylimidazolium bromide
n-methacryloyloxyhexyl-N-methylimidazolium bromide
69.2
82
16.9
9.6
15.2
6.9
5.2
-
62.0
41.4
10.6
6.1
6.8
4.9
3.6
-
1
1
1
1
1
1
-propenyl-3-methyl-imidazolium bromide
-propenyl-3-octyl-imidazolium bromide
-propyl boronic acid-3-octyl-imidazolium bromide
-propyl boronic acid-3-decyl-imidazolium bromide
-propyl boronic acid-3-dodecyl-imidazolium bromide
-octyl-3-methylimidazolium chloride
6.4
9.91
4.1
3.8
8.7
55
Table 5.1-L3S4 ER Descriptors of Solutes Used to Characterize Ionic
3
system constants calculated from the sorption coefficients
Liquids
log(V /V ) and from the gas-liquid partition coefficient log
L
N
L
solutes
E
S
A
B
L
K . There is some dependence of the system constants on the
hexane
-methylpentane
heptane
,2,4-trimethylpentane
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2.668
2.581
3.173
3.106
3.677
4.182
2.816
2.964
3.323
3.704
2.768
3.325
3.778
3.839
3.839
3.939
2.572
2.51
phase loading. The LSER coefficients vary with phase loading.
This result confirms that interfacial adsorption has an important
influence on the determination of physicochemical properties
of ionic liquids using inverse gas chromatography.
3
2
octane
nonane
The system constants for [BMIM][BF ] studied in this work
methylcyclopentane
cyclohexane
methylcyclohexane
cycloheptane
benzene
0.225
0.305
0.244
0.35
0.1
0.1
0.1
0.1
4
at 313.15 K but also for other ionic liquid stationary phases are
summarized in Table 7. The system constants for ionic liquids
1
6-20,48
not studied in this work are taken from the literature.
0.61
0.52
0.52
0.51
0.52
0.52
0.56
0.08
0.23
0.23
0.7
0.68
0.66
0.75
0.44
0.42
0.42
0.36
0.39
0.42
0.6
0.25
0.19
0.49
0.57
0.38
0.90
0.95
0.95
0.15
0.84
0.57
0.73
0.65
0.65
0.14
0.14
0.15
0.16
0.16
0.16
0.07
0.1
toluene
0.601
0.613
0.623
0.613
0.663
0.078
0.166
0.16
0.166
0.143
0.154
0.329
0.278
0.246
0.236
0.212
0.217
0.224
0.015
0.041
0
0.425
0.387
0.458
0.237
0.313
0.242
0.101
0.631
0.687
0.22
LSER coefficients of [BMIM][BF ] are slightly different from
4
ethylbenzene
m-xylene
p-xylene
o-xylene
-hexene
-hexyne
-heptyne
-butanone
-pentanone
-pentanone
,4-dioxane
methanol
ethanol
-propanol
-propanol
-methyl-1-propanol
-butanol
,2,2-trifluoroethanol
diethylether
diisopropylether
chloroform
dichloromethane
tetrachloromethane
acetonitrile
nitromethane
-nitropropane
triethylamine
pyridine
thiophene
those obtained with other ionic liquids of the imidazolium
bromide type. The (c + lL) term gives information on the effect
of cohesion of the ionic liquids on solute transfer from the gas
4
8
1
1
1
2
2
3
1
phase. In general, the ionic liquids are cohesive solvents. The
ionic liquid interacts via nonbonding and π-electrons (e system
constant) and is not much different from other polar nonionic
0.12
0.12
0
0.1
3
0.51
0.51
0.51
0.64
0.47
0.48
0.48
0.56
0.48
0.48
0.25
0.45
0.41
0.02
0.05
0
0.32
0.31
0.31
0.79
0.52
0.15
0.33
0.45
0.45
2.287
2.755
2.811
2.892
0.97
1.485
2.031
1.764
2.413
2.601
1.224
2.015
2.482
2.48
2.019
2.833
1.739
1.892
2.894
3.04
3.022
2.819
0.73
0
0
0
liquids. Dipolarity/polarizality of [BMIM][BF ] is slightly higher
4
than the most dipolar/polarizable ionic and nonionic stationary
phases. The polarizability decreases slightly when the alkyl chain
length is increased on the imidazolium ring. As expected, the
hydrogen-bond basicity of the ionic liquid (a system constants)
is considerably larger than values obtained for nonionic phases
(0.11 < a < 2.3), but this value is the lowest found with
0.43
0.37
0.37
0.33
0.37
0.37
0.57
0
1
2
2
1
2
imidazolium-based ionic liquids. [BMIM][BF ] is sligthly
4
hydrogen-bond acidic. Ionic liquids have structural features that
would facilitate hydrogen-bond acceptor basicity interactions
(electron-rich oxygen, nitrogen, and fluorine atoms). Imidazo-
lium bromide based ionic liquids containing a (meth)acryloy-
loxyalkyl chain have the highest hydrogen-bond basicity with
an a constant of about 5.4. This is great support for the idea
that the interactions between the -OH group and ionic liquids
are very strong. The evolution of the LSER coefficients of
0
0.15
0.1
0
0.07
0.06
0
1
0
0
0
0
0
0
[
BMIM][BF ] with respect to temperature is presented in Figure
formaldehyde
propionaldehyde
butyraldehyde
4
0.196
0.187
1.815
2.27
9. All LSER coefficients decrease with an increase of temper-
ature. This indicates that the selectivity of the ionic liquids
toward mixtures containing sulfur organic compounds (or polar
compounds) and hydrocarbons is higher at low temperature.
Finally, the LSER treatment indicates that the largest selectivity
is found when two components have different polarity and
different hydrogen bond acidity.
regression of the logarithm of the gas-liquid partition coef-
ficients log KL of 44 solutes. LSER parameters of organic
compounds used for the determination of LSER coefficients are
given in Table 5.
35,54
System constants determined at different phase loadings from
log(V /V ) but also from the extrapolated values of the
Sprunger and co-workers
proposed LSER correlations for
the prediction of the partition coefficients of solutes in ionic
liquids. The calculated cation-specific and anion-specific coef-
ficients needed in eq 4 are taken from the literature. Figure 10
N
L
gas-liquid partition coefficients are summarized in Table 6.
We can notice that there is a statistical difference between the

Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009 99
a
Table 6. System Constants for 1-Butyl-3-methylimidazolium Tetrafluoroborate
system constants
statistics
F
T/K
100 w
e
s
a
b
l
c
F
n
3
3
3
3
03.35
25.29
0.46
2.59
(0.08)
2.69
(0.07)
2.67
(0.06)
2.60
(0.07)
2.82
(0.08)
2.53
(0.07)
2.66
(0.06)
2.61
(0.06)
2.50
(0.06)
2.75
(0.08)
2.56
(0.07)
2.57
(0.06)
2.52
(0.07)
2.46
(0.07)
2.66
(0.07)
2.47
3.21
(0.10)
3.19
(0.09)
3.19
(0.09)
3.12
(0.09)
3.27
(0.11)
3.06
(0.09)
3.07
(0.09)
3.25
(0.09)
2.97
(0.09)
3.16
(0.11)
3.01
(0.08)
2.92
(0.09)
2.96
(0.08)
2.89
(0.09)
3.03
(0.10)
2.92
0.53
(0.07)
0.35
(0.07)
0.32
(0.06)
0.43
(0.07)
0.48
(0.09)
0.47
(0.08)
0.32
(0.06)
0.31
(0.06)
0.35
(0.06)
0.40
(0.09)
0.31
(0.06)
0.26
(0.06)
0.28
(0.06)
0.32
(0.08)
0.32
(0.07)
0.30
0.53
(0.02)
0.53
(0.02)
0.54
(0.02)
0.55
(0.02)
0.50
(0.02)
0.49
(0.08)
0.50
(0.02)
0.55
(0.02)
0.51
(0.02)
0.47
(0.02)
0.46
(0.02)
0.46
(0.02)
0.47
(0.02)
0.48
(0.02)
0.44
(0.02)
0.44
-0.70
(0.07)
-0.67
(0.07)
-0.66
(0.06)
-0.67
(0.07)
-0.77
(0.08)
-0.72
(0.07)
-0.71
(0.07)
-0.83
(0.06)
-0.64
(0.06)
-0.79
(0.08)
-0.76
(0.06)
-0.70
(0.06)
-0.72
(0.06)
-0.70
(0.06)
-0.78
(0.07)
-0.79
(0.06)
-0.75
(0.06)
-0.73
(0.07)
-0.72
(0.06)
1042
0.993
42
(
0.09)
0.34
0.07)
0.29
0.07)
0.29
0.08)
0.56
0.09)
0.45
0.02)
0.32
0.08)
0.29
0.07)
0.26
0.07)
0.56
0.09)
0.40
0.07)
0.33
0.07)
0.32
0.07)
0.28
0.07)
0.52
0.08)
0.41
0.07)
0.35
0.07)
0.31
0.07)
0.31
0.07)
20.00
15.30
10.10
1216
1235
1088
977
0.994
0.994
0.993
0.992
0.994
0.993
0.994
0.993
0.992
0.995
0.993
0.994
0.994
0.992
0.994
0.994
0.992
0.993
43
43
43
43
42
44
43
43
43
42
44
43
42
44
42
44
43
43
(
(
(
log KL
(
12.55
22.55
32.55
25.29
1105
1151
1208
1054
947
(
2
1
1
0.00
5.30
0.10
(
(
(
log KL
(
25.29
1330
1245
1226
1123
1000
1173
1323
963
(
2
1
1
0.00
5.30
0.10
(
(
(
log KL
(
25.29
(
(0.07)
2.53
(0.06)
2.40
(0.07)
2.32
(0.06)
(0.08)
2.85
(0.08)
2.84
(0.09)
2.70
(0.08)
(0.06)
0.23
(0.06)
0.29
(0.06)
0.38
(0.06)
(0.02)
0.43
(0.02)
0.44
(0.02)
0.44
(0.02)
2
1
1
0.00
5.30
0.10
(
(
1084
(
log KL
0.52
0.08)
2.50
(0.07)
2.85
(0.10)
0.38
(0.08)
0.42
(0.02)
-0.79
(0.07)
866
0.992
43
(
a
w: phase loading; F: Fischer statistic; F: multiple correlation coefficient; and n: number of solutes.
Figure 10. Comparison of experimental log KL data and predicted values
based on the Abraham model with the cation-specific and anion-specific
equation.
Figure 9. Evolution of LSER coefficients as function of temperature. [,
contribution from interactions with lone pair electrons “e”; 9, contribution
from dipole-type interactions “s”; 2, hydrogen bond basicity “a”; ×,
hydrogen bond acidity “b”; b, cavity formation and dispersion interactions
Nevertheless, this application shows that the predictive model
proposed by Sprunger et al. may be a powerful tool to estimate
the behavior of solutes in ionic liquids.
“
l”.
compares the calculated value of log K against the experimental
values. Calculated log K are in good agreement with experi-
mental data except for the low value and more precisely data
of apolar solutes. This important deviation may be explained
Concluding Remarks
Activity coefficients at infinite dilution of organic compounds
3
5,54
45
by the fact that Sprunger et al.
used Foco et al. and Zhou
in [BMIM][BF ] have been measured from (303.35 to 332.55)
4
5
3
et al. data sets to estimate the coefficients of eq 4. Moreover,
K. Through this work, we have shown that interfacial adsorption
plays a significant role in the retention mechanism of apolar
these log K are not corrected from interfacial adsorption.

1
00 Journal of Chemical & Engineering Data, Vol. 54, No. 1, 2009
a
Table 7. LSER Descriptors of Ionic Liquids Determined at 313.15 K
system constants
statistics
SE
ionic liquids
e
s
a
b
l
c
F
n
1
-butyl-3-methylimidazolium tetrafluoroborate
0.56
2.82
(0.08)
2.88
3.27
(0.11)
5.50
(0.19)
5.36
(0.18)
5.19
(0.18)
4.96
(0.16)
4.89
(0.17)
4.87
(0.16)
4.05
(0.14)
4.81
(0.19)
2.76
(0.16)
2.66
(0.10)
3.38
(0.28)
3.50
(0.10)
3.06
3.67
3.20
0.48
(0.09)
0
0.50
(0.02)
0.48
(0.06)
0.57
(0.05)
0.53
(0.05)
0.57
(0.05)
0.66
(0.04)
0.72
(0.03)
0.68
(0.03)
0.48
(0.03)
0.45
(0.02)
0.47
(0.01)
0.21
(0.04)
0.36
(0.01)
0.32
0.51
0.49
-0.77
(0.08)
-1.03
(0.119)
-0.87
(0.11)
-1.86
0.992
0.065
43
(
0.09)
n-acryloyloxypropyl-N-methylimidazolium bromide
n-methacryloyloxyhexyl-N-methylimidazolium bromide
0
0.99
0.080
0.088
0.089
0.088
0.089
0.088
0.082
0.080
0.058
0.032
0.089
0.037
30
28
28
28
28
28
29
29
23
23
17
23
(
0.14)
2.46
0.10)
2.16
0.09)
1.72
0.08)
1.73
0.07)
1.44
0.07)
1.47
0.06)
0
0
0
0
0
0
0
0.99
(
1
1
1
1
1
1
-propenyl-3-methyl-imidazolium bromide
-propenyl-3-octyl-imidazolium bromide
-propenyl-3-decyl-imidazolium bromide
-propenyl-3-dodecyl-imidazolium bromide
-butyl-3-methylimidazolium octyl sulfate
-ethyl-3-methylimidazolium tosylate
0
0.990
0.989
0.990
0.991
0.990
0.99
(
0
-1.60
-1.58
-1.51
(
0
(
0
(
0
-0.237
(0.09)
-0.84
(0.12)
-0.75
(0.10)
-0.6
(0.06)
-0.87
(0.20)
-0.97
(0.07)
-0.80
-0.83
-0.91
-0.94
(
0.54
2.40
(0.12)
1.65
(0.09)
1.73
(0.06)
2.21
(0.16)
2.02
(0.06)
1.96
1.57
1.76
0.17
(0.14)
1.32
(0.11)
0.68
(0.07)
1.03
(0.17)
0.9
(0.07)
0
0
0
0
(
0.12)
0.14
0.09)
0.30
0.05)
0.27
0.16)
0.25
0.06)
n-butylammonium thiocyanate
di-n-propylammonium thiocyanate
ethylammonium nitrate
0.995
0.998
0.994
0.998
(
(
(
n-propylammonium nitrate
(
2
2
2
4
-bis(2-hydroxyethyl)amino)ethanesulfonate
-(cyclohexylamino)ethanesulfonate
-hydroxy-4-morpholinepropanesulfonate
-morpholinepropanesulfonate
0.27
0.07
0
0.996
0.996
0.994
0.990
0.048
0.060
0.053
0.097
27
18
18
34
0
1.60
3.41
0.44
a
F: Multiple correlation coefficient; SE: standard error in the estimation; and n: number of solutes.
compounds. When corrected, important increases of activity
coefficients at infinite dilution of nonpolar compounds were
observed. Interfacial adsorption contribution of polar solutes in
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BMIM][BF ] is lower than in imidazolium-based ionic liquids
4
with a bromide anion.
In the separation of aliphatic hydrocarbons from thiophene
9
02, pp 83-96.
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15) Alonso, L.; Arce, A.; Francisco, M.; Soto, A. Solvent extraction of
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Received for review September 1, 2008. Accepted October 16, 2008.
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