Phase equilibria of (1-hexyl-3-methylimidazolium thiocyanate + water, alcohol, or hydrocarbon) binary systems

Article abstract of DOI:10.1021/je900460m

Imidazolium ionic liquid has been prepared from 1-methylimidazolium as a substrate. The work includes specific basic characterization of a synthesized compound by NMR spectra, water content, and a glass transition temperature determined by the differential scanning calorimetry (DSC). The mutual solubilities of 1-hexyl-3-methylimidazolium thiocyanate, [HMIM][SCN], with water, alcohols, n-alkanes (n-hexane, n-heptane, n-octane, n-nonane, or n-decane), aromatic hydrocarbons (benzene, toluene, or ethylbenzene), and cyclic hydrocarbons (cyclohexane or cycloheptane) have been measured at ambient pressure by a dynamic method in a range of temperatures from (200 to 420) K. The simple eutectic system was observed for water with complete miscibility in the liquid phase. Complete miscibility has been observed in the systems of [HMIM][SCN] with alcohols ranging from methanol to 1-decanol at a temperature of T = 298.15 K. The upper critical solution temperatures (UCSTs) were observed for the systems with n-alkanes and the lower critical solution temperatures (LCSTs) for the systems with aromatic hydrocarbons. The solubility decreases with an increase of the molecular weight of the solvent. The liquid-liquid phase equilibria (LLE) have been correlated using the nonrandom two-liquid (NRTL) equation. The average root-mean square deviation of the equilibrium mole fraction for all of the LLE data was 0.0021.

Full text of DOI:10.1021/je900460m

J. Chem. Eng. Data 2010, 55, 773–777
773
Phase Equilibria of (1-Hexyl-3-methylimidazolium Thiocyanate + Water, Alcohol,
or Hydrocarbon) Binary Systems
Urszula Doman´ska,* Marta Kro´likowska, and Monika Arasimowicz
Department of Physical Chemistry, Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw,
Poland
Imidazolium ionic liquid has been prepared from 1-methylimidazolium as a substrate. The work includes
specific basic characterization of a synthesized compound by NMR spectra, water content, and a glass
transition temperature determined by the differential scanning calorimetry (DSC). The mutual solubilities
of 1-hexyl-3-methylimidazolium thiocyanate, [HMIM][SCN], with water, alcohols, n-alkanes (n-hexane,
n-heptane, n-octane, n-nonane, or n-decane), aromatic hydrocarbons (benzene, toluene, or ethylbenzene),
and cyclic hydrocarbons (cyclohexane or cycloheptane) have been measured at ambient pressure by a dynamic
method in a range of temperatures from (200 to 420) K. The simple eutectic system was observed for water
with complete miscibility in the liquid phase. Complete miscibility has been observed in the systems of
[HMIM][SCN] with alcohols ranging from methanol to 1-decanol at a temperature of T ) 298.15 K. The
upper critical solution temperatures (UCSTs) were observed for the systems with n-alkanes and the lower
critical solution temperatures (LCSTs) for the systems with aromatic hydrocarbons. The solubility decreases
with an increase of the molecular weight of the solvent. The liquid-liquid phase equilibria (LLE) have
been correlated using the nonrandom two-liquid (NRTL) equation. The average root-mean square deviation
of the equilibrium mole fraction for all of the LLE data was 0.0021.
{[BMIM][SCN] + n-alkane}10 and with the lower critical solution
Introduction
temperature (LCST) in mixtures of {[BMIM][SCN] + aromatic
hydrocarbon}.10 The liquidus curves exhibited a similar shape for
Ionic liquids (ILs) have received considerable attention in
recent years because of their unique physical and chemical
different solvents. The evident differences were observed in the
properties and solution thermodynamic behavior.1–5 The im-
miscibility of ILs with n-alkanes and several acyclic organic
solvents makes ILs ready to replace traditional organic solvents
liquid phase for aromatic hydrocarbons: the mutual solubility of
[BMIM][SCN] in benzene and its alkyl derivatives decreases with
an increase of the alkyl substituent at the benzene ring.10 Thiocy-
in many chemical and manufacturing processes. Knowledge
anate-based ILs are soluble in water. A simple eutectic system was
observed for [BMIM][SCN].10
about physicochemical properties such as viscosity, density, or
heat capacity and thermodynamic properties including phase
The phase diagrams of ILs with benzene and benzene
equilibria is necessary to design any process involving ILs on
derivatives differ from those for the aliphatic hydrocarbons. ILs
present a usually much lower immiscibility gap in benzene than
an industrial scale.2–10 The solid-liquid phase equilibria (SLE)
and liquid-liquid phase equilibria (LLE) measurements of IL
systems based on imidazolium cations3,5,6 are attracting increas-
ing attention for applications in liquid-liquid extraction.
It was proved by Doman´ska and Laskowska8 by the measure-
ments of the activity coefficient at infinite dilution, γ∞13, and by
Doman´ska and Marciniak9 that thiocyanate anion [SCN]- has
high extraction efficiency. The selectivities S∞ij ) γi∞3/γj∞3 for the
hexane/thiophene or hexane/benzene separation problems were
calculated for [BMIM][SCN]8 and [EMIM][SCN]9 from the γ∞13.
The selectivities for hexane/thiophene at T ) 298.15 K are 186.2
and 231.5, respectively. The capacity k∞j ) 1/γj∞3 for the sulfur
(thiophene) separation problem is 0.82, which is quite high. The
selectivities for hexane/benzene at T ) 298.15 K are 106.1 and
95.4, respectively. The capacities k∞j ) 1/γj∞3 for the (benzene)
separation problem are 0.47 and 0.29. These are very promising
results for the separation of sulfur from mixtures of an industrial
importance and for the separation of alkanes from aromatics.
in alkanes. The solubility of ILs is much higher in aromatic
hydrocarbons than in aliphatic hydrocarbons, which is the result
of interaction with the benzene ring.
The present study continues our characterization of the
thiocyanate-based ILs. This work is concerned with the in-
vestigation of phase equilibria of mixtures containing the
[HMIM][SCN] with water, alcohols (from C1 to C10),
n-alkanes (from C6 to C10), aromatic hydrocarbons (benzene,
toluene, or ethylbenzene), and cyclic hydrocarbons (cyclo-
hexane or cycloheptane).
Experimental Section
Materials. Water for the solubility measurements was twice
distilled, degassed, deionized, and filtered with Milipore Elix
3. The other solvents used, that is, 1-alcohols, were obtained
from Sigma Aldrich with a purity of over 99.8 %. The other
chemicals were as follows: n-hexane (CAS No. 110-54-3,
Merck, 99 %); n-heptane (CAS No. 142-82-5, Sigma-Aldrich,
99 %); n-octane (CAS No. 111-65-9, Sigma-Aldrich, 99 %);
n-nonane (CAS No. 111-84-2, Sigma-Aldrich, > 99 %); n-
decane (CAS No. 124-18-5, Sigma-Aldrich, > 99 %); benzene
The LLE diagrams with a miscibility gap with the upper critical
solution temperature (UCST) were observed in mixtures of
* Corresponding author. Telephone: + 48-22-6213115. Fax: + 48-22-
6282741. E-mail: ula@ch.pw.edu.pl.
10.1021/je900460m  2010 American Chemical Society
Published on Web 11/12/2009

774 Journal of Chemical & Engineering Data, Vol. 55, No. 2, 2010
Table 1. Thermophysical Constants of the Pure ILa
Table 2. Experimental SLE Data for the Binary System
{[HMIM][SCN] (1) + Water (2)}: the Mole Fraction (x1),
Temperature (TSLE), and Activity Coefficient of the Solvent (γ2)
M
F298.15
g ·mol-1 kg·m-3 mPa·s
[HMIM][SCN] 211.33 1.05692 93.6206 189.9
η298.15 Ttr,1(g)
∆Cp(g)
J·K-1 ·mol-1
118
Tdec
K
535b
IL
K
x1
TSLE/K
γ2
x1
TSLE/K
γ2
0.2950
0.2566
0.2089
0.1495
0.1088
235.0a
244.6
254.9
264.2
268.5
1.67
1.90
1.98
2.08
2.15
0.0832
0.0566
0.0304
0.0005
0.0000
267.0
271.1
272.2
272.9
273.1
2.20
2.26
2.32
2.39
2.39
a Molecular mass, M; density, F298.15; viscosity, η298.15; temperature of
glass transition, Ttr,1(g); ∆Cp(g) at the glass transition and temperature of
the decomposition, Tdec.
b The step of the decomposition, 20 % mass
loss.
a The results are, for example, (235.0 ( 0.1) K.
(CAS No. 71-43-2, Sigma-Aldrich, > 99.97 %); toluene (CAS
No. 108-88-3, Fluka, > 99.7 %); ethylbenzene (CAS No. 100-
41-4, Sigma-Aldrich, 99 %), cyclohexane (CAS No. 110-82-7,
Sigma-Aldrich, 99.5 %); cycloheptane (CAS No. 291-64-5,
Sigma-Aldrich, 98 %). The solvent’s purities are in mass
fraction.
the glass transition temperature was Tg,1 was (189.9 ( 0.1) K
with ∆Cp(g),1 of (118 ( 3) J ·mol-1 ·K-1 (average over three
scans).
Decomposition of Compound. Simultaneous thermogravi-
metric and differential thermal analysis (TG/DTA) experiments
was performed using a MOM Hungary derivatograph PC. In
general, runs were carried out using matched labyrinth platinic
crucibles with Al2O3 in the reference pan. The crucible design
hampered the migration of the volatile decomposition products,
reducing the rate of gas evolution and, in turn, increasing the
contact time of the reactants. All of the TG/DTA curves were
obtained at 5 K ·min-1 heating rate with a nitrogen dynamic
atmosphere (flow rate 20 dm3 ·h-1). Temperature of decomposi-
tion is presented in Graph 4 in the Supporting Information. We
can see that up to 511 K the decomposition is not observed
and at temperature (535 ( 3) K the decomposition is 20 %.
Phase Equilibria Measurements. Solubilities have been
determined using a dynamic method that has been described in
detail previously.11 Appropriate mixtures of IL and solvent
placed under the nitrogen in a drybox into a Pyrex glass cell
were heated very slowly (less than 2 K ·h-1 near the equilibrium
temperature) with continuous stirring inside a cell. The sample
was placed in a glass thermostat filled with silicone oil, water,
or acetone with dry ice. The temperature of the liquid bath was
varied slowly until one phase was obtained. The two phase
disappearance temperatures in the liquid phase were detected
visually during an increasing temperature regime. The temper-
ature was measured with an electronic thermometer P550
(DOSTMANN electronic GmbH) with the probe totally im-
mersed in the thermostatting liquid. The thermometer was
calibrated on the basis of ITS-90. Mixtures were prepared by
mass, and the uncertainty was estimated to be better than (
0.0002 and ( 0.1 K in the mole fraction and temperature,
respectively. The results of the SLE/LLE measurements for the
binary systems of {[HMIM][SCN] (1) + water or hydrocarbons
(2)} are presented in Tables 2, 3, 4, and 5. The tables include
the direct experimental results of the SLE/LLE temperatures,
TSLE or TLLE versus x1, the mole fraction of the IL at the
equilibrium temperatures for the investigated systems.
For the synthesis a 250 mL flask, equipped on a magnetic
stirrer and condenser, was used. The substances 1-methylimi-
dazolium (0.4 mol) (Merck 99 %, distilled over KOH) and
1-bromohexane (0.5 mol) (Aldrich 98 %, used as received) were
charged. The reaction mixture was stirred at a temperature of
333 K for 3 h. 1-Bromohexane has been removed by extraction
with hexane, ethyl acetate, and diethyl ether. Product was dried
in vacuum (0.37 mol, yield 93 %).
1-Hexyl-3-methylimidazolium bromide (0.37 mol), sodium
thiocyanate (0.37 mol, Aldrich 98 % in mass fraction), and 100
mL of distilled water were charged into a flask and stirred for
24 h at room temperature. Water was removed by evaporation
under reduced pressure. After removing the solvent, 100 mL
of CH2Cl2 (POCH, 99 % in mass fraction) was added. Then,
the mixture was filtered and was left up to the evaporation of
the solvent. Product was dried in vacuum for 24 h at 300 K
(yield 95 %). NMR, differential scanning calorimetry (DSC),
and elemental analysis identified the obtained IL.
All solvents were fractionally distilled over different drying
reagents until a mass fraction purity better than 99.8 % was
obtained and were stored over freshly activated molecular sieves
of type 4A (Union Carbide). All compounds were checked by
gas-liquid chromatography (GLC) analysis, and no significant
impurities were found. The physicochemical characterization
of the IL is presented in Table 1.
Nuclear Magnetic Resonance. 1HNMR and 13CNMR spectra
in CDCl3 solutions were recorded on a Varian Gemini 2000
spectrometer. The uncertainty was estimated to be on the level
of 5 %. A description of the spectra is presented in Graphs 1
and 2 of the Supporting Information.
Water Content. Water content was analyzed by Karl Fischer
titration (with TitroLine Method). Samples of [HMIM][SCN]
and the solvents were dissolved in dry methanol and titrated
with steps of 2.5 µL. The analysis showed that the water mass
fraction in the solvents and in the mixtures with the IL was
less than (250 ·10-6 ( 10·10-6).
Differential Scanning Microcalorimetry. Basic thermal
characteristics of the IL, that is, glass transition temperature
(Tg,1) and change of heat capacity at the glass transition
temperature, Tg,1 (∆Cp(g),1), have been measured using a dif-
ferential scanning microcalorimetry technique at the 5 K ·min-1
scan rate with the power sensitivity of 16 mJ ·s-1 and with the
recorder sensitivity of 5 mV. The instrument (Perkin-Elmer Pyris
1) was each time calibrated with the indium sample, which
purity was 99.9999 in mole fraction. The calorimetric accuracy
was ( 3 %. The thermophysical properties (average over three
scans) are shown in Table 1, and the DSC diagram is shown as
Graph 3 in the Supporting Information. The average value of
Results and Discussion
The formula of the IL, the abbreviation, and the physico-
chemical properties are presented in Table 1 and in Figure 1.
The thiocyanate anion, [SCN]-, is less viscous, more hydro-
lytically stable, and more environmentally friendly than other
popular anions such as bis{(trifluoromethyl)sulfonyl}imide
[NTf2]-, hexafluorophosphate, [PF6]-, or tetrafluoroborate,
[BF4]-. Unfortunately, the [HMIM][SCN] is thermally less
stable than [BMIM][SCN]. The IL investigated in this work
has revealed the first decomposition temperature at 511 K, while
[BMIM][SCN] is at 523 K. The compound has been decom-
posed in one step.
The experimental data of SLE/LLE of the measured binary
systems of [HMIM][SCN] are shown in Figures 2, 3, 4, and 5.

Journal of Chemical & Engineering Data, Vol. 55, No. 2, 2010 775
Table 3. Experimental LLE in the {[HMIM][SCN] (1) + Aliphatic
Hydrocarbon (2)} Binary Systems
Table 5. Experimental LLE in the {[HMIM][SCN] (1) +
Cycloalkane (2)} Binary Systems
x1
TLLE/K
x1
TLLE/K
x1
TLLE/K
x1
TLLE/K
n-Hexane
Cyclohexane
0.9755
0.9629
0.9529
0.9497
0.9477
0.9453
0.9444
286.6a
299.6
308.3
313.0
316.3
320.6
321.1
0.9418
0.9397
0.9362
0.9288
0.9177
0.9061
0.8962
324.3
329.9
333.5
341.1
351.2
359.4
367.3
0.9727
0.9269
0.9150
0.9022
0.8927
0.8817
0.8685
0.8553
289.1a
305.6
318.6
332.5
341.5
354.7
364.9
373.1
0.8468
0.8346
0.8191
0.8012
0.7911
0.7815
0.7613
376.5
380.8
386.6
392.8
397.2
400.3
407.8
n-Heptane
n-Octane
Cycloheptane
0.9839
0.9673
0.9535
0.9401
282.6
325.9
348.6
363.2
0.9279
0.9140
0.9012
376.0
395.0
408.8
0.9698
0.9573
0.9455
0.9330
0.9203
279.6
291.9
309.8
324.0
342.3
0.9096
0.8995
0.8885
0.8755
0.8640
353.6
367.3
381.7
397.0
411.1
0.9906
0.9843
0.9820
0.9793
0.9732
0.9703
284.7
302.2
310.1
318.1
331.4
339.2
0.9676
0.9651
0.9537
0.9481
0.9402
359.2
363.2
377.5
389.1
402.3
a The results are, for example, (289.1 ( 0.1) K.
n-Nonane
n-Decane
0.9901
0.9866
0.9769
312.15
341.85
368.69
0.9684
0.9613
396.4
416.8
Figure 1. Formula of the 1-hexyl-3-methylimidazolium thiocyanate.
0.9941
0.9903
0.9873
310.4
328.2
346.5
0.9829
0.9802
0.9740
369.3
384.0
410.6
a The results are, for example, (286.6 ( 0.1) K.
Table 4. Experimental LLE in the {[HMIM][SCN] (1) + Aromatic
Hydrocarbon (2)} Binary Systems
x1
TLLE/K
x1
TLLE/K
Benzene
Toluene
0.2824
0.2784
0.2734
0.2694
346.3a
332.3
319.3
306.9
0.2643
0.2609
0.2598
294.7
284.4
279.2
0.4356
0.4184
0.4137
0.4092
0.4047
0.4003
0.3960
0.3920
0.3880
0.3839
355.7
313.7
292.7
282.1
272.6
267.7
262.9
259.6
255.9
252.8
0.3799
0.3758
0.3719
0.3684
0.3648
0.3612
0.3576
0.3541
0.3509
248.9
245.0
240.1
239.6
236.8
233.9
229.6
226.1
221.8
Ethylbenzene
0.5033
0.5835
0.5662
0.5524
0.5398
0.5310
0.5222
0.5161
0.5101
359.0
332.7
300.4
272.7
261.0
250.7
242.1
232.6
227.0
223.1
220.9
219.2
217.7
216.3
214.2
211.7
0.4968
0.4867
0.4790
0.4698
0.4642
0.4471
0.4305
Figure 2. SLE diagram of the binary system {[HMIM][SCN] (1) + water
(2)}: b, experimental points; solid line, calculated by the UNIQUAC
equation.
a The results are, for example, (346.3 ( 0.1) K.
The UCSTs of the curves were not observed because the boiling
temperatures of solvents were much lower. For the investigated
mixtures, it was impossible to detect, by the visual method, the
mutual solubility of the IL in the solvent-rich phase. However,
it was measured with UV-vis spectroscopy for a similar IL,
For the shorter chains of an n-alkane10 and the alkyl
substituent at the benzene ring,7 the area of the immiscibility is
always lower than that for the longer n-alkane chains. In fact,
this is typical solution behavior, observed for every IL measured
by us.
Figure 2 shows the experimental liquidus curve of water in
the IL. Figure 3 presents the equilibrium curves of solubility of
the IL in five n-hydrocarbons. Equilibrium curves for the three
[BMIM][SCN], and the solubility was in a range of x1
)
1.7·10-5 to 3.5 ·10-5 for n-hexane; x1 ) 1.7·10-3 to 2.2 ·10-3
for benzene; and x1 ) 2.1·10-5 to 4.3 ·10-5 for cyclohexane.10

776 Journal of Chemical & Engineering Data, Vol. 55, No. 2, 2010
Figure 3. LLE diagrams for the binary systems {[HMIM][SCN] (1) + n-alkane
(2)}: b, n-hexane; O, n-heptane; 2, n-octane; 4, n-nonane; [, n-decane; solid
lines, calculated using the nonrandom two-liquid (NRTL) equation.
Figure 5. LLE diagrams for the binary systems {[HMIM][SCN] (1) +
cycloalkane (2)}: b, cyclohexane; O, cycloheptane; solid line, calculated
using the NRTL equation.
4. As can be observed, the solubility decreases as the alkyl chain
at the benzene ring increases. The differences in solubility
between the benzene and the toluene in the IL are the same as
those for toluene and ethylbenzene in the IL. The same results
were presented by us earlier for [BMIM][SCN] in aromatic
hydrocarbons.10 As can be seen from Figure 4, the solubility
of benzene in [HMIM][SCN] is much higher than those in
[BMIM][SCN].10
Experimental phase diagrams with cyclohydrocarbons, in-
vestigated in this work, are characterized by the typical order
in solubility: cyclohexane > cycloheptane.
The best solubility was observed in water, alcohols, and
benzene probably because of the interaction between molecules
of the IL (imidazolium ring, thiocyanate anion) and the polar
solvent. It can be hydrogen bonding with water and alcohols
and n-π and/or π-π interactions with benzene and alkylben-
zenes. Packing effects or conformational changes of the
investigated molecules in the mixtures are difficult to categorize,
especially in comparison with possible hydrogen bonding. All
of these interactions have an influence on LLE.
SLE and LLE Correlation
For the correlation of the solubility of water in [HMIM][SCN]
and the calculation of the solute activity coefficients γ1, the
UNIQUAC equation12 was chosen as the better one than the
NRTL equation.13 As a measure of the reliability of the
correlations, the root-mean-square deviation of temperature σT/K
has been calculated according to the following definition:
Figure 4. LLE diagrams for the binary systems {[HMIM][SCN] (1) + an
aromatic hydrocarbon (2)}: b, benzene; O, toluene; 2, ethylbenzene; ×,
comparison with the system {[BMIM][SCN] (1) + benzene (2)}.10 Solid
lines, calculated using the NRTL equation.
2
1/2
n
(Texp,i - Tcalc,i
n - 2
)
σT )
(1)
∑
{
}
i)1
binary systems studied with aromatic hydrocarbons as a function
of temperature for different compositions are shown in Figure
The values of the parameters and the corresponding root-mean-
square deviations of temperature are: ∆u12 ) 3528.68 J ·mol-1
,

Journal of Chemical & Engineering Data, Vol. 55, No. 2, 2010 777
Table 6. Correlation of the LLE Data by Means of the NRTL
Equation: Parameters (g12 - g22 ) a12 + b12T), (g21 - g11 ) a21
b21T), and the Mole Fraction Deviations σx
aromatic hydrocarbons, the LCST was noted as it was for
the previously published results for the [BMIM][SCN].10 The
solubility of every tested solvent in [HMIM][SCN] was
higher than those observed in [BMIM][SCN].10
+
NRTL parametersa
(g12 - g22)
J·mol-1
(g21 - g11)
J·mol-1
The existence of the liquid-liquid equilibria is the evidence
that the interaction between the IL and the solvent is not
significant (besides the water and alcohol solutions).
Knowledge of the impact of different factors on the liquid-
phase behavior of IL in comparison with other traditional liquids
is useful for developing IL as designer solvents. The presented
results may give new possibilities in extraction processes.
solvent
a12
b12
a21
b21
σx
n-hexane
n-heptane
n-octane
n-nonane
n-decane
benzene
toluene
ethylbenzene
cyclohexane
cycloheptane
14364
14019
13213
14500
13759
-3087.8
-3607
158.2
-50.16
-44.90
-39.15
-37.65
-33.25
-38.59
-25.39
-30.06
-55.75
-39.40
-889.9
-13856
-6806.4
-12881
-9382.9
4384.8
103.7
134.7
113.0
123.2
111.4
102.2
83.17
131.9
153.8
129.7
0.0014
0.0010
0.0013
0.0006
0.0003
0.0003
0.0026
0.0062
0.0061
0.0011
Supporting Information Available:
5128
1HNMR, 13CNMR, DSC, and TG/DTA graphs of [HMIM][SCN].
This material is available free of charge via the Internet at http://
pubs.acs.org.
-12326
-17452
-10430
15065
10520
a R ) 0.1.
Literature Cited
∆u21 ) 480.66 J·mol-1, and σT/K ) 1.7 K. The resulting curve
is presented together with the experimental points in Figure 2.
The LLE was correlated with the NRTL model describing
the excess Gibbs energy.13 The equations were described by us
earlier.10 The NRTL R parameter was set to a value of R )
0.1, which has given the best results of the correlations. For
LLE, the temperature-dependent model adjustable parameters
(g12 - g22 ) a12 + b12T) and (g21 - g11 ) a21 + b21T) were
found by minimization of the objective function, OF:
(1) Holbrey, J. D.; Lo´pez-Martin, I.; Rothenberg, G.; Seddon, K. S.;
Silvero, G.; Zheng, X. Desulfurization of Oils Using Ionic Liquids:
Selection of Cationic and Anionic Components to Enhance Extraction
Efficiency. Green Chem. 2008, 10, 87–92.
(2) Łachwa, J.; Szydłowski, J.; Najdanovic-Visak, V.; Rebelo, L. P. N.;
Seddon, K. R.; Nunes da Ponte, M.; Esperanca, J. M. S. S.; Guedes,
H. J. R. Evidence for Critical Solution Behavior in Ionic Liquid
Solution. J. Am. Chem. Soc. 2005, 127, 6542–6543.
(3) Alonso, L.; Arce, A.; Francisco, M.; Soto, A. Phase Behaviour of
1-Methyl-3-octylimidazolium Bis[trifluoromethylsulfonyl]imide with
Thiophene and Aliphatic Hydrocarbons: The Influence of n-Alkane
Chain Length. Fluid Phase Equilib. 2008, 263, 176–181.
(4) Nebig, S.; Liebert, V.; Gmehling, J. Measurement and Prediction of
Activity Coefficients at Infinite Dilution (γ∞), Vapor-Liquid equilibria
(VLE) and Excess Enthalpies (HE) of Binary Systems with 1,1-Dialkyl-
pyrrolidinium Bis(trifluoromethylsulfonyl)imide Using Modified UNI-
FAC (Dortmund). Fluid Phase Equilib. 2009, 277, 61–67.
(5) Neves, C. M. S. S.; Ventura, S. P. M.; Freire, M. G.; Marrucho, I. M.;
Coutinho, J. A. P. Evaluation of Cation Influence on the Formation
and Extraction Capability of Ionic-Liquid-Based Aqueous Biphasic
Systems. J. Phys. Chem. B 2009, 113, 5194–5199.
n
* 2
1 i
OF )
[(∆x )2 + (∆x ) ]
(2)
∑
1 i
i)1
where n is the number of experimental points and ∆x is defined
as
∆x ) xcalc - xexp
(3)
(6) Doman´ska, U.; Marciniak, A. Phase Behaviour of 1-Hexyloxymethyl-
3-methyl-imidazolium and 1,3-Dihexyloxymethyl-imidazolium Based
Ionic Liquids with Alcohols, Water, Ketones and Hydrocarbons: The
Effect of Cation and Anion on Solubility. Fluid Phase Equilib. 2007,
260, 9–18.
(7) Doman´ska, U.; Paduszyn´ski, K. Phase Equilibria Study in the Binary
Systems (Tetra-n-butylphosphonium Tosylate Ionic Liquid + 1-Al-
cohol, or Benzene, or n-Alkylbenzene). J. Phys. Chem. B 2008, 112,
11054–11059.
(8) Doman´ska, U.; Laskowska, M. Measurements of Activity Coefficients
at Infinite Dilution of Aliphatic and Aromatic Hydrocarbons, Alcohols,
Thiophene, Tetrahydrofuran, MTBE and Water in Ionic Liquid
[BMIM][SCN] using GLC. J. Chem. Thermodyn. 2009, 41, 645–650.
(9) Doman´ska, U.; Marciniak, A. Measurements of Activity Coefficients
at Infinite Dilution of Aromatic and Aliphatic Hydrocarbons, Alcohols,
and Water in the New Ionic Liquid [EMIM][SCN] using GLC.
J. Chem. Thermodyn. 2008, 40, 860–866.
(10) Doman´ska, U.; Laskowska, M.; Pobudkowska, A. Phase Equilibria
Study of Their Binary Systems (1-Butyl-3-methylimidazolium Thio-
cyanate Ionic Liquid + Organic solvent, or Water). J. Phys. Chem. B
2009, 113, 6397–6404.
The root-mean-square deviation of mole fraction for the LLE
calculations was defined as follows:
n
n
1/2
* 2
(∆x )2 +
(∆x )
1 i
∑
∑
1 i
i)1
i)1
(
)
σx )
(4)
2n - 2
By analogy to [BMIM][SCN], it was assumed in this work
that the solubility at the solvent-rich phase was in the range of
x1 ) 2·10-5 in n-alkanes, x1 ) 2·10-3 in benzene and
alkylbenzenes, and x1 ) 2·10-5 in cyclohydrocarbons.
The results of the correlations, values of model parameters
and the corresponding standard deviations, are given in Table
6. For the systems presented in this work the average root-mean
square deviation σx equals 0.0021. The results of the correlations
are presented in Figures 3 to 5. Positive deviations from ideality
were found. The values of activity coefficients of the IL in the
saturated solution, coming from the correlation data, were higher
than one (γ1 > 1).
(11) Doman´ska, U. Vapour-Liquid-Solid Equilibrium of Eicosanoic Acid
in One- and Two-component Solvents. Fluid Phase Equilib. 1986,
26, 201–220.
(12) Abrams, D. S.; Prausnitz, J. M. Statistical Thermodynamics of Liquid
Mixtures: A New Expression for the Excess Gibbs Energy of Partly
or Completely Miscible Systems. AIChE J. 1975, 21, 116–128.
(13) Renon, H.; Prausnitz, J. M. Local Composition in Thermodynamic
Excess Functions for Liquid Mixtures. AIChE J. 1968, 14, 135–144.
Conclusion
The SLE for one and LLE for 10 new binary IL + organic
solvent systems were determined. Complete miscibility in
the liquid phase was observed with water and 1-alcohols.
The experimental data of LLE in binary systems of [HMIM-
][SCN] with n-hydrocarbons and cyclohydrocarbons dem-
onstrate typical behavior: the miscibility gap in the liquid
phase increases with an increase of the chain length of the
alkane and of the ring of cycloalkane. In the systems with
Received for review May 28, 2009. Accepted November 1, 2009. This
work has been supported by the European Union in the framework of
European Social Fund through the Warsaw University of Technology
Development Programme. Authors wish to thank Mr. M. Zawadzki for
the synthesis of [HMIM][SCN].
JE900460M