Measurement of high-pressure densities and atmospheric viscosities of ionic liquids: 1-hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide and 1-Hexyl-3-methylimidazolium chloride

Article abstract of DOI:10.1021/je4007844

Atmospheric densities and viscosities of ionic liquids, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C ₆C₁Im][Tf₂N]) and 1-hexyl-3-methylimidazolium chloride ([C₆C₁Im][Cl]), were measured with a Stabinger viscometer at temperatures from (293 to 373) K. High-pressure densities (p ≤ 200 MPa) for [C₆C₁Im][Tf₂N] and [C ₆C₁Im][Cl] were measured with a bellows type apparatus at temperatures from (312 to 452) K. Samples were analyzed for the water and 1-methylimidazole content before and after the measurements. For [C ₆C₁Im][Tf₂N], combined expanded uncertainties were estimated to be (1.0 and 1.8) kg·m^-3 for atmospheric and high-pressure density, respectively, and 0.85 % for viscosity. For [C ₆C₁Im][Cl], combined expanded uncertainties were estimated to be (1.1 and 2.5) kg·m^-3 for atmospheric and high-pressure density, respectively, and 1.59 % for viscosity. The measured densities and viscosities of [C₆C₁Im][Tf₂N] in this work agreed with some of the available literature values within their experimental uncertainties. The effect of colored impurities and the source of sample on densities and viscosities of [C₆C₁Im][Cl] were determined to be less than the experimental uncertainties. The [C₆C ₁Im][Tf₂N] did not decompose over the full temperature range during the measurements, while [C₆C₁Im][Cl] decomposed at temperatures greater than 392 K.

Full text of DOI:10.1021/je4007844

Article
pubs.acs.org/jced
Measurement of High-Pressure Densities and Atmospheric
Viscosities of Ionic Liquids: 1‑Hexyl-3-methylimidazolium
Bis(trifluoromethylsulfonyl)imide and 1‑Hexyl-3-methylimidazolium
Chloride
Masayuki Iguchi,†,§ Yuya Hiraga, Yoshiyuki Sato, Taku Michael Aida, Masaru Watanabe,
‡
†
‡
†
,†,‡
and Richard L. Smith, Jr.*
†
‡
Graduate School of Engineering, Research Center of Supercritical Fluid Technology, and Graduate School of Environmental
Studies, Tohoku University Aramaki Aza Aoba 6-6-11, Aoba-ku, Sendai 980-8579, Japan
*
S Supporting Information
ABSTRACT: Atmospheric densities and viscosities of ionic
l i q u i d s , 1 - h e x y l - 3 - m e t h y l i m i d a z o l i u m b i s -
(
trifluoromethylsulfonyl)imide ([C C Im][Tf N]) and 1-
6 1 2
hexyl-3-methylimidazolium chloride ([C C Im][Cl]), were
6
1
measured with a Stabinger viscometer at temperatures from
293 to 373) K. High-pressure densities (p ≤ 200 MPa) for
C C Im][Tf N] and [C C Im][Cl] were measured with a
(
[
6
1
2
6 1
bellows type apparatus at temperatures from (312 to 452) K.
Samples were analyzed for the water and 1-methylimidazole
content before and after the measurements. For [C C Im]-
6
1
[
Tf N], combined expanded uncertainties were estimated to
2
−3
be (1.0 and 1.8) kg·m for atmospheric and high-pressure
density, respectively, and 0.85 % for viscosity. For [C C Im][Cl], combined expanded uncertainties were estimated to be (1.1
6
1
and 2.5) kg·m− for atmospheric and high-pressure density, respectively, and 1.59 % for viscosity. The measured densities and
3
viscosities of [C C Im][Tf N] in this work agreed with some of the available literature values within their experimental
6
1
2
uncertainties. The effect of colored impurities and the source of sample on densities and viscosities of [C C Im][Cl] were
6
1
determined to be less than the experimental uncertainties. The [C C Im][Tf N] did not decompose over the full temperature
6
1
2
range during the measurements, while [C C Im][Cl] decomposed at temperatures greater than 392 K.
6
1
INTRODUCTION
to an ionic liquid are considered as side reaction products,
because most ionic liquids are clear colorless liquids. However,
the color of an ionic liquid does not seem to strongly affect
■
8
1
Research on ionic liquids is spread over many fields with each
field requiring many types of physical properties. Density and
viscosity are two of the most essential physical properties that
are relevant to fluid dynamics and transport phenomena. The
reliability of physical property measurements depends on the
ionic liquid purity, its handling, and its stability.
Impurities in the sample can be classified into three groups:
i) residual starting materials and side reaction products, (ii)
water contamination either before or after the experimental
measurements, and (iii) decomposition products that form
during the measurement.
Residual starting materials include 1-methylimidazole for
imidazolium-based ionic liquids and halides for nonhalide ionic
2
many of its physical properties, although this point has not
7
been studied in detail. Absorbents, such as activated charcoal,
alumina or silica, are used to remove colored impurities from
9
,10
3
,4
ionic liquids.
The color of an ionic liquid can be evaluated
9,11 11
by UV−vis analysis
and by fluorescence analysis.
During the sample preparation and measurement, an ionic
liquid can absorb water from the air or residual water present
on the surfaces of the apparatus. Most of ionic liquids exhibit a
(
1
2−15
decrease in the density with an addition of water;
however,
there are some cases for which the slight amount of water in an
ionic liquid causes an increase in the density as has been
1
6,17
reported for 1-hexyl-3-methylimidazolium chloride
and 1-
liquids, respectively. The presence of 1-methylimidazole in an5
1
8
ethyl-3-methylimidazolium acetate. The residual water
content generally causes a decrease in the density of a dried
ionic liquid, and the density reduction becomes larger with
imidazolium-based ionic liquid causes the viscosity to decrease.
The presence of chloride impurity in an ionic liquid causes the
density to decrease and the viscosity to increase. Distillation
5
can be applied to remove the 1-methylimidazole content from
6
ionic liquids. For determining the residual 1-methylimidazole
Received: August 29, 2013
Accepted: February 7, 2014
Published: February 17, 2014
1
in an ionic liquid, UV−vis analysis is preferable to H NMR
7
analysis due to limits of detection. Impurities that impart color
©
2014 American Chemical Society
709
dx.doi.org/10.1021/je4007844 | J. Chem. Eng. Data 2014, 59, 709−717

Journal of Chemical & Engineering Data
Article
1
2,14,15
increasing temperatures.
Karl Fischer titration is
zole was distilled under potassium hydroxide (Wako), 1-
chlorohexane was dried with molecular sieves 4A (Wako), and
acetonitrile was dried with molecular sieves 3A (Wako). All
[C C Im][Cl] samples were dried under a reduced pressure at
commonly used for the determination of water content in
ionic liquids.
Decomposition products from imidazolium-based ionic
liquids contain 1-methylimidazole. Determination of 1-
methylimidazole in the ionic liquid can be made by HPLC-
UV method, GC-FID method, colorimeter, and potentio-
1
3
6
1
19
343 K over 1 d before each measurement.
All ionic liquids were identified by 1H and 13C NMR
analyses. The residual content of 1-methylimidazole in all ionic
7
,20
7
21
1
9
metric titration.
liquids was measured with HPLC-UV method, and was wMIm =
In this work, the densities of 1-hexyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([C C Im][Tf N]) and 1-
hexyl-3-methylimidazolium chloride ([C C Im][Cl]) were
measured at pressures up to 200 MPa from (312 to 452) K,
and the viscosities of these ionic liquids were measured at
atmospheric pressure from (293 to 373) K. The ionic liquid
C C Im][Tf N] was chosen to verify the procedures of
measurement because many data are available in the
(100 w ≤ 0.05) for all ionic liquids. The water content of ionic
liquids was determined with Karl Fischer titration and found to
be wH2O = (100 w = (0.002 ± 0.001)) for [C C Im][Tf N] and
6
1
2
6
1
6
1
2
wH2O = (100 w = (0.011 ± 0.004)) for [C C Im][Cl],
6
1
respectively. The purities of [C C Im][Tf N] and [C C Im]-
6
1
2
6 1
[Cl] are estimated to be above 99.9 % taking into account the
[
6 1 2
amounts of 1-methylimidazole and water as impurities in the
ionic liquid. Detailed descriptions of the analyses are given in
the Supporting Information (Table S2).
Acetonitrile (99.9 %, Sigma-Aldrich) was used as a mobile
phase in the HPLC analysis. Ethyl acetate (99 %, Wako) and
activated charcoal (Darco, Sigma-Aldrich) were used for
1
3,22−29
literature,
and IUPAC has proposed this ionic liquid
30,31
as a reference substance.
The ionic liquid [C C Im][Cl]
6
1
32
can dissolve cellulose, and so it has some technological
importance for processing of biomass and lignocellulose
materials. For [C C Im][Tf N], although densities and
viscosities at atmospheric pressure are available, density data
at high pressures are limited in the range of temperature and
pressure (T ≤ 423 K, p ≤ 140 MPa).
literature values of density and viscosity at atmospheric pressure
6
1
2
washing and decolorizing of synthesized [C C Im][Cl],
6
1
respectively. Water that had a conductivity of less than 6 μS·
2
2,24,29
−1
m
was used as a solvent for the decolorization, in the HPLC
For [C C Im][Cl],
6 1
analysis and in the calibration of the density measurement.
Potassium dihydrogenphosphate (99 %, Wako) was used to
control the pH in the HPLC analysis. Deuterated dimethyl
1
6,17,33−36
do not agree within their uncertainties,
and density
data at high pressures have not been reported. Samples in the
literature generally specify the water content only before the
measurement with the exception of the work of David et al.
Table S1, Supporting Information).
water content in the measured [C C Im][Cl] is needed
sulfoxide, DMSO-d
(99.9 %, Aldrich), deuterated water, D
O
2
6
(99.9 %, Acros) and deuterated dichloromethane, CD
Cl (99.9
2
2
1
6,17,33−37
(
The analysis of
%, Wako) were used in the NMR analyses. In the calibration
procedure for the density and viscosity measurements at
atmospheric pressure, certified reference fluids JS20 (Nippon
Grease), N44 (Cannon), N415 (Cannon) and JS2000 (Nippon
Grease) were used. For determining the water content of the
ionic liquids with Karl Fischer titration, Coulomat AG (Fluka)
and Coulomat CG (Fluka) were used as an anolyte solution
and as a catholyte solution, respectively.
6
1
because ionic liquids with a chloride readily absorb
3
8,39
moisture.
The effect of colored impurities and the source
of ionic liquid (synthesis and commercial) on densities and
viscosities of [C C Im][Cl] were investigated in this work.
Long-term thermal stabilities for [C C Im][Tf N] and
C C Im][Cl] are unavailable so far, and although this is
6
1
6
1
2
40
[
6 1
not addressed in this work, analyses were made to assess the
stability of the ionic liquids over the period of measurement. To
examine the decomposition and the water uptake of the ionic
liquid during the measurements, concentrations of 1-methyl-
imidazole and water in the ionic liquid were analyzed both
before and after the experimental measurements.
Density and Viscosity Measurement at Atmospheric
Pressure. Densities and viscosities at atmospheric pressure
were measured simultaneously with a Stabinger viscometer
4
1
(Anton Paar, SVM3000). The measured density was
corrected for the viscosity effect according to the instrument
operational features, and standard uncertainties of the apparatus
were u(T) = 0.02 K, u(ρ) = 0.5 kg·m− and u (η) = 0.35 %. The
3
r
EXPERIMENTAL METHODS
Materials. The 1-hexyl-3-methylimidazolium bis-
trifluoromethylsulfonyl)imide ([C C Im][Tf N], 99 %,
temperature was controlled to within 0.005 K, and the wait
time after temperature stabilization for each measurement was
■
(
3
0 s. Stabilities of density and viscosity were judged by the
6
1
2
−3
change of density and viscosity being within 0.3 kg·m and
Merck) used in the study was supplied by a commercial
source. The reported halide content in [C C Im][Tf N] by the
0
.07 %, respectively, over a period of 60 s. The calibration of
6
1
2
the apparatus was performed with certified reference fluids
described in the previous section. Measurements of the certified
reference fluids and water were carried out over the range of
temperatures from (293.15 to 373.15) K that corresponded to
the range of densities (778.7 to 997.0) kg·m− and viscosities
(5.85 to 1780) mPa·s.
manufacturer was less than 100 w = 0.001. The ionic liquid was
dried under a reduced pressure at 333 K over 10 h before each
measurement. Four types of 1-hexyl-3-methylimidazolium
chloride ([C C Im][Cl]) were used for purposes of compar-
6
1
3
ison between their properties: (i) commercial [C C Im][Cl] (>
6
1
97 %, Fluka) without decolorization treatment, (ii) synthesized
[
C C Im][Cl] without decolorization treatment, (iii) synthe-
Measurements in duplicate of the ionic liquid with the
Stabinger viscometer were performed from (293.15 to 373.15)
6
1
sized [C C Im][Cl] with single-pass decolorization treatment,
and (iv) synthesized [C C Im][Cl] with triple-pass decoloriza-
tion treatment as described in detail in the Supporting
Information (Table S2 and Figures S1 and S2). The
6
1
K for [C
[C Im][Cl], respectively. Due to the calibration range of the
Stabinger viscometer, viscosities of [C C Im][Cl] at the lower
C Im][Tf N] and from (303.15 to 373.15) K for
6
1
6 1 2
C
6 1
6
1
[
%
(
C C Im][Cl] was synthesized from 1-methylimidazole (99
, Aldrich) and 1-chlorohexane (99 %, Aldrich) in acetonitrile
99.9 %, Sigma-Aldrich). Before the synthesis, 1-methylimida-
temperatures (303.15 and 313.15) K are not reported. Prior to
sample loading, nitrogen gas was flowed into the instrument at
333.15 K for 30 min to dry the measurement cell. When the
6
1
7
10
dx.doi.org/10.1021/je4007844 | J. Chem. Eng. Data 2014, 59, 709−717

Journal of Chemical & Engineering Data
Article
sample was loaded, the first 2 mL of sample was used for
wetting the surfaces in the viscometer. Subsequently, 1 mL of
sample was added and the measurement was started from the
lowest temperature to the highest temperature of 373.15 K.
After the measurement at 373.15 K was made, 1 mL of sample
was added and the measurement was started from 373.15 K to
the lowest temperature of the measurement. This cycle was
repeated twice, that is, the four runs were made for each
measurement. The water content in the sample after each set of
runs was determined by Karl Fischer titration. When the
second cycle was finished, the measured sample was analyzed
with NMR and HPLC to characterize the sample and to
quantify the content of 1-methylimidazole. For verifying the
apparatus, measurements of the certified reference fluids were
performed from (293.15 to 373.15) K after cleaning and drying
of the measurement cell.
estimated to be 0.01 % from results of calibrations with water.
Therefore, the uncertainty of densities at atmospheric pressure
was estimated to be equal to that value at high pressure.
The NMR spectra of measured samples did not change from
that of the sample before and after the measurements. The
concentration of 1-methylimidazole in the dmeasured samples
was less than 100 w = 0.05 for [C
(0.62 ± 0.03) for [C Im][Cl], respectively. This indicates
that, although [C Im][Tf N] did not decompose, some
decomposition of [C Im][Cl] did occur during the measure-
ments. The water content of the measured samples increased to
100 w = (0.005 ± 0.002) for [C Im][Tf N] and 100 w =
0.107 ± 0.013) for [C C Im][Cl], respectively.
C Im][Tf N] and 100 w =
6 1 2
C
6 1
C
6 1
6
1
C
2
C
1
6
2
(
6
1
For [C C Im][Tf N], the uncertainty of water content as
6
1
2
−3
13
u(wH2O) = (100 w = 0.003) gave u(ρ) = 0.05 kg·m . The
uncertainties of loading mass, volume, temperature, and
The NMR spectra of measured samples did not change from
that of sample before and after the measurements. The
concentration of 1-methylimidazole in the measured samples
was less than 100 w = 0.05, which is evidence that no
decomposition occurred during the measurements. The water
content of the measured samples increased to 100 w = (0.004 ±
pressure in apparatus gave u(ρ) = (0.11, 0.60, 0.09, and 0.28)
−3
kg·m , respectively. The uncertainty of density at atmospheric
0
−3
pressure was u(ρ ) = 0.51 kg·m , which is the combined
uncertainty of the measured density with the Stabinger
viscometer. The uncertainty of measurements calculated from
the difference between first and second runs was u(ρ) = 0.21
̅
−3
0
.002) for [C C Im][Tf N] and 100 w = (0.022 ± 0.008) for
kg·m . The combined expanded uncertainties with a level of
6
1
2
[
C C Im][Cl], respectively, and this can probably be attributed
confidence of 0.95 (k = 2) was estimated to be U (ρ) = 1.8 kg·
6
1
c
−3
to the residual water in the apparatus or the absorption of water
during recovery of the measured sample.
m .
For [C C Im][Cl], the uncertainty of water content as
6
1
−3
16
For [C C Im][Tf N], the uncertainty of water content as
u(wH2O) = (100 w = 0.096) gave u(ρ) = 0.72 kg·m . The
uncertainties of mass of the loaded sample, volume, temper-
ature and pressure in apparatus gave u(ρ) = (0.11, 0.50, 0.06
6
1
2
−
3
u(wH2O) = (100 w = 0.004) gave u(ρ) = 0.06 kg·m and u (η)
r
1
3
=
0.21 %. The uncertainty of temperature in the apparatus
−3
−3
and 0.14) kg·m , respectively. The uncertainty of density at
0
gave u(ρ) = 0.02 kg·m and u (η) = 0.08 %. The uncertainties
of measurements were u(ρ) = 0.10 kg·m and u (η) = 0.08 %.
Combined expanded uncertainties with a level of confidence of
.95 (k = 2) were estimated to be U (ρ) = 1.0 kg·m and
r
−3
−3
atmospheric pressure was u(ρ ) = 0.57 kg·m , which is the
combined uncertainty of the measured density with the
Stabinger viscometer. The uncertainty of measurements
calculated from the difference between first and second runs
̅
r
̅
−3
0
c
U (η) = 0.85 %.
c,r
−3
was u(ρ) = 0.72 kg·m , and this includes the influence of
decomposition of the measured sample to the density. The
̅
For [C C Im][Cl], the uncertainty of water content as
6
1
−
3
u(wH2O) = (100 w = 0.019) gave u(ρ) = 0.27 kg·m and u (η)
r
combined expanded uncertaintY with a level of confidence of
1
6
=
0.70 %. The uncertainty of temperature in the apparatus
−3
0
.95 (k = 2) was estimated to be U (ρ) = 2.5 kg·m .
c
−3
gave u(ρ) = 0.01 kg·m and u (η) = 0.11 %. The uncertainties
of measurements were u(ρ) = 0.03 kg·m and u (η) = 0.06 %.
r
−3
̅
r
̅
CORRELATION METHODS
■
Combined expanded uncertainties were estimated to be U (ρ)
c
1.1 kg·m−3 and U (η) = 1.59 % with a level of confidence of
To correlate the measured densities at high pressure in this
work, the Tait equation was used in the following form:
=
c,r
46
0.95 (k = 2).
Density Measurement at Pressures up to 200 MPa.
0
−3
ρ /kg·m
ρ/kg·m−
=
3
Densities at high pressure were measured with a bellows type
4
2−44
⎡B + (p / MPa)⎤
apparatus.
Standard uncertainties of the apparatus were
1 − C ln⎣
B + 0.1
⎦
(
1)
u(T) = 0.1 K, u(p) = 0.10 MPa at less than 90 and 0.25 MPa at
above 90 MPa, and u(v) = 0.04 %. The reference condition for
density was at 312 K under atmospheric pressure, and the
density was measured with the Stabinger viscometer. Measure-
ments of ionic liquids were performed over the range of (312 to
where B in eq 1 has units of Pa and is expressed as a function of
the absolute temperature as follows:
B = b exp[b (T/K)]
(2)
0
1
4
52) K and (10 to 200) MPa. The procedure for the
‑1
45
Parameters in eqs 1 and 2 (C, b /Pa, and b /K ) for each ionic
0 1
measurements followed that of Machida et al. After the
isobaric series of measurements at (451 to 452) K were
completed, the measurement at (312 to 313) K was made again
to verify the apparatus and the integrity of the sample. The
measured sample was analyzed with NMR, HPLC, and Karl
Fischer titration. Densities at atmospheric pressure from (331
to 452) K were extrapolated from isothermal densities at high
pressure using the Tait equation (eq 1), since the Tait equation
can provide good correlation of liquid densities over a wide
range of conditions. The uncertainty of extrapolations that used
the Tait equation for densities at atmospheric pressure was
liquid were obtained by fitting the density data using
47
Levenberg−Marquardt algorithm with analytical derivatives.
0
In eq 1, ρ represents the density at atmospheric pressure and
was described as
1
2
=
a + a (T/K) + a (T/K)
0
−3
0
1
2
ρ /kg·m
(3)
3
.
‑1
The determination of parameters in eq 3 (a /m kg , a /
0
1
3.
‑1. ‑1
3. ‑1. ‑2
m kg K , and a /m kg K ) for each ionic liquid was
2
obtained by fitting the density data at atmospheric pressure
7
11
dx.doi.org/10.1021/je4007844 | J. Chem. Eng. Data 2014, 59, 709−717

Journal of Chemical & Engineering Data
Article
4
7
using singular value decomposition. For the correlation of
measured viscosities, the following equation was used:
each temperature. Densities measured with the Stabinger
viscometer and those extrapolated from high-pressure data
agreed within our reported uncertainties. Determined param-
⎛
ln⎜
⎝
⎞
η/mPa·s
d1
3. ‑1
−4
3. ‑1. ‑1
eters were a = 0.60583 m kg , a = 3.4273·10 m kg K
⎟ = d +
0
1
0
0
−7
3. ‑1. ‑2
η
⎠
d2 + (T/K)
(4)
and a = 2.368·10 m kg K for eq 3, and d = −1.967, d =
2
0
1
8
24.2/K, and d = −165.707/K for eq 4, respectively. The
2
0
where η = 1 mPa·s and d , d /K, and d /K are adjustable
0
1
2
values of bias and ARD were (+0.01 and 0.02) % for density
and (< 0.01 and 0.02) % for viscosity, respectively.
parameters that are determined by fitting the viscosity data of
each ionic liquid using Levenberg−Marquardt algorithm with
Figures 1 and 2 show relative deviation plots of atmospheric
densities and viscosities of [C C Im][Tf N] for values reported
47
analytical derivatives. Adjustable parameters in eqs 1−4 were
6
1
2
determined by minimizing the following objective function
in this work compared with the literature. In Figure 1, densities
at temperatures below 373 K agreed with literature values of
(
O.F.)
2
5
30
2
Ahosseini et al. except at 348 K, IUPAC group, Safarov et
29 28
n ⎛
⎞
⎠
Xcal,i − Xexp ,i
Uc(Xexp ,i)
1
n
al. and Seoane et al. within the combined expanded
uncertainty for this work [(0.07 to 0.08) %]. The uncertainties
of density reported by Ahosseini et al. (0.15 %) and Tariq et
al. (0.4 %) are consistent with the uncertainty of this work.
For densities at temperatures greater than 373 K, data of this
work agreed with values of Tariq et al. within the uncertainty
of this work [(0.13 to 0.15) %], but were larger than values of
O. F. = ∑ ⎜
⎟
⎟
⎜
⎝
(5)
i=1
25
26
where X refers to the density or viscosity, U (X) is the
c
combined expanded uncertainty of X measurement, n is the
number of measurements, and the subscripts of “cal” and “exp”
refer to calculated and experimental measured values,
respectively. For evaluation of the correlation, values of bias
and average relative deviation (ARD) were used as follows:
26
29
Safarov et al. The difference in densities between this work
and Safarov et al. tends to become greater at temperatures
29
higher than 373 K. The deviation of values reported by Safarov
et al. (0.06 %) and values in this work can be attributed to
n ⎛
⎞
⎠
Xcal,i
29
1
n
bias = 100· ∑ ⎜
− 1⎟
⎜
⎟
Xexp ,i
following points. Safarov et al. estimated the uncertainty only
⎝
(6)
i=1
29
from the viscosity effects on the density measurement, which
causes an underestimation of the uncertainty. Further, the
higher residual water content in the ionic liquid of Safarov et al.
n
Xcal,i
1
n
ARD = 100·
∑
− 1
Xexp ,i
29
i=1
(7)
(100 w ≤ 0.03) than that of this work [100 w = (0.002−
0
.005)] causes a decrease in the density of the dried ionic liquid
Derivatives of the Tait equation were used to estimate the
isobaric thermal expansivities and the isothermal compressibil-
ities of each ionic liquid (Supporting Information).
at high temperatures.
In Figure 2, viscosities of this work agreed with literature
30
27
values of IUPAC group and Tariq et al. within the
combined expanded uncertainty for this work (0.85 %) and the
literature (2 %). Viscosities reported by Ahosseini and Scurto
RESULTS AND DISCUSSION
Measured Densities and Viscosities of [C C Im][Tf N]
at Atmospheric Pressure as Shown in Table 1. Table 2
shows atmospheric densities extrapolated from high-pressure
data to atmospheric pressure using the Tait equation (eq 1) at
■
23
28
6
1
2
except at 298 K and Seoane et al. were smaller than values
of this work. Ahosseini and Scurto measured samples that
contained 100 w = 0.013 water content after measurement and
less than 100 w = 0.001 bromide content using an oscillating-
23
piston viscometer. The trends of data reported in this work
23
Table 1. Measured Densities ρ and Viscosities η at
Atmospheric Pressure over the Temperature T Range
293.13 to 373.15) K for 1-Hexyl-3-methylimidazolium
Bis(trifluoromethylsulfonyl)imide ([C C Im][Tf N]) and 1-
Hexyl-3-methylimidazolium Chloride ([C C Im][Cl])
were similar to those reported by Ahosseini and Scurto, so
that the difference in the values between these works is
probably due to the method for viscosity measurement. Seoane
et al. measured samples that contained 100 w = 0.007 water
content before measurement and less than 100 w = 0.01 halide
(
6
1
2
a
6
1
28
content using an Ubbelohde type viscometer. The smaller
[
C C Im][TF N]
[C C Im][Cl]
6 1
6
1
2
28
values of Seoane et al. than those of this work can be
attributed to the absorption of water in the sample during the
measurement, because it is difficult to prevent the water
absorption with this type of viscometer.
3
ρ/kg·m−3
T/K
ρ/kg·m−
η/mPa·s
η/mPa·s
2
93.15
03.15
13.15
23.15
33.15
43.15
53.15
63.15
73.15
1376.3
1367.1
1358.0
1348.9
1339.9
1331.0
1322.2
1313.3
1304.7
90.06
56.25
37.44
26.25
19.21
14.55
11.36
9.091
7.434
3
3
3
3
3
3
3
3
1035.1
1029.5
1023.9
1018.4
1012.8
1007.4
1002.1
997.1
B
B
Density Measurements of [C C Im][Tf N] at High
6
1
2
1806
810.3
404.3
220.6
129.7
81.34
Pressures as Shown in Table 2. Densities were represented
by eqs 1−3 with values of bias and ARD as (<0.01 and 0.01) %
−3
‑1
with parameters b = 566.5/Pa, b = −4.224 × 10 /K , and C
0
1
=
0.08645. Figure 3 shows a relative deviation plot of the
densities for [C C Im][Tf N] between this work and the
6
1
2
literature. Densities agreed with literature values of Esperanca
̧
24
22
a
et al. and Kandil et al. within the combined expanded
uncertainty for this work [(0.12 to 0.15) %] and the literature
Standard uncertainty is u(T) = 0.02 K, and combined expanded
uncertainties with a 0.95 level of confidence (k = 2) are U (ρ) = (1.0
c
24
22
−3
(0.11 % for Esperanc a̧ et al. and 0.3 % for Kandil et al. ).
and 1.1) kg·m for [C C Im][Tf N] and [C C Im][Cl], respectively,
6
1
2
6 1
29
Densities reported by Safarov et al. at temperatures below
373 K agreed with values of this work within the uncertainty of
this work and the literature [(0.05 to 0.06) %], but those at
and U (η) = (0.85 and 1.59) % For [C C Im][Tf N] and
C C Im][Cl], Respectively. Value out of Calibration Range for
the Stabinger Viscometer.
c,r
6
1
2
B
[
6 1
7
12
dx.doi.org/10.1021/je4007844 | J. Chem. Eng. Data 2014, 59, 709−717

Journal of Chemical & Engineering Data
Article
Table 2. Measured Densities ρ at High Pressures p up to 200 MPa for 1-Hexyl-3-methylimidazolium
Bis(trifluoromethylsulfonyl)imide ([C C Im][Tf N]) over the Temperature T Range (312.6 to 452.3) K
a
6
1
2
T/K
p/MPa
312.6
332.4
352.3
372.5
392.7
412.7
432.6
452.3
ρ/kg·m−
3
b
c
c
c
c
c
c
c
0
.1
1358.5
1365.7
1373.0
1380.1
1386.7
1392.8
1399.0
1404.6
1410.2
1415.5
1420.7
1425.8
1430.8
1435.5
1440.1
1444.5
1448.9
1453.0
1457.6
1461.6
1465.9
1340.0
1348.1
1355.9
1363.3
1370.4
1377.0
1383.2
1389.3
1395.1
1400.5
1406.3
1411.5
1416.5
1421.3
1426.1
1430.9
1435.4
1439.7
1444.0
1448.4
1452.6
1322.2
1330.9
1339.3
1347.3
1354.5
1361.5
1368.2
1374.6
1380.6
1386.5
1392.0
1397.5
1402.7
1408.0
1412.8
1417.6
1422.1
1426.8
1431.4
1435.5
1439.9
1304.4
1286.8
1296.8
1306.3
1315.1
1323.4
1331.1
1338.5
1345.4
1352.1
1358.3
1364.5
1370.3
1376.0
1381.5
1386.8
1391.9
1397.0
1401.8
1406.5
1411.1
1415.7
1269.8
1280.4
1290.4
1299.8
1308.4
1316.5
1324.3
1331.5
1338.5
1345.0
1351.3
1357.5
1363.2
1368.9
1374.3
1379.8
1384.9
1389.9
1394.7
1399.4
1404.0
1252.4
1263.7
1274.3
1284.2
1293.3
1301.7
1309.7
1317.3
1324.5
1331.2
1337.8
1344.1
1350.3
1356.1
1361.9
1367.3
1372.4
1377.5
1382.5
1387.4
1392.2
1235.6
1247.6
1258.8
1269.2
1278.8
1287.6
1295.9
1303.9
1311.3
1318.3
1325.1
1331.8
1338.0
1344.1
1349.9
1355.5
1360.8
1366.2
1371.3
1376.4
1381.2
1
2
3
4
5
6
7
8
9
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1313.7
1322.6
1330.9
1338.6
1346.0
1353.0
1359.6
1366.0
1372.1
1378.0
1383.7
1389.1
1394.3
1399.4
1404.4
1409.3
1414.0
1418.5
1423.1
1427.4
1
1
1
1
1
1
1
1
1
1
2
00.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
00.0
a
Standard uncertainties are u(T) = 0.1 K, u(p) = 0.1 MPa for 0.1 < p < 90 and 0.25 MPa for p ≥ 90 MPa, and the combined expanded uncertainty is
c
−3
b
c
U (ρ) = 1.8 kg·m with a level of confidence of 0.95 (k = 2). Measured value with Stabinger viscometer. Extrapolated value from high-pressure
data to atmospheric pressure using the Tait equation (eq 1) at each temperature.
Figure 1. Relative deviation plot for densities measured at atmospheric
p r e s s u r e f o r 1 - h e x y l - 3 - m e t h y l i m i d a z o l i u m b i s -
Figure 2. Relative deviation plot for viscosities measured at
atmospheric pressure for 1-hexyl-3-methylimidazolium bis-
(trifluoromethylsulfonyl)imide ([C C Im][Tf N]). Calculated values
(
trifluoromethylsulfonyl)imide ([C C Im][Tf N]). Calculated values
6 1 2
6
1
2
were obtained from eq 3 in which parameters were obtained by fitting
data of this work; ⊙, Measured values with the Stabinger viscometer in
this work; ●, calculated values from measurements with the
were obtained from eq 4 in which parameters were obtained by fitting
23
data of this work; ⊙, this work; ⊡, Ahosseini and Scurto; dotted
30
down triangle, calculated values from IUPAC proposed equation; +,
2
5
28
27
dilatometer in this work using eq 1; ⊡, Ahosseini et al.; dotted
Seoane et al.; ◬, Tariq et al. Dashed lines are the uncertainty of
3
0
down triangle, calculated values from IUPAC proposed equation; ×,
data reported in this work (0.85 %).
29
28
26
Safarov et al.; +, Seoane et al.; ◬, Tariq et al. Dashed and dash-
dotted lines are the uncertainties of data reported in this work for
measured values [(0.07 to 0.08) %] and calculated values with eq 1
1
2,14,15
this work.
The high pressure density data of Safarov et
2
9
al. are inconsistent with data reported in this work.
Using the Tait equation (eq 1) with the fitting parameters
determined from the density data reported in this work,
[
(0.13 to 0.15) %], respectively.
temperatures above 373 K were smaller than values of this
isobaric thermal expansivities, α , and isothermal compressibil-
p
work. The difference in densities between this work and Safarov
ities, β , for [C C Im][Tf N] were calculated (Tables S3 and
T
6
1
2
2
9
et al. tends to become large at high pressures and at
temperatures above 373 K (Figure S3, Supporting Informa-
tion), which can be attributed to the higher residual water
S4, Supporting Information). For α of [C C Im][Tf N], two
p 6 1 2
trends were noted for the variation of α with temperature at a
p
given pressure (Table S3, Supporting Information). At
pressures less than 30 MPa, for a given pressure, the calculated
29
content of the ionic liquid used in Safarov et al. than that of
7
13
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Journal of Chemical & Engineering Data
Article
48
by Navia et al.2, but were in conflict with values reported by
9
Safarov et al. (Figure S4, Supporting Information). For
isothermal compressibilities, calculated values of this work
decreased with increasing pressures at all temperatures and
2
4,29
were in agreement with the available literature
and Figure S5, Supporting Information).
(Table S4
Measured Densities and Viscosities of [C C Im][Cl] at
6
1
Atmospheric Pressure as Shown in Table 1. Combined
uncertainties of density and viscosity for each source of
[
C C Im][Cl] were compared (Tables S5 and S6, Supporting
6 1
Information). Both the source of the sample and the colored
impurities had an indistinguishable effect on densities and
viscosities within the uncertainties of the measurement in this
work. Table 3 shows atmospheric densities extrapolated from
high-pressure data to atmospheric pressure using the Tait
equation (eq 1) at each temperature. Densities measured with
the Stabinger viscometer and those extrapolated from high-
pressure data agreed to within our reported uncertainties.
Figure 3. Relative deviation plot for densities measured at high
p r e s s u r e s f o r 1 - h e x y l - 3 - m e t h y l i m i d a z o l i u m b i s -
(
trifluoromethylsulfonyl)imide ([C C Im][Tf N]). Calculated values
6 1 2
were obtained from eqs 1 to 3 in which parameters were obtained by
2
4
fitting data of this work; ⊙, this work; ⊡, Esperanc a̧ et al.; dotted
2
2
29
diamond, Kandil et al.; ×, Safarov et al. Dashed lines are the
3. ‑1
Determined parameters were a = 0.8257 m kg , a = 4.1113·
0
1
uncertainty of data reported in this work [(0.12 to 0.15) %].
−4
3. ‑1. ‑1
−7
3. ‑1. ‑2
1
0
m kg K , and a = 1.768·10 m kg K for eq 3 and d
2
0
=
−3.19947, d = 1309.517/K, and d = −200.794/K for eq 4,
1
2
respectively. The values of bias and ARD were (+0.01 and 0.02)
αp showed a slight maximum as temperature was increased. At
%
for eq 3 and (−0.03 and 0.02) % for eq 4, respectively.
pressures of 30 MPa and higher generally, the calculated α of
p
Figures 4 and 5 show relative deviation plots of atmospheric
[
C C Im][Tf N] always decreased with increasing temperature
6 1 2
at a given pressure. Safarov et al. reported an the increase in
isobaric thermal expansivities with temperatures at all
pressures, which is inconsistent with values estimated in the
literature and in this work. Navia et al. showed experimentally
that an increasing temperature cause a decrease in the isobaric
thermal expansivities. Trends of the isobaric thermal
expansivities with temperature were similar to results reported
densities and viscosities for [C
and the literature. In Figure 4, densities in this work agreed
with literature values of Gom
within 0.2 %, with those of He et al. to within 0.3 %, and with
those of Sastry et al. to within 0.6 %. These deviations can
probably be explained by the absorption of water by the ionic
liquid during the measurements made by those researchers.
C Im][Cl] between this work
6 1
2
9
16
36
́
ez et al. and Ning et al. to
4
8
35
17
4
8
Table 3. Measured Densities ρ at High Pressures p up to 200 MPa for 1-Hexyl-3-methylimidazolium chloride ([C C Im][Cl])
6
1
a
over the Temperature T Range (311.5 to 451.2) K
T/K
p/MPa
.1
311.5
331.2
351.2
371.5
ρ/kg·m−
391.6
411.6
431.4
451.2
3
b
c
c
c
c
c
c
c
0
1030.4
1034.2
1038.2
1041.9
1045.5
1049.0
1052.4
1055.7
1058.9
1061.9
1065.1
1067.9
1070.9
1073.6
1076.5
1079.1
1081.7
1084.5
1087.1
1089.6
1092.0
1019.1
1023.3
1027.4
1031.3
1035.1
1038.8
1042.3
1045.7
1049.1
1052.3
1055.4
1058.5
1061.5
1064.4
1067.2
1070.1
1072.8
1075.5
1078.1
1080.7
1083.4
1007.8
1012.3
1016.7
1020.9
1024.9
1028.7
1032.4
1036.0
1039.4
1042.8
1046.0
1049.3
1052.3
1055.3
1058.2
1061.1
1063.9
1066.7
1069.4
1072.0
1074.6
997.1
986.5
991.4
976.2
981.3
965.7
971.1
955.0
960.7
966.2
971.4
976.4
981.1
985.6
989.9
994.1
998.3
1
2
3
4
5
6
7
8
9
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
1001.8
1006.3
1010.7
1014.9
1018.8
1022.7
1026.4
1030.0
1033.4
1036.9
1040.2
1043.3
1046.4
1049.4
1052.4
1055.3
1058.0
1060.9
1063.5
1066.2
996.2
986.3
976.3
1000.8
1005.2
1009.3
1013.3
1017.2
1020.9
1024.6
1028.0
1031.4
1034.7
1037.9
1041.0
1044.1
1047.1
1050.0
1052.8
1055.6
1058.4
991.0
981.3
995.5
986.0
999.8
990.6
1004.0
1008.0
1011.9
1015.6
1019.2
1022.7
1026.1
1029.4
1032.7
1035.9
1038.9
1041.9
1044.8
1047.7
1050.5
994.9
999.0
1003.1
1006.9
1010.6
1014.2
1017.7
1021.2
1024.4
1027.7
1030.9
1033.9
1037.0
1039.9
1042.8
1
1
1
1
1
1
1
1
1
1
2
00.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
00.0
1002.1
1005.8
1009.4
1012.9
1016.4
1019.6
1022.9
1025.9
1029.1
1032.1
1035.1
a
Standard uncertainties are u(T) = 0.1 K, u(p) = 0.1 MPa for 0.1 < p < 90 and 0.25 MPa for p ≥ 90 MPa, and the combined expanded uncertainty of
−3
b
c
density is U (ρ) = 2.5 kg·m with a 0.95 level of confidence (k = 2). Measured value with Stabinger viscometer. Extrapolated value from high-
c
pressure data to atmospheric pressure with the Tait equation (eq 1) at each temperature.
7
14
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Journal of Chemical & Engineering Data
Article
viscosity in this work still remain. The larger values of Ning et
36
34
al. and Fendt et al. compared with those in this work are not
easily explained by factors of water or 1-methylimidazole
content in the samples.
Measured Densities of [C C Im][Cl] at High Pressures
6
1
as Shown in Table 3. Densities were represented by eqs 1−3
with values of bias and ARD as (<0.01 and 0.01) % with
−
3
‑1
parameters b = 662.0/Pa, b = −3.242·10 /K , and C =
0
1
0
.0887. Figure 6 shows measured densities of [C C Im][Cl]
6 1
Figure 4. Relative deviation plot for densities measured at atmospheric
pressure for 1-hexyl-3-methylimidazolium chloride ([C C Im][Cl]).
6
1
Calculated values were obtained from eq 3 in which parameters were
obtained by fitting data of this work; ⊙, Measured values with the
Stabinger viscometer in this work; ●, calculated values from
measurements with the dilatometer in this work using eq 1; ◬,
1
6
35
36
Gomez et al.; dotted down triangle, He et al.; +, Ning et al.; ⊡,
́
17 33
Sastry et al.; ×, Seddon et al. Dashed and dash-dotted lines are the
uncertainties of data reported in this work for measured values (0.11
%
) and calculated values with eq 1 [(0.25 to 0.26) %], respectively.
Figure 6. Measured densities of 1-hexyl-3-methylimidazolium chloride
(
[C C Im][Cl]) plotted against the pressure at several temperatures:
6 1
⊙
, 312 K; ⊡, 331 K; ◬, 351 K; dotted down triangle, 372 K; dotted
diamond, 392 K; dotted pentagon, 412 K; ◬, 431 K; dotted down
triangle, 451 K; ◐, measured with the Stabinger viscometer in this
work. Filled symbols denote extrapolated values from high-pressure
data to atmospheric pressure with eq 1 at each temperature. Lines are
fitted to this work with eqs 1−3.
plotted over the pressure range from (0.1 to 200) MPa at
several temperatures from (312 to 451) K. As mentioned
Figure 5. Relative deviation plot for viscosities measured at
atmospheric pressure for 1-hexyl-3-methylimidazolium chloride
before, the HPLC analysis showed that some [C C Im][Cl]
(
[C C Im][Cl]). Calculated values were obtained from eq 4 in
6 1
6
1
which parameters were obtained by fitting data of this work; ⊙, This
decomposed to 1-methylimidazole during the measurements.
Meine et al. reported that imidazolium-based ionic liquids with
a chloride easily decompose to imidazoles by heating compared
with ionic liquids having a bis(trifluoromethylsulfonyl)imide
34
16
́
work; dotted diamond, Fendt et al.; ◬, Gomez et al.; +, Ning et
3
6
33
al.; × , Seddon et al. Dashed lines are the uncertainty of data
reported in this work (1.59 %).
19
anion. After heating [C C Im][Cl] to 451 K, densities at 312
6
1
33
Deviations of data reported by Seddon et al. and values
reported in this work were from (0.5 to 0.6) %. Although
Seddon et al. made the measurements of samples that
K under high pressure decreased from those before heating.
This is probably due to partial decomposition of [C C Im][Cl]
6
1
to 1-methylimidazole, from which it can be inferred that an
increase in the 1-methylimidazole content caused the density to
decrease. The average deviation of measured densities between
33
contained 100 w = 0.757 water content, the reported values
3
3
by Seddon et al. were smaller than this work, and this is most
likely due to the presence of 1-methylimidazole in the sample as
discussed later.
−3
before and after heating to (451−452) K was 0.72 kg·m for
−3
[C C Im][Cl] and 0.21 kg·m for [C C Im][Tf N], respec-
6
1
6
1
2
36
In Figure 5, viscosities reported by Ning et al. agreed with
tively (Table S7, Supporting Information). However, for
[C C Im][Tf N] heating to 392 K, the average deviation was
3
4
this work to within 4 %. Literature values of Fendt et al.,
6
1
2
1
6
33
−3
Gom
́
ez et al., and Seddon et al. were 5 % higher than those
ez et al. and Seddon et al. measured samples
0.17 kg·m which was almost the same value as that
determined for [C C Im][Tf N] after heating to 452 K.
in this work. Gom
́
6
1
2
that had a water content of 100 w = (0.048 and 0.757) before
measurement using an Ubbelohde type viscometer and a cone−
Thus, the measured [C C Im][Cl] at temperatures below 392
6 1
K did not seem to undergo decomposition and the uncertainty
of measurements at temperatures below 392 K was less than
16,33
plate viscometer, respectively.
́
The smaller values of Gomez
1
6
33
−3
et al. and Seddon et al. than those in this work can be
attributed to the high water content in the samples and the
absorption of water during their measurements. A decrease in
the viscosity is caused by residual content of 1-methylimidazole
the estimated uncertainty from all density data (2.5 kg·m ).
Assuming that the uncertainty of measurements was u(ρ) =
̅
−3
0.17 kg·m , the combined expanded uncertainties with a level
of confidence of 0.95 (k = 2) was estimated to be U (ρ) = 2.0
kg·m . The isobaric thermal expansivities and the isothermal
c
5
−3
in the samples, however other factors for higher values of
7
15
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Journal of Chemical & Engineering Data
Article
compressibilities for [C C Im][Cl] were calculated using the
ACKNOWLEDGMENTS
6
1
■
Tait equation (eq 1) with parameters fitted to the density data
reported in this work (Tables S8 and S9, Supporting
Information). The trends of calculated values were similar for
both [C C Im][Cl] and [C C Im][Tf N] ionic liquids (Figures
The authors thank Syunsuke Kayamori (Tohoku University)
for the assistance with NMR and fluorescence analyses.
6
1
6
1
2
REFERENCES
S6 and S7, Supporting Information).
■
(
1) Hallett, J. P.; Welton, T. Room-Temperature Ionic Liquids:
Solvents for Synthesis and Catalysis. 2. Chem. Rev. 2011, 111, 3508−
3576.
(2) Aparicio, S.; Atilhan, M.; Karadas, F. Thermophysical Properties
of Pure Ionic Liquids: Review of Present Situation. Ind. Eng. Chem. Res.
CONCLUSIONS
■
New high-pressure densities (p ≤ 200 MPa) are reported for 1-
hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide
2
(
010, 49, 9580−9595.
(
(
[C C Im][Tf N]) and 1-hexyl-3-methylimidazolium chloride
6 1 2
3) Franca, J. M. P.; Nieto de Castro, C. A.; Lopes, M. M.; Nunes, V.
̧
[C C Im][Cl]). Agreement of measured high-pressure
6
1
M. B. Influence of Thermophysical Properties of Ionic Liquids in
densities and atmospheric viscosities of [C C Im][Tf N]
6
1
2
Chemical Process Design. J. Chem. Eng. Data 2009, 54, 2569−2575.
were within the uncertainty of some of the available literature
values. Deviation of density and viscosity values among colored
and colorless [C C Im][Cl] samples, synthesized and commer-
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6
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AUTHOR INFORMATION
■
(15) Oliveira, F. S.; Freire, M. G.; Carvalho, P. J.; Coutinho, J. A. P.;
Corresponding Author
Lopes, J. N. C.; Rebelo, L. P. N.; Marrucho, I. M. Structural and
Positional Isomerism Influence in the Physical Properties of
Pyridinium NTf2-Based Ionic Liquids: Pure and Water-Saturated
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*
Tel./Fax: +81-22-795-5863. E-mail: smith@scf.che.tohoku.ac.
jp.
Present Address
́
́ ́
(16) Gomez, E.; Gonzalez, B.; Domínguez, A.; Tojo, E.; Tojo, J.
§
Faculty of Food Science and Technology, Universiti Putra
Dynamic Viscosities of a Series of 1-Alkyl-3-methylimidazolium
Chloride Ionic Liquids and Their Binary Mixtures with Water at
Several Temperatures. J. Chem. Eng. Data 2006, 51, 696−701.
Malaysia, Serdang, Selangor 43400, Malaysia.
Funding
(17) Sastry, N. V.; Vaghela, N. M.; Macwan, P. M. Densities, Excess
The authors are grateful for Japan Society for the Promotion of
Science scholarship support and the partial financial support of
the Ministry of Education, Science, Sports and Culture for
support of this work.
Molar and Partial Molar Volumes for Water +1-Butyl- or, 1-Hexyl- or,
1-Octyl-3-methylimidazolium Halide Room Temperature Ionic
Liquids at T = (298.15 and 308.15) K. J. Mol. Liq. 2013, 180, 12−18.
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18) Quijada-Maldonado, E.; Van der Boogaart, S.; Lijbers, J. H.;
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Viscosities and Surface Tensions of the Ionic Liquids Series 1-Ethyl-3-
methylimidazolium Acetate and Dicyanamide and Their Binary and
Notes
The authors declare no competing financial interests.
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