Viscosity and diffusivity for the ionic liquid 1-hexyl-3-methyl-imidazolium Bis(trifluoromethylsulfonyl)amide with 1-octene

Article abstract of DOI:10.1021/je1009224

In order to correlate and predict interfacial mass transfer rates for ionic liquids and organic components, transport properties are required at various temperatures and, importantly, compositions. Here, the viscosity of mixtures of 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf ₂N]) with 1-octene to the liquid-liquid saturation limit were measured at four different isotherms [(10, 25, 50, and 75) °C]. The viscosity of a [HMIm][Tf₂N] + 1-octene mixture decreases up to 33 % over the pure ionic liquid in the temperature range studied. The computed viscosity deviation ("excess viscosity") demonstrates a negative trend throughout the composition range and diminishes with increasing temperature. The self-diffusivity of both 1-octene and [HMIm][Tf₂N] (cation) were measured at (25 and 50) °C and increased up to 40 % with increasing composition of 1-octene. The self-diffusivities were of the order of (10 ^-11 and 10^-10) m²·s^-1 for the cation and 1-octene, respectively.

Full text of DOI:10.1021/je1009224

ARTICLE
pubs.acs.org/jced
Viscosity and Diffusivity for the Ionic Liquid 1-Hexyl-3-methyl-
imidazolium Bis(trifluoromethylsulfonyl)amide with 1-Octene
Azita Ahosseini, Laurence R. Weatherley, and Aaron M. Scurto*
Department of Chemical & Petroleum Engineering and Center for Environmentally Beneficial Catalysis, University of Kansas,
Lawrence, Kansas 66045, United States
ABSTRACT: In order to correlate and predict interfacial mass transfer rates for ionic liquids and organic components, transport
properties are required at various temperatures and, importantly, compositions. Here, the viscosity of mixtures of 1-hexyl-3-
methylimidazolium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf2N]) with 1-octene to the liquidꢀliquid saturation limit were
measured at four different isotherms [(10, 25, 50, and 75) °C]. The viscosity of a [HMIm][Tf2N] + 1-octene mixture decreases up
to 33 % over the pure ionic liquid in the temperature range studied. The computed viscosity deviation (“excess viscosity”)
demonstrates a negative trend throughout the composition range and diminishes with increasing temperature. The self-diffusivity of
both 1-octene and [HMIm][Tf2N] (cation) were measured at (25 and 50) °C and increased up to 40 % with increasing composition
of 1-octene. The self-diffusivities were of the order of (10ꢀ11 and 10ꢀ10) m2 sꢀ1 for the cation and 1-octene, respectively.
3
’ INTRODUCTION
1-octene and a model ionic liquid, [HMIm][Tf2N]. The viscosity
and self-diffusivities of both an IL-rich phase and a 1-octene rich
phase is reported at temperatures of (10, 25, 50, and 75) °C and
compositions to the saturation condition.
Room temperature ionic liquids (ILs) are organic salts with
a combination of cation/anion that are liquid at a wide range of
temperatures. The physicochemical properties of ILs can be
molecularly designed to positively affect different kinds of
processes by varying these anions and cations.1 The ILs’ negli-
gible vapor pressure and low flash point make them relatively
safer solvents. Various applications of ionic liquids are often
based upon biphasic liquidꢀliquid systems which are being
developed for extraction,2ꢀ4 absorption -desorption in chromato-
graphy,5 chemical reactions6ꢀ8 and even biochemical reactions.9,10
However, there is a lack of information for systems involving ionic
liquids in interfacial mass transfer. Therefore, fundamental studies
on interfacial mass and momentum transfer for biphasic systems
are necessary for any process intensification and implementation.
We have recently reported11 on the thermodynamic and phase
equilibrium properties of 1-octene (1) and a model ionic liquid,
1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide
([HMIm][Tf2N]) (2; see Figure 1). [HMIm][Tf2N] is a com-
mon ionic liquid and was selected by the IUPAC committee on
“Thermodynamics of ionic liquids, ionic liquid mixtures, and the
development of standardized systems” to be used as a model and
standard ionic liquid.12,13 From the liquidꢀliquid equilibrium,
1-octene is fairly soluble in the IL (≈ 0.2 mol fraction at 25 °C),
whereas the solubility of the IL in the octene phase is very small
(< 0.0001 mol fraction at 25 °C). Thus, in a dynamic li-
quidꢀliquid contracting system, the mass transfer will occur in
virtually one direction, i.e., 1-octene into the IL. As the 1-octene
is fairly soluble, the density of the mixture changes with increas-
ing composition of 1-octene. The surface tension of mixtures was
also measured at different compositions and temperatures in
addition to the saturated interfacial tensions of the two-phase
system. We have also reported on the homogeneously catalyzed
hydrogenation and hydroformylation of 1-octene in [HMIm]-
[Tf2N] with and without compressed CO2.6ꢀ8
’ EXPERIMENTAL METHODS
Synthesis of Ionic Liquid. [HMIm][Tf2N] was prepared by
anion exchange from the corresponding bromide salt of the im-
idazolium cation([HMIm][Br]) with lithium bis(trifluoromethy-
lsulfonyl)amide (Li[Tf2N]) in deionized water as described in
the literature.14,15 The bromide salt of the imidazolium cation
was prepared from a quaternization reaction of 1-methylimida-
zole with a slight excess amount of the corresponding 1-bromo-
hexane in acetonitrile at 40 °C under an argon atmosphere with
stirring for three days. Caution: This reaction is highly exother-
mic, and adequate solvent volumes and/or cooling must be
provided during the reaction. The bromide salt of 1-hexyl-3-
methyl-imidazolium was purified with activated charcoal (10 %)
by stirring the mixture for 24 h. Acetonitrile was added to reduce
the viscosity of the ionic liquid, and the mixture was filtered. The
mixture was then passed through a plug of Celite (depth = 7 cm,
diameter = 3 cm) and through a short column (height = 20 cm,
diameter = 2.5 cm) of acidic alumina. The solvent was removed
on a rotary evaporator under reduced pressure at 40 °C and then
connected to a high vacuum (< 0.1 Pa) at 50 °C for at least 48 h.
[HMIm][Tf2N] was synthesized by anion exchange between the
[HMIm][Br] and Li[Tf2N]. The denser hydrophobic IL phase
was decanted and washed with water 6 to 8 times until the
bromide concentration was less than 8 10ꢀ6 weight fraction.
3
The sample was dried under a high vacuum (< 0.1 Pa) at 50 °C
for at least 48 h and contained less than 50 10ꢀ6 mass fraction in
3
Received: September 9, 2010
Accepted: August 10, 2011
Published: September 08, 2011
This contribution represents further studies into the mass
and momentum transport properties for a biphasic system of
r
2011 American Chemical Society
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Table 1. Comparison of Viscosity (η) of Pure
[HMIm][Tf2N] and 1-Octene from Our Laboratory and
Literature Sources
η [mPa s] [HMIm][Tf2N]
ref
η [mPa s] 1-octene
ref
3
3
t = 25 °C
70.1 ( 0.8
68
a
0.47 ( 0.01
0.478
b
23
22
25
28
69.7
0.447
43
70.2
0.48
29,44
t = 50 °C
25.8 ( 0.3
26.25
a
0.37 ( 0.01
0.365
b
25
22
24
28
43
27
25.8
0.351
Figure 1. Structure of 1-octene and 1-n-hexyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)amide ([HMIm][Tf2N]).
24.76
0.346
a From our previous report ref 45. b This work.
mass of water. The original sample of ionic liquid was then stored
in a Schlenk tube under an atmosphere of dry argon.
(PFG) method. The software used to analyze the data was
Topspin version 1.3. In a pulsed-field gradient (PFG), the reduc-
tion of a signal intensity resulting from the combination of mole-
cular diffusion and magnetic force gradient pulses on nuclear
spins can be measured. The reduction of the signal intensity is
based on the diffusion time as well as the gradient parameters:
gradient strength and length of gradient. The intensities for the
sample are given by the following equation:16
1H NMR chemical shifts (relative to TMS internal standard)
and coupling constants J/Hz: δ = 8.65 (s, 1H), 7.39 (t, 1H, J =
1.76), 7.37 (t, 1H, J = 1.48), 4.17 (t, 2H, J = 7.4), 3.93 (s, 3H),
1.87 (m, 2H), 1.32 (m,6H), 0.87 (t, 3H, J = 6.53). Analysis
calculated for C12H19N3F6S2O4: C, 32.2; H, 4.28; N, 9.39; S,
14.33. Found: C, 32.21; H, 4.27; N, 9.25; S, 14.19. From NMR
and elemental analysis, the estimated purity is 99+ %.
ꢀ ꢁ
ꢀ
ꢁ
Analysis. Elemental analysis was performed by Desert Analy-
tics Transwest Geochem. 1H NMR spectra were recorded on a
Bruker 400 NMR Spectrometer using TMS as a reference for 1H
chemical shifts. The water content was determined by a Mettler
Toledo DL32 Karl Fisher Coulometer and the Br content was
measured by a Cole Parmer Bromide Electrode (27502-05) read
with an Oakton Ion 510 series meter.
Materials. 1-Methyl-imidazole, (CAS no. 616-47-7) 99+ %,
acetonitrile g 99.9 %, 1-octene (CAS no. 111-66-0) 98 %, and
lithium bis(trifluoromethylsulfonyl)amide (CAS no. 90076-65-6)
99.95 % were purchased from Sigma-Aldrich. Bromohexane
(CAS no. 111-25-1) 99+ % and aluminum oxide (activated,
acidic, for column chromatography; (100 to 500) μm) were
obtained from Acros. Bromo-hexane and 1-methylimidazole
were vacuum distilled directly prior to use. Activated carbon
50 to 200 mesh was obtained from Fisher Scientific. Compressed
argon (CAS no. 7440-37-1) (ultra high purity (UHP) grade) was
obtained from Airgas, Inc.
I
Io
δ
τ
2
ln
¼ ꢀ ðγδgÞ D Δ ꢀ
ꢀ
ð1Þ
3
2
where I is the intensity of the NMR peak, I0 is initial intensity of
NMR peak, γ is the gyromagnetic ratio equal to 26 750 Gꢀ1 sꢀ1
3
for 1H NMR, g is the gradient strength (G mꢀ1), δ is the length
3
of gradient (sec), Δ is the diffusion time (s), τ is the time between
rf gradients (s), and D = diffusion coefficient (m2 sꢀ1). For a
3
more detailed description of the NMR method used for diffusion
see other related references.17,18
For diffusion measurements, the NMR spectrometer must be
calibrated and the applied gradient strength (g) determined by
knowing all other parameters in eq 1. Two standards were
utilized to determine, e.g., hexane (D = 4.15 10ꢀ9 m2 sꢀ1 19
)
3
3
and water (D = 2.30 10ꢀ9 m2 sꢀ1 20 at 298.15 K. All measure-
)
3
3
ments were performed without deuterated solvents by manual
shimming. For the calibrations, all of the time parameters, Δ, δ,
and τ remained constant, while the applied gradient strength was
Interfacial Transport Properties. Viscosity. The viscosity at
ambient pressure (at different temperatures) was measured using
a Wells-Brookfield Cone/Plate (DV-III ULTRA) viscometer/
rheometer. The relative uncertainty of the apparatus is within (
1.0 %. Reproducibility is to within ( 0.2 %. The temperature
range is from (0 to 100) °C with an uncertainty of ( 0.1 °C. The
standard gravimetric method is used to make the solutions of
1-octene in ionic liquid. The mixture is prepared by weighing a
specific amount of each part into a 25 mL vial with an uncertainty
of ( 0.0002 g with an uncertainty in mole fraction of better
than 0.01.
altered. To protect the gradient coil from damage, the maximum
21
gradient strength used was g = 0.7gmax
.
The applied gradient
strength alteration was between g = 0.05gmax to g = 0.7gmax using
equal increments.17,21 From the two calibrations, the total
applied gradient strength was determined as 49.5 (G mꢀ1).
3
To validate the gradient strength obtained from experiments the
cation diffusion coefficient for pure [HMIm][Tf2N] at 298.15 K
was determined to be 1.79 10ꢀ11 m2 sꢀ1 and compared with
3
3
the literature, 1.75 10ꢀ11 m2 sꢀ1 22
The relative standard
.
3
3
deviation of the diffusion coefficients measurements out of five
different experiments are less than 3 %.
Diffusivity. Self-diffusion is the random translational move-
ment of molecules from internal energy.16 A proton NMR
method is used here to determine the self-diffusion of the ionic
liquid or specifically the cation (as the anion has no protons) and
the dissolved 1-octene. A Bruker 400 MHz 1H NMR was used to
measure the translational diffusion with a pulsed-field gradient
’ RESULTS AND DISCUSSION
Viscosity of the 1-Octene and [HMIm][Tf2N] System. The
experimental results of dynamic viscosity for pure 1-octene and
[HMIm][Tf2N] and their mixtures to saturation at different
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represents the saturated conditions, after which a two-phase
system emerges. Initially, adding 1-octene only slightly decreases
the liquid viscosity, but after approximately x1 = 0.05, the
decrease becomes larger. At higher temperatures, the composi-
tion effect appears relatively linear. At the saturated composition,
the viscosity of [HMIm][Tf2N] phase decreases by 34 % at
10 °C, 35 % at 25 °C, 28 % at 50 °C, and 21 % at 75 °C over the
pure component at the same temperature.
Figure 3 illustrates that the viscosity of the IL-phase with
temperature at five compositions: x1 = 0, 0.05, 0.10, 0.15, and 1.
The classic exponential decay with temperature is observed at
each composition. As shown, pure 1-octene is significantly less
viscous than [HMIm][Tf2N] or mixtures thereof. The cation and
anion of ionic liquids have molecular forces of electrostatics,
dispersion, and dipoles that interact with each other and the
neutral nonpolar solute. The electrostatic interactions between
cations and anions in IL (or between the ion pairs and other ion
pairs) are affected by the neutral molecules of 1-octene which
decreases the frictional forces during flow.
Figure 2. Viscosity of [HMIm][Tf2N] with increasing amounts of
1-octene (1) at 10 °C (blue circle), 25 °C (green square), 50 °C
(orange triangle), and 75 °C (red diamond). Lines are smoothed data.
From our previous report, we have measured the density of the
mixture at the same compositions as in the current study. Thus,
the kinematic viscosity can be computed and is listed in Table 2.
The kinematic viscosity follows similar qualitative trends as the
dynamic viscosity. However, the relative percent decreases may
be slightly different. For instance, the difference in the saturated
viscosity and pure IL viscosity at 25 °C is approximately 35 %
lower for dynamic viscosity and approximately 29 % lower for the
kinematic viscosity.
Few reports exist in the literature of the mixture viscosity of
[HMIm][Tf2N] or other ILs with partially miscible (LLE)
organic compounds. The viscosity of water-saturated [HMIm]-
[Tf2N] has been reported31 and other studies of the effect of
water on the viscosity of other ILs.32,33 [HMIm][BF4] and
1-pentanol form a liquidꢀliquid system at room temperature.
Wagner et al.34 measured the viscosity of a mixture at the upper
critical solution composition (0.31 mass fraction of the IL) at
temperatures just above the critical solution temperature of
41.8 °C, i.e., 1-phase. Andreatta et al.35,36 measured the viscosity
of mixtures of 1-octyl-3-methylimidazolium [Tf2N] with alcohols
and alkyl esters (ethyl acetate, etc.) across the full composition
range.
Figure 3. Effect of temperature and composition on viscosity of
[HMIm][Tf2N] at different concentrations of 1-octene (x1): x1 = 0
(blue circle), x1 = 0.05 (green square), x1 = 0.1 (orange triangle), x1 =
0.15 (red diamond), and x1 = 1 (black triangle). Lines are smoothed data.
temperatures were measured at (10, 25, 50, and 75) °C at
ambient pressure. IL in the 1-octene phase is generally very
small (x1 < 0.001) except at the highest temperature investigated
(75 °C), where x1 = 0.04. These small concentrations render the
viscosity of the 1-octene phase virtually identical to the pure
component values within experimental error. The saturation
compositions in the IL-rich phase as determined in our previous
study11 were x1 = 0.16, 0.19, 0.23, and 0.28 at (10, 25, 50,
and 75) °C, respectively. Table 1 lists the viscosity of both pure
components at (25 and 50) °C from our method and from the
literature. As shown, the relative viscosity of [HMIm][Tf2N] at
the two temperatures is within 3% of several literature reports.22ꢀ25
The relative viscosity of pure 1-octene is between 0.2% and 5.8%
of several literature reports.26ꢀ30
Figure 2 illustrates the mixture viscosity of the liquid phase
with increasing composition of the 1-octene at the four iso-
therms. At all isotherms, the viscosity decreases with increasing
composition of 1-octene. For instance at 25 °C, the viscosity at
x1 = 0.15 1-octene is 27 % lower than the pure ionic liquid.
However, at 75 °C, the viscosity decrease at the same composi-
tion is only ≈ 16 % lower. The last data point at each isotherm
Due to the wide range of possible molecular interactions
between the two components, deviations can occur from ideal
behavior. These viscosity deviations can be quantified by the
viscosity deviation, Δη, also known as “excess viscosity” in other
sources:
Δη ¼ ηm ꢀ ðx1η1 þ x2η2Þ
ð2Þ
where ηm is the mixture viscosity and η1 and η2 are the pure
component properties. This is not a strict “excess” property in the
thermodynamic sense which is defined as the difference between
a mixture property and its ideal solution value. The results for the
viscosity deviation of 1-octene and [HMIm][Tf2N] solutions are
presented in Figure 4. Plots of the viscosity deviation with mole
fraction of 1-octene for a binary 1-octene and [HMIm][Tf2N]
system at different temperatures demonstrates negative values
throughout the composition range. Low compositions of 1-oc-
tene have nearly ideal mixture behavior (Δη ≈ 0) as the 1-octene
possibly resides in the free volume of ionic liquid structure
changing little the electrostatic and dipolar interactions of the
cation and anions. However, as more 1-octene dissolves, the
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Figure 4. Effect of 1-octene composition on viscosity deviation of
mixtures with [HMIm][Tf2N] at 10 °C (blue circle), 25 °C (green
square), 50 °C (orange triangle), and 75 °C (red diamond). Lines are
smoothed data.
Table 3. Self-Diffusivity for Mixtures of 1-Octene +-
[HMIm][Tf2N] at (25 and 50) °C to the Saturation Limit
1011D12 [m2 sꢀ1
]
1011D21 [m2 sꢀ1 a
]
3
3
x1
25 °C
5.4c
50 °C
24.3c
25 °C
50 °C
0
1.7 ( 0.1
1.8 ( 0.1
2.0 ( 0.1
2.1 ( 0.2
2.3 ( 0.2
2.4 ( 0.2
5.5 ( 0.4
5.7 ( 0.4
6.5 ( 0.5
7.3 ( 0.5
7.7 ( 0.5
0.01
0.05
0.1
5.5 ( 0.6
6.5 ( 0.5
7.4 ( 0.5
9.0 ( 0.6
9.1 ( 0.6
24.9 ( 2.0
26.3 ( 1.8
29.3 ( 2.1
31.3 ( 2.2
0.15
0.19b
0.23b
1
31.0 ( 2.2
344 ( 24
7.7 ( 0.5
228 ( 16
a Diffusivity of cation only. b Saturated composition at respective tem-
perature. c Extrapolated infinite dilution value (D12
)
∞
electrostatic and dipolar forces of the cation and anion (or ion
pair) possibly become more screened and thus decrease long-
range interactions. Without these long-range interactions, the
barrier to motion decreases. However, the excess viscosities at
higher temperatures (50 °C and 75 °C) are very close to zero
indicating that the kinetic energy may overcome any solvation
and simply act as a diluent of relatively low viscosity. Negative
excess molar volume was computed for this system in our
previous paper.11 Similar to the viscosity deviation, the excess
molar volume changes very little from zero with small amounts of
1-octene. However, larger negative values occur approaching the
saturation limit at all temperatures, not just at the lower
temperatures as seen in the viscosity deviation measurements.
Wang et al.37 measured both the excess molar volume, VE, and
viscosity, Δη, in the miscible system, 1-butyl-3-methylimidazo-
lium [PF6] and 3-pentanone, and found that the composition
that produces a maximum in VE produces a minimum in ln(ηE),
which they discuss in terms of ionꢀdipole interactions. However,
with few systems available with both excess volume and viscosity,
clear trends are difficult to infer.
Self-Diffusivity in the 1-Octene and [HMIm][Tf2N] System.
The self-diffusivities of 1-octene and the cation of [HMIm]-
[Tf2N] at (25 and 50) °C were measured at different composi-
tions and listed in Table 3. As shown in Figure 5, the self-
diffusivity of 1-octene in a mixture with [HMIm][Tf2N] increases
as the composition of 1-octene is increased. From a x1 of 0.01 to
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the increase is approximately 40 % to the same composition. This
lower percent increase at 25 °C may be due to a larger influence
on specific interactions of the unsaturated 1-octene with the
cation’s delocalized electron system. This interaction would
create a stronger complex at lower temperatures than at 50 °C,
which has higher kinetic energy. The infinite dilution diffusion
coefficients using a Taylor-dispersion technique have been
reported for [HMIm][Tf2N] in water, methanol, and acetonitrile
by Sarraute et al.41 with values on the order of 10ꢀ9 (m2 sꢀ1).
3
The StokesꢀEinstein relationship, which relates the self-dif-
fusivity to the viscosity and hydrodynamic radius, σ, is given by42
kBT
Figure 5. Self-diffusivity of 1-octene in a mixture with [HMIm][Tf2N]:
D21 at 25 °C (green square) and 50 °C (orange triangle). Lines are
StokesꢀEinstein predictions.
D ¼
ð3Þ
6πση
where kB is the Boltzmann constant. Assuming the hydrody-
namic radius remains constant, the diffusivity is inversely related
to the viscosity of the mixture and can be rearranged to the form
of
D0
η
ꢀ
ꢁ
Dij ¼
ð4Þ
η0
Here, D0 and η0 are taken as the pure IL self-diffusivity and
viscosity respectively. For the case of the self-diffusivity of
1-octene in the mixture, the infinitely dilute diffusivity is utilized
for D0 = D12∞. The mixture viscosities, η, were interpolated by an
exponential function from the data in Table 2. This prediction is
illustrated for each of the self-diffusivities in Figures 5 and 6. As
shown, a relatively good prediction is achieved using the initial
diffusivities and mixture viscosity data. The average absolute
relative deviations (AARD) for both D12 and D21 from the
prediction over both isotherms was less that 5 %. However, the
assumption of constant hydrodynamic radius is probably not
entirely valid across all of the conditions.
Figure 6. Self-diffusivity of the cation of [HMIm][Tf2N] with a mixture
of 1-octene: D21 at 25 °C(green square) and 50 °C (orange triangle).
Lines are StokesꢀEinstein predictions.
0.15, the self-diffusivity at 25 °C increases by approximately
64 % in the range of approximately (25 to 30) 10ꢀ11 (m2 sꢀ1) .
3
3
At the same compositions and at 50 °C, diffusivities increased
just ≈ 26 %. The infinitely dilute diffusivity of 1-octene in the IL
mixture, D12∞, was estimated by extrapolating the experimental
data to a mole fraction of 0 and presented in Table 3. As the
solubility of the IL in the 1-octene phase was so low, a corres-
’ CONCLUSIONS
Transport properties are necessary for ultimate understand-
ing and designing important chemical processes including
reactions and separations. However, there is a distinct lack of
data in this area for biphasic systems involving ionic liquids,
which inhibit their implementation as a potential sustainable
media. In this work, the system of 1-hexyl-3-methyl-imidazo-
lium bis(trifluoromethylsulfonyl)amide ([HMIm][Tf2N]) and
1-octene was investigated and the mixture viscosity and self-
diffusivities were measured. These transport properties of the
ionic liquid phase experience a significant improvement, i.e.,
lower viscosity and higher diffusivity, with the addition of
1-octene up to its saturation value. This is important as ionic
liquids generally have a higher viscosities and lower diffusivities
than conventional organic solvents. It appears that small addi-
tions of the octene may first fill the free volume of the ionic liquid
followed by some level of interaction or solvation by the alkene
group, which reduces the electrostatic and dipolar interactions of
the cation and anion. Realistic applications will invariably feature
mixtures whose properties will be superior to simply the pure
component properties. These properties and the thermodynamic
properties are being utilized in current interfacial mass transfer
experiments.
∞
ponding D21 could not be experimentally obtained using the
current technique. Morgan et al.38 measured the tracer diffusion
coefficient of the olefin, 1-butene, in [BMIm][Tf2N] and ob-
tained a value of 27 10ꢀ11 (m2 sꢀ1) at 30 °C. However, these
3
3
mixture diffusivities are over an order of magnitude less than the
diffusivity of pure 1-octene: 228.3 10ꢀ11 (m2 sꢀ1) at 25 °C and
3
3
344.2 10ꢀ11 (m2 sꢀ1) at 50 °C. Literature reports of the self-
3
3
diffusivity of pure 1-octene are unknown to the authors. However,
Kasahara et al.39 report the self-diffusivity of 1-hexene at 40 °C
is approximately 500 10ꢀ11 (m2 sꢀ1). Smuda et al.40 report the
3
3
self-diffusivity of n-octane at 20 °C as approximately 230 10ꢀ11
3
(m2 sꢀ1) .
3
Figure 6 illustrates that the diffusivity of the [HMIm] cation
of [HMIm][Tf2N] increases with increasing composition of 1-
octene at (25 and 50) °C. The self-diffusion coefficients for
the pure IL (cation) are 1.67 10ꢀ11 (m2 sꢀ1) at 25 °C and
3
3
5.54 10ꢀ11 m2 sꢀ1 at 50 °C. These results compare favorably
3
3
with literature reports of 1.75 10ꢀ11 (m2 sꢀ1) at 25 °C and
3
3
5.05 10ꢀ11 (m2 sꢀ1) at 50 °C.22 At 25 °C, the diffusivity of the
3
3
IL cation in the mixture increases by ≈ 35 % from the pure
component to 0.15 mol fraction of 1-octene. However, at 50 °C,
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’ AUTHOR INFORMATION
(16) Price, W. Pulse-Field Gradient Nuclear Magnetic Resonance
as a Tool for Studying Translational Diffusion: Part 1. Basic Theory,
Concepts Magn. Reson. 1997, 9, 299–336.
(17) Price, W. S. Pulse-field gradient nuclear magnetic resonance as a
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Corresponding Author
*Phone: +1 (785) 864-4947. Fax: +1 (785) 864-4967. E-mail:
ascurto@ku.edu.
Funding Sources
(18) Schleicher, J. C., Kinetics and Solvent Effects in the Synthesis of
This work was supported by the U.S. National Science Founda-
tion (CBET-0731244). A.M.S. appreciates the support of the
DuPont Young Professor Award.
Ionic Liquids. MS Thesis, 2007.
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’ ACKNOWLEDGMENT
Dr. David van derVelde (now at Caltech) is thanked for NMR
method development. Prof. Jerzy Petera of the Technical Uni-
versity of yodꢀz, Poland is thanked for helpful discussions.
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