Thermophysical Characterization of Ionic Liquids Able To Dissolve Biomass

Full text

Page 1

Published:October 17, 2011
r2011 American Chemical Society
4813
dx.doi.org/10.1021/je200790q|J. Chem. Eng. Data 2011, 56, 4813–4822
ARTICLE
pubs.acs.org/jced
Thermophysical Characterization of Ionic Liquids Able To Dissolve
Biomass
Mara G. Freire,†Ana Rita R. Teles,†Marisa A. A. Rocha,‡Bernd Schr€ oder,†Catarina M. S. S. Neves,†
Pedro J. Carvalho,†Dmitry V. Evtuguin,†Luís M. N. B. F. Santos,‡and Jo~ ao A. P. Coutinho*,†
†Departamento de Química, CICECO, Universidade de Aveiro, 3810-193 Aveiro, Portugal
‡CIQ, Departamento de Química e Bioquímica, Faculdade de Ci^ encias, Universidade do Porto, R. Campo Alegre 687,
P-4169-007 Porto, Portugal
b
S Supporting Information
ABSTRACT: Among new potential solvents for lignocellulosic materials, ionic liquids (ILs) are attracting considerable attention.
Hence, the knowledge of the thermophysical properties of such fluids is essential for the design of related industrial processes.
Therefore, in this work, a set of thermophysical properties, namely, density, viscosity, and refractive index, as a function of
temperature, and isobaric thermal expansivity and heatcapacities at a constant temperature, were determined for eight ionic liquids
with the 1-ethyl-3-methylimidazolium cation combined with the following anions: acetate, methylphosphonate, methanesulfonate,
trifluoromethanesulfonate, dicyanamide, thiocyanate, tosylate, and dimethylphosphate. Imidazolium-based ILs were chosen since
thesearethemoststudiedionicfluidsinbiomassdissolutionapproaches,whilealargearrayofanionswasinvestigatedbecauseitwas
already demonstrated that it is the IL anion that mainly governs the dissolution.
’INTRODUCTION
Wood is composed of cellulose, (35 to 50) %, lignin, (18 to
30) %, hemicelluloses, (15 to 30) %, and small amounts of
extractivecompounds.1Becauseofthecomplexcompositionand
structure of lignocellulosic materials, their fractionation, in an
effective and rentable way, is still a challenge target. Industrially,
wood fractionation into cellulosic pulp and lignin is predomi-
nantly attained by the kraft process, which is not comprehensive
in the utilization of noncellulosic components and causes com-
plaints from the standpoint of environmental concerns.2In this
context, ionic liquids (ILs) have been recently explored as novel
solvents for lignocellulosic materials.3?5ILs are liquid salts (by
common definition with melting temperatures below 100 ?C)
constituted by large and asymmetric organic cations and organic
or inorganic anions. Due to the ions' large size and their
conformational flexibility, ILs present low lattice enthalpies and
largeentropychangesuponmeltingwhichfavortheliquidstate.
In general, ILs present a large liquid temperature range, high
thermal and chemical stabilities, high ionic conductivities, and
negligiblevaporpressures,whichfurtherallowthefluidrecycling
in many processes. One of the main and additional attributes of
ILs falls on their enhanced ability to dissolve the most diverse
compounds.6?8
A pioneer work by Rogers and co-workers9has shown that
hydrophilic ILs can efficiently dissolve cellulose. In the same
line of research, later on, it was demonstrated that the solubility
of cellulose increases almost linearly with the increase on the
hydrogen bond accepting ability of the anions composing the
ILs.10IL anions that can strongly coordinate with the hydrogen
bonddonorgroupsofcelluloseareabletotriggersolute?solvent
interactions that are required to an improved dissolution.11As a
result, the control of the dissolution of cellulose in ILs has
provided a new platform for the polymer processing.12,13
Subsequently, it was found that not only cellulose could be
dissolvedinILs,butalsowoodcanbedissolvedinthesamefluids
after mild grinding and that biomass could be selectively sepa-
rated into its components with relative efficiency.14?16Recent
reports17,18have additionally shown that ILs are also able to
extract different polysaccharides from wood and others forms of
lignocellulosicbiomass.ILshavefurtherbeenappliedforthepre-
treatment and conversion of lignocellulosic materials.19In addi-
tion,itwasestablishedthatbiomaterialstreatedinILmediahada
higher rate of enzymatic hydrolysis and yield of reducing sugars
than those treated by traditional pretreatment methods.20,21In
the past fewyears, acid-catalyzeddehydration ofsaccharidesinto
furanic compounds making use of ILs has also received signifi-
cant attention.22,23
In summary, the IL ability for biomass processing depends
largelyon the hydrogen-bond accepting ability of theanionsthat
composed them. Due to their relative novelty and to the large
arrayofpossibleILs,mostofthemstillhavetheirthermophysical
properties poorly characterized, and a complete database is far
from being accomplished. In the current work, the thermophy-
sical properties of eight ILs, namely, the density, viscosity, and
refractive index, in broad temperature ranges, as well as isobaric
thermal expansivity and heat capacities, at a constant tempera-
ture, were measured and presented. Since it was previously
shown that the IL anion plays a crucial role toward the pretreat-
ment and processing of biomass, the ILs studied here share the
cation 1-ethyl-3-methylimidazolium while being combined with
Special Issue: Kenneth N. Marsh Festschrift
Received:
Accepted:
July 26, 2011
September 27, 2011

Page 2

4814
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
a variety of different anions. The effect of the IL anion upon the
measured properties is presented and discussed.
’EXPERIMENTAL SECTION
Materials. Eight ionic liquids were studied in this work:
1-ethyl-3-methylimidazoliumacetate,[C2mim][CH3CO2],1-ethyl-3
-methylimidazolium methylphosphonate, [C2mim][CH3OHPO2],
1-ethyl-3-methylimidazolium methanesulfonate, [C2mim]-
[CH3SO3],1-ethyl-3-methylimidazoliumtrifluoromethanesulfo-
nate (triflate), [C2mim][CF3SO3], 1-ethyl-3-methylimidazolium
dicyanamide, [C2mim][N(CN)2], 1-ethyl-3-methylimidazolium
thiocyanate, [C2mim][SCN], 1-ethyl-3-methylimidazolium
tosylate, [C2mim][Tos], and 1-ethyl-3-methylimidazolium
dimethylphosphate, [C2mim][(OCH3)2PO2]. All ILs were ac-
quiredatIolitec,withtheexceptionof1-ethyl-3-methylimidazolium
methylphosphonate, which was purchased from Solvionic.
The chemical structures of all investigated ILs are presented in
Table 1.
To remove water and volatile impurities, IL samples were
dried by heating (≈ 343 K), with constant stirring, and at high
vacuum (≈ 10?4Pa) for a minimum time period of 48 h. After
this procedure, the purity of all IL samples was checked by1H
and13C (and19F NMR for [C2mim][CF3SO3]) NMR, where it
wasshowntobeg0.99massfraction.Beforethedeterminationof
the thermophysical properties of ILs, their water mass fraction
contentwasdeterminedbyKarlFischertitration,usingaMetrohm
831 Karl Fischer coulometer. The reagent used was Hydranal
Coulomat AG from Riedel-de Ha€ en. After the measurements
on the IL thermophysical properties, the water mass content
was further determined to ascertain the water uptake of ILs
during the experimental procedures. No significant differences
Table 1. Chemical Structures of the Ionic Liquids Studied

Page 3

4815
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
were observed. The average water content in each IL is reported
in Table 2.
Experimental Procedure. Density and Viscosity. Measure-
ments of density, F, and dynamic viscosity, η, were performed
using an automated SVM 3000 Anton Paar rotational Stabinger
viscometer?densimeter. Density and viscosity measurements
were carried out in the temperature range from (278.15 to
363.15) K and at p ≈ 0.1 MPa. Since the ILs [C2mim][Tos]
and [C2mim][(OCH3)2PO2] are solid at room temperature,
densities and viscosities for these ILs were only determined
above their melting temperatures. The SVM 3000 Anton Paar
rotational Stabinger viscometer?densimeter uses Peltier ele-
ments for fast and efficient thermostatization. Further details
regarding the operational system can be found elsewhere.24The
uncertainty in temperature is within ( 0.02 K. The relative
uncertaintyinthedynamicviscosityis(0.35%,andtheabsolute
uncertainty in density is ( (5310?4) g3cm?3. The viscometer-
densimeterequipmentusedinthisworkforthedeterminationof
density and viscosity of ILs was validated in previous works
published by our group.24?26
Heat Capacity. The heat capacities of the studied ILs were
measured at T = 298.15 K, using a high-precision heat capacity
dropcalorimeter,whichisdescribedindetailintheliterature.27?29
Thecalorimeterwascalibratedwithwaterandsapphire(α-Al2O3
pellets, NIST-RM 720) based on a ΔT = 10 K drop procedure,
using the respective standard molar heat capacities at 298.15 K
reported in literature, Cp,m
(α-aluminum oxide) = (79.03 (
0.08) J3K?13mol?1and Cp,m
mol?1.30Thecalibrationconstantwasfoundtobeε=(6.6329(
0.0046) W3V?1. The accuracy of the apparatus for the measure-
ments of the heat capacities of liquids and solids was evaluated
before, based on the measurements of benzoic acid and hexa-
fluorobenzene.28Since the calorimeter was used to measure the
heat capacity of ILs, its accuracy was additionally checked based
on the results obtained for 1-hexyl-3-methylimidazolium bis-
(trifluoromethylsulfonyl)imide, [C6mim][NTf2].31The deter-
mined Cp,m
([C6mim][NTf2], 298.15 K) = (629.46 ( 1.63)
J3K?13mol?1is in excellent agreement with the available
literature data (Cp,m
([C6mim][NTf2], 298.15 K) = (631.6 (
0.5) J3K?13mol?1).31?33The IL [C2mim][(OCH3)2PO2] is
solidatroomtemperature,anditsheatcapacityat298.15Krefers
to the subcooled liquid.
Refractive Index. The refractive indices were measured at the
sodiumD-lineusingaBellinghammodelRFM340refractometer
(( 3310?5stated precision), as a function of temperature, with
temperatures above the respective ionic liquid melting points.
Theapparatuswascalibratedbymeasuringtherefractiveindexof
degassedwater(Milliporequality)andtoluene.Thetemperature
in the refractometer cell was controlled using an external ther-
mostatic bath and measured by a 1/10 class Pt100 RTD in a
Keithleydataacquisitionsystem2700/7700DMM/MUXandin
a four-wire mode. The Pt100 temperature probe was previously
calibrated against a calibrated platinum resistance thermometer,
SPRT100(Fluke-HartScientific1529Chub-E4),traceabletothe
NationalInstituteofStandardsandTechnology(NIST),withan
o
o(H2O) = (75.32 ( 0.01) J3K?13
o
o
Table 3. Experimental Density Values, G, for the Studied Ionic Liquids as a Function of Temperature and at 0.1 MPa
T
F/(kg3m?3)
K
[C2mim]
[CH3CO2]
[C2mim]
[CH3OHPO2]
[C2mim]
[CH3SO3]
[C2mim]
[CF3SO3]
[C2mim]
[N(CN)2]
[C2mim]
[SCN]
[C2mim]
[Tos]
[C2mim]
[(OCH3)2PO2]
278.15
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
1112.4
1108.9
1105.6
1102.4
1099.3
1096.2
1093.6
1090.0
1087.0
1084.0
1081.0
1078.0
1075.0
1072.1
1069.2
1066.3
1063.4
1060.6
1222.2
1218.6
1215.1
1211.7
1208.3
1205.0
1201.8
1198.6
1195.5
1192.3
1189.2
1186.1
1183.0
1179.9
1176.9
1173.9
1170.9
1167.9
1257.1
1253.3
1249.5
1245.9
1242.4
1239.0
1235.6
1232.2
1228.8
1225.5
1222.2
1218.9
1215.6
1212.3
1209.1
1205.9
1202.8
1199.7
1403.3
1398.9
1394.5
1390.2
1385.9
1381.6
1377.3
1373.1
1368.9
1364.8
1360.6
1356.5
1352.5
1348.4
1344.4
1340.4
1336.4
1332.5
1117.9
1114.3
1110.9
1107.4
1104.0
1100.6
1097.3
1094.0
1090.7
1087.4
1084.2
1081.0
1077.8
1074.7
1071.6
1068.5
1065.4
1062.3
1129.7
1126.5
1123.3
1120.1
1117.0
1113.9
1110.8
1107.8
1104.8
1101.8
1098.8
1095.9
1093.0
1090.1
1087.2
1084.3
1081.5
1078.7
1223.4
1220.0
1216.6
1213.2
1210.0
1206.8
1203.7
1200.6
1197.6
1194.5
1191.5
1188.5
1185.5
1213.9
1210.5
1207.1
1203.8
1200.5
1197.2
1193.9
1190.6
1187.4
1184.2
1181.0
1177.8
1174.7
Table 2. Average Water Content (Before and After the
Experimental Measurements) for the Studied Ionic Liquids
ionic liquidwater content/(wt %)
[C2mim][CH3CO2]
[C2mim][CH3OHPO2]
[C2mim][CH3SO3]
[C2mim][CF3SO3]
[C2mim][N(CN)2]
[C2mim][SCN]
[C2mim][Tos]
[C2mim][(OCH3)2PO2]
0.124
0.078
0.029
0.002
0.006
0.027
0.056
0.014

Page 4

4816
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
uncertainty lower than (2310?3) K. The temperature is typically
controlled within a temperature fluctuation of (( 5310?3) K,
measured with a resolution better than (1310?3) K. Samples
were directly introduced into the flow cell (prism assembly)
using a syringe; the flow cell was kept closed after sample injec-
tion. At least three independent measurements were taken for
eachsampleandateachtemperature.Therefractiveindiceswere
measured with respect to air, and no corrections were applied.
The ILs studied only show weak absorptions around 589 nm;
hence they were considered as a nonabsorbing medium.
’RESULTS AND DISCUSSION
Density. The experimental density data for the eight ILs con-
sidered in this work are presented in Table 3. Both [C2mim]-
[Tos] and [C2mim][(OCH3)2PO2] are solid at room tem-
perature; thus, their density measurements were only carried
out above 303.15 K.
Figure 1 displays the relative deviations between the data
measured in this work and literature results.34?37The relative
deviations on density values range between ?0.56 % and 1.32 %
for [C2mim][N(CN)2] and [C2mim][Tos], respectively. These
differencescouldbeattributedtothepurityoftheionicliquid,its
water content,and theexperimentaltechniqueused, amongother
factors. Nevertheless, a good agreement between our results and
those reported by Vercher et al.37for [C2mim][CF3SO3] and by
Doma? nska et al.34for [C2mim][SCN] is verified.
Thedensitydatameasuredinthisworkwereusedtowidenthe
parameter table for the extension of the Ye and Shreeve group
contribution method previously proposed by Gardas and
Coutinho.38The ionic volume parameter for the anion thiocya-
nate, previously not available, was estimated based on the data
gathered in this work combined with 60 experimental density
valuestakenfromliteratureforILswithsimilaranions.34,39,40For
the remaining anions, methylphosphonate, dimethylphosphate,
and tosylate, their ionic volumes were determined based only on
the densityvalues reported inthis work due to the lack of further
data in literature. The new proposed ionic volumes are reported
inTable4alongwiththosepreviouslyreportedbyourgroup.38,41
Figure 2 compares the experimental density data with the pre-
dicted density values based on the group contribution method38
and their dependence on temperature. The predicted values are
ingoodagreementwiththeexperimentaldata,presentingmaximum
absolute relative deviations of 0.41 % for [C2mim][CH3CO2],
0.52 % for [C2mim][CH3OHPO2], 0.46 % for [C2mim]-
[CH3SO3],0.21 %for[C2mim][CF3SO3],0.25%for[C2mim]-
[N(CN)2],0.49%for[C2mim][SCN],0.41%for[C2mim][Tos],
and0.31%for[C2mim][(OCH3)2PO2].Thismethodshowstobe
valuable in the prediction of density data for new ILs, when
experimental data are still not available. The relative deviations
between the experimental density data and those predicted for
the entire temperature interval are reported in the Supporting
Information (Figure S1).
Foracommontemperature,thedensitydecreaseswiththefol-
lowingILanionsequence:[CF3SO3]?>[CH3SO3]?>[Tos]?>
[(OCH3)2PO2]?>[CH3OHPO2]?>[SCN]?>[N(CN)2]?>
[CH3CO2]?. In general, fluorinated anions, toluenesulfonic-,
phosphate-, and phosphonate-based anions present higher den-
sities when compared to lower molecular weight anions, such as
acetate, thiocyanate, and dicyanamide. The molecular weight of
theanions[CF3SO3]?,[(OCH3)2PO2]?,[CH3SO3]?,[Tos]?,
[CH3OHPO2]?, [SCN]?, [N(CN)2]?, and [CH3CO2]?
are (149.07, 125.04, 95.10, 171.19, 95.02, 58.08, 66.04, and
59.04) g3mol?1, respectively, and follow a close pattern to the
Figure 1. Relative deviations between the experimental density mea-
sured in this work (Fexp) and those reported in literature (Flit) as a func-
tionoftemperaturefortheILs:9,[C2mim][CF3SO3];37grayb,[C2mim]-
[N(CN)2];35gray [, [C2mim][SCN];34gray 2, [C2mim][Tos].36
Table 4. Ionic Volumes, V, Determined with the Gardas and
Coutinho Group Contribution Model38
ionic speciesV/Å3
Cation
1,3-dimethylimidazolium38
154
Anion
acetate38
methylphosphonate
methanesulfonate41
triflate38
dicyanamide41
thiocyanate
tosylate
dimethylphosphate
86
78
89
129
72
53
57
139
Additional Groups
CH238
28
Figure 2. Experimental density (symbols) as a function of temperature
(at 0.1 MPa) and respective description with the Gardas and Coutinho
group contribution method38(lines) for the ILs: b, [C2mim]-
[CH3CO2]; (, [C2mim][CH3OHPO2]; 2, [C2mim][CH3SO3]; 9,
[C2mim][CF3SO3]; gray b, [C2mim][N(CN)2]; gray [, [C2mim]-
[SCN]; gray 2, [C2mim][Tos]; gray 9, [C2mim][(OCH3)2PO2].

Page 5

4817
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
density results obtained. The density dependence on the anion
molecular weight was recently demonstrated by Kolbeck et al.42
for a large number of IL anions, whose results highlighted a
general trend on the density decrease with the decrease of the
anion molecular weight.
The isobaric thermal expansion coefficients (αp) of each IL
were calculated using eq 1,
?
αp¼ ?1
F
∂F
∂T
?
p
¼ ?
∂ ln F
∂T
??
p
ð1Þ
whereFisthedensityinkg3m?3,TisthetemperatureinK,andp
is the pressure in MPa.
The αpvalues of all studied ILs are presented in Table 5, for
the temperature of 308.15 K, and were calculated from the linear
relationshipbetweenlnFandTusingtheexperimentaldatamea-
sured.Fromtheobtained values,itshouldbepointedoutthatno
significantdependenceofαpontemperaturewasobservedinthe
temperature range studied in this work. The αpvalues displayed
in Table 5 are in good agreement with literature data for
[C2mim][CF3SO3]43and [C2mim][SCN].34For the selected
temperature, the αp values follow the IL anion sequence:
[CF3SO3]?> [N(CN)2]?> [CH3CO2]?> [CH3SO3]?>
[SCN]?> [(OCH3)2PO2]?> [CH3OHPO2]?> [Tos]?.
Viscosity. The experimental dynamic viscosity data for the
eight ionic liquids studied are presented in Table 6. The relative
deviations between the data collected in this work and those
reported in literature are depicted in Figure 3.34,44?46Larger
differences are observed in the viscosity data compared to the
density relative deviations among different authors. Viscosity
measurements are nontrivial and are more affected by the pre-
sence of impurities (particularly water) than densities. The
relative deviations of viscosity are in general below 10 %, with
the exception of the data for the [C2mim][CH3CO2], where
significant differences were observed. With this IL, both large
Table 5. Thermal Expansion Coefficients, αp, for the Studied
Ionic Liquids at 308.15 K and at 0.1 MPa
104(αp( σa)
ionic liquidK?1
[C2mim][CH3CO2]
[C2mim][CH3OHPO2]
[C2mim][CH3SO3]
[C2mim][CF3SO3]
[C2mim][N(CN)2]
[C2mim][SCN]
[C2mim][Tos]
[C2mim][(OCH3)2PO2]
aStandard deviation.
5.550 ( 0.004
5.284 ( 0.004
5.440 ( 0.004
6.047 ( 0.004
5.943 ( 0.004
5.426 ( 0.004
5.156 ( 0.004
5.399 ( 0.004
Table 6. Experimental Viscosity Values, η, for the Studied Ionic Liquids as a Function of Temperature and at 0.1 MPa
T
η/(mPa3s)
K
[C2mim]
[CH3CO2]
[C2mim]
[CH3OHPO2]
[C2mim]
[CH3SO3]
[C2mim]
[CF3SO3]
[C2mim]
[N(CN)2]
[C2mim]
[SCN]
[C2mim]
[Tos]
[C2mim]
[(OCH3)2PO2]
278.15
283.15
288.15
293.15
298.15
303.15
308.15
313.15
318.15
323.15
328.15
333.15
338.15
343.15
348.15
353.15
358.15
363.15
723.62
451.35
295.70
202.29
143.61
105.30
79.324
61.327
48.415
38.948
31.873
26.470
22.273
18.961
16.314
14.164
12.407
10.952
916.06
598.79
406.82
285.80
206.76
153.63
116.89
90.832
71.925
57.939
47.385
39.293
32.995
28.020
24.047
20.830
18.199
16.027
805.33
505.92
336.04
232.44
166.59
123.14
93.482
72.642
57.617
46.541
38.203
31.814
26.837
22.901
19.753
17.187
15.083
13.333
99.825
78.928
63.507
51.865
42.936
35.980
30.482
26.087
22.527
19.615
17.208
15.206
13.523
12.099
10.885
9.8447
8.9477
8.1695
32.507
26.670
22.233
18.793
16.088
13.916
12.159
10.718
9.5187
8.5175
7.6735
6.9511
6.3268
5.7883
5.3188
4.9095
4.5485
4.2292
54.573
43.510
35.360
29.214
24.505
20.793
17.858
15.493
13.560
11.970
10.642
9.5283
8.5821
7.7727
7.0758
6.4717
5.9453
5.4846
1417.4
842.45
531.73
351.97
242.85
173.69
128.18
97.207
75.508
59.902
48.424
39.806
33.215
192.68
144.32
110.51
86.322
68.641
55.463
45.472
37.776
31.759
26.991
23.167
20.067
17.528
Figure 3. Relative deviations between the experimental viscosity mea-
sured in thiswork (ηexp)and thosereported inliterature (ηlit)asafunc-
tion of temperature for the ILs: b, [C2mim][CH3CO2];449, [C2mim]-
[CF3SO3];45gray b, [C2mim][N(CN)2];46gray [, [C2mim][SCN].34

Page 6

4818
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
positive and negative relative deviations to the same data source
are observed.44The reasons for such a disparity must be related
toeitherthetemperaturecontrolortheabsorptionofwaterduring
the experiments. In addition, the purity of the samples (that also
include the preparation procedures), the measurement method
employed,andsamplehandlingarealsoadditionalfactorsthatmay
explain the differences observed.
The Vogel?Tammann?Fulcher model, as described in eq 2,
was used to correlate the experimental viscosity data,
Bη
ðT ? T0ηÞ
where η is dynamic viscosity in Pa3s, T is the temperature in K,
and Aη, Bη, and T0ηare adjustable parameters. The parameters
Aη, Bη, and T0η, determined from the correlation of the experi-
mental data for pure ILs, are presented in Table 7. The average
absolute relative deviations between the experimental data and
the correlated values are 0.42 % for [C2mim][CH3CO2], 0.82 %
for [C2mim][CH3OHPO2], 0.27 % for [C2mim][CH3SO3],
0.03 % for [C2mim][CF3SO3], 0.11 % for [C2mim][N(CN)2],
0.05 % for [C2mim][SCN], 0.24 % for [C2mim][Tos], and
0.09 % for [C2mim][(OCH3)2PO2]. The relative deviations
between the experimental data and those correlated for the
entire temperature interval are reported in the Supporting Infor-
mation (Figure S2).
The prediction of viscosities for the studied ILs was also carried
out with the group contribution method previously proposed
by Gardas and Coutinho,47which makes use of the Vogel?
Tammann?Fulchermodeldescribedineq2.Inthiscase,Aηand
Bηare obtained by a group contribution method accordingly to
the following equations,
ln η ¼ Aη þ
ð2Þ
Aη¼∑
k
i¼1
k
niai,η
ð3Þ
Bη¼∑
i¼1
nibi,η
ð4Þ
whereniisthenumberofgroupsoftypei,kisthetotalnumberof
different groups in the molecule, and T0ηis taken as constant
with a value of 165.06 K. Parameters aiηand biηfor the studied
ILs are provided in Table 8. New values for these parameters for
the ions [Tos]?, [CH3OHPO2]?, [CH3SO3]?, [SCN]?, and
[N(CN)2]?were estimated and are proposed here. These new
parameters were estimated from the experimental viscosity
values measured in this work along with additional experimental
data reported in literature.40,46,48
The description of the viscosity data using the group contri-
bution model, applying eqs 3 and 4, along with the experimental
datarepresentation,isdepictedinFigure4.Theaverageabsolute
relativedeviationsbetweenthefittingandtheexperimentaldata
are of 41.11 % for [C2mim][CH3CO2], 2.34 % for [C2mim]-
[CH3OHPO2], 4.08 % for [C2mim][CH3SO3], 7.08 % for
[C2mim][CF3SO3], 5.78 % for [C2mim][N(CN)2], 0.18 % for
[C2mim][SCN], 5.98 % for [C2mim][Tos], and 0.93 % for
[C2mim][(OCH3)2PO2]. The group contribution method pro-
vides, in general, a good prediction of the viscosity data. Never-
theless, large deviations are observed for the acetate-based ionic
liquid.Thisisaparticularexamplewheremoreexperimentaldata
are in crucial need to allow further and proper predictions of the
corresponding group contribution parameters.
Theviscositydescribestheinternalresistanceofafluidtoward
a shear stress, and as it is well-known, ILs present higher visc-
osities than common molecular solvents. Since viscosity is
dependent on intermolecular interactions (hydrogen-bonding,
Table 7. Correlation Parameters Aη, Bη, and T0ηObtained
from the Vogel?Tammann?Fulcher Correlation Applied to
the Viscosity Experimental Data
ionic liquidAη
Bη/KT0η/K
[C2mim][CH3CO2]
[C2mim][CH3OHPO2]
[C2mim][CH3SO3]
[C2mim][CF3SO3]
[C2mim][N(CN)2]
[C2mim][SCN]
[C2mim][Tos]
[C2mim][(OCH3)2PO2]
?8.611
?8.884
?8.254
?8.640
?8.319
?8.320
?8.357
?8.791
684.69
864.80
658.48
824.96
581.69
621.90
685.48
846.72
195.54
179.83
196.22
147.94
158.02
163.27
224.41
184.64
Table8. GroupContributionParameters,ai,ηandbi,η,forthe
Group Contribution Method Proposed by Gardas and Cou-
tinho47Based on the Vogel?Tammann?Fulcher Correlation
ionic speciesai,η
bi,η/K
Cation
1,3-dimethylimidazolium47
?7.271 510.51
Anion
acetate47
methylphosphonate
methanesulfonate
triflate47
dicyanamide
thiocyanate
tosylate
dimethylphosphate
?2.739
?2.198
?2.406
?1.150
?1.263
?0.925
?4.551
?2.230
618.50
510.12
510.44
176.97
46.60
55.52
1111.5
540.52
Additional Groups
CH247
?7.528310?2
40.92
Figure 4. Experimental viscosity (symbols) as a function of temperature
(at 0.1 MPa) and the group contribution method proposed by Gardas and
Coutinho47(lines) for the ILs: b, [C2mim][CH3CO2]; (, [C2mim]-
[CH3OHPO2]; 2, [C2mim][CH3SO3]; 9, [C2mim][CF3SO3]; gray
b, [C2mim][N(CN)2]; gray [, [C2mim][SCN]; gray 2, [C2mim]-
[Tos]; gray 9, [C2mim][(OCH3)2PO2]. The dashed line corresponds
to [C2mim][CH3CO2].

Page 7

4819
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
dispersive, and Coulombic interactions), an increase in tempera-
ture will substantially decrease the intensity of H-bonding inter-
actions, and therefore the viscosity decreases, as displayed in
Figure 4.The experimentalvalues depictedinFigure 4show that
theILviscositiesarelargelydependentontheanion'snature.The
viscosityof[C2mim]-basedILs,atafixedtemperature,decreases
in the following sequence: [Tos]?> [(OCH3)2PO2]?> [CH3-
OHPO2]?> [CH3SO3]?> [CH3CO2]?> [CF3SO3]?>
[SCN]?> [N(CN)2]?. This sequence is closely related with
theintermolecularinteractionsthatoccuratthebulkliquid;yet,a
molecular-based understanding of the ionic liquids' dominating
interactionsthatcould explaintheviscosity trend isachallenging
task. Their electrical charges, polarity, and molecular and elec-
tronic structure result in a multifaceted combination of specific
interactions (Coulombic,vander Waals, hydrogen-bonding, and
π3 3 3π interactions). In general, anions with an enhanced
hydrogen bond acceptor character, such as [CH3OHPO2]?,
[CH3CO2]?, and [(OCH3)2PO2]?, present higher viscosities.
Heat Capacity. The standard molar heat capacities obtained
in this work and the available literature data for the studied
ionic liquids,48?52at T = 298.15 K, are presented in Table 9. For
the ionic liquids [C2mim][CH3CO2], [C2mim][CH3OHPO2],
and [C2mim][(OCH3)2PO2], no literature data were found.
In this work, the heat capacity data were measured with a
Table 9. Heat Capacities, Cp,m
o, at 298.15 K for the Studied Ionic Liquids
Cp,m
o
cp
o
cp,V
o a
Cp,m
o
ionic liquidJ3K?13mol?1
J3K?13g?1
J3K?13cm?3
J3K?13mol?1
ThisWork
1.8912 ( 0.0018
1.7200 ( 0.0039
1.6751 ( 0.0024
1.3941 ( 0.0015
Literature
[C2mim][CH3CO2]
[C2mim][CH3OHPO2]
[C2mim][CH3SO3]
[C2mim][CF3SO3]
321.90 ( 0.30
354.64 ( 0.81
345.52 ( 0.50
362.80 ( 0.39
2.0790 ( 0.0020
2.0783 ( 0.0047
2.0811 ( 0.0030
1.9321 ( 0.0021
328 ( 36 (DSC)48
377 ( 49 (DSC)49
362 ( 40 (DSC)50
363.2 ( 11 (DSC)51
380 ( 19 (DSC)52
384 ( 19 (MDSC)52
370 ( 18 (Tian-Calvet)52
326 ( 42 (DSC)49
287 ( 32 (DSC)51
[C2mim][N(CN)2]
[C2mim][SCN]
[C2mim][(OCH3)2PO2]b
aDerivedvolume-specificheatcapacity,takingintoaccountthedensityvalueat298.15Kextrapolatedfromthelinearfittingoftheexperimentaldensity
values as a function of temperature.bSubcooled liquid.
314.64 ( 0.56
281.45 ( 0.66
411.78 ( 0.86
1.7755 ( 0.0032
1.6629 ( 0.0039
1.7433 ( 0.0036
1.9602 ( 0.0035
1.8575 ( 0.0044
2.1214 ( 0.0044
Table 10. Experimental Refractive Indices at the Sodium D-Line, nD, for the Studied Ionic Liquids as a Function of Temperature
and at 0.1 MPa
TnD
K
[C2mim]
[CH3CO2]
[C2mim]
[CH3OHPO2]
[C2mim]
[CH3SO3]
[C2mim]
[CF3SO3]
[C2mim]
[N(CN)2]
[C2mim]
[SCN]
[C2mim]
[Tos]
[C2mim]
[(OCH3)2PO2]
288.37
293.28
298.19
303.10
308.01
312.91
317.82
322.73
325.68
327.64
329.61
332.55
334.52
336.48
338.44
340.41
342.37
1.50371
1.50233
1.50091
1.49949
1.49807
1.49666
1.49534
1.49390
1.49249
1.49115
1.48982
1.48854
1.48714
1.49823
1.49682
1.49542
1.49399
1.49254
1.49114
1.43572
1.43432
1.43296
1.43159
1.43025
1.42886
1.51745
1.51585
1.51428
1.51269
1.51112
1.50956
1.48175
1.48050
1.47909
1.47771
1.47636
1.475111.53844
1.53757
1.53703
1.53649
1.53570
1.53509
1.53461
1.53409
1.53356
1.53304
1.47384
1.53909
1.53850
1.53794
1.53739
1.53682
1.53636

Page 8

4820
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
considerable low uncertainty [(0.1 to 0.3) %], and our data
differ from literature48?52less than 6 %. At 298.15 K, the molar
heat capacities decrease with the following anion sequence:
[(CH3O)2PO2]?> [CF3SO3]?> [CH3OHPO2]?> [CH3SO3]?
> [CH3CO2]?> [N(CN)2]?> [SCN]?. For each IL, the
specific heat capacity, cp
Vo, at 298.15 K were also derived, using the density values at the
same temperature (from Table 3) and are presented in Table 9.
Refractive Index. The measured refractive index data are
presented in Table 10; they cover the temperature range from
(288to313)K,instepsof5K,whilethetemperatureintervalwas
scanned upward and downward. No temperature hysteresis ef-
fects were observed. The refractive indices of [C2mim][SCN],
[C2mim][Tos], and [C2mim][(OCH3)2PO2] were determined
onlyathighertemperatures,sincetheirrefractiveindicesatlower
temperatures exceeded the maximum range of the refractometer
used(nD=1.54),while[C2mim][Tos]and[C2mim][(OCH3)2-
PO2] solidified at lower, yet not well-defined temperatures.
Refractive index literature data on the ionic liquids studied
here are scarce. At 298.15 K, for [C2mim][CF3SO3], the value
obtained here is nearly identical (relative deviation of ?0.02 %)
with the one found in literature,53while in the case of [C2mim]-
[N(CN)2] the relative deviations are lower than 0.3 %.35
As reported before54the refractive indices of ionic liquids are
strongly dependent on the anion present, and the following
trend was observed for the studied ILs: [SCN]?> [Tos]?>
[N(CN)2]?> [CH3CO2]?> [CH3SO3]?> [CH3OHPO2]?>
[(OCH3)2PO2]?> [CF3SO3]?.
For an overall comparison, the derived refractive indices of all
ionic liquids, at T = 298.15 K, are compiled in Table 11 along
with the observed temperature derivative of the refractive index,
dnD/dT. The average absolute deviation of the derived ref-
ractive index is less than 7310?5(cf. Table T1 in the Supporting
Information).
In the temperature interval, any value of nD, at a specific
temperature, T, can be estimated using the following equation,
o, and volume-specific heat capacity, cp,
nDðT=KÞ ¼ nDð298:15 KÞ þ dnD=dTðT=K ? 298:15KÞ
ð5Þ
Thetemperaturedependenceoftherefractiveindexofeachionic
liquid is very small and depends on the nature of the ionic liquid.
For ILs, a decrease in the refractive index of 0.00027 to 0.00032
perkelvinisobserved,whichislesspronouncedthanthatverified
in most molecular solvents (ca. 0.00045 per K). The absolute
deviation associated to the temperature derivative is less than
(5310?6) K?1(seetheSupportingInformationforfurtherdetails).
The derived molar refractions, Rm, and the free volumes, fm,
were additionally calculated and are displayed in Table 11.
However, it should be remarked that Rmroughly represents
theoccupiedpartofthemolarvolume,andtherestrictionsofthe
applied model should be kept in mind.53?55
Theprediction of the refractive indices for the studied ILs was
alsoaccomplishedwiththegroupcontributionmethodproposed
by Gardas andCoutinho,47which follows a linear function of the
form,
nD¼ AnD?BnDT
where
ð6Þ
AnD¼∑
k
i¼1
niai,nD
ð7Þ
BnD¼∑
k
i¼1
nibi,nD
ð8Þ
Table 11. Refractive Indices of the Studied Ionic Liquids at 298.15 K, the Corresponding Temperature Derivative, dnD/dT,
Calculated Molar Refractions, Rm, and the Calculated Free Volumes, fm
1043(dnD/dT)Rm
fm
ionic liquidnD(298.15 K)K?1
cm33mol?1
cm33mol?1
[C2mim][CH3CO2]
[C2mim][CH3OHPO2]
[C2mim][CH3SO3]
[C2mim][CF3SO3]
[C2mim][N(CN)2]
[C2mim][SCN]
[C2mim][Tos]
[C2mim][(OCH3)2PO2]
aValues derived by linear extrapolation of the experimental data; all other data nD(298.15 K) have been calculated via linear interpolation using the
derivative dnD/dT and the experimental result at 298.19 K, nD(298.19 K).bSubcooled liquid.
1.50092
1.49250
1.49543
1.43297
1.51429
1.54871a
1.54513a
1.48176b
?2.88
?2.76
?2.90
?2.79
?3.21
?2.81
?2.74
?2.71
45.61
49.55
48.45
48.80
48.35
48.18
109.22
121.09
117.57
138.97
112.17
103.34
Table 12. Group Contribution Parameters, ai,nDand bi,nD, for
the Group Contribution Method According to Gardas and
Coutinho47for the Calculation of Refractive Indices
ionic speciesai,η
bi,η/K
Cation
1,3-dimethylimidazolium47
1.4436 2.268310?4
Anion
acetate
methylphosphonate
methanesulfonate
triflate47
dicyanamide
thiocyanate
tosylate
dimethylphosphate
0.1387
0.1267
0.1338
0.0783
0.1619
0.1844
0.1787
0.1145
5.661310?5
4.461310?5
5.861310?5
8.653310?5
8.961310?5
4.961310?5
4.261310?5
3.961310?5
Additional Groups
CH247
0.00454.587310?6

Page 9

4821
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
where niis the number of groups of type i, and k is the total
number of different groups in the molecule.
Theestimatedparametersai,nDandbi,nDforthestudiedILsare
given in Table 12. New values for ai,nDand bi,nDfor the ions
[SCN]?, [Tos]?, [N(CN)2]?, [CH3CO2]?, [CH3SO3]?,
[CH3OHPO2]?, and [(OCH3)2PO2]?were estimated and are
proposed here.
’CONCLUSIONS
Thesetofionicliquidsstudiedinthisworkwaschosen,taking
into account their potential in approaches regarding biomass
dissolution. Aiming at gathering a complete database on the
thermophysical properties of such ionic liquids, allowing there-
fore the design of related industrial processes, the density, visco-
sity, refractive index, isobaric thermal expansivity, and heat
capacity of eight ionic liquids based on the cation 1-ethyl-3-
methylimidazolium, combined with different anions, were deter-
mined. The impact of the IL anion on the properties studied was
discussed, and novel parameters for the Gardas and Coutinho
group contribution models are proposed.
Among the studied ionic liquids, [C2mim][CH3CO2] is still
the best candidate for cellulose dissolution coupled to a low vis-
cosity and density-favorable properties for further industrial
applications.
’ASSOCIATED CONTENT
b
S
Supporting Information.
the experimental density (Figure S1) or viscosity (Figure S2)
values and those predicted by the Gardas and Coutinho group
contribution method and average absolute deviation of the ref-
ractive index and standard error in the estimate of the tempera-
ture derivative (Table T1). This material is available free of
charge via the Internet at http://pubs.acs.org.
Relative deviations between
’AUTHOR INFORMATION
Corresponding Author
*Tel.:+351-234-370200.Fax:+351-234-370084.E-mailaddress:
jcoutinho@ua.pt.
Funding Sources
This work was funded by project QREN SI-I&DT Project No.
11551 from UE/FEDER through the COMPETE program. The
authors also thank Fundac -~ ao para a Ci^ encia e a Tecnologia for
the postdoctoral Grants SFRH/BPD/41781/2007 and SFRH/
BPD/38637/2007from M.G.F.and B.S., respectively,and Ph.D.
Grants SFRH/BD/60513/2009, SFRH/BD/70641/2010, and
SFRH/BD/41562/2007 from M.A.A.R., C.M.S.S.N., and P.J.C.,
respectively.
’DEDICATION
Kenneth N. Marshhas been aninspiring figure for the authors of
this work both through his activitiesas aresearcher and as Editor
of the Journal of Chemical & Engineering Data. His supportive
attitudes and suggestions often helped us to enhance the quality
of our work and persevere through some harsh criticism. This
work which focuses on the main axis of research that Ken has led
during the past decade on thermophysical properties, ionic
liquids and cellulose solubility,3?5has been carried out with
the main purpose to pay homage to the researcher and acknowl-
edge him for his contribution to get where we are today.
’REFERENCES
(1) Freire, C. S. R.; Silvestre, A. J. D.; Neto, C. P.; Cavaleiro, J. A. S.
Lipophilic Extractives of the Inner and Outer Barks of Eucalyptus
Globulus. Holzforschung 2002, 372–379.
(2) M€ aki-Arvela,P.;Anugwom,I.;Virtanen,P.;Sj€ oholm,R.;Mikkola,
J. P. Dissolution of Lignocellulosic Materials and its Constituents Using
Ionic Liquids ? A Review. Ind. Crops Prod. 2010, 32, 175–201.
(3) Pinkert, A.; Marsh, K. N.; Pang, S.; Staiger, M. P. Ionic Liquids
and their Interaction with Cellulose. Chem. Rev. 2009, 109, 6712–6728.
(4) Pinkert, A.; Marsh, K. N.; Pang, S. Alkanolamine Ionic Liquids
and their Inability to Dissolve Crystalline Cellulose. Ind. Eng. Chem. Res.
2010, 49, 11809–11813.
(5) Pinkert,A.;Marsh,K.N.;Pang,S.ReflectionsontheSolubilityof
Cellulose. Ind. Eng. Chem. Res. 2010, 49, 11121–11130.
(6) Oliveira,F.S.;Freire,M.G.;Pratas,M.J.;Pauly,J.;Daridon,J.L.;
Marrucho, I. M.; Coutinho, J. A. P. Solubility of Adamantane in
Phosphonium-Based Ionic Liquids. J. Chem. Eng. Data 2009, 55,
662–665.
(7) Zakrzewska, M. E.; Bogel-Lukasik, E.; Bogel-Lukasic, R. Solubi-
lity of Carbohydrates in Ionic Liquids. Energy Fuels 2010, 24, 737–745.
(8) Rosatella, A. A.; Branco, L. C.; Afonso, C. A. M. Studies on
Dissolution of Carbohydrates in Ionic Liquids and Extraction from
Aqueous Phase. Green Chem. 2009, 11, 1406–1413.
(9) Swatloski, R. P.; Spear, S. K.; Holbrey, J. D.; Rogers, R. D.
DissolutionofCellulosewithIonicLiquids.J.Am.Chem.Soc.2002,124,
4974–4975.
(10) Xu, A.; Wang, J.; Wang, H. Effects of Anionic Structure and
Lithium Salts Addition on the Dissolution of Cellulose in 1-Butyl-3-
methylimidazolium-based Ionic Liquid Solvent Systems. Green Chem.
2010, 12, 268–275.
(11) Vitz, J.; Erdmenger, T.; Haensch, C.; Schubert, U. S. Extended
dissolution studies ofcellulose in imidazolium basedionic liquids.Green
Chem. 2009, 11, 417–424.
(12) Freire, M. G.; Teles, A. R. R.; Ferreira, R. A. S.; Carlos, L. D.;
Lopes-da-Silva,J.A.;Coutinho,J.A.P.ElectrospunNanosizedCellulose
Fibers using Ionic Liquids at Room Temperature. Green Chem. 2011,
DOI:10.1039/C1GC15930E.
(13) Fukaya, Y.; Hayashi, K.; Wada, M.; Ohno, H. Cellulose
Dissolution with Polar Ionic Liquids Under Mild Conditions: Required
Factors for Anions. Green Chem. 2008, 10, 44–46.
(14) Sun, N.; Rahman, M.; Qin, Y.; Maxim, M. L.; Rodriguez, H.;
Rogers,R.D.CompleteDissolutionandPartialDelignificationofWood
in the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate. Green Chem.
2009, 11, 646–655.
(15) Zavrel, M.; Bross, D.; Funke, M.; B€ uchs, J.; Spiess, A. C. High-
throughput Screening for Ionic Liquids Dissolving (Ligno-)cellulose.
Bioresour. Technol. 2009, 100, 2580–2587.
(16) Pu, Y.; Jiang, N.; Ragauskas, A. J. Ionic Liquid as a Green
Solvent for Lignin. J. Wood Chem. Technol. 2007, 27, 23–33.
(17) Kilpel€ ainen,I.;Xie,H.; King,A.;Granstrom, M.;Heikkinen,S.;
Argyropoulos, D. S. Dissolution of Wood in Ionic Liquids. J. Agric. Food
Chem. 2007, 55, 9142–9148.
(18) Fort,D.A.;Remsing,R.C.;Swatloski,R.P.;Moyna,P.;Moyna,
G.; Rogers, R. D. Can Ionic Liquids Dissolve Wood? Processing and
Analysis of Lignocellulosic Materials with 1-n-Butyl-3-methylimidazo-
lium Chloride. Green Chem. 2007, 9, 63–69.
(19) Zhao, H.; Baker, G. A.; Cowins, J. V. Fast Enzymatic Sacchar-
ificationofSwitchgrassafterPretreatmentwithIonicLiquids.Biotechnol.
Prog. 2010, 26, 127–133.
(20) Liu, L.; Chen, H. Enzymatic Hydrolysis of Cellulose Materials
Treated with Ionic Liquid [BMIM] Cl. Chin. Sci. Bull. 2006, 51, 2432–
2436.
(21) Dadi,A.P.;Varanasi,S.;Schall,C.A.EnhancementofCellulose
Saccharification Kinetics Using an Ionic Liquid Pretreatment Step.
Biotechnol. Bioeng. 2006, 95, 904–910.
(22) Sidhpuria,K.B.;Daniel-Da-Silva,A.L.;Trindade,T.;Coutinho,
J. A. P. Supported Ionic Liquid Silica Nanoparticles (SILnPs) as an

Page 10

4822
dx.doi.org/10.1021/je200790q |J. Chem. Eng. Data 2011, 56, 4813–4822
Journal of Chemical & Engineering Data
ARTICLE
Efficient and Recyclable Heterogeneous Catalyst for the Dehydration of
Fructose to 5-Hydroxymethylfurfural. Green Chem. 2011, 13, 340–349.
(23) Zakrzewska, M. E.; Bogel-yukasik, E.; Bogel-yukasik, R. Ionic
Liquid ? Mediated Formation of 5-Hydroxymethylfurfural ? A Pro-
misingBiomass-derivedBuildingBlock.Chem.Rev.2011,111,397–417.
(24) Carvalho, P. J.; Regueira, T.; Santos, L.; Fernandez, J.;
Coutinho, J. A. P. Effect of Water on the Viscosities and Densities of
1-Butyl-3-methylimidazoliumDicyanamideand1-Butyl-3-methylimida-
zolium Tricyanomethane at Atmospheric Pressure. J. Chem. Eng. Data
2010, 55, 645–652.
(25) Neves, C.; Batista, M. L. S.; Claudio, A. F. M.; Santos, L.;
Marrucho, I. M.; Freire, M. G.; Coutinho, J. A. P. Thermophysical
Properties and Water Saturation of [PF6]-Based Ionic Liquids. J. Chem.
Eng. Data 2010, 55, 5065–5073.
(26) Oliveira, F. S.; Freire, M. G.; Carvalho, P. J.; Coutinho, J. A. P.;
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 Mixtures. J. Chem.
Eng. Data 2010, 55, 4514–4520.
(27) Suurkuusk, J.; Wads€ o, I. Design and Testing of an Improved
Precise Drop Calorimeter for the Measurement of the Heat Capacity of
Small Samples. J. Chem. Thermodyn. 1974, 6, 667–679.
(28) Santos, L. M. N. B. F.; Rocha, M. A. A.; Rodrigues, A. S. M. C.;
?Stejfa,V.;Fulem,M.;Bastos,M.ReassembleandTestofHigh-Precision
Heat Capacity Drop Calorimeter. Heat Capacities at 298.15 K of Some
Polyphenyls. J. Chem. Thermodyn. 2011, DOI:10.1016/j.jct.2011.06.010.
(29) Konicek, J.; Suurkuusk, J.; Wads€ o, I. A Precise Drop Heat
Capacity Calorimeter for Small Samples. Chem. Scr. 1971, 1, 217–220.
(30) Sabbah, R.; Xu-wu, A.; Chickos, J. S.; Leit~ ao, M. L. P.; Roux,
M.V.;Torres,L.A.ReferenceMaterialsforCalorimetryandDifferential
Thermal Analysis. Thermochim. Acta 1999, 331, 93–204.
(31) Chirico,R.D.;Diky,V.;Magee,J.W.;Frenkel,M.;Marsh,K.N.
Thermodynamic andThermophysical Properties ofthe Reference Ionic
Liquid: 1-Hexyl-3-methylimidazolium Bis[(trifluoromethyl)sulfonyl]-
amide (Including Mixtures). Part 2. Critical Evaluation and Recom-
mended Property Values. Pure Appl. Chem. 2009, 81, 791–828.
(32) Blokhin, A. V.; Paulechka, Y. U.; Kabo, G. J. Thermodynamic
Properties of [C6mim][NTf2] in the Condensed State. J. Chem. Eng.
Data 2006, 51, 1377–1388.
(33) Shimizu, Y.; Ohte, Y.; Yamamura, Y.; Saito, K.; Atake, T. Low-
Temperature Heat Capacity of Room-Temperature Ionic Liquid, 1-
Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide. J. Phys.
Chem. B 2006, 110, 13970–13975.
(34) Doma? nska, U.; Kr? olikowska, M.; Kr? olikowski, M. Phase Beha-
viourandPhysico-chemicalPropertiesoftheBinarySystems{1-Ethyl-3-
methylimidazolium Thiocyanate, or 1-Ethyl-3-methylimidazolium To-
sylate + Water, or + an Alcohol}. Fluid Phase Equilib. 2010, 294, 72–83.
(35) Fr€ oba,A.P.;Kremer,H.;Leipertz,A.Density,RefractiveIndex,
Interfacial Tension, and Viscosity of Ionic Liquids [EMIM][EtSO4],
[EMIM][NTf2], [EMIM][N(CN)2], and [OMA][NTf2] in Depen-
dence on Temperature at Atmospheric Pressure. J. Phys. Chem. B 2008,
112, 12420–12430.
(36) Hern? andez-Fern? andez,F.J.;Ríos,A.P.;G? omez,D.;Rubio,M.;
Tom? as-Alonso, F.; Víllora, G. Ternary Liquid-liquid Equilibria for Mix-
tures of an Ionic Liquid + n-Hexane + an Organic Compound Involved
in the Kinetic Resolution of Rac-1-phenyl Ethanol (Rac-1-phenyl
Ethanol, Vinyl Propionate, Rac-1-phenylethyl Propionate or Propionic
Acid) at 298.2 K and Atmospheric Pressure. Fluid Phase Equilib. 2008,
263, 190–198.
(37) Vercher, E.; Llopis, F. J.; Gonz? alez-Alfaro, M. V.; Martínez-
Andreu, A. Density, Speed of Sound, and Refractive Index of 1-Ethyl-3-
methylimidazolium Trifluoromethanesulfonate with Acetone, Methyl
Acetate, and Ethyl Acetate at Temperatures from (278.15 to 328.15) K.
J. Chem. Eng. Data 2009, 55, 1377–1388.
(38) Gardas, R. L.; Coutinho, J. A. P. Extension of the Ye and
Shreeve Group Contribution Method for Density Estimation of Ionic
Liquids in a Wide Range of Temperatures and Pressures. Fluid Phase
Equilib. 2008, 263, 26–32.
(39) Doma? nska, U.; Laskowska, M. Temperature and Composition
Dependence of the Density and Viscosity of Binary Mixtures of {1-
Butyl-3-methylimidazolium Thiocyanate + 1-Alcohols}. J. Chem. Eng.
Data 2009, 54, 2113–2119.
(40) S? anchez, L. G.; Espel, J. R.; Onink, F.; Meindersma, G. W.;
Haan, A. B. Density, Viscosity, and Surface Tension of Synthesis Grade
Imidazolium, Pyridinium, and Pyrrolidinium Based Room Temperature
Ionic Liquids. J. Chem. Eng. Data 2009, 54, 2803–2812.
(41) Tom? e,L.I.N.;Gardas,R.L.;Carvalho, P.J.;Pastoriza-Gallego,
M. J.; Pi~ neiro, M. M.; Coutinho, J. A. P. Measurements and Correlation
of High-Pressure Densities of Phosphonium Based Ionic Liquids.
J. Chem. Eng. Data 2011, 56, 2205–2217.
(42) Kolbeck, C.; Cremer, T.; Lovelock, K. R. J.; Paape, N.; Schulz,
P. S.; Wasserscheid, P.; Maier, F.; Steinr€ uck, H. P. Influence of Different
Anions on the Surface Composition of Ionic Liquids Studied Using
ARXPS. J. Phys. Chem. B 2009, 113, 8682–8688.
(43) Vercher, E.; Orchill? es, A. V.; Miguel, P. J.; Martínez-Andreu, A.
Volumetric and Ultrasonic Studies of 1-Ethyl-3-methylimidazolium
TrifluoromethanesulfonateIonicLiquidwithMethanol,Ethanol,1-Pro-
panol, and Water at Several Temperatures. J. Chem. Eng. Data 2007,
52, 1468–1482.
(44) Fendt, S.; Padmanabhan, S.; Blanch, H. W.; Prausnitz, J. M.
Viscosities of Acetate or Chloride-based Ionic Liquids and Some of
Their Mixtures with Water or Other Common Solvents. J. Chem. Eng.
Data 2011, 56, 31–34.
(45) Rodríguez, H.; Brennecke, J. F. Temperature and Composition
Dependence ofthe Density andViscosity ofBinary Mixtures ofWater+
Ionic Liquid. J. Chem. Eng. Data 2006, 51, 2145–2155.
(46) Schreiner, C.; Zugmann, S.; Hartl, R.; Gores, H. J. Fractional
Walden Rule for Ionic Liquids: Examples from Recent Measurements
and a Critique of the So-called Ideal KCl Line for the Walden Plot.
J. Chem. Eng. Data 2009, 55, 1784–1788.
(47) Gardas, R. L.; Coutinho, J. A. P. Group Contribution Methods
for the Prediction of Thermophysical and Transport Properties of Ionic
Liquids. AIChE J. 2009, 55, 1274–1290.
(48) Ficke,L.E.;Novak,R.R.;Brennecke,J.F.Thermodynamicand
Thermophysical Properties of Ionic Liquid + Water Systems. J. Chem.
Eng. Data 2010, 55, 4946–4950.
(49) Yu, Y.-H.; Soriano, A. N.; Li, M.-H. Heat Capacities and
Electrical Conductivities of 1-Ethyl-3-methylimidazolium-based Ionic
Liquids. J. Chem. Thermodyn. 2009, 41, 103–108.
(50) Ficke,L.E.;Rodríguez,H.;Brennecke,J.F.HeatCapacitiesand
Excess Enthalpies of 1-Ethyl-3-methylimidazolium-Based Ionic Liquids
and Water. J. Chem. Eng. Data 2008, 53, 2112–2119.
(51) García-Miaja,G.;Troncoso,J.;Romaní,L.ExcessPropertiesfor
Binary Systems Ionic Liquid + Ethanol: Experimental Results and
Theoretical Description Using the ERAS Model. Fluid Phase Equilib.
2008, 274, 59–67.
(52) Diedrichs, A.; Gmehling, J. Measurement of Heat Capacities of
Ionic Liquids by Differential Scanning Calorimetry. Fluid Phase Equilib.
2006, 244, 68–77.
(53) Vercher,E.;Llopis,F.J.;Gonz? alez-Alfaro,V.;Martínez-Andreu,
A. Refractive Indices and Deviations in Refractive Indices for Binary
Mixtures of 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate
with Methanol, Ethanol, 1-Propanol, and 2-Propanol at Several Tem-
peratures. J. Chem. Eng. Data 2009, 55, 1430–1433.
(54) Tariq, M.; Forte, P. A. S.; Gomes, M. F. C.; Lopes, J. N. C.;
Rebelo, L. P. N. Densities and Refractive Indices of Imidazolium- and
Phosphonium-based Ionic Liquids: Effect of Temperature, Alkyl Chain
Length, and Anion. J. Chem. Thermodyn. 2009, 41, 790–798.
(55) Shimizu, K.; Tariq, M.; Gomes, M. F. C.; Rebelo, L. P. N.;
Lopes, J. N. C. Assessing the Dispersive and Electrostatic Components
of the Cohesive Energy of Ionic Liquids Using Molecular Dynamics
Simulations and Molar Refraction Data. J. Phys. Chem. B 2010, 114,
5831–5834.