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Fluid Phase Equilibria 263 (2008) 26–32
Extension of the Ye and Shreeve group contribution method for
density estimation of ionic liquids in a wide range
of temperatures and pressures
Ramesh L. Gardas, Jo˜ ao A.P. Coutinho
∗
CICECO, Departamento de Qu´ ımica, Universidade de Aveiro, 3810-193 Aveiro, Portugal
Received 27 April 2007; received in revised form 25 September 2007; accepted 26 September 2007
Available online 29 September 2007
Abstract
An extension of the Ye and Shreeve group contribution method [C. Ye, J.M. Shreeve, J. Phys. Chem. A 111 (2007) 1456–1461] for the estimation
of densities of ionic liquids (ILs) is here proposed. The new version here presented allows the estimation of densities of ionic liquids in wide ranges
of temperature and pressure using the previously proposed parameter table. Coefficients of new density correlation proposed were estimated using
experimental densities of nine imidazolium-based ionic liquids. The new density correlation was tested against experimental densities available in
literature for ionic liquids based on imidazolium, pyridinium, pyrrolidinium and phosphonium cations. Predicted densities are in good agreement
with experimental literature data in a wide range of temperatures (273.15–393.15 K) and pressures (0.10–100 MPa). For imidazolium-based ILs,
the mean percent deviation (MPD) is 0.45% and 1.49% for phosphonium-based ILs. A low MPD ranging from 0.41% to 1.57% was also observed
for pyridinium and pyrrolidinium-based ILs.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Ionic liquid; Density; Correlation; Group contribution; High pressure
1. Introduction
Ionic liquids (ILs) are a combination of bulky, asymmetric
N-containing organic cations (e.g., imidazole, pyrrole, pyridine,
etc.) and anions of wide variety, ranging from simple inorganic
ions (e.g., halides) to more complex organic species (e.g., tri-
flate). Since a large number of cationic and anionic structures
Abbreviations: IL, ionic liquid; PVT, pressure, volume and temperature; EOS, equation-of-state; AAV, average atom volume; MPD, mean percent
deviation; [C
2
mim][NTf
2
], 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [C
3
mim][NTf
2
], 1-propyl-3-methylimidazolium bis(trifluoromethyls-
ulfonyl)imide; [C
4
mim][NTf
2
], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [C
5
mim][NTf
2
], 1-pentyl-3-methylimidazolium bis(trifluoro-
methylsulfonyl)imide; [C
6
mim][NTf
2
], 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [C
7
mim][NTf
2
], 1-heptyl-3-methylimidazolium bis(tri-
fluoromethylsulfonyl)imide; [C
8
mim][NTf
2
], 1-octyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; [C
10
mim][NTf
2
], 1-decyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide; [C
2
mim][BF
4
], 1-ethyl-3-methylimidazolium tetrafluoroborate; [C
4
mim][BF
4
], 1-butyl-3-methylimidazolium tetrafluo-
roborate; [C
8
mim][BF
4
], 1-octyl-3-methylimidazolium tetrafluoroborate; [C
4
mim][PF
6
], 1-butyl-3-methylimidazolium hexafluorophosphate; [C
6
mim][PF
6
],
1-hexyl-3-methylimidazolium hexafluorophosphate; [C
8
mim][PF
6
], 1-octyl-3-methylimidazolium hexafluorophosphate; [C
4
mim][C(CN)
3
], 1-butyl-3-
methylimidazolium tricyanomethane; [C
4
mim][MeSO
4
], 1-butyl-3-methylimidazolium methylsulphate; [(C
6
H
13
)
3
P(C
14
H
29
)][NTf
2
], trihexyl(tetradecyl)
phosphonium bis[(trifluoromethyl) sulfonyl]imide; [(C
6
H
13
)
3
P(C
14
H
29
)][Cl], trihexyl(tetradecyl) phosphonium chloride; [(C
6
H
13
)
3
P(C
14
H
29
)][Ac], tri-
hexyl(tetradecyl) phosphonium acetate; [C
2
py][NTf
2
], 1-ethylpyridinium bis[(trifluoromethyl) sulfonyl]imide; [C
2
py][BF
4
], 1-ethylpyridinium tetrafluoroborate;
[C
4
py][BF
4
], 1-butylpyridinium tetrafluoroborate; [C
4
mpy][BF
4
], 1-butyl-4-methyl pyridinium tetrafluoroborate; [C
4
mpyr][NTf
2
], 1-butyl-1-methyl pyrrolidinium
bis[(trifluoromethyl) sulfonyl]imide.
∗
Corresponding author. Tel.: +351 234 370200; fax: +351 234 370084.
E-mail address: jcoutinho@dq.ua.pt (J.A.P. Coutinho).
combinations are possible it is impossible to measure the ther-
mophysical properties for all conceivable ionic liquids. During
the last few years, measurements of the thermophysical and ther-
modynamic properties of ILs have increased remarkably but they
are by no means exhaustive [1–34]. Although experimental mea-
surements are available for common fluids, experimental data for
many new fluids of industrial interest are non-existent or tend
0378-3812/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.fluid.2007.09.016