Handbook of Solvents - George Wypych - ChemTech - Ventech!

1478 D.W. Rooney, K.R. Seddon
Table 21.2.12. Densities of the
[C4-mim][PF6] and [C4-mim][BF4] ionic liquids when compared
against other solvents at room
temperature
Solvent ρ, kgm -3
trichloromethane 1483
[C4-mim][PF6] 164
1372
dichloromethane 1327
[C4-mim][BF4] 164
1208
water 1000
diethyl ether 714
toluene 867
2-propanol 786
benzene 877
21.2.5.2 Density
Information on solvent density is also another important
physical property. This is a particularly used in
fluid flow calculations and for the design of liquid/liquid
two phase mixer-settler units. Given that
many of the ionic liquids have a “heavy” anion it
would be expected that their density would be relatively
high when compared to normal industrial solvents.
However it can be seen from the Table 21.2.12
that the density of the [C4-mim][PF6] and
[C4-mim][BF4] ionic liquids fall within the region of
the chlorinated solvents.
Overall the density of ionic liquids is somewhat
easier to model than the viscosity. In general the
change of density with temperature has been fitted to
linear equations of the form
ρ= a + b × T [21.2.8]
where a and b are constants. 155-157
The fitted parameters for N-alkylpyridinium are displayed in Table 21.2.13. The bromide
containing melts showed a much higher density than the chloride ones which is to be
expected. It has also been shown that the lengthening of the alkyl chain smoothly decreases
the density. 155,156
Table 21.2.13. Fitted parameters for the density of N-alkylpyridinium 155
Melt Mol ratio a -b ×10 3
Temp range, o C
[NC1-py]Cl -AlCl3 1:2 1.4625 0.87103 25-75
[NC2-py]Cl -AlCl3 1:2 1.4307 0.91446 25-67
[NC3-py]Cl -AlCl3 1:2 1.3973 0.8847 26-75
[NC4-py]Cl -AlCl3 1:2 1.3680 0.86042 31-76
[NC2-py]Br -AlCl3 1:2 1.5473 0.93059 25-32
The variation of density with different concentrations of aluminum trichloride in
1,3-dialkylimidazolium chloride- aluminum chloride melts is not however a smooth function.
156 In the study carried out by Wilkes et al. on the density of 1-methyl-3-ethylimidazolium
bromide aluminum bromide systems, the change of the parameters a and b
with composition, X, were successfully fitted to polynomials of third order. The constants
obtained from this study are shown in Table 21.2.14.
Table 21.2.14. Calculated constants for third order polynomial
Neutral and basic melts
0.35 ≤ X ≤ 0.50
c0 c1 c2 c3
a 1.0588 3.8594 -2.8945 0.00
b 1.2907×10 -3
-1.0448×10 -2
1.1519×10 -2
0.00