# Viscosities of Pure Ionic Liquids Using Combinations of Free Volume Theory or Friction Theory with the Cubic, the Cubic Plus Association, and the Perturbed-Chain Statistical Associating Fluid Theory Equations of State at High Pressures

journal contribution

posted on 06.02.2017, 00:00 by Reza Haghbakhsh, Khalil Parvaneh, Alireza ShariatiIn
this study, the behaviors of viscosities of nine ionic liquids
(ILs) over wide ranges of pressures and temperatures were determined.
The investigated ILs belonged to the three imidazolium-based families
of tetrafluoroborate, hexafluorophosphate, and bis[(trifluoromethyl)sulfonyl]imide.
The two well-known cubic equations of state (EoS’s) of Peng–Robinson
(PR) and the Soave–Redlich–Kwong (SRK), as well as the
two more-sophisticated EoS’s of cubic plus association (CPA),
and perturbed-chain statistical associating fluid theory (PC-SAFT),
were each coupled with two well-known theoretical viscosity models,
namely the friction theory and the free volume theory. Calculated
results showed that the free volume model, coupled with PC-SAFT, has
superior results in comparison to the free volume model with the CPA
EoS. For the viscosity model of free volume, the studied cubic EoS’s
did not give accurate results. When the friction model was used, the
PC-SAFT EoS once more showed better accuracy than the CPA EoS; however,
the CPA results in this model were quite close to that of the PC-SAFT,
while the differences were great with the free volume model. One of
the remarkable conclusions for the friction theory model was the unexpectedly
reliable results that it gave with the cubic EoS’s. This suggests
that when highly accurate results are not crucial, this combination
can be the best choice because of the significantly greater simplicity
of a cubic EoS over an association EoS.