(783e) Study of Interfacial Phenomena, Viscosity and Derivative Properties of Common Ionic Liquids with the Soft-SAFT EoS

Ionic
Liquids (ILs) are a family of compounds with a very wide variety of properties
due to their particular physicochemical characteristics. In particular, their
extremely low volatility marks them as environmentally benign alternatives to
volatile organic solvents for separation processes. Thermodynamic models tend
to focus only on particular properties, such as the density or the solubility.
However, it is difficult to find theoretical tools able to reproduce several
features of ionic liquids and, in particular, their interfacial, derivative and
transport properties.

In this
contribution, within the framework of the soft-SAFT EoS [1] coupled with the
Density Gradient Theory (DGT) [2] and the Free-Volume-Theory, the single-phase
equilibrium, surface tensions, viscosities, as well as the critical
temperature, pressure and density have been estimated for different ionic
liquid families and compared with those reported in the literature from
experimental or simulation data. In particular, two different cations
(imidazolium and pyridinium) and several anions (BF4, PF6, Tf2N?) have been
revised and compared. A correlation for the influence parameter as a function
of the molecular weight was obtained, empowering the predictive capabilities of
the equation for interfacial tensions of compounds of the family for which
experimental data is scarce or unavailable [3]. In addition, surface
thermodynamic properties were also derived from the dependence of the surface
tension values, and compared with those obtained within the same framework. The
viscosity of those compounds is also provided in good agreement with the
experimental data. Finally, several second-order thermodynamic properties such
as the heat capacities, the isothermal compressibility or the Joule-Thomson
coefficient are evaluated. The effect of the molecular parameters on those
properties is further discussed.  

F. Llovell acknowledges a TALENT grant from
AGAUR, Generalitat de Catalunya. M. B. Oliveira acknowledges the financial
support from Fundação para a Ciência e a Tecnologia for her Post-Doctoral grant
(SFRH/BPD/71200/2010). This work is partially financed by the Spanish
Government under project CTQ2008-05370  and CEN2008-01027. Additional support
from the Catalan Government is also acknowledged (SGR- 2009SGR-666).

[1]  
F.J. Blas, L.F Vega, Mol. Phys. 92 (1997) 135-150

[2]   J.D. van der Waals,  Z. Phys. Chem. 13 (1894) 657-725

[3]  
O.Vilaseca and L.F.
Vega, Fluid Phase Equilib. 306 (2011) 4-14