Two popular thermodynamic modeling
frameworks, namely, the PC-SAFT
equation of state and the COSMO-RS model, are benchmarked for their
performance in predicting the thermodynamic properties of pure ionic
liquids (ILs) and the solubility of CO2 in ILs. The ultimate
goal is to provide an illustration of what to expect from these frameworks
when applied to ILs in a purely predictive way with established parametrization
approaches, since the literature generally lacks their mutual comparisons.
Two different modeling approaches with respect to the description
of the molecular structure of ILs are tested within both models: a
cation–anion pair as (i) a single electroneutral supermolecule
and (ii) a pair of separately modeled counterions (ion-based approach).
In general, we illustrate that special attention should be paid when
estimating unknown thermodynamic data of ILs even with these two progressive
thermodynamic frameworks. For both PC-SAFT and COSMO-RS, the supermolecule
approach generally yields better results for the vapor pressure and
the vaporization enthalpy of pure ILs, while the ion-based approach
is found to be more suitable for the solubility of CO2.
In spite of some shortcomings, COSMO-RS with the supermolecule approach
shows the best overall predictive capabilities for the studied properties.
The ion-based strategy within both models has significant limitations
in the case of the vaporization properties of ILs. In COSMO-RS, these
limitations can, to a certain extent, be surpassed by additional quantum
mechanical calculations of the ion pairing in the gas phase, while
the ion-based PC-SAFT approach still needs a sophisticated improvement
to be developed. As an initiating point, we explore one possible and
simple route considering a high degree of cross associations between
the counterions in the gas phase.