We will present results obtained by using the soft-SAFT EoS to describe the solubility of gases in ionic liquids. The particular systems are chosen because of their scientific and technological relevance. We focus here on imidazolium-based ILs with three different anions: BF4, PF6 and Tf2N. Before applying the equation to mixtures, a model for the pure components should be proposed, from which, by fitting to experimental data, the molecular parameters of the equation are obtained. We have observed that the molecular parameters of the imidazolium-based ILs correlate with the molecular weight as the chain length of the alkyl chain increases, making the equation a predictive tool for other compounds not included in the fitting procedure. The solubility of CO2 and other gases in these ionic liquids, at low and high pressures, is predicted with high accuracy. The molecular basis of the equation allow to a fundamental understanding of the solubility process, showing, that at least for these ILs, the solubility of CO2 in them is a physical process, with no specific interactions between CO2 and the ILs.
This work is funded by the Spanish government (CTQ2005-00296/PQ), the Catalan government (SGR2005-00288). Additional funding from MatGas and Air Products is gratefully acknowledged.