Assessing the N2O/CO2 high pressure separation using ionic liquids with the soft-SAFT EoS

Abstract

The capabilities of the soft-SAFT EoS to accurately describe the thermophysical properties of ionic liquids (ILs) and the phase equilibria of their mixtures with greenhouse gases is extended in this work to address the CO2 and the N2O solubilities in [C(4)mim](+) ILs from different anion families. In addition to the commonly studied [BF4](-) and [NTf2](-) anions, the solubility of these gases in ILs with the anions [N(CN)(2)](-), [SCN](-) and [Ac](-) is also studied and compared among them, searching for the best system for separation purposes. A coarse-grained molecular model is proposed within the soft-SAFT framework for each newly studied IL based on structural information, guidance obtained from quantum calculations and previous work. The most adequate set of molecular parameters are selected from the ILs density description and from the ability to reproduce the N2O/CO2 solubilities in these ILs at the lowest and highest temperatures for which experimental data are available. A discussion about the association molecular parameters values and their relation with the anion nature is also presented. With these molecular models, the description of the high pressure phase equilibria of the binary systems composed of the two gases and the ILs referred above are described with soft-SAFT for the remaining isotherms. For most systems, the equilibria behavior of the mixtures is predicted without using any binary parameter. When good agreement with the experimental data is not achieved, a single temperature independent binary parameter is enough to allow a good description. Finally, Henry's law constants are calculated from soft-SAFT to evaluate the selectivity of those ILs for the CO2/N2O separation. (C) 2014 Elsevier B.V. All rights reserved.