Development of a robust soft-SAFT model for protic ionic liquids using new high-pressure density data

Abstract

New experimental density data in a wide range of temperatures (283–363) K and pressures (0.1–95) MPa is here reported for five protic ILs based on the N,N-diethylethanolammonium ([DEEA]) cation, combined with the following anions: acetate ([Ace]), propanoate ([Prop]), butanoate ([But]), pentanoate ([Pent]) and hexanoate ([Hex]) in a 1:1 acid:base proportion. The molar volumes of the different ILs and derivative properties such as the isothermal compressibility and isobaric thermal expansivity were determined from the experimental density data. Moreover, considering the importance of having a robust and transferable thermodynamic model of these ILs that can be used in further studies including CO2 capture, the new experimental data was used to develop a coarse-grain molecular model of the studied ILs, in the framework of the soft-SAFT EoS, employing a 2/2 association scheme to account for the hydrogen bonding character of the ILs. The proposed model was found to provide an excellent description of the experimental pρT data with average relative deviations lower than 0.11% for all the ILs, while still providing reasonable predictions of the second-order derivative properties. Furthermore, the optimized molecular parameters were found to be correlated with the ILs molecular weight, highlighting the physical meaning and consistency of the parameters obtained.