Densities and Derived Volumetric Properties of Ionic Liquids with [Nf(2)] and [NTf2] Anions at High Pressures

Abstract

The densities of four ionic liquids: 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([E(3)Mim][Nf(2)]), n-propyl-n-methylpyrrolidinium bis(fluorosulfonyl)imide ([PMpyr][Nf(2)]), 1-butyl-l-methylpyrrolidinium bis(fluorosulfonyl)imide ([BMpyr][Nf(2)]), and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonil)imide ([BMpyr][NTf2]) were measured at temperatures (293.15 to 413.15) K and pressures (0.1 to 60) MPa. The experimental density data were modeled using the modified Tammann-Tait equation and the average absolute percentage deviations between measured and calculated values for all studied ionic liquids were less than 0.004%. The optimized parameters were used to calculate the isothermal compressibility, the isobaric thermal expansivity, the internal pressure, and the difference between specific heat capacities at constant pressure and at constant volume. The cation and anion influences on the properties of the ionic liquids were examined. The longer alkyl chains on cations are related to lower density of ionic liquids and ionic liquids with imidazole based cation are denser than those with pyrrolidinium cation. The presence of more stabile [NTf2](-) anion in ionic liquids leads to greater densities comparing to [Nf(2)](-) anion.