Cation effect on bis(trifluoromethylsulfonyl)imide-based ionic liquids with triethylsulfonium, 1,2-dimethyl-3-propylimidazolium, 1-methyl-1-propylpyrrolidinium, and 1-butyl-2,3-dimethylimidazolium density at high pressure

Abstract

In this work, cation effect on density for four commercial ionic liquids (ILs) based on bis(trifluoromethylsulfonyl) imide ([(CF3SO2)2N]) anion were determined at high pressure and high temperature (HPHT) at P = (0.20 to 100.00) MPa and T = (298.15 to 398.15) K, using the vibrating tube method. Triethylsulfonium ([S222]), 1,2-dimethyl-3-propylimidazolium ([C3C1C1Im]), 1-methyl-1-propylpyrrolidinium ([C3C1pyr]), and 1-butyl-2,3-dimethylimidazolium ([C4C1C1Im]) cations were combined with bis(trifluoromethylsulfonyl) imide ([(CF3SO2)2N]) anion to form four different ionic liquids. Density increases in the following order: [C4C1C1Im][(CF3SO2)2N] < [C3C1pyr][(CF3SO2)2N] < [C3C1C1Im][(CF3SO2)2N] < [S222][(CF3SO2)2N], in accordance to the packing effect. Experimental density data were correlated by using Tammann-Tait-type equation, with an average absolute relative deviation (%AARD) less than 0.0090 % for [S222][(CF3SO2)2N], [C3C1C1Im][(CF3SO2)2N], and [C4C1C1Im][(CF3SO2)2N], and less than 0.0150 % for [C3C1pyr][(CF3SO2)2N]. Furthermore, seven group contribution estimation methods were successfully used to density prediction for these ionic liquids. Finally, isothermal compressibility (κT), isobaric expansivity (αp), thermal pressure coefficient (γv), and internal pressure (Pi) were determined from these experimental data, showing their relationship with anion and cations structural packing effect.