Solubility of carbon dioxide (CO2) in four bis (trifluoromethyl-sulfonyl)imide ([Tf2N]) based ionic liquids

Abstract

The solubility of carbon dioxide (CO2) in four bis(trifluoromethylsulfonyl)imide ([Tf2N]) based ionic liquids was investigated in this study. The solubility of CO2 in four ionic liquids {N,n-dimethyl-n-ethyl-n-(3-methoxypropyl)ammonium bis(trifluoromethylsulfonyl)imide ([DMEMP][Tf2N]), 1-Allyl-3H-imidazolium bis(trifluoromethylsulfonyl)imide ([P(3)HIm][Tf2N]), 1-(3-Hydroxypropyl)-3-methylimidazolium bis(trifluoromethyl-sulfonyl)imide ([HP(3)MIm][Tf2N]) and N,n-diethyl-n-methyl-n(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide ([DEME][Tf2N])} was measured at (303.15, 323.15, and 343.15) K and at pressures up to 1.5 MPa using a gravimetric microbalance. The densities of these ionic liquids (ILs) were also measured at a temperature range varying from (293.15 K–343.15 K) at atmospheric pressure (95.1 kPa with 0.8 kPa uncertainty). The experimental solubility data were correlated with the Peng-Robinson (PR) equation of state using three mixing rules (i) van der Waals one (vdW1), (ii) van der Waals two (vdW2), and (iii) Wong-Sandler mixing rules combined with NRTL model (WS-NRTL). Henry's law constants for the absorption of CO2 in these ionic liquids were estimated from the solubility data, and the enthalpy and entropy for the absorption of CO2 in these ILs at infinite dilution were also calculated from the estimated Henry's law constants. Results show that [DMEMP][Tf2N] has one of the highest capacities for CO2 compared to other ionic liquids of similar sizes in the literature.