Investigation on the Solubility of SO2 and CO2 in Imidazolium-Based Ionic Liquids Using NPT Monte Carlo Simulation

The solubility of sulfur dioxide (SO2) and carbon dioxide (CO2) at P = 1 bar in a series of imidazolium-based room-temperature ionic liquids (RTILs) is calculated by Monte Carlo simulation in NPT ensemble using the OPLS-UA force field and Widom particle insertion method. The studied ILs were 1-butyl-3-methylimidazolium ([bmim](+)) tetrafluoroborate ([BF4](-)), [bmim](+) hexafluorophosphate ([PF6](-)), [bmim](+) bromide ([Br](-)), [bmim](+) nitrate ([NO3](-)), [bmim](+) bis-(trifluoromethyl) sulfonylimide ([Tf2N](-)), and 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim] [BE4]). To validate the simulations, the liquid density of studied Its and the solubility of CO2 in [bmim] [PF6] was compared with corresponding experimental and theoretical studies reported in the literature, and a. good agreement was obtained. The results of SO2 solubility demonstrate that the SO2 gas has the highest solubility in [bmim] [NO3] and [bmim] [Br] ILs and the lowest solubility in [bmim][PF6]. To describe the solubility order of polar gases such as SO2 and nonpolar gases like CO2, we have simulated the SO2/IL and CO2/IL mixtures which made possible to investigate the interaction of solute molecules with anions and cations in the liquid phase. We introduced the ratio of solute-IL interaction over cation-anion interaction energy density as an index for solubility of gases in ILs. The results show that the proposed index can describe the solubility order of SO2 as well as CO2 and it might be used as an alternative to standard methods of infinite dilution Henry's constant calculations when the solubility order is desired.