Investigation On the Solubility of SO2 in Several Imidazolium Based Ionic Liquids Using NPT Monte Carlo Simulation

Tthe solubility of sulfur dioxide (SO2) at P=1 bar and several temperatures in a series of Room Temperature Ionic Liquids (RTILs) has been calculated by Monte Carlo simulation at NPT ensemble. The 1-butyl-3-methylimidazolium ([bmim]+) cation in combination with tetrafluoroborate ([BF4]-), bromide ([Br]-), nitrate ([NO3]-) and bis-(trifluoromethyl) sulfonylimide ([Tf2N]-), plus 1-ethyl-3-methylimidazolium tetrafluoroborate ([emim][BF4]) and 1,3-dimethylimidazolium bis-(trifluoromethyl) sulfonylimide ([dmim][Tf2N)]) are studied RTILs. The systems were chosen to study the influence of anion, alkyl chain length of cation and temperature on the solubility of SO2. Also, the micro-structure of pure RTILs and solutions has been studied via various center of mass and site-site Radial Distribution Functions (RDFs). For computing the potential energy and the solubility, the OPLS-AA force field and Widom Particle Insertion Method have been used, respectively. The long- range coulombic forces are taken into account using Wolf Method. The results show that for pure ionic liquids, there is a good agreement between experimental data and calculated liquid density, but the obtained solubility does not reproduce the experimental data with high accuracy which can be a result of incompatible force field and/or the method. The results demonstrate that the SO2 gas has the highest solubility in [bmim][NO3] and the lowest solubility in [dmim][Tf2N], where the solubility increases with alkyl chain length of cation and charge density on anions and it decreases with temperature.