(55d) Phase Equilibria, Structural, and Dynamical Properties of so2-binary Ionic Liquid Systems

Ionic liquids have been investigated for their capability to separate gases for almost two decades now. However, the majority of the publications have primarily focused on evaluating the effect of cation, anion, and/or substituents on the ions on gas solubility. Very few research articles study the effect of ionic liquid mixture compositions on gas solubility. In this contribution, we investigate the solubility of the SO₂ in a two-component ionic liquid system using molecular simulations. The binary ionic liquid system is composed of the cation 1-n-butyl-3-methylimidazolium [C₄mim]⁺ and the anions chloride (Cl^-) and bis(trifluoromethanesulfonyl)imide [NTf₂]^-. The solubility of gases in terms of Henry’s constants is computing at various molar ratios of [Cl]^-/[NTf₂]^-: 100/0, 75/25, 50/50, 25/75, and 0/100, enabling determination of the effects anion concentration has on the gas solubility. Furthermore, the temperature dependence of the solubility is investigated by calculating the Henry’s constants at 333 K, 353 K, and 373 K. We calculate the enthalpy of absorption and entropy of absorption for these gases and find that SO₂ dissolves due to the favorable energetic interactions with the ionic liquids with entropy opposing the dissolution process. To provide molecular-level details on the solvation process, we conduct molecular dynamics simulations of SO₂ and binary ionic liquid mixtures. The structural properties of the mixtures will be elucidated in terms of radial distribution functions and spatial distribution functions, which will pinpoint to the strong SO₂-Cl interactions. We will also present results of the hydrogen bond dynamics with and without SO₂ in the binary ionic liquid mixtures to elucidate the effect of SO₂ on the system fluidity.