Molecular Dynamics Simulation Study on the Absorption of Ethylene and Acetylene in Ionic Liquids

As environmentally friendly and designable solvents, ionic liquids (ILs) have great potential in the separation of C₂H₄ and C₂H₂, which is quite important in chemical industry. The microscopic insight into the intermolecular interaction and the diffusion dynamics at a molecular level is crucial for designing more efficient ILs. In this work, the interaction mechanism and diffusion dynamics for C₂H₄/C₂H₂ absorption and separation with five ILs, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]­[BF₄]), 1-butyl-3-methylimidazolium acetate ([bmim]­[OAc]), 1-butyl-3-methylimidazolium trifluoroacetate ([bmim]­[TFA]), 1-butyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([bmim]­[Tf₂N]), and 1-butyl-1-methylpyrrolidinium bis­(trifluoromethylsulfonyl)­imide ([bmpyrr]­[Tf₂N]), were investigated by molecular dynamics (MD) simulation. The result suggests that the van der Waals interaction between C₂H₄ and cation plays an important role in C₂H₄ dissolution in ILs, but the hydrogen bonding interaction between C₂H₂ and anion is foremost in C₂H₂ dissolution. Moreover, the interaction energy analysis matches better with the experimental solubility than our previous quantum chemical calculation, indicating the superiority of the MD simulation approach in studying the interaction mechanism of IL-based systems where multiple interactions are often present. The self-diffusion coefficients of cations and anions of ILs do not change obviously after adding C₂H₄, while they have a significant increase after dissolving C₂H₂, particularly in relatively strong hydrogen bonding systems [bmim]­[OAc]–C₂H<sub>2