(602a) Engineering Gas-Liquid Interfaces for CO2 Capture Using Ionic Liquid Additives

Neat ionic liquids (ILs) are typically explored as solvents for physical and chemical CO₂ capture due to their exceptional thermophysical and phase-equilibria properties such as high molar CO₂ solubility, low volatility, and chemical and thermal stability. However, when mixed at low concentrations in combination with other solvents, ILs can also improve the overall CO₂ capture performance by enhancing the interfacial properties of such mixtures. Differences in the polarity, charge density, and functional groups on cations and anions of ionic liquids can promote solvophilic or solvophobic interactions that induce redistribution of the ions into the bulk or at the gas-liquid interface. This creates local chemical environments that are favorable towards CO₂ capture due to higher CO₂ affinity, lower surface tension, enhanced diffusivity etc. This work uses molecular dynamics (MD) simulations to examine these effects due to the addition of ILs to a non-aqueous CO₂ capture system containing a mixture of ethylene glycol (EG) and potassium hydroxide (KOH). The effect of the choice of anions is investigated across a variety of fluorinated and non-fluorinated anions such as bistriflimide (NTf₂), triflate (TfO), hexafluorophosphate (PF₆), and dicyanamide (DCA). The influence of the solvophobic nature of the cations is probed using methyl imidazolium cation as the core with ethyl (C₂mim), butyl (C₄mim), and octyl (C₈mim) substitutions. Furthermore, the effect of concentration is studied at IL concentrations ranging between 0.5 – 4.0 %. The impact due to the addition of ILs is characterized by estimation of CO₂ Henry’s constant, the number density, self-diffusion coefficient, cluster analysis, and association lifetimes for various species. Thus, we offer insights into using unique properties of ILs to engineer gas-liquid interfaces for highly efficient CO₂ capture.