(572g) Understanding and Virtual Design of Low-Volatility Ionic Liquid Solvents for Spacecraft CO2 Separations

Separating Carbon Dioxide (CO2) from other light gases for purposes such as carbon capture or removal of metabolically-produced CO2 from space vehicles, remains an exorbitantly expensive process in 2022. Liquid solvents, such as the industry standard monoethylamine (MEA), are leading contenders for energy-efficient CO2 separations. Classical molecular dynamics (MD) simulations are a valuable tool for predicting CO2-separation performance properties in liquid solvents at the atomic scale. Ionic liquids, composed of free-floating cations and anions, are exceedingly stable in the liquid phase, which is a particularly important consideration for in-space systems where solvent losses are exceedingly difficult to replace. Ionic Liquid viscosities have been drastically reduced in recent years, but little work has been done to characterize design tradeoffs between volatility and viscosity in ionic liquids versus other solvents. In this work, we developed and refined force field parameters for over 25 ionic liquids as part of the Interface Force Field (IFF), including some unusual chemistries, as well as several recently characterized CO2 separation amines such as 2-EEMPA. The IFF incorporates atomic charges that closely represent chemical bonding and non-reactive chemical bonding as well as non-bonded van der Waals and electrostatic interactions, and its wide transferability across organic and inorganic compounds enabled us to model diverse solvent molecules within the same framework. The models were validated with experimental densities, as well as vaporization enthalpies when possible, to ensure enough accuracy to observe trends in the desired properties. We then applied the models in extensive molecular dynamics simulations of bulk properties, internal molecular recognition, CO₂ adsorption, CO2 solubility, viscosity, heat capacity, and relative volatility. The developed models show that while both amines and ionic liquids can achieve lower solvent viscosities by reducing intermolecular interactions such as hydrogen bonding, ionic liquids will still exhibit lower volatility due to their split-ion nature. We will share detailed trends in molecular recognition and for a series of properties. Preliminary results indicate that, in contrast to other liquid solvents, ionic liquids can be designed for superior low volatilities while maintaining satisfactory CO2 separation performance.