(376x) Molecular Dynamics Simulations of New Ionic Liquids with Crystal-like Structures As Highly Selective Membrane Materials for CO2 Separation

For over a decade, ionic liquids (ILs) and polymerized ILs have been investigated as advanced materials for CO₂ capture and separation applications.¹ Herein, we are exploring a new approach for achieving high performance (high selectivity, high diffusivity) IL-based materials for industrial gas separation. By leveraging the strong electrostatic interactions and steric constraints present within different IL formulations, we are designing highly-ordered, liquid-crystal like structures that maximize gas diffusivity while simultaneously preserving selectivity. This is a combined computational and experimental investigation of unique IL architectures, including C₁₄H₁₆N₄²⁺; C₁₈H₂₁N₆³⁺; C₂₂H₂₆N₈⁴⁺; C₁₀H₆O₆S₂^2-; C₁₂H₆F₆N₂O₈S₄^2-; C₆H₃O₉S₃^3- combined within in a methanol or N-methyl-2-pyrrolidone (NMP) solvent.

In our work, we are using molecular dynamics methods to provide information about how the cations and anions interact with each other at a molecular level. Our simulation techniques are being used to capture information about structural correlation functions, molecular diffusivity, as well as an explicit accounting of the balance of van der Waals and electrostatic interactions in the system. Also, due to the porous nature of our materials, we also provide quantitative information about the fractional free volume (FFV), surface area, and pore size distribution.² These properties can provide useful screening information for predicting gas adsorption/separation performance, and this is being verified by directly simulating gas adsorption isotherms with grand canonical Monte Carlo (GCMC) simulations. Our simulations are being rigorously benchmarked against the on-going experimental investigations, and this will provide essential information for future experimental and computational design of highly selective membrane materials.

REFERENCES

1. Li, P.; Paul, D.; Chung, T.-S., High performance membranes based on ionic liquid polymers for CO₂ separation from the flue gas. Green Chem. 2012, 14, 1052-1063.
2. Abedini, A.; Crabtree, E.; Bara, J. E.; Turner, C. H., Molecular Simulation of Ionic Polyimides and Composites with Ionic Liquids as Gas-Separation Membranes. Langmuir 2017, 33, 11377-11389.