Separation of propylene/propane using IL/Silver ion facilitated transport: Insights from computational molecular approach

Membrane technology is being used increasingly for olefin/paraffin separation, and the facilitated transport of ionogel membranes provides unprecedented possibilities to circumvent the permeability/selectivity trade-off. An in-depth understanding of the essence of the concept of gas sorption and diffusion in silver-assisted facilitated transport mechanisms remains relatively unfathomed, which motivated the present work. Herein, the computational molecular approach consisting of molecular dynamics (MD) simulation, grand canonical Monte Carlo (GCMC), and density functional theory (DFT) shed light on the possible interactions between the components of membrane and gas species. The solvation free energy as a function of silver concentration was calculated to determine the contribution of coulombic and van der Waals forces quantitatively. The solvation-free energy of propylene in the IL electrolyte is highly favorable and follows a decreasing trend when compared to propane. The DFT calculations were performed to establish a clear connection between molecular structure and solubility results. From radial distribution functions (RDFs), it was found that the π-π interaction of propylene/cation of IL and propylene/Ag+ is the key point in its higher solubility. Solubility of propylene in IL electrolyte increases from 0.0016 to 0.013 cm3(STP)/cm3.cmHg upon the addition of silver salt up to 1 M. Relative concentration distribution proves the layering of the components adjacent to the pore wall which could be the reason for larger gas diffusion coefficient (50–100%) in the membrane compared to bulk IL. This simulation work is expected to be noteworthy toward a detailed understanding of facilitated mechanisms and provides useful guidance for designing new concept membranes for olefin/paraffin separation.