Modeling Adsorption and Transport Properties of Gases in Amorphous Polymers

Developing greener and more cost-effective polymer membranes for gas separation is of major interest within the industry of gas purification, in particular with regard to H₂ separation. In this work, molecular modeling was used to aid experimental efforts to optimize furan-based and fluorinated polymer membranes for high H₂ permeance selectivity. Preliminary findings for furan-based membranes showed potential for advancing this goal but further investigation yielded insufficient permeance selectivity of H₂ over N₂. Present findings show that fluorinated membranes are also a promising medium for gas separation with much higher selectivities for H₂ observed. To guide a detailed understanding of this behavior a molecular-level approach has been applied with both Monte Carlo and molecular dynamics simulation. Permeability is comprised of the product of solubility and diffusivity, both of which are highly accessible computationally. Gibbs-Ensemble Monte Carlo was used to calculate gas solubility and allowed for the determination of preferred adsorption sites within the polymer systems. Molecular dynamics simulation was then used to calculate rates of gas diffusion with each polymer studied. Fluorinated polymers of interest also possessed differing tacticities whose unique structures were examined in hopes that they may offer an additional degree of freedom for polymer optimization. Gaining an understanding of these processes on a molecular level will help guide the optimization of polymer structures and conditions needed to develop efficient separation membranes.