CBE Seminar: Molecular Modeling of the Gas Separation Performance of Composite Ionic Polyimide + Ionic Liquid Membranes

Abstract:

Polyimides are at the forefront of advanced membrane materials for CO2 capture and gas purification processes.  Recently, “ionic polyimides” (i-PIs) have been reported as a new class of condensation polymers which combine structural components of both ionic liquids (ILs) and polyimides through covalent linkages. In this work, the CO2 separation characteristics of ionic polyimides are modeled using molecular dynamics simulations in combination with grand canonical Monte Carlo calculations.  The performance of neat i-PI systems is evaluated, as well as composite structures containing both i-PIs and various ionic liquids (ILs). The i-PI+IL composites are based on combinations of 1-n-butyl-3-methylimidazolium ([C4mim+]) cations with three common molecular anions: (bis(trifluoromethylsulfonyl)imide ([Tf2N-]), tetrafluoroborate ([BF4-]), and hexafluorophosphate ([PF6-]). It is found that 50 mol% IL inclusion can increase CO2/CH4 selectivity by 16% in [BF4-]-based materials and by 36% in [PF6-]-based materials from mixtures of 5% CO2 / 95% CH4. While the [BF4-]-based system shows higher CO2/CH4 selectivity, the [Tf2N-]-based system shows higher CO2/N2 gas selectivity. A comprehensive structural analysis (fractional free volume (FFV), pore size distribution, surface area, etc.) is used to highlight the underlying differences among the different i-PI+IL systems that lead to the different adsorption properties.

Biography:

Prof. Turner completed his B.S. in Chemical Engineering from Auburn University and his Ph.D. in Chemical Engineering from NC State University.  He spent several years in industry with Monsanto, Birmingham Steel, and Trinity Consultants.  He joined the University of Alabama as an assistant professor in 2003, and he is now a Professor and Department Head.  Over the past few years, he has been a visiting Faculty Fellow at NASA-Langley, the Naval Research Lab, and the Air Force Research Lab, Visiting Professor at Vanderbilt University, and an International Distinguished Professor at Shanghai University of Engineering Science.