(704d) Multi-Scale Simulation of Ionic Polyimide Composite Membranes Based on Structural and Electrostatic Maps
AIChE Annual Meeting
2019 AIChE Annual Meeting
Computational Molecular Science and Engineering Forum
Practical Applications of Computational Chemistry and Molecular Simulation II
Thursday, November 14, 2019 - 1:15pm to 1:30pm
Based on a molecular-level description of the i-PI membrane, MD and GCMC simulations are used to generate a lattice model of the pore structure and the local electrostatic environment relevant to the diffusing gas molecules (CO2/CH4). This discretized membrane information is used to populate a comprehensive KMC model that can be used to make predictions of gas separation performance on experimentally-relevant time scales. Using this KMC model, we can predict permeability, selectivity, and other transport behavior and connect these metrics directly to the ongoing experimental synthesis work.
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. Overall, we find that some of the commonly-used design equations for membrane performance provide inconsistent predictions, as compared to our multi-scale simulation analysis that can capture important molecular-level details (pore blocking, neighbor interactions, pore percolation, etc.).