Leveraging Free Volume Manipulation to Improve the Membrane Separation Performance of Amine‐Functionalized PIM‐1
Abstract
Gas-separation polymer membranes display a characteristic permeability-selectivity trade-off that has limited their industrial use. The most comprehensive approach to improving performance is to devise strategies that simultaneously increase fractional free volume, narrow free volume distribution, and enhance sorption selectivity, but generalizable methods for such approaches are exceedingly rare. Here, we present an in situ crosslinking and solid-state deprotection method to access previously inaccessible sorption and diffusion characteristics in amine-functionalized polymers of intrinsic microporosity. Free volume element (FVE) size can be increased while preserving a narrow FVE distribution, enabling below-upper bound polymers to surpass the H2 /N2 , H2 /CH4 , and O2 /N2 upper bounds and improving CO2 -based selectivities by 200 %. This approach can transform polymers into chemical analogues with improved performance, thereby overcoming traditional permeability-selectivity trade-offs.
Investigation of the FVM approach was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Separation Science program under Award Number DE‐SC0019087. Functionalization and characterization efforts related to PIM‐NH2 were supported with a research agreement between the MIT Energy Initiative (MITei) and ExxonMobil. K. Mizrahi Rodriguez was supported by a Ford Foundation Pre‐doctoral Fellowship administered by the National Academies of Sciences, Engineering, and Medicine. A. X. Wu was supported through an NSF‐GRFP (DGE‐1122374). C. M. Doherty acknowledges support from the Veski Inspiring Women Fellowship. This work made use of the shared experimental facilities at MIT supported partly by the MRSEC program of the NSF under award number DMR‐1419807. Acknowledgements are also made to Walter Massefski, Bruce Adams, and John Grimes for their support in running solid‐state 13C NMR at the MIT Department of Chemistry Instrumentation Facility, Charlie Settens for his help with WAXS experiments, and the members of the Smith lab for their helpful suggestions related to sorption analysis, potential deprotection mechanisms, and data interpretation.
