New “Doubly Segmented” Ionene Membrane Increases Carbon Dioxide Permeability During Separation

The Science

CO₂ separation is a key aspect of natural gas purification, but conventional techniques are also high-emission processes. Membrane-based separation technologies offer a promising alternative to conventional methods like distillation and sorption methods, resulting in a nearly 90% reduction in energy consumption. In this study, a novel, doubly segmented PEEK-ionene membrane (PEEK = poly[ether ether ketone]) was loaded with a stoichiometric equivalent of an ionic liquid (IL; consists of a large organic cation and an inorganic anion and remains liquid at room temperature), resulting in a CO₂-selective membrane that enhances diffusion and solubility coefficients and thereby CO₂ permeability.

The Impact

To the best of the authors’ knowledge, this particular doubly segmented PEEK-ionene membrane architecture has not been reported before. Ionenes are ion-containing polymers where charged groups reside within the polymer backbone and are typically synthesized from two small molecules via the Menshutkin reaction. This study introduces a new and innovative approach to make polymer materials by utilizing a doubly segmented PEEK with imidazole ends, combined with other aromatic and aliphatic linkages. This advanced membrane increases CO₂ permeability, and its design may be extendable to other classes of high-performance polymers.

Summary

Membrane separation technology offers an alternative to traditional separation systems, such as distillation and sorption, due to its smaller footprint and mechanical simplicity. Current state-of-the-art polymer materials offer promising macromolecular structures and design strategies for high-performing CO₂ permeability with moderate permselectivity. Incorporation of “free” ILs into PEEK-ionene materials resulted in a mechanically stable, free-standing membrane that has improved permeability and selectivity because ILs have a strong affinity toward polar molecules like CO₂. PEEK-ionenes can hold up to 50 wt% of free IL within their structures, demonstrating properties akin to liquid-like materials, whereas commercial PEEK lacks the ability to retain an IL within its structure. This finding further validates that the ionic domains in a polymer exclusively interact with the free IL. This novel PEEK-ionene architecture creates unique opportunities for improved CO₂ separation performances and, with further study, may be able to outperform commercial polymers.

Contact

Jason Bara, University of Alabama, jbara@eng.ua.edu

Dave Heldebrant, Pacific Northwest National Laboratory, david.heldebrant@pnnl.gov

Funding

This work was funded by the Department of Energy, Office of Science, Basic Energy Sciences program, Chemical Sciences, Geosciences, and Biosciences Division, Materials Science and Separation Science programs through FWP 76830.