(98b) Selective CO2 Separation By Facilitated Transport in Ionic Liquid Gel Membranes

Membrane-based gas separation represent an attractive low energy separation route to a wide range of gas and liquid based separations providing an improvement to the overall economic and environmental acceptability. High performance membranes offer the potential to provide game-changing process energy advances, provided that sufficiently high levels of selectivity and permeability can be achieved for the target separation. However, selectivity and permeability are typically inversely related and increasing the selectivity typically comes with a penalty of decreased permeability. One critical process is the separation and capture of CO₂ to reduce greenhouse gasses. Numerous membrane-based processes for CO₂ separation exist, but improvements in selectivity will continue to drive down costs. Thin, nonporous membranes or membrane coatings have been demonstrated with processes such as facilitated transport to enhance the selectivity for a range of important target gases. Facilitated transport membranes incorporating targeted redox species have been shown to provide significant benefits in selectivity, however, the permeability penalties persist even with extremely thin, nanometer thick membrane layers.

Mainstream conducted research on an electrochemically-driven facilitated transport membrane to provide both enhanced selectivity for carbon dioxide, while simultaneously driving the permeability of the target gas. To address these selectivity and permeability limitations, targeted biomimetic redox molecules are integrated into an ionic liquid-based gel membrane to provide controlled transport of CO₂ across the membrane and membrane electrode assemblies (MEAs). This presentation will discuss the simultaneous enhancement of the gas separation selectivity and permeability for separation of CO₂ from a range of mixed gas feed compositions using low power, low voltage electrochemically driven separation. The membrane was evaluated in a single 5 cm² cell and scaled to a five cell 54 cm² stack. Results will be presented on the impact of the configuration, applied field, and CO₂ concentration, achieving an increased permeability of up to 100 times the target CO₂ over the nitrogen and oxygen, significantly increasing its selectivity. We will demonstrate the effect of CO₂ concentration (410 ppm to 5%) in air, with resulting permeate gas concentrations of 54% CO₂ for 410 ppm CO₂ and 90% CO₂ for the 5% CO₂ in room air.