(353b) High-Performance Non-Aging Rubbery Thin Film Composite Membranes for Post-Combustion CO2 Capture: From Material Synthesis to Field Demonstration

The U.S. government is targeting a net-zero carbon-emission economy by 2050, offering an exciting opportunity for membrane-based post-combustion CO₂ capture from industrial point sources. Given that industrial flue gas (mainly a CO₂-N₂ mixture) has low CO₂ partial pressures (about 0.05-0.3 bar) and high volumetric flowrates, high-permeance and CO₂-selective membranes are needed to make membrane technology an economically viable option for large-scale deployment. Thin film composite (TFC) membranes, comprised of a thin selective layer and a porous support layer, are necessary for practical implementation because they can provide high permeance while minimizing the use of selective materials. Currently, most studies of TFC membranes for CO₂/N₂ separation focus on developing ultra-high permeability selective materials (e.g., polymers of intrinsic microporosity (PIMs) and mixed-matrix membranes) while relying on commercial ultrafiltration membranes as a membrane support. These material combinations encounter several challenges in realization as high-permeance TFCs, such as accelerated physical aging of PIM-based thin selective layers, difficulties in forming defect-free mixed-matrix thin films, and significant mass transfer resistance imposed by membrane supports. To overcome all of those issues, this study reports the rational design and fabrication of a highly permeable non-aging TFC membrane achieved by: (i) synthesizing a high-performance rubbery polyphosphazene-based selective material; (ii) developing a high-porosity membrane support; and (iii) optimizing coating methods to assemble the two materials into scalable membranes. The novel selective layer material shows mixed-gas CO₂ permeability of 930 Barrer and CO₂/N₂ selectivity of 44, exceeding the 2008 Robeson upper bound. Furthermore, this material exhibits not only excellent performance stability under conditions up to full humidity, but also maintained its separation properties in a 360-hour field demonstration at the U.S. Department of Energy’s National Carbon Capture Center using both natural gas and coal flue gas. The high molecular weight (M_w > 10⁶ Dalton) of the polymer makes it possible to cast ultra-thin (100–300 nm) selective layers on our proprietary membrane support, which was optimized to exhibit negligible transport resistance (i.e., high N₂ permeance of 3×10⁵ GPU and high surface porosity of 20%), a smooth coating surface (i.e., small surface pores of <40 nm), and compatibility with a wide variety of coating solvents. The resulting TFC membrane from optimized thin-film coating methods yields remarkably high CO₂ permeance of 4,500 GPU and CO₂/N₂ selectivity of 34, and more importantly, there is no reduction in gas permeance when challenged with a 1000-hour physical aging test. This promising technology is currently being submitted for a U.S. patent and is being scaled up in a roll-to-roll fabrication process. This presentation will also cover the design and construction of membrane modules and membrane testing equipment for an upcoming scaled-up field demonstration of capturing CO₂ from the blast furnace waste gas of a steel mill from a major steel producer in the U.S., which will be the first demonstration of membrane-based CO₂ capture for this application.