Synergy of Block and Microporous Polymers with Tailored Zeolitic Imidazole Frameworks for Membrane-Based Direct Air Capture.

Direct air capture (DAC) concerns the separation from air of carbon dioxide (CO2), the most significant greenhouse gas in the atmosphere, as a means of producing negative emissions. The challenge for the scientific and industrial communities is tremendous, and membrane technology is postulated as an efficient alternative in terms of energy, costs, and ease of implementation. Two polymers, commercial elastomeric PolyActive and high-performance polymer of intrinsic microporosity (PIM-1), with complementary permeation-selectivity features, to form both dense and thin film composite membranes, are studied to operate in the 500 ppm to 15% range of CO2 feed concentration and at 10-50 °C temperatures. A study on its synergistic pairing for a multistage DAC process is evaluated and to enhance the separation performance, the membranes are modified with zeolitic imizadolate frameworks (ZIF), capable of modification by solvent-assisted ligand exchange (SALE). A sequential SALE process is designed using two different ligands, one hydrophilic and the other hydrophobic, to modify nanosized ZIF-8 and produce a ZIF with tailored ligand composition. This is aimed at improving both the CO2 interaction and compatibility of MOF with the membrane polymer, achieving at 500 ppm a CO2 permeance of 1037 GPU with a CO2/N2 selectivity of 16.2.