Metal–organic frameworks (MOFs) can be advantageous over traditional materials in applications such as reaction catalysts, gas desulfurization and carbon dioxide capture. Building on MOFs diverse range of applications they are suited to act as separation media within a pressure swing adsorption (PSA) nitrogen generator. The properties of some MOFs; large surface area, high O2/N2 selectivity, large micropore volume and tunable pore size make MOFs ideal for this separation technique. These criteria, along with cost of synthesis and relative abundance in large quantities, were used to identify three viable materials within the MOF family: MIL-101 (Cr), ZIF-8, and UiO-66 (Zr). The material properties of the three MOFs are given, with a comparison made to the most commonly used separation media─carbon molecular sieve (CMS). Proposals are then presented for the potential ways MOF media could be used in a PSA nitrogen generator; either as a direct swap for CMS or utilizing the properties of MOFs to rearrange the generation system. The merits and limitations of MOFs when combined with binding material are analyzed in forms, such as mixed-matrix membranes (MMMs), powder, and monoliths. Nonseparation performance requirements of a viable PSA nitrogen generation MOFs are discussed, focusing on lifetime, robustness, and resistance to contaminants. The gaps in readiness before a MOF can be used within a manufactured PSA generator are identified with production repeatability, lack of testing within a generator, and uncertainty around the best MOF-based material structure forming the chief barriers to adoption.
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The authors acknowledge the support of Parker Hannifin and special appreciation to S. Kelly for providing adsorption expertise
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