Orthogonal-array dynamic molecular sieving of propylene/propane mixtures

Rigid molecular sieving materials work well for small molecules with the complete exclusion of large ones1–3, and molecules with matching physiochemical properties may be separated using dynamic molecular sieving materials4–6. Metal–organic frameworks (MOFs)7–9 are known for their precise control of structures and functions on a molecular level10–15. However, the rational design of local flexibility in the MOF framework for dynamic molecular sieving remains difficult and challenging. Here we report a MOF material (JNU-3a) featuring one-dimension channels with embedded molecular pockets opening to propylene (C3H6) and propane (C3H8) at substantially different pressures. The dynamic nature of the pockets is revealed by single-crystal-to-single-crystal transformation upon exposure of JNU-3a to an atmosphere of C3H6 or C3H8. Breakthrough experiments demonstrate that JNU-3a can realize high-purity C3H6 (≥99.5%) in a single adsorption–desorption cycle from an equimolar C3H6/C3H8 mixture over a broad range of flow rates, with a maximum C3H6 productivity of 53.5 litres per kilogram. The underlying separation mechanism—orthogonal-array dynamic molecular sieving—enables both large separation capacity and fast adsorption–desorption kinetics. This work presents a next-generation sieving material design that has potential for applications in adsorptive separation.