Orthogonal-array dynamic molecular sieving of propylene/propane mixtures.

Rigid molecular sieving materials work well for small molecules with the complete exclusion of large ones, and molecules with matching physiochemical properties may be separated using dynamic molecular sieving materials. Metal-organic frameworks (MOFs) are known for their precise control of structures and functions on a molecular level. 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 (CH) and propane (CH) 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 CH or CH. Breakthrough experiments demonstrate that JNU-3a can realize high-purity CH (≥99.5%) in a single adsorption-desorption cycle from an equimolar CH/CH mixture over a broad range of flow rates, with a maximum CH 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.