Orthogonal-array dynamic molecular sieving of propylene/propane mixtures

摘要

Rigid molecular sieving materials work well for small molecules with the complete exclusion of large ones~(1-3), and molecules with matching physiochemical properties may be separated using dynamic molecular sieving materials~(4-6). Metal-organic frameworks (MOFs)~(7-9)are known for their precise control of structures and functions on a molecular level~(10-15). 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 (C_(3)H_(6)) and propane (C_(3)H_(8)) 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 C_(3)H_(6)or C_(3)H_(8). Breakthrough experiments demonstrate that JNU-3a can realize high-purity C_(3)H_(6)(≥99.5%) in a single adsorption-desorption cycle from an equimolar C_(3)H_(6)/C_(3)H_(8)mixture over a broad range of flow rates, with a maximum C_(3)H_(6)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.