Control of intracrystalline diffusion in a bilayered metal-organic framework for efficient kinetic separation of propylene from propane

Kinetic adsorptive separation represents a promising solution to improve the energy efficiency in industrially important gas separation processes that are prevailingly accomplished by traditional thermal-driven methods. Currently, pore-size tuning is deemed as a universal strategy to prompt the kinetic adsorptive separation but still meets with limited success for gas mixtures with highly similar kinetic size. Here, we report the high-efficient kinetic separation of propylene (C3H6) and propane (C3H8) in a bilayered metal-organic framework Zn-ATA (ATA = deprotonated 5-aminotetrazole) for the first time by manipulating intracrystalline diffusion and surface permeation. Flake-like Zn-ATA crystals featuring millimetric dimension and highly oriented growth were directly synthesized by hydrothermal method. Unexpectedly, with the adsorption kinetics dominated by intracrystalline diffusion, the material affords quasi-molecular-sieving kinetic separation of C3H6 and C3H8 with an excellent selectivity of 60, which is 50 times higher than nanometric Zn-ATA crystals. Breakthrough experiments indicate that high-purity C3H6 (93%) can be separated from C3H6/C3H8 mixture within only one adsorption-desorption cycle, setting a new benchmark for kinetic C3H6/C3H8 separation. Density-functional theory calculations were conducted and revealed the separation mechanism at the molecular level.