Metal-organic frameworks with two different-sized aromatic ring-confined nanotraps for benchmark natural gas upgrade

Recovery of light alkanes from natural gas is of great significance in petrochemical production. Herein, a promising strategy utilizing two types of size-complementary aromatic ring-confined nanotraps (called bi-nanotraps here) is proposed to efficiently trap ethane (C₂H₆) and propane (C₃H₈) selectively at their respective sites. Two isostructural metal-organic frameworks (MOFs, SNNU-185/186), each containing bi-nanotraps decorated with six aromatic rings, are selected to demonstrate the feasibility of this method. The smaller nanotrap acts as adsorption sites tailored for C₂H₆ while the larger one is optimized in size for C₃H₈. The separation is further facilitated by the large channels, which serve as mass transfer pathways. These advanced features give rise to multiple C-H⋯π interactions and size/shape-selective interaction sites, enabling SNNU-185/186 to achieve high C₂H₆ adsorption enthalpy (43.5/48.8 kJ mol^-1) and a very large thermodynamic interaction difference between C₂H₆ and CH₄. Benefiting from the bi-nanotrap effect, SNNU-185/186 exhibits benchmark experimental natural gas upgrade performance with top-level CH₄ productivity (6.85/6.10 mmol g^-1), ultra-high purity and first-class capture capacity for C₂H₆ (1.23/0.90 mmol g^-1) and C₃H₈ (2.33/2.15 mmol g^-1).