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 & ctdot;pi 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). Aromatic ring-confined bi-nanotraps, along with the coupled thermodynamic-molecular sieving effects in metal-organic framework adsorbents, give rise to benchmark performance in the separation process for natural gas upgrade.