Design of polyhedral cage-engineered MOFs for efficient methane purification from natural gas

The development of adsorbents with balanced adsorption capacity and selectivity is critical for achieving efficient adsorptive separation of CH 4 from natural gas, but it still remains challenging. The formation of large pores composed of polyhedral cages provides sufficient space for gas admission to ensure adsorption capacity, and creates pore confinement to maximize guest-host interactions for enhanced selectivity. Herein, the two iso-structured metal-organic frameworks were synthesized, which feature tailored cage dimensions and functionalized pore surfaces integrating N-containing groups and sulfate anions. At 298 K and 100 kPa, both MOFs exhibit high uptake for C 3 H 8 and C 2 H 6 but a negligible adsorption for CH 4 . Breakthrough tests demonstrate that both MOFs enable effective separation of C 3 H 8 /C 2 H 6 /CH 4 from the home-made gas mixture simulating raw natural gas, yielding CH 4 with a purity of > 99.9%. Crystal structure characterization and computational modeling demonstrate that the optimal cage size and polar surface microenvironment of Co-TPT-TATBA, induced by nitrogen-containing moieties and sulfate anions, facilitate favorable intermolecular interactions with C 3 H 8 and C 2 H 6 molecules—thereby directly underpinning its exceptional gas adsorption and separation capabilities. Furthermore, the good chemical stability renders the obtained MOFs an efficient adsorbent for CH 4 purification. • Two isostructural MOFs featuring typical polyhedral cage-like cavities have been successfully synthesized. • Co-TPT-TATBA and Ni-TPT-TATBA have remarkable adsorption capacities for C 3 H 8 (7.05 mmol/g and 9.02 mmol/g) and C 2 H 6 (3.85 mmol/g and 4.76 mmol/g) at 298 K and 1.0 bar. • Breakthrough experiments demonstrate that Co-TPT-TATBA achieves efficient separation of the ternary natural gas mixture C 3 H 8 /C 2 H 6 /CH 4 , yielding CH 4 with a purity of > 99.9% • Co-TPT-TATBA and Ni-TPT-TATBA show good chemical stability after immersion in aqueous solutions (pH = 4-10).