A stable ultramicroporous Cd(II)-MOF with accessible oxygen sites for efficient separation of light hydrocarbons with high methane production

Abstract

Metal-organic frameworks (MOFs) have garnered increasing attention for their effective separation of light hydrocarbons owing to their prominent separation selectivity and energy-efficient adsorption process. Here, we constructed a robust stable ultramicroporous Cd(II)-MOF ([Cd 5 (NTA) 4 (H 2 O) 2 ] (Me 2 NH 2 + ) 2 ·10H 2 O ( 1 )) with abundant accessible oxygen sites and investigated its adsorption performance for recovering high-purity methane (CH 4 ) from natural gas (NG) including C 1 (CH 4 )/C 2 (C 2 H 6 )/C 3 (C 3 H 8 ) mixtures. At ambient conditions, the theoretical equilibrium separation selectivity of 1 for C 2 H 6 /CH 4 (v/v = 10/85) and C 3 H 8 /CH 4 (v/v = 5/85) were found to be 34.3 and 223.8, respectively. The CH 4 /C 2 H 6 /C 3 H 8 (v/v/v = 85/10/5) mixture breakthrough experiments for 1 , conducted at 298 K, demonstrated effective separation performance with breakthrough times of up to 136 and 280 min·g −1 for C 2 H 6 and C 3 H 8 . Particularly, the CH 4 productivity (purity > 99.9 %) with 9.8 mmol·g −1 ranked the third in reported literatures, lower to the reported maximum value of 13.28 mmol·g −1 for Ni(TMBDC)(DABCO) 0.5 . Furthermore, Grand Canonical Monte Carlo (GCMC) simulations and first-principles density functional theory (DFT) calculations revealed that the high uptake and selectivity for C 3 H 8 and C 2 H 6 can be attributed to the abundant oxygen sites present in the pores. The dynamic breakthrough experiments comprehensively demonstrated that the proposed MOF can be an effective potential adsorbent for the practical separation of CH 4 /C 2 H 6 /C 3 H 8 mixtures.