Separation of CH4/N2 by an ultra-stable metal-organic framework with the highest breakthrough selectivity

Selectively separating CH4 from N-2 in natural gas purification is extremely important, but challenging. Herein, a copper-based metal-organic framework (MOF) NKMOF-8-Me with inert pore environment was reported for efficient CH4/N-2 separation. Adsorption results show that this material owns the highest CH4 uptake (1.76 mmol/g) and initial adsorption heat (Q(st)(0)) of CH4 (28.0 kJ/mol) as well as difference in Q(st)(0) (9.1 kJ/mol) among all materials with good water stability. Breakthrough experiments confirm that this MOF can completely separate the CH4/N-2 mixture with the highest CH4/N-2 breakthrough selectivity (7.8) reported so far. Theoretical calculations reveal the separation mechanism is the short average distance between CH4 and pore wall, resulting in a stronger adsorption affinity for CH4. In addition, this MOF exhibits highly structural stability and regeneration. These results guarantee this MOF as a promising adsorbent for the recovery of CH4 from coalbed methane.