A Stable Cu(I)-Based Ultramicroporous NKMOF-8-Br with High CH4 Uptake for Efficient Separation of CH4/N2 Mixtures

Due to the very close physical properties and kinetic diameters of CH4 and N2, the development of adsorbents for the efficient capture of methane from coal-bed methane (CBM) is a significant challenge. Porous materials can be used as adsorbents to separate CH4/N2 mixtures with low energy consumptions. However, most adsorbents suffer from poor stability and relatively low adsorption capacity of CH4, limiting their practical applications. Herein, we report a stable ultramicroporous Cu(I)-based metal–organic framework (MOF), NKMOF-8-Br, exhibits an excellent CH4 (1.84 mmol/g) adsorption capacity with a high CH4/N2 (50/50, v/v) selectivity (8.9), at 298 K and 1.0 bar. The CH4 adsorption capacity exceeds all water stable MOFs and other kinds of adsorbents used for CH4/N2 separation. Cyclic dynamic breakthrough experiments indicate that this sample can separate the CH4/N2 mixtures completely with good breakthrough regenerability. Therefore, it is a promising adsorbent for enriching CH4 from CBM.