Water Resistant and Flexible MOF Materials for Highly Efficient Separation of Methane from Nitrogen

Abstract

The highly efficient separation of CH 4 /N 2 remains a great challenge, but it is vital to make the most of diverse natural gas resources and contributes to mitigating global warming. In this work, two isostructural metal−organic frameworks (MOFs), M-MA-BPY where M is Co and Ni, were elaborately selected and synthesized to serve the purpose. These MOFs were thoroughly characterized and found to have favorable framework flexibility, endowing them with narrow and uniform pore networks suitable for the adsorptive separation of CH 4 /N 2 . Further studies revealed the M-MA-BPY MOFs' excellent stability toward water and moist air. Pure gas adsorption experiments suggested they have decent CH 4 capacities (0.92 and 1.01 mmol•g −1 for Co-and Ni-MA-BPY), prominent CH 4 /N 2 selectivities (7.2 and 7.4 for Co-and Ni-MA-BPY, IAST selectivity with equimolar CH 4 /N 2 gas mixture) at 298 K and 1 bar, and desirable heats of adsorption for CH 4 (22.8 and 23.5 kJ•mol −1 for Co-and Ni-MA-BPY). Dynamic breakthrough experiments and multiple adsorption−desorption cycling tests for CH 4 /N 2 binary mixtures with different gas ratios of 5:95, 15:85, 30:70, and 50:50 (v/v) confirmed the high separation performance of M-MA-BPY MOFs. Together with their relatively simple synthesis and cheap raw reagents, this work demonstrates M-MA-BPY MOFs are very promising adsorbents for the capture of methane from low-quality natural gas resources in ambient conditions.

Separation and Purification of Hydrocarbons with Porous Materials

“…Two isostructural MOF materials, Co‐MA‐BPY and Ni‐MA‐BPY, with intriguing pillar‐layer structures, have prominent IAST CH 4 /N 2 selectivities of 7.2 and 7.4 (CH 4 /N 2 =50/50,v/v), respectively, at 298 K and 1 bar. [48] Lately, the zinc‐based pillar‐layer MOF Zn 2 (5‐aip) 2 (bpy) also has been effectively used for CH 4 /N 2 separation (Figure 3 ). [37c] Molecular simulation indicated that within its narrow pore environment, the spheroidal molecular structure of CH 4 could be more adequately packed than the linear molecular structure of N 2 .…”

Review on Flexible Metal‐Organic Frameworks

“…The selectivity and capacity for methane are verified from pure gas adsorption experiments and dynamic breakthrough studies for binary gas mixtures besides; the reusability of M‐MA‐BPY MOFs is confirmed by cycling breakthrough tests. The flexible MOF M‐MA‐BPY shows CH4 adsorption than N 2 because the polarizable structure of methane has strong interactions with the MOF as compared to the nitrogen molecule [59] . This MOFalso has an advantage over the pre‐existing MOFs for separation purposes.…”

Separation and Purification of Hydrocarbons with Porous Materials

“…Two isostructural MOF materials, Co-MA-BPY and Ni-MA-BPY, with intriguing pillar-layer structures, have prominent IAST CH 4 /N 2 selectivities of 7.2 and 7.4 (CH 4 /N 2 = 50/50,v/v), respectively, at 298 K and 1 bar. [48] Lately, the zinc-based pillar-layer MOF Zn 2 (5-aip) 2 -(bpy) also has been effectively used for CH 4 /N 2 separation (Figure 3). [37c] Molecular simulation indicated that within its narrow pore environment, the spheroidal molecular structure of CH 4 could be more adequately packed than the linear molecular structure of N 2 .…”