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

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journal contribution
posted on 24.10.2019 by Xiao-Wei Liu, Yi-Ming Gu, Tian-Jun Sun, Ya Guo, Xiao-Li Wei, Sheng-Sheng Zhao, Shu-Dong Wang
The highly efficient separation of CH4/N2 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 CH4/N2. Further studies revealed the M-MA-BPY MOFs’ excellent stability toward water and moist air. Pure gas adsorption experiments suggested they have decent CH4 capacities (0.92 and 1.01 mmol·g–1 for Co- and Ni-MA-BPY), prominent CH4/N2 selectivities (7.2 and 7.4 for Co- and Ni-MA-BPY, IAST selectivity with equimolar CH4/N2 gas mixture) at 298 K and 1 bar, and desirable heats of adsorption for CH4 (22.8 and 23.5 kJ·mol–1 for Co- and Ni-MA-BPY). Dynamic breakthrough experiments and multiple adsorption–desorption cycling tests for CH4/N2 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.