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The enrichment and purification of coal-bed methane provides a source of energy and helps offset global warming. In this work, we demonstrate a strategy involving the regulation of the pore size and pore chemistry to promote the separation of CH4 /N2 mixtures in four nickel-based coordination networks, named Ni (ina) 2, Ni (3-ain) 2, Ni (2-ain) 2, and Ni (pba) 2, (where ina=isonicotinic acid, 3-ain=3-aminoisonicotinic acid, 2-ain=2-aminoisonicotinic acid, and pba=4- (4-pyridyl) benzoic acid). Among them, Ni (ina) 2 and Ni (3-ain) 2 can effectively separate CH4 from N2 with top-performing performance because of the suitable pore size (≈0. 6 and 0. 5 nm) and pore environment. Explicitly, Ni (ina) 2 exhibits the highest ever reported CH4 /N2 selectivity of 15. 8 and excellent CH4 uptake (40. 8 cm3 g-1) at ambient conditions, thus setting new benchmarks for all reported MOFs and traditional adsorbents. The exceptional CH4 /N2 separation performance of Ni (ina) 2 is confirmed by dynamic breakthrough experiments. Under different CH4 /N2 ratios, Ni (ina) 2 selectively extracts methane from the gaseous blend and produces a high purity of CH4 (99 %). Theoretical calculations and CH4 -loading single-crystal structure analysis provide critical insight into the adsorption/separation mechanism. Ni (ina) 2 and Ni (3-ain) 2 can form rich intermolecular interactions with methane, indicating a strong adsorption affinity between pore walls and CH4 molecules. Importantly, Ni (ina) 2 has good thermal and moisture stability and can easily be scaled up at a low cost (25 per kilogram), which will be valuable for potential industrial applications. Overall, this work provides a powerful approach for the selective adsorption of CH4 from coal-bed methane.
Wang et al. (Tue,) studied this question.