Microporous Adsorbents for CH₄ Capture and Separation from Coalbed Methane with Low CH₄ Concentration: Review

A rapid increase in natural gas consumption has resulted in a shortage of conventional natural gas resources, while an increasing concentration of CH₄ in the atmosphere has intensified the greenhouse effect. The exploration and utilization of coalbed methane (CBM) resources not only has the potential to fill the gap in natural gas supply and promote the development of green energy, but could also reduce CH₄ emissions into the atmosphere and alleviate global warming. However, the efficient separation of CH₄ and N₂ has become a significant challenge in the utilization of CBM, which has attracted significant attention from researchers in recent years. The development of efficient CH₄/N₂ separation technologies is crucial for enhancing the exploitation and utilization of low-concentration CBM and is of great significance for sustainable development. In this paper, we provide an overview of the current methods for CH₄/N₂ separation, summarizing their respective advantages and limitations. Subsequently, we focus on reviewing research advancements in adsorbents for CH₄/N₂ separation, including zeolites, metal-organic frameworks (MOFs), and porous carbon materials. We also analyze the relationship between the pore structure and surface properties of these adsorbents and their adsorption separation performances, and summarize the challenges and difficulties that different types of adsorbents face in their future development. In addition, we also highlight that matching the properties of adsorbents and adsorbates, controlling pore structures, and tuning surface properties on an atomic scale will significantly increase the potential of adsorbents for CH₄ capture and separation from CBM.