Efficient separation of CO₂ from CH₄ and N₂ in an ultra-stable microporous metal-organic framework

The efficient separation of CO₂ from CH₄ and N₂ is essential for the upgrading of biogas and reducing carbon emissions in flue gas, but is challenging in the energy industry. Developing ultra-stable adsorbents with high CO₂ adsorption performance in adsorption separation technology is deemed an effective solution for the separation of CO₂/CH₄ and CO₂/N₂. Herein, we report an ultra-stable yttrium-based microporous metal-organic framework (Y-bptc) used for the efficient separation of CO₂/CH₄ and CO₂/N₂. The single-component equilibrium adsorption capacity of CO₂ reached 55.1 cm³ g^-1 at 1 bar and 298 K, while the adsorption capacity of CH₄ and N₂ was almost negligible and thus resulted in a high adsorption ratio for CO₂/CH₄ (45.5) and CO₂/N₂ (18.1). GCMC simulations revealed that the μ₃-OH^- functional groups distributed in the pore cage of Y-bptc provide stronger adsorption sites for CO₂via hydrogen-bonding interactions. The relatively lower heat of adsorption of CO₂ (24 kJ mol^-1) further reduces the desorption regeneration energy consumption. Dynamic breakthrough experiments using Y-bptc for the separation of CO₂/CH₄ (1/1) and CO₂/N₂ (1/4) mixtures could obtain high purity (>99%) CH₄ and N₂, and the CO₂ dynamic adsorption capacities reached 52 and 31 cm³ g^-1, respectively. More importantly, the structure of Y-bptc remained intact under hydrothermal conditions. The high adsorption ratio, low heat of adsorption, great dynamic separation performance, and ultra-stable structure of Y-bptc make it one of the candidate adsorbents suitable for the separation of CO₂/CH₄ and CO₂/N₂ in real-world applications.