Fe-mordenite for high-performance N₂ rejection

Nitrogen (N₂) rejection holds great significance in natural gas industry. However, it is challenging due to the similarities in chemical and physical properties between N₂ and methane (CH₄), making it crucial to find N₂-selective materials. Here, we report on Fe-mordenite (Fe-MOR), a modified zeolite with remarkable N₂/CH₄ separation performance, achieving a high N₂ uptake of 0.85 mmol/g at atmospheric conditions with a non-equilibrium N₂/CH₄ selectivity of 6.9. Due to the much slower CH₄ adsorption kinetics, the N₂/CH₄ kinetic selectivity is as high as 49.8. This kinetic difference was supported by density functional theory calculations, suggesting a higher energy barrier passing through Fe-containing channels for CH₄ than for N₂. The potential of Fe-MOR was manifested through pressure swing adsorption processes, achieving 99.1 % CH₄ purity and 94.9 % CH₄ recovery from a 10:90 N₂/CH₄ feed mixture. The corresponding energy consumption using this process for nitrogen rejection is only 10 % of that by cryogenic distillation.