Separation of CH₄/N₂ on ZIF-8 adsorbent and its thermodynamic properties

With triethylamine (TEA) as structure directing agent, ZnSO₄ as metal ion source and water as the solvent, zeolitic imidazolate framework-8 (ZIF-8) adsorbent was prepared by hydrothermal synthesis and used in the separation and enrichment of exhausted coal-bed methane. XRD, physical adsorption, dynamic adsorption equilibrium and inverse gas chromatography (IGC) methods were employed to characterize the physical structure, chemical stability, adsorption and separation performance of the ZIF-8 adsorbent; the adsorption thermodynamics of CH₄ and N₂ on it was also considered. The results indicated that ZIF-8 structure is stable in the acid, alkali and strongly polarized solvent. At 298 K, the separation factor of the ZIF-8 adsorbent towards CH₄/N₂ is up to 3.4, which is comparable to activated carbon; however, ZIF-8 should be more promising in practical application, because the adsorption heat over it is about 20% lower than that over activated carbon.