Molecular simulations for adsorption and separation of natural gas in IRMOF-1 and Cu-BTC metal-organic frameworks

We use Monte Carlo simulations to study the adsorption and separation of the natural gas components in IRMOF-1 and Cu-BTC metal-organic frameworks. We computed the adsorption isotherms of pure components, binary, and five-component mixtures analyzing the siting of the molecules in the structure for the different loadings. The bulk compositions studied for the mixtures were 50: 50 and 90: 10 for CH₄-CO₂, 90: 10 for N₂-CO ₂, and 95: 2.0: 1.5: 1.0: 0.5 for the CH₄-C ₂H₆-N₂-CO₂-C₃H ₈ mixture. We choose this composition because it is similar to an average sample of natural gas. Our simulations show that CO₂ is preferentially adsorbed over propane, ethane, methane and N₂ in the complete pressure range under study. Longer alkanes are favored over shorter alkanes and the lowest adsorption corresponds to N₂. Though IRMOF-1 has a significantly higher adsorption capacity than Cu-BTC, the adsorption selectivity of CO₂ over CH₄ and N₂ is found to be higher in the latter, proving that the separation efficiency is largely affected by the shape, the atomic composition and the type of linkers of the structure.