Assessment of Isoreticular Metal−Organic Frameworks for Adsorption Separations:  A Molecular Simulation Study of Methane/n-Butane Mixtures

A wide variety of new nanoporous metal−organic materials are being synthesized by many research groups using supramolecular chemistry and directed assembly in a building block approach based on corner units and linker molecules. These materials may lead to revolutionary advances in adsorption separations because the properties of these materials may be tailored in a synthetically predictable manner. In this paper, we use molecular simulations to assess the suitability of one group of metal organic materials, namely, isoreticular metal−organic frameworks (IRMOFs), as adsorbents for mixture separations. By using grand canonical Monte Carlo simulations, the influence of the linker molecule on the adsorption of methane, n-butane, and their mixtures is determined. Detailed analysis of the energetics as well as the siting of molecules in the cavities allows us to resolve the impact of the linker molecules on the selectivity and to propose new, not yet synthesized materials, which show even higher selectivities. The predicted selectivities are as good as or better than experimentally observed selectivities in other adsorbents, suggesting that IRMOFs are promising materials for the separation of hydrocarbons.