In the last two decades, several novel metal-organic frameworks (MOFs) structures with the greatest porosity, very high sorption capability and high surface area never observed in other crystalline porous materials have been synthesized. These unique features have made MOFs ideal candidates for a wide range of potential applications which include light gas molecules separations. In this regard, one of the most important processes in petroleum refining is the separation of olefin-paraffin gas mixtures. This task is currently achieved via cryogenic distillation, making it an extremely expensive procedure both from an energetic and economic point of view. In the attempt to reduce such costs, the use of materials such as MOF-74, able to act as selective sorption frameworks is among the most promising alternatives. This work provides for the first time a detailed description of different diffusion processes of CH4, C2H2, C2H4, C2H6, and H2O along and within the cavity of MOF-74-Mg. Together with our recent investigations on heats of adsorption, lateral interaction, and IR frequency shifts, a quantum mechanical comprehensive description of the binding processes of these molecules in MOF-74-Mg is now available at periodic boundary conditions approach. The molecular diffusion is modeled via climbing-image nudge elastic band (CI-NEB) simulations coupled with density functional theory (DFT). Long-range interactions driving the adsorption and diffusion processes of the gas molecules are taken into consideration by adopting the Van der Waals functional (vdW-DF) together with ultra-soft pseudopotentials as implemented in the Quantum Espresso package.

Diffusion processes of small hydrocarbons in MOF-74-Mg addressed via CI-NEB periodic calculations

254th National Meeting (2017)

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