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ZIF-67, a Co-substituted ZIF-8 structure, is investigated as a candidate for the industrially highly demanding propylene/propane separation, with the use of computational techniques for the first time. A new force field for the ZIF-67 framework based on density functional theory calculations is reported along with a recently developed force field for ZIF-8. The new force field is validated through comparison with structural data for ZIF-67 from the literature. Molecular dynamics simulations are reported for ZIF-67, showing a dramatic increase of propylene/propane corrected diffusivities ratio when compared to ZIF-8, implying a huge improvement in the separation of the mixture. The sieving mechanism of ZIF frameworks is investigated, and the results yield a dependency of the swelling motion of the gates from the bonding of the metal atom with its surrounding atoms. The presence of Co in the modified framework results in a tighter structure with a smaller oscillation of the gate opening, which leads to a narrower aperture. The results from the simulations and experiments in ZIF-67 place this new structure at the top of the candidates for propylene/propane separation.
Krokidas et al. (Thu,) studied this question.