Reverse shape selectivity of hexane isomer in ligand inserted MOF-74.

Separation of linear, mono-branched, and di-branched isomers is critically important in the petrochemical industry. In this computational study, we demonstrate that the ligand inserted Mg-MOF-74 structure leads to a reverse selectivity effect ( i.e. phenomenon that preferentially allows larger species molecules to permeate in a gas mixture) of hexane isomers in the resulting material. Molecular dynamics simulations suggest that strong confinement of the di-branched hydrocarbons in the small pores lead to reverse selectivity. Over a magnitude difference in diffusivity between linear alkanes and their di-branched isomers was observed, clearly showing the steric effects imposed by the pore structure.