Exploring the Potentials of Metal-Organic Frameworks as Adsorbents and Membranes for Separation of Hexane Isomers

Molecular modelling and computational science tools were employed to select a number of metal organic frameworks (MOFs) from a pool of 4764 structures to investigate and assess their kinetic and adsorption-based separation performances in separating hexane isomers. The self-diffusivities of all single-component isomers were obtained from molecular dynamics simulations at infinite dilution and at a loading of 4 molecules/unit cell and at several temperatures. The self-diffusivities of the binary mixtures of the hexane isomers were also computed to obtain the kinetic separation metrics. The diffusivities at infinite dilution and at 298 K show a variety of trends as a degree of branching in the chosen MOFs. The linear hexane diffuses faster than other isomers in majority of the MOFs. On the other hand, the MOFs considered here show reverse adsorption selectivity, with the dibranched isomers adsorbing more than the linear one. The diffusivities at infinite dilution, as a function of temperature, of all isomers in the MOFs considered in the present study show Arrhenius behavior. The activation energies calculated from the Arrhenius plots complement the diffusivities. Further, the performances of these chosen MOFs were assessed in separating the linear hexane from the two dibranched ones as well as the dibranched ones from each other. MOF IYIHUU shows the highest membrane selectivity of the dibranched hexanes over the linear one at 433 K and at a pressure of 10 bar. Several MOFs show membrane selectivity of 22DMB over 23DMB, close to two or more indicating their ability to distinguish the two dibranched isomers kinetically.