Hexane Isomers in Faujasite: Anomalous Diffusion and Kinetic Separation

2017-06-15T00:00:00Z (GMT) by Angela Mary Thomas Yashonath Subramanian
Adsorption and diffusion properties of the five hexane isomers in zeolite Y have been obtained from molecular dynamic simulations. The self-diffusivities (<i>D</i><sub>s</sub>) of the isomers exhibit an anomalous dependence on their molecular diameter, where the larger-sized doubly branched hexane isomer 2,2- dimethylbutane shows the maximum <i>D</i><sub>s</sub> among all the isomers. This anomalous dependence of <i>D</i><sub>s</sub> as well as the computed activation energies <i>E</i><sub>a</sub> are in excellent agreement with the predictions of the levitation effect. These findings also explain the trends in <i>E</i><sub>a</sub> of hexane isomers in zeolite BEA, which was observed by Bárcia et al. in their experimental study. The order of exit of different isomers from a zeolite Y column depends on the order of their <i>D</i><sub>s</sub> at different temperature ranges. <i>n</i>-Hexane shows a tendency to bend by increasing its gauche conformer population in order to reduce the energetic barrier it experiences at the 12-ring window of the zeolite Y cage.