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Hexane Isomers in Faujasite: Anomalous Diffusion and Kinetic Separation

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posted on 15.06.2017 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 (Ds) 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 Ds among all the isomers. This anomalous dependence of Ds as well as the computed activation energies Ea are in excellent agreement with the predictions of the levitation effect. These findings also explain the trends in Ea 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 Ds at different temperature ranges. n-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.