Molecular mechanism of selective adsorption and separation of n-butane/i-butane on MFI zeolite

Abstract

Abstract MFI zeolite is one of the most attractive molecular sieve materials for selective adsorption and separation of C4 hydrocarbon isomers. The correlation of channel structure and adsorption thermodynamics and kinetic behavior of butane isomers has been explored using Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results of single com-ponent and binary competitive adsorption isotherms of n-butane/i-butane at 273 K, 303 K, 343K, and 373 K substantiated the excellent low pressure loading and adsorption selectivity for n-butane on MFI zeolite. The density distribution maps and the RDFs data revealed that there are different preferential adsorption sites for n-butane and i-butane molecules in MFI zeolite. Due to the van der Waals repulsion occurring, the adsorption energy of i-butane is less than that of n-butane, which makes that i-butane cannot be apt to be adsorbed in the two channels, but preferentially in the cross channel of MFI zeolite. Moreover, the mean square displacement (MSD) and calculated diffusion coefficient proved that the diffusion rate of n-butane is faster than that of i-butane by more than two orders of magnitude. These findings clarify the molecular mechanism of selective adsorption and separation of n-butane/i-butane on the rational designed MFI zeolite-based materials.