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Transport of aromatic molecules in NaY Zeolite powders
Author(s) -
Chmelka B. F.,
Gillis J. V.,
Petersen E. E.,
Radke C. J.
Publication year - 1990
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690361012
Subject(s) - zeolite , adsorption , chemistry , xenon , molecule , hexamethylbenzene , molecular sieve , crystallite , diffusion , chemical engineering , crystallography , catalysis , organic chemistry , thermodynamics , physics , engineering , benzene
Xenon‐129 NMR is used to probe macroscopic distributions of aromatic molecules adsorbed in a packed bed of 1‐μm NaY zeolite particles. Relative rates of guest transport through the intracrystalline (micro) and intercrystalline (macro) pores play a unique role in the axial distribution of sorbate molecules, such as hexamethylbenzene, in a zeolite powder. Xenon‐129 NMR spectra show that a sharp HMB adsorption front advances through a bed of dehydrated NaY crystallites at 523 K. However, at 573 K or in the presence of coadsorbed water, HMB species disperse through the bed without forming a sharp boundary between adsorption zones. When guest transport is controlled by pseudosteady‐state diffusion in the macropores, axial penetration of the bed by vapor‐phase guest species occurs in a sharp adsorption front. A shrinking‐core transport model then quantitatively estimates the intracrystalline diffusivities of HMB in dehydrated and partially hydrated NaY zeolite of 10 −11 and 10 −13 m 2 /s, respectively, at 523 K. Xenon‐129 NMR proves to be a powerful tool for probing adsorbed guest distribution in zeolites, allowing relative time scales to be established for transport of molecular guests in NaY powders.