TRANSPORT DIFFUSION AND SELF-DIFFUSION OF BENZENE IN NAX AND CAX ZEOLITE CRYSTALS STUDIED BY ZLC AND TRACER ZLC METHODS

Citation
S. Brandani et al., TRANSPORT DIFFUSION AND SELF-DIFFUSION OF BENZENE IN NAX AND CAX ZEOLITE CRYSTALS STUDIED BY ZLC AND TRACER ZLC METHODS, Microporous materials, 7(6), 1996, pp. 323-331
Citations number
20
Categorie Soggetti
Chemistry Physical","Material Science","Chemistry Applied
Journal title
ISSN journal
09276513
Volume
7
Issue
6
Year of publication
1996
Pages
323 - 331
Database
ISI
SICI code
0927-6513(1996)7:6<323:TDASOB>2.0.ZU;2-L
Abstract
Transport and self-diffusion of benzene in NaX and CaX zeolite crystal s has been studied by zero length column (ZLC) and tracer ZLC methods. In order to investigate the possible intrusion of extracrystalline ma ss transfer limitations a series of experiments was performed in which the sample quantity, crystal size, sorbate partial pressure and the n ature of the purge gas (He or N-2) were changed. At higher sorbate pre ssures and with larger samples the intrusion of external effects becom es evident but, under properly selected conditions, with sufficiently large crystals, desorption rates are clearly controlled by intracrysta lline diffusion. Under these conditions there is good agreement betwee n the limiting transport and tracer exchange diffusivities, confirming the absence of any heat transfer limitation. Diffusivities for benzen e-NaX are consistent with earlier reported ZLC values but are substant ially smaller than the values obtained from PFG NMR self-diffusion mea surements. Diffusivities for benzene-CaX are somewhat smaller than for the NaX system but the trends with concentration are similar. In the presence of water vapour the diffusivity is increased slightly but the effect is not dramatic.