Db. Shah et al., INTRACRYSTALLINE DIFFUSION OF BENZENE IN SILICALITE - EFFECT OF STRUCTURAL HETEROGENEITY, Journal of the Chemical Society. Faraday transactions, 91(7), 1995, pp. 1143-1146
Citations number
22
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The sorption kinetics of benzene in silicalite have been measured grav
imetrically using large silicalite crystals of sizes 350 mum x 105 mum
x 105 mum and 270 mum x 70 mum x 70 mum in the temperature range 283-
343 K. Experiments were performed under conditions that ensured isothe
rmal operation with intracrystalline diffusion control. An analytical
expression for the Darken's correction factor (delta In P/delta In a)
was derived based on the Hill-de-Boer equation and was used to determi
ne the variation of corrected diffusivity with concentration. The tran
sport diffusivity varied significantly with the adsorbed-phase concent
ration but the corrected diffusivity was found to be essentially indep
endent of the concentration. However, at temperatures below the surfac
e transition temperature, a maximum in corrected diffusivity was obser
ved at an adsorbed-phase concentration of four molecules per unit cell
(uc). This maximum is the direct result of the type IV isotherm exhib
ited by the silicalite-benzene system below the surface transition tem
perature. It is proposed that the increase in corrected diffusivity at
the critical adsorbed-phase concentration of 4 molecules uc-1 arises
from reorientation of benzene molecules resulting in a much more effic
ient packing in the pore channel system.