S. Brandani et al., Counterdiffusion of p-xylene/benzene and p-xylene/o-xylene in silicalite studied by the zero-length column technique, IND ENG RES, 39(3), 2000, pp. 821-828
This paper describes the extension of the zero-length column (ZLC) method o
f measuring intracrystalline diffusion to the study of counterdiffusion. Th
eoretical ZLC response curves are derived for two simple models considering
chemical potential gradient as the driving force for transport with the in
trinsic mobilities either constant or inversely dependent on total loading.
Experimental response curves for benzene-p-xylene and p-xylene-benzene in
silicalite are shown to be consistent with the first of these models. The r
esponse curves conform quantitatively to the response predicted from this m
odel using the measured pure component diffusivities. However, the behavior
of the benzene-o-xylene and p-xylene-o-xylene systems does not conform to
the simple model. The retardation caused by o-xylene is substantially great
er than that predicted from the single-component diffusivity data. A simple
microdynamic explanation is suggested to account for this apparent anomaly
.