Intracrystalline diffusivities of Y-type zeolite were measured at 323 to 573K for benzene, toluene, ortho- and para-xylene, n-hexane, n-heptane, n-octane and iso-octane (figure 17). Three model equations for calculating the intracrystalline

diffusivity were derived; each based upon one of the factors thought to control the diffusion: the probability for a molecule to jump from a super-cage to a neighbouring super-cage through a narrow window, the Lennard Jones (12.6)-potential induced by the van der Waals attraction and the electrostatic field formed in a supercage. The measured intracrystalline diffusivity was found to be well represented by model equations based upon the electrostatic field mechanism.

Measurement and Prediction of the Diffusivity of Y-Type Zeolite. T.Masuda, K.Fukada, Y.Fujikata, H.Ikeda, K.Hashimoto: Chemical Engineering Science, 1996, 51[10], 1879–88

Figure 17

Intracrystalline Diffusivity of Paraffins in Y Zeolite

(a: n-hexane, b: n-heptane, c: n-octane)