Uptake into silicalite

Also, pyridine was reversibly adsorbed into the essentially nonacidic silicalite-1 (sample No. 4), which has the same MFI structure as H-ZSM-5, but no acid centers. A set of spectra of pyridine uptake into silicalite-1 was scanned in short intervals and is displayed in Fig. 13. 

The diffusion of the alcohols in silicalite with water as the carrier solvent in the LC system may be considered similar to the counterdiffusion of an adsorbate into silicalite already saturated with a less adsorptive solvent (23). The diffusivities thus measured by the HPLC technique depend on the properties of the sorbate, the adsorbent and the carrier solvent. The diffusivities reported in Table II are in the range of iO- to 10 cm /s. This is approximately in the same order of magnitude as those of pure vapor diffusion by the adsorption uptake measurements (6) and the GC measurements (7)... 

Fig. 13 Set of FTIR spectra of successive states of uptake of pyridine into silicalite-1 (sample No. 4)...

Adsorption and diffusion of linear and branched Ce alkanes in silicalite-1 were investigated by Zhu et al. (34,35). They also developed a mathematical model taking into account the thermodynamical factor for intercrystalline diffusivities, enabling the determination of intracrystalline diffusivity from the uptake curve operated outside the linear adsorption range, van Donk et al. (36) also made transient uptake measurements to investigate the diffusivity of -hexane in Pt/H-mordenite. 

Finally, the zeolite HZSM-5 and its aluminium-free analogue Silicalite I are placed into Group III. These adsorbents may be termed truly hydrophobic since their affinity for water vapour remains low over the entire range of p/p as shown by the small values of 0(o.oi) (0.95) Table I. The low uptake of water vapour exhibited by these zeolites is exemplified in Figure 3... 

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