FREQUENCY-RESPONSE DIFFUSION OF PROPANE IN SILICALITE-1

The frequency response spectra of propane in silicalite-l were measure d at equilibrium pressures of 0.5-8.0 Torr and temperatures of 303-363 K and analysed by non-isothermal diffusion, two independent diffusion processes, and single-diffusion models. The first model is physically feasible for the explanation of the bimodal FR behaviour of this syst em, but the heat effect can be eliminated by reducing the coverage in the zeolite. Compared with propane, the bimodal form of the frequency response curves of p-xylene in silicalite-1 is attributed to two diffu sion processes occurring separately in the sinusoidal and straight cha nnels of the sorbent. The intracrystalline self-diffusion coefficient of propane in silicalite-1 determined in the present work is of the or der of 10(-9) m(2)s(-1) and decreases with increasing concentration of the adsorbate in the zeolite. This result is consistent with PFG NMR and previous FR studies.