The frequency response spectra of propane in silicalite-1 were measured at equilibrium pressures of 0.5 to 8.0Torr, at 303 to 363K, and analyzed by non-isothermal diffusion, two independent diffusion processes, and single-diffusion models. The first model was physically feasible for the explanation of the bimodal FR behaviour of this system, but the heat effect could 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 was attributed to two diffusion processes occurring separately in the sinusoidal and straight channels of the sorbent. The intracrystalline self-diffusion coefficient of propane in silicalite-1 determined in the present work was of the order of 10−9m2/s and decreases with increasing concentration of the adsorbate in the zeolite. This result was consistent with PFG NMR and previous FR studies.

Frequency Response Diffusion of Propane in Silicalite-1. L.Song, L.V.C.Rees: Microporous Materials, 1996, 6[5–6], 363–74