ANALYSIS OF BIMODAL FREQUENCY-RESPONSE BEHAVIOR OF P-XYLENE DIFFUSIONIN SILICALITE-1

The bimodal frequency-response spectra of p-xylene diffusion in silica lite-1 at 373 K have been analysed using the two independent diffusion processes, diffusion-rearrangement and non-isothermal diffusion model s. The FR parameters and equilibrium constants derived from these thre e models have been compared. it was found that the two independent dif fusion and diffusion-rearrangement models can well represent the exper imental data and give similar equilibrium constants and diffusion time constants. It may be due to the similar principles used in these two models that the molecules in the straight channels are mobile, while t hose absorbed in the sinusoidal channels are 'immobile'. On the other hand, the non-isothermal diffusion model gives a poor fit of the exper imental data. The non-isothermality parameter gamma obtained from data fitting is not consistent with the value calculated from the K consta nt obtained from the same fit. The frequency-response spectra obtained within the hysteresis loop region of the p-xylene isotherm at 348 K a re also discussed.