FREQUENCY-RESPONSE TECHNIQUE MEASUREMENTS OF P-XYLENE DIFFUSION IN SILICALITE-1 AND SILICALITE-2

The diffusivity of p-xylene in silicalite-2 at 375-435 K and under equilibrium pressures of 0.431-1.29 Torr has been measured using a frequency response (FR) technique. In contrast to the p-xylene diffusion in silicalite-1 in which two diffusion processes have been found, the p-xylene diffusion in silicalite-2 shows only one diffusion process. The difference in the diffusion of p-xylene between silicalite-2 and silicalite-1 may be explained by the difference in their channel networks. The diffusion coefficient of p-xylene in silicalite-2 under the above conditions is in the order of 10(-11) m2 s-1, which is in good agreement with the diffusion coefficients of p-xylene diffusing in the straight channels of silicalite-1 obtained by the FR technique, but about one order of magnitude larger than the corresponding coefficients for diffusing in the sinusoidal channels of silicalite-1.