DIFFUSION OF BENZENE, P-XYLENE AND THEIR MIXTURE IN SILICALITE-1 USING A FREQUENCY RESPONSE TECHNIQUE

Abstract

The diffusion of p-xylene, benzene and their mixtures in silicalite-1 has been studied using the frequency response (FR) method. Various intracrystalline diffusion processes; e.g. the co-diffusion of binary mixtures and the adsorption resistance at the external surface of crystals have been extracted from these results. The FR data of p-xylene, benzene and their mixtures at 395 K and the loadings of 0.5-2 molecules per unit cell show that (i) the diffusivity of p-xylene is more than one order of magnitude larger than that of benzene, (ii) in the system of p-xylene/silicalite-1, two intracrystalline diffusion processes were observed, which are related to the different diffusivities of p-xylene in the straight and sinusoidal channels of silicalite-1, and (iii) in the benzene/p-xylene mixture/silicalite-1 systems, the external film resistance of p-xylene diffusion was found to increase with increase in the partial pressure of benzene, and the diffusivity of p-xylene decreased. The activation energy of p-xylene diffusion in the straight channels is 19±2 kJ/mol, which is smaller than 24±2 kJ/mol of benzene. The activation energy of p-xylene diffusion in the sinusoidal channels was found to be 35±4 kJ/mol, i.e. almost twice as larger as in the straight channels.