By extrapolation, the adsorptive diffusivity of 2,3-dimethylbutane in silicalite-1 at 373 to 473K was compared with the diffusivity deduced from diffusion-limited cracking reactions over large aluminated silicalite-l crystals at 673 to 773K. The volumetric method was used in the adsorption kinetics experiments. The cracking reactions were performed in a fixed-bed continuous-flow reactor. The reaction rates were limited by the intracrystalline diffusion of 2,3-dimethylbutane. Silicalite-1 was aluminated with gaseous AlCl3 at 773K. Electron microprobe analysis of polished crystals indicated that aluminum was randomly deposited throughout the silicalite-1 crystal, with elevated deposition on the external surface. Analysis of the 2,3-dimethylbutane cracking rates with the Thiele model predicted experimental reaction effectiveness factors that were close to theory. The activation energy for the reaction-limiting diffusivity (table 38) of 2,3-dimethylbutane in aluminated silicalite-1 was found to be much higher than the activation energy of the corresponding adsorptive diffusivity. It was shown that this was characteristic of the catalyst sample.

The Adsorptive and Reaction Limiting Diffusion of 2,3-Dimethylbutane in Large Crystals of (Aluminated) Silicalite-1. P.Voogd, H.Van Bekkum: Industrial and Engineering Chemistry Research, 1991, 30[9], 2123-33

Table 38

Reaction-Limiting Diffusivity of

2,3-Dimethylbutane in Silicalite-1