(The) effect of chemical reaction on effectivediffusivity within biporous catalysts

Abstract

The effect of chemical reaction on the effective diffusivities within mono-and bi-distributed porous catalyst was investigated experimentally and theoretically. An experimental method was developed to study the adsorption and diffusion of reactant and product with chemical reaction by simultaneously analyzing the responses of both product and reactant to small perturbation in the inlet of a recycle reactor. Zeolite Y is used as catalyst, of which three types, LiY, NaY, and KY, are prepared by exchanging the cation. For each type, powder and binderless spherical pellets are used to study the contribution of micro and macropore diffusion to the overall mass transfer. The reaction used is the isomerization of cyclopropane in which molar volume does not change. To study the effect of reaction on the effective diffusivity, the knowledge of precise adsorption and diffusion characteristics is necessary under both nonreactive and reactive conditions. The first experimental part deals with the measurements of equilibrium adsorption coefficients and diffusivities under nonreactive condition. In the second part of experiments adsorption coefficient effective diffusivities in macro- and micropore, and reaction rate constant are measured under reaction condition using recycle reactor and compared with the values obtained under nonreactive condition. The equilibrium adsorption constant obtained ranged from 49.6 to 8995 $cm^3$/g in the range of temperature between 30℃ and 200℃. The isosteric heat of adsorption was also found to increase in the order, LiY ＜ NaY ＜ KY, and ranged from 7.5 to 8.7 Kcal/g-mole. The intraparticle diffusivities are measured by constant volumetric dynamic sorption method at temperatures between 30℃ and 70℃. The values obtained ranged from 3.75x$10^{-13}$ to 2.39x$10^{-11}cm^2$/sec and increased in the order, KY＜NaY＜LiY. The activation energy varied from 12.1 to 13.5 Kcal/mole, increasing in the order, LiY＜NaY = KY. The results show that the diffusiv...