Catalytic reaction and fouling effects on intraparticle diffusion

Abstract

A pellet of gamma alumina with a unimodal pore structure and a mean pore radius of 47 Å was exposed to cycles involving counterdiffusing butenes and helium, counterdiffusing nitrogen and helium, and varying catalyst treatments. When butenes were present and the catalyst was active, the isomerization of 1-butene to cis- and trans-2-butene occurred. In the nonreacting nitrogen-helium system, the helium diffusion rate was about 11% less through an air-fouled catalyst than through the catalyst immediately after activation; it was about 13% less through the catalyst when butene-fouled than through the freshly activated catalyst. In the reacting butenes-helium system, the helium diffusion rate was about 17% less through the air-fouled catalyst than through the freshly activated catalyst; it was about 32% less through the butene-fouled catalyst than through the freshly activated catalyst. Only in the freshly activated catalyst was the helium diffusion rate in the reacting system predictable from the helium diffusion rate in the nonreacting system. It is proposed that the diffusion behavior differences between the reacting and nonreacting systems result from differences in adsorption characteristics of the fouled and active surfaces. The differences in adsorption characteristics in turn may cause different degrees of pore blockage. The experimental temperature was 154 °C, and the pressure range was 1–2.5 atm for the butenes-helium system, and 1–13 atm for the nitrogen-helium system.