Considerations of Particle and Bed Characteristics

Characteristics of a catalyst particle include its chemical composition, which primarily determines its catalytic activity, and its physical properties, such as size, shape, density, and porosity or voidage, which determine its diffusion characteristics. We do not consider in this book the design of catalyst particles as such, but we need to know these characteristics to establish rate of reaction at the surface and particle levels (corresponding to levels (1) and (2) in Section 1.3). This is treated in Section 8.5 for catalyst particles. Equations 8.5-1 to -3 relate particle density pp and intraparticle voidage or porosity p. 

The shape of a particle may be one of many that can be formed by extrusion or tabletting. As in Chapter 8, we restrict attention to three shapes (solid) cylinder, sphere, and flat plate. The size for use in a packed bed is relatively small usually about a few mm. 

At the bed level (corresponding to level (3) in Section 1.3), we also use characteristics of density and voidage. The volume of the bed for a cylindrical vessel is 

The bulk density, pB, of the bed is the ratio of the total mass W to the total volume V  

---