ABSTRACT
Crushing and screening constitute the procedure most frequently used on the laboratory scale to produce a granular material that can be examined in a laboratory-scale reactor. Frequently one reads of granules being used that are 4–8 mesh or 12–20 mesh, and this is in general a way in which they can be derived. Some catalysts, notably the iron molybdate types used for the oxidation of methanol to formaldehyde, suffer so severely during a pilling or extrusion operation that they are processed solely to produce a mat or lump of catalyst that is then granulated and screened and a useful screen size is selected for charging to even plant-scale converters. Ordinarily, the granular material is not sufficiently hard or abrasion-resistant, and certain hardening agents are included. As examples, colloidal silica or alumina gel derived from aluminum hydroxide are frequently used. Other hardening agents are colloidal zirconia, calcium aluminate, sodium aluminate, sodium silicate, magnesium hydroxide, and aluminum hydroxynitrate.
