Attrition-resistant porous microspheres

We spray dried the slurries in a Bowen Engineering Co. No.l Ceramic Type Spray Dryer. The spray dried products were screened to obtain active and selective attrition resistant powders made of 45 to 150 Jm diameter porous microspheres of the catalyst with a thin silica-rich peripheral layer. 

Figure 1. Diagrams illustrating two different concepts to confer attrition resistance to porous microspheres (PMS). (Reproduced with permission from Ref. 2. Copyright 1987 Elsevier. )...

Spray drying the slurry to form porous microspheres of attrition resistant catalyst, catalyst precursor or catalyst support particles. 

Supplementary to the aforesaid summary, the process of this process comprises forming a sufficiently stable slurry comprised of catalyst, catalyst precursor or catalyst support particles dispersed in a solution of a solute which consists essentially of an oxide precursor, spray drying the slurry to form porous microspheres, and calcining the spray dried microspheres. This process results in the formation of an oxide-rich layer at the periphery of each calcined microsphere. This oxide-rich surface layer is typically 5-10 [xm thick and contains substantially all the oxide provided by the oxide precursor solute. Since substantially all of the oxide is in the peripheral layer, good attrition resistance is attained with a small amount of oxide, that is, the weight of the oxide is about 3-15%, preferably about 5-12% (except as noted above... 

The small particle size of the silica is important not only in enabling the silica to flow to the peripheral region of the porous microsphere but also in forming the hard peripheral oxide-rich shell. Particles of silica 2-3 nm in diameter sinter together to some extent even under the temperature conditions encountered in a conventional spray drying process, whereas particles 10-100 nm do not sinter below 700-1000°C. As a result, attrition resistance of the catalyst, catalyst precursor or catalyst support particle is a function of the particle size and degree of aggreggation of the silica formed by dehydration. 

Discrete particles of silica 2-3 nm in diameter, such as those present in the polysilicic acid described above, form hard shells on the resulting porous microspheres under conventional drying conditions. The green attrition resistance, that is, the attrition resistance before calcinations, of the porous microspheres of, for example, a... 

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