Spray drying, attrition-resistant porous particles

Attrition-Resistant Porous Particles Produced by Spray Drying... 

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. 

Attrition-resistant microspheroidal catalyst particles for fluidized beds are manufactured by means of spray drying. The catalyst particles, for instance zeolite crystals, are suspended in an aqueous sol or hydrogel of binder particles that, after processing, serve as a mechanically strong and porous matrix. Typical binders are silica-alumina and alumina gels, clays (e.g. kaolin, bentonite), and... 

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