Microspheroidal catalysts

The FCC unit uses a microspheroidal catalyst, which behaves like a liquid when properly aerated by gas. The main purpose of the unit... 

In recent years, the process has been modified to increase the yield of lower olefines, too. Continually improved since then, especially in the mid-1960s with the replacement of the original silica-alumina catalyst by a zeolite. The catalyst is now typically a zeolite Y, bound in a clay matrix. The feed is vaporized and contacted in a pipeline reactor with concurrently flowing microspheroidal catalyst particles. The catalyst is then separated from the hydrocarbon products and is continuously regenerated by burning off the coke in a fluidized bed. The process is licensed by UOP several hundred units are in operation worldwide. See also HS-FCC. 

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... 

Spray-dried microspheroidal catalyst introduced by Davison. 

High-alumina silica/alumina microspheroidal catalyst. 

Cince the first commercial H-Oil unit came on-stream at Lake Charles in 1963, a variety of feedstocks have been processed, including heavy cycle oils, atmospheric bottoms, vacuum bottoms, and cutback propane deasphalter bottoms. The unit has operated successfully with both microspheroidal and extrudate catalysts and has been expanded to 6000 bbl/day. 

Catalyst. Microspheroidal and extrudate catalysts have been used commercially. These catalysts consist of a combination of metals such as cobalt and molybdenum or nickel and molybdenum on an alumina support. An earlier publication reported that a 1/32 inch extrudate performs (3) better than a 1/16 inch extrudate (5). The most active catalyst is the one with the greatest surface area (6, 7). 

Among the most effective catalysts are the supported V-Cr-0 catalysts promoted with boron, phosphorus, and molybdenum developed by Mitsubishi Gas Chemical Co. in 1970s (64,65). Ammoxidation of toluene at 435°C produces ben-zonitrile at 85% yield, para-xylene ammoxidation yields 85% terephthalonitrile at a 395°C reaction temperature, and me a-xylene ammoxidation at 380°C gives an 83% yield of isophthalonitrile. These catalysts have been successfully prepared for fluid-bed reactor operation by using silica as a binder to provide the requisite attrition resistance. This is achieved by including colloidal silica sol in the catalyst slurry and then spray-drying to produce microspheroidal particles of the catalyst precursor. 

Burkhard E. Wagner and coworkers at Union Carbide characterized the fragmentation of silica-supported catalysts [49]. They proposed that catalysts supported on silica undergo a similar fragmentation pattern in which the silica pore volume fills with polyethylene and the shear forces of the particle growth fragments the silica particle into microspheroidal aggregates of 0.05-0.1 microns in diameter. 

Early silica/alumina catalysts contained 10-13% AI2O3, which, at the time, appeared to be optimum. Increased alnmina content had httle effect on activity and produced gasoline with a lower octane nnmber, while forming more coke. Powdered silica/alumina catalysts were used until spray-dried microspheroidal particles were introduced in 1948. 

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