Catalysts, general fluidized

The PSD is an indicator of the fluidization properties of the catalyst. In general, fluidization improves as the fraction of the 0-40 micron particles is increased however, a higher percentage of 0-40 micron particles will also result in greater catalyst losses. 

Reactors may be operated batchwise or continuously, e.g. in tubular, tubes in shell (with or without internal catalyst beds), continuous stirred tank or fluidized bed reactors. Continuous reactors generally offer the advantage of low materials inventory and reduced variation of operating parameters. Recycle of reactants, products or of diluent is often used with continuous reactors, possibly in conjunction with an external heat exchanger. 

Catalyst powders with carefully specified particle size distribution have been known to possess good fluidization characteristics. Generally, addition of fine particles to coarse particles tends to improve the latter s fluidization characteristics. Experiments were thus conducted on binary particle mixtures, each consisting of a fairly close particle size distribution. 

Reactions in moving-particle reactors in general, and in fluidized-bed reactors in particular, may be catalytic or noncatalytic. That is, the particles may be catalyst particles or reactant particles. Examples are as follows ... 

Figure 7-4 Slurry reactor (left) for well-mixed gas-solid reactions and fluidized bed reactor (center) for liquid-solid reactions. At the right is shown a riser reactor in which the catalyst is carried with the reactants and separated and returned to the reactor. The slurry reactor is generally mixed and is described by the CSTR model, while the fluidized bed is described by the PFTR or CSTR models.

Fluidize. In general to convert to a liquid state but in recent technology the term refers to processes in which a finely divided solid is caused to behave like a fluid by bringing it into suspension in s moving or liquid. The solids so treated are frequently catalysts and hence the term "fluid catalysts . In such a case the fluidized catalyst is brought into intimate contact and causes a desired reaction in the suspending liquid or gas mixture. Local over-... 

By use of this technique, it is possible to prepare fine spherical catalyst particles in the 10-100/rm diameter range, as arc required for typical fluidized-bed catalytic processes. In this technique used for large-scale catalyst manufacture, the feed is generally dilute hydrogel or sol that is sprayed from the top of a tower while hot air is blown in a cocurrcnt or countercurrent direction to dry the droplets before they reach the bottom of the tower. The fine droplets arc produced or atomized by pumping the hydrogel or sol under pressure cither... 

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