Page 37 - Principles of Catalyst Development
P. 37

STRUCTURE  OF  CATALYSTS


            What  They  Contain







           2.1.  CATALYST  ENGINEERING

           The ability to engineer desired functions into particles is perhaps the ultimate
           achievement  of the  catalyst  designer.  In  many  cases,  direct  and  obvious
           procedures  are  sufficient;  in others, more  subtle  and innovative measures
           are  called for.  Although catalyst designs tend to  evolve slowly  as  process
           experience accumulates, anticipating future problems will decrease develop-
           ment time.
               In this chapter, we examine the architecture or structure of the catalyst;
           what it contains and why.


           2.2.  THE  BALANCED  PARTICLE-A  COMPROMISE


               Correct formulation of the catalyst is a compromise between good fluid
           flow, activity, and stability. The relative importance of these factors depends
           upon the  reaction,  reactor  design,  process  conditions,  and economics.  In
           Fig.  2.1,  these  are  represented  as  three  sides  of a  triangle  to  emphasize
           mutual dependence and interaction.
               Good  flow  distribution  and  low  pressure  drop  are  achieved  through
           proper selection of the shape and size of the particle, (34) mechanical strength
           during  manufacture.  (35)  These  are  questions  of formulation-making  the
           particle-and must  be  matched to  demands  of the  process  for  which  the
           catalyst is intended. Generally, the greater the severity of process conditions
           (e.g.,  heavier feedstocks,  higher temperatures  and  pressures,  larger space
           velocities)  the greater these demands become.  For example, the  preferred

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