Reactor Choice for a Deactivating Catalyst

Considering the main features of fixed-bed and fluidized-bed reactors, it appears that the fluidized bed is a better choice for a rapidly deactivating catalyst. In these cases we are usually concerned with activity losses of less than 1 % in less than a minute of exposure (due to carbon deposition), and production rates of several hundred tons per day. The catalyst is usually regenerated in a second reactor called the regenerator. This is seldom the situation in organic technology, 

Restricting the treatment to isothermal plug flow, the continuity equation for a reactor containing a time-decaying catalyst through which reactant A is passing and reacting under diffusion-free conditions may be written as 

Now using the basic equation given by Equation 12.43, we develop the governing equations for fixed- and fluidized-bed reactors and compare their performances. 

The reaction time in a fixed-bed reactor is evidently the same as the total decay (or reaction) time /pi, when viewed from the standpoint of catalyst decay. Hence, the time can be normalized with respect to /pi, and Equation 12.43 recast in dimensionless form as 

Equation 12.44 can be simplified if the first term can be neglected. It is entirely reasonable to do so because the constant A in that term, which represents the ratio of feed transit time to decay time, is usually negligibly small. Thus Equation 12.44 reduces to 

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Heat transfer controlled Reactor choice for a deactivating catalyst Basic equation Eixed-bed reactor... 

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