Semibatch or Semiflow Reactors

For semibatch or semiflow reactors, all four of the terms in the basic material and energy balance relations [equations (8.0.1) and (8.0.3)] can be significant. The feed and effluent streams may enter and leave at different rates so as to cause 

It may be desirable to operate in semibatch fashion to enhance reaction selectivity or to control the rate of energy release by reaction via manipulation of the rate of addition of one reactant. Other situations in which semibatch operation is employed include a variety of biological fermentations where various nutrients may be added at predetermined rates to achieve optimum production capacity and cases where one reactant is a gas of limited solubility that can be fed only as fast as it will dissolve. 

By working in terms of total mass, the reaction term in equation (8.6.2) disappears because the principle of conservation of mass must be satisfied. 

There are a number of specific cases of equation (8.6.1) that are of potential interest for commercial applications. We wish to consider one mode of semibatch operation using Illustration 8.11 to indicate the general principles involved 

Reagent A undergoes an essentially irreversible isomerization reaction that obeys first-order kinetics  

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Semibatch or Semiflow Reactors. Semibatch or semiflow operations usually take place in a single stirred tank using equipment extremely similar to that described for batch operations. Figure 8.1 indicates some of the many modes in which semibatch reactors may be operated. 

Semibatch or semiflow processes are among the most difficult to analyze from the viewpoint of reactor design because one must deal with an open system under nonsteady-state conditions. Hence the differential equations governing energy and mass conservation are more complex than they would be for the same reaction carried out batchwise or in a continuous flow reactor operating at steady state. 

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