Why to Reduce the Accumulation

There are essentially two reasons to minimize the accumulation of the fed reactant. First, if the reactant B enters in side reactions, its concentration has to be maintained as low as possible for selectivity reasons. Some examples of such reaction schemes are given below  

It is clear that a low concentration of B will maximize the formation of the desired product P and minimize the formation of the secondary product S. This goal can be achieved with a semi-batch reactor where B is added progressively to the reaction mass. 

The second reason, for which the concentration of B should be maintained at a low level, is a safety related reason. A low concentration of B during the reaction 

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