Scale-up of Stirred-Tank Batch Reactors-Runaway Reactions

5 Scale-up of Stirred-Tank Batch Reactors-Runaway Reactions 

In general, the histories of temperature, concentrations and mixing conditions in a full-scale reactor differ significantly from those in a laboratory reactor. Therefore, it is not surprising that selectivities usually change upon scale-up, as a result of undesired side reactions, unless proper measures have been taken. 

The influence of heat transfer on yield and selectivity in scaling up batch and semibatch reactors will be illustrated using a series reaction, taking place in an ideal jacketed stirred-tank reactor. This reaction is composed of two irreversible elementary steps, both exothermic and both with first order kinetics  

A is the reactant, P the desired product, and S an undesired by-product. ki and 2 are the reaction rate constants (s ). An example of such a reaction is the partial hydrogenation of an alkyne (A) to an alkene (P) and further to an alkane (S). Table 3 lists the variables used in the simulations. 

3 mol m s It was assumed, for purposes of simplicity, that the volume of the reaction mixture and its physical properties did not ehange during dosing. Clearly, this semibatch reactor performs well-the yield is ca 40%, better even than in the laboratory-size batch reactor. This is remarkable, because again the cooling was certainly not optimum. 

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