Limitations of the Methods for Synthesis and Design: the Scale-Up Problem

It has been shown what can be achieved using the tools and methods developed in the last few years and especially in the first EU project. A question that is at least as interesting is what can, and cannot yet be achieved. In this context, attention should be focused on the main and secondary reactions of a simple esterification, see Fig. 2.9. For such a reaction system it is frequently the case, for time and cost reasons, that a complete kinetic model cannot be developed.

It may be of little consequence whether the process development chemist or engineer lacks an understanding of the secondary reactions on the basis of customary kinetic studies, since they frequently play hardly any role, as long as the distillation does not continuously shift the equilibrium. However, the careful process engineer will carry out experiments in a reaction column to verify the achievable purities and yields. And with the results of these experiments a scale-up problem exists. The reason is that in these experiments, reaction and mass transfer interact with one another. This interaction can be explained with reference to the main reaction, Fig. 2.10. If a separation process is superimposed on this reaction, the products water and ester (as an example, not valid for every ester) are separated off as low- and high-boilers respectively. However, the removal of the product accelerates the forward reaction. If the forward reaction is accelerated by raising the tempera-

Fig. 2.9 Main and side

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