Mastering the Reaction Is the Key to Successful Design of Heterogeneously Catalyzed Reactive Distillation: A Comprehensive Case Study of Hexyl Acetate Synthesis

This work condenses the results of extensive experimental and modeling and simulation work on heterogeneously catalyzed reactive distillation and relates them to basic questions that must be answered in designing that complex integrated process. As a test case, hexyl acetate synthesis was chosen. The results summarized and evaluated here make it one of the most thoroughly and comprehensively studied examples of reactive distillation processes in the literature. In well-documented reactive distillation experiments, carried out in two scales, all relevant process parameters were studied. Modeling and simulation of the reactive distillation process, carried out both with the equilibrium stage and with the rate-based approach, are based on careful experimental and modeling work on the underlying vapor−liquid and liquid−liquid equilibria and the reaction equilibrium and kinetics. It is shown that the separation side of the process can be well described with conventional methods and that the equilibrium stage concept is sufficient. However, contrarily to other examples from the literature, the results for the system studied here clearly show that reaction kinetics measured in the laboratory, in this case with a plug flow reactor, cannot always directly be used to successfully describe the reactive distillation. Here, this was only possible after introducing a transfer factor, which proved to be constant over a broad parameter range. To clarify why the transfer factor is needed, trickle bed reactor experiments with the same packing as used in the reactive distillation were carried out. They show that a substantial part of the correction is caused by the fluid dynamic nonidealities in the packing. Using the transfer factor determined in laboratory scale allows a safe scale-up. Enlarging the reaction zone may give additional security, yet this is only an option if side reactions do not pose a problem, as shown by side product formation studies in the present work. A Damkoehler number is derived for the overall process, which can be used to support and assess the sizing of the reaction zone. All in all, this work shows that mastering the reaction is the key to successful design and scale-up and provides methods and experience needed for this end.