Model-based Derivation of the Safety Operating Limits of a Semi-batch Reactor for the Catalytic Acetoacetylation of Pyrrole Using a Generalized Sensitivity Criterion

G. Maria, A. Dan and D. Stefan

Abstract
The safe operation of a semi-batch catalytic reactor remains a sensitive issue when highly exothermic side reactions may occur, and various elements such as controllability, stability, safety, and economic aspects have to be considered in the process development. Nominal operating conditions are set to avoid excessive thermal sensitivity to variations in the process parameters. Several shortcuts or model-based methods are used to estimate the safety limits and runaway boundaries for the operating variables. Among them, the Morbidelli & Varma (MV) generalized sensitivity criterion proved to be a powerful method for assessing the critical conditions of a chemical process. The approached case study concerns a semi-batch reactor used for the acetoacetylation of pyrrole with diketene in homogeneous liquid phase. The catalytic process is known to be of high risk because of the very exothermic side-reactions involving reactive diketene and, as a consequence, it requires rigorous control of the operating parameters. Previous studies tried to maximize the isothermal reactor performances by using various optimal feeding policies of the co-reactant under semi-empirically derived safety constraints. The present work illustrates how the runaway critical conditions can be precisely assessed and the safe operating region well established based on an extensive safety analysis and an adequate process model of reduced complexity. In addition, by screening the influential variables, the study also proves the close connection between the operating safety limits and the process kinetics/thermodynamics, initial/inlet and cooling conditions, offering a better support for the reactor optimization.

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Keywords
Runaway conditions, semi-batch reactor, generalized sensitivity, pyrrole, diketene