(95b) Model-Based Design of Optimal Reactors Considering Catalyst Deactivation

Catalyst deactivation causes temporal and spatial activity gradients in the reactor. This gradient changes the corresponding optimal reaction conditions, and the reaction conditions further determine the future activity profile. This interplay is commonly neglected in reactor design, however, the optimal design based on the assumption of a given (constant) reaction kinetics is usually not the optimum with regard to the overall performance for the whole catalyst lifetime. This work aims to take this interplay explicitly into consideration and provides a new optimal reactor design methodology.

In this regard, a recently proposed reactor design methodology [1] based on the concept of elementary process functions [2] serves as the basis. The fundamental idea of the methodology is to track a fluid element traveling through the reactor and to change its state within. By continuously providing the fluid element with optimal fluxes, which are adjusted according to the state of the fluid element, optimal reaction conditions in the reactor are achieved at any time. The optimal fluxes can be calculated by solving a dynamic optimization problem, which is formulated based on the apparatus-independent model equations including balance equations, reaction and transfer kinetics, thermodynamics and design bounds.

To consider deactivation of the catalyst, an additional time scale for the catalyst needs to be added to the problem. A new optimization problem with multiple time/length scales is solved and the best reactor configuration and operating conditions are determined simultaneously. Dynamic operating conditions are included in order to achieve the best performance. In addition, the potential of new catalysts can be identified by comparing the overall performance over the whole catalyst lifetime. The new method has been exemplified on different case studies for heterogeneously catalyzed reactions with different rates of catalyst deactivation for validation and illustration of its advantage. In the present contribution, special focus is on the ethylene oxide synthesis as industrially relevant example.

References
[1] A. Peschel, H. Freund, K. Sundmacher, Methodology for the design of optimal chemical reactors based on the concept of elementary process functions, Ind. Eng. Chem. Res., 49 (2010) 10535-10548.
[2] H. Freund, K. Sundmacher, Towards a methodology for the systematic analysis and design of efficient chemical processes. Part 1. From unit operations to elementary process functions, Chem. Eng. Process., 47 (2008) 2051-2060.