(581a) Coupling Exothermic and Endothermic Reactions in Adiabatic Reactors

Coupling exothermic and endothermic reactions in a single reaction vessel is one of the process intensification tools to improve the process efficiency and to reduce the size of the reactors. It is observed that in the direct mode of coupling, such as carrying out the exothermic and endothermic reactions simultaneously in a packed bed reactor or in a slurry reactor, there exists different operating regimes based on the relative magnitude of the rate of heat consumption and the heat generation rate. These reactors can qualitatively behave as an isothermal reactor, endothermic reactor or an exothermic reactor (in packed bed and slurry reactor) or these can exhibit a regime where the exothermic reaction is predominant in the initial section of the reactor followed by the endothermic reaction and vice versa (mainly in packed bed reactor). In the later cases of operating regimes, the exothermic and endothermic reactions compete with each other and the both the reactions take place within the catalyst pores. In such situations, the catalyst particles exhibit multiplicity. In this work, the boundary element method (BEM) based arc-length continuation technique is used to analyze the coupling of exothermic and endothermic reactions within the catalyst pore and the effect of the presence of endothermic reactions in reducing the range of multiplicity. This study is also extended to investigate the multiplicity in the slurry reactors (where the particle level model is coupled to the rector level model and solved using above BEM based technique). The robustness of BEM based continuation technique to determine the multiple steady states in the distributed parameter systems will be discussed.

We have also compared the steady state and dynamic performance of the slurry reactor and the packed bed reactor, for coupling exothermic and endothermic reactions, in different operating regimes. The existence of hot spot and cold spot in the packed bed reactor and the other operating regimes in the slurry reactor are analytically identified, apriori, for the limited cases and are presented. Some of the interesting dynamic behavior exhibited by these reactors, especially during the reactor start-up, is also presented which are important from the control point of view.