(314d) Identification of Optimal Catalyst Distributions in Heat Exchanger Reactors

Reactors integrating endothermic and exothermic reactions in a single vessel such that, the exothermic reaction acts as the heat source to drive the endothermic reaction continue to garner industrial interest for process intensification. Two commonly encountered extremes in thermal behavior are (i) hotspot formation, occurring when heat generated by the exothermic channel is not consumed at the same rate by the endothermic channel, or (ii) reactor extinction, occurring when endothermic reaction heat duty exceeds that of the exothermic reaction rate(Frauhammer et al., 1999; Kolios et al., 2000). The most common method reported in literature for alleviating hotspot magnitude is to tailor the activity of the catalyst along the reactor length(Ramaswamy et al., 2006). In this work, the challenge of optimizing both endothermic and exothermic catalyst activity profiles in a heat exchanger reactor is addressed using optimal control theory by considering both catalyst distributions as inputs and defining an objective function that maximizes the sum of the conversion of both endothermic and exothermic reactions. A fundamental study is done to show that when gas-solid transfer resistances are negligible, the optimum consists of fully inert, fully active regions and/or constraint arcs. Several scenarios where optimizing catalyst distribution is shown to be beneficial to heat exchanger reactors are shown like separation of reaction zones, small exothermic reaction intervals, high endothermic reaction rates.

References

Frauhammer, J., Eigenberger, G., Hippel, L., Arntz, D., 1999. A new reactor concept for endothermic high-temperature reactions. Chemical Engineering Science 54, 3661-3670.

Kolios, G., Frauhammer, J., Eigenberger, G., 2000. Autothermal fixed-bed reactor concepts. Chemical Engineering Science 55, 5945-5967.

Ramaswamy, R., Ramachandran, P., Duduković, M., 2006. Recuperative coupling of exothermic and endothermic reactions. Chemical Engineering Science 61, 459-472.