Optimal design of an autothermal membrane reactor coupling the dehydrogenation of ethylbenzene to styrene with the hydrogenation of nitrobenzene to aniline

Coupling the dehydrogenation of ethylbenzene to styrene with the hydrogenation of nitrobenzene to aniline in a catalytic fixed bed membrane reactor has the potential for significantly improving both processes (Abo-Ghander et al., 2008. Modeling of a novel membrane reactor to integrate dehydrogenation of ethylbenzene to styrene with hydrogenation of nitrobenzene to aniline. Chemical Engineering Science, 63 (7), 1817-1826). In a continuing effort to realize this potential, an optimal design is sought for a co-current coupled flow, catalytic membrane reactor configuration. To achieve this objective, two conflicting objective functions, namely: the yield of styrene on the dehydrogenation side and the conversion of nitrobenzene on the hydrogenation side, are considered. The total number of the decision variables considered in the optimization problem is 12, representing a set of operating and dimensional parameters. The problem is solved numerically by two deterministic multi-objective optimization approaches: the normalized normal constraint method and the normal boundary intersection method. It was found that the integrated reactor system can be operated to produce a maximum styrene yield of 97% when production of styrene is emphasized and, on the other hand, up to 80% of nitrobenzene conversion when nitrobenzene conversion is concentrated on. The resulting sets of Pareto optimal solutions obtained by both techniques are shown to be identical. Qualitative explanations are provided for the effect of the decision variables on both objectives.