Modeling and optimization of the industrial production of maleic anhydride from n-butane in catalytic fixed-bed reactors

Maleic anhydride (MSA) is mainly produced industrially by the selective oxidation of n-butane catalyzed on vanadium phosphorus oxide. The reaction is carried out in salt bath-cooled tube bundle reactors with up to 30,000 individual tubes. Due to the high exothermicity, the complex reaction kinetics and the small tube to particle diameter ratio, classical reactor models reach their limits in this process. As part of the project, a particle-resolved CFD simulation was therefore used to model the processes in the catalytic fixed bed in detail. The reaction is described by means of kinetics measured in the transport-limitation-free microreactor. A particular focus of the modeling was on the unevenly distributed flow velocity in the catalyst bed as well as on mass and heat transport within the fixed bed and the individual catalyst particles. The results of the CFD simulation were to be validated with experimental measurements.

The data generated from the CFD simulation can be used to identify weaknesses in the classic reactor models and improve them by modifying the models. The current main problem of industrial MSA synthesis from n-butane is the overheating of catalyst particles and the formation of a pronounced hot spot at the beginning of the fixed bed due to insufficient heat removal. This increases overoxidation and reduces the yield of MSA. CFD simulation can be used to investigate the influence of particle geometry on heat transport and MSA yield in order to find a more suitable particle shape for the process.