Differential Recycle Reactors for the Investigation of Heterogeneously Catalyzed Gas-Liquid Reactions under Industrially Relevant Conditions

Knowledge of the kinetics of a chemical reaction is important for scale-up, reactor design, troubleshooting and process optimization. In order to directly transfer the kinetic information obtained from laboratory measurements to the production scale, the reaction conditions and especially the fluid dynamics must be similar in both scales and therefore have to be well defined. A reactor concept providing those well defined fluid dynamics is the differential recycle reactor (DRR) operated in batch mode. The reactor itself is a short tube filled with catalyst through which the liquid reaction mixture is passed along with the gas phase. The reaction mixture is then fed to a buffer vessel from which it is recycled back to the tubular reactor. In this work, we consider heterogeneously catalyzed gas-liquid reactions in fixed bed reactors. In this case, the internal mass and heat transfer between the phases in the laboratory reactor must be comparable to that in a production reactor. Using a combination of simulative and experimental methods, the reactor geometry was optimized to ensure similar fluid dynamic conditions in the DRR compared to the industrial scale fixed bed reactor. A key objective was to prevent maldistributions in the catalyst bed. To this end, experimental and simulative studies, including CFD simulations, were conducted to optimize the reactor diameter and outlet design. In a DRR, the ratio between the reactor volume in which the liquid phase is pre-saturated and the reactor volume in which the reaction takes place and the gaseous species is consumed is significantly larger than in an industrial fixed-bed reactor. Therefore, it is possible that the impact of resistance in the gas-liquid mass transfer on the reactions may be underestimated when experimental data from the DRR is employed to predict the behaviour of the industrial fixed-bed reactor. To assess this risk, a comprehensive simulative study was carried out, which identified conditions under which this risk is negligible. Finally, the suitability of the DRR for investigating industrially relevant reactions was demonstrated with a heterogeneously catalyzed selective ring hydrogenation. The results show that the optimization yielded a laboratory reactor which provides reliable kinetic data that can be used for the design and scale-up of industrial reactors.