Numerical calculation of flow and reaction safety with different particle sizes in a fixed bed reactor for propene epoxidation with H2 and O2

For the explosive and strongly exothermic direct propene epoxidation with H2 and O2 to synthesize propylene oxide, maintaining uniform gas flow and moderate reaction in the packed bed reactor is of prime industrial and scientific significance. Herein, randomly packed beds of spherical particles were simulated with resolved particle 3D computational fluid dynamics (CFD) under industrial conditions. Effect of particle size (i.e., 6, 8 and 10 mm) on performance of gas-phase propene epoxidation was numerically simulated. The fluid flow and temperature fields were fully coupled to the species and reaction distribution, including reactions in the particles and on catalyst surface. Based on the results of velocity, pressure drop, temperature and species distribution, heat transfer together with catalytic performance inside the fixed bed reactor, it is found that PPD-6 (Packed Particle Diameter 6 mm) model has a more uniform flow distribution, higher thermal conductivity and a lower temperature compared with PPD-8 and PPD-10. In addition, as packed particle diameter increases, the heat transfer capacity reduces and the temperature rise increases. As a result, the maximum hot spot temperature for the PPD-6 model is about 3 and 8 K lower than PPD-8 and PPD-10 model, respectively. In addition, the PPD-6 model has a more uniform reaction rate within the particles compared with the PPD-8 and PPD-10 models due to short diffusion path and high mass transfer capacity. Therefore, the PPD-6 model shows superior safety together with optimum conversion and selectivity. This work harbors tremendous referential significance to the design and scale-up of industrial reactors for propene epoxidation.