Study of a silicon carbide catalytic heat-exchanger reactor for titanium-catalyzed epoxidation of alkenes: Experimental and modeling insights

This work investigates a milli-structured silicon carbide heat-exchanger (HEX) reactor for the epoxidation of cyclohexene over heterogeneous titanium-based catalysts. The channels in this reactor allow for the arrangement of catalyst particles as milli-fixed bed reactors in series. Experimental investigations were combined with residence time distribution analysis, kinetic modeling, and multiphysics simulations to evaluate the performance of the continuous-flow system for two different catalyst supports: silica and silicon carbide extrudates. Batch-derived kinetic data for the Ti-SiO 2 catalyst were successfully transposed to the continuous system by equating the catalyst-liquid contact times. The milli-fixed bed HEX reactor was then used to evaluate the reaction kinetics of the Ti-SiC catalyst. For both catalysts, epoxidation proceeded according to the Eley-Rideal mechanism with inhibition, but with different activation energies due to internal diffusion limitations. The thermal effects inside the reactor were further analyzed using pseudo-homogeneous 1D and 2D axisymmetric models, and an original 1D-3D hybrid approach including temperature gradients within the solid structure of the reactor. Simulations showed how the SiC structure efficiently removed heat from the system. Moreover, the use of SiC as catalyst carrier not only reduced internal diffusion limitations, but also helped maintain near-isothermal conditions inside the milli-fixed bed for severe conditions, including solvent-free operation. The results highlight how combining milli-structuration with a high thermal conductivity material, such as SiC for both reactor construction and catalyst support, enables safe and efficient operation, even for highly exothermic catalytic reactions.