Analysis of particle and reactor-scale transport-kinetic interactions CO2 methanation

The design of an externally cooled fixed-bed reactor for CO2 methanation has been performed using microscopic forms of reaction engineering models that account for both particle-scale and reactor-scale transport-kinetic interactions. The predictions of various multicomponent specie flux models were compared to analyze the transport-kinetics interactions for a spherical catalyst particle shape. Flux models that included Knudsen diffusion resulted in an increase in both the CO2 conversion and CH4 yield as the pore diameter was reduced from 40 nm to 10 nm. Both 1-dimensional (1-D) and 2-dimensional (2-D) models for different catalyst shapes were also simulated to quantify particle-scale performance for CO2 methanation. A spherical catalyst shape was shown to produce a higher CH4 average concentration, while a 4-hole cylindrical shape has the lowest diffusion limitation. An externally cooled 1-D heterogeneous fixed bed reactor was simulated using spherical catalyst pellets. The high exothermicity of the CO2 methanation reaction creates significant hot spot formation. In order to control the axial reactor temperature within a user-prescribed bound, the optimal catalyst loading profile was determined by using an energy conservation equation-based approach. It is shown that the reactor hot spot temperature can be controlled within a reasonable range