Comparison of multi-component diffusion models in a single reactive particle

Catalytic particles commonly appear in many multiphase reactors in the chemical industry. The transport-reaction behaviour in the particle has a significant impact on the overall reactor performance. In this work, the diffusive transport in the particle is modelled with the rigorous Maxwell-Stefan equations and simple Fick-Wilke diffusion. Several Fick—Wilke formulations are compared to the Maxwell—Stefan model for a ternary system with either a parallel or consecutive reaction scheme, considering variations in rate constants and binary diffusion coefficients. These include: (1) a formulation that resolves all components, (2) three variants in which one component is not resolved, and (3) a flux-corrected variant that enforces mass conservation. However, they are incapable of accurately capturing the whole range of behaviours or simultaneously capturing the effectiveness factor as well as the selectivity accurately. The study focuses on a simplified equimolar system to isolate the role of the diffusion closure; limitations, computational aspects of the Maxwell—Stefan formulation, and directions for future extensions are discussed.