Providing an Entry Length in Heterogeneous Catalytic Reactors with Fast Diffusion

D. Dalle Nogare[1] and P. Canu[1]

[1]Department of Chemical Engineering Principles and Practice, University of Padova, Padova, Italy

This work investigates the effects of boundary conditions on the species profiles in heterogeneous catalysis, with low Péclet systems. Hydrogen combustion in Helium was chosen because of the high diffusivities. Furthermore, already at T=300°C over a Pt catalyst, kinetics is very fast and the composition gradients at the inlet extremely steep. The issue is analyzed with 1D models, showing the difference between Plug Flow and Dispersed Plug Flow, the latter with Dirichlet BCs or with an Entry Length that reproduces the open-open vessel boundary condition. The same circumstances are also analyzed with 2D models. The gradients in the mean cross section profiles are lower, due to the transfer resistances, but local gradients are stronger, giving rise to larger diffusive fluxes.