Fixed Bed Reactor for Catalytic Hydrocarbon Oxidation

Tubular reactors are generally modelled with the assumption that the concentration and temperature gradients only occur in the axial direction. The only transport mechanism operating in this direction is the overall flow itself, which is considered to be of plug-flow.

In this example a more general approach is taken, an approach that accounts for variations of the concentrations and temperature in the radial direction. Furthermore, mixing in the axial direction is accounted for through effective diffusivities and conductivities, which is due to turbulence and the presence of packing.

The example models the partial oxidation of o-xylene in air to phthalic anhydrid (PA) in a multitube fixed-bed reactor. The reaction is exothermic and it requires good cooling to occur at optimal rates, therefore a cooling flux at the outer boundary is included as a function of the temperature.

Boundary and slice plot showing the temperature and the concentration of phthalic anhydride.