The oxidation of o-xylene to phthalic anhydride was carried out in a pilot plant with a tubular reactor in order to investigate the heat transfer properties of different types of catalytic fixed beds through analysis of the temperature profiles arising upon polytropic o-xylene conversion. Ceramic sponges of different materials and pore densities were compared to a packed bed of spheres, all of which were coated with novel flame-made vanadia/titania catalyst nanoparticles. The temperature profiles were smoother and hot spot temperatures were found to be lower when sponges were employed as catalyst supports. The strongest reduction of the hot spot temperature was achieved with a sponge packing made of silicon carbide, showing the potential to significantly improve the productivity of the process.
Fitting Solid Sponges into a Reactor Tube Concerning the Partial Oxidation of o-Xylene as an ExampleSolid open-cell sponges, often denoted as foams in literature, are promising packing materials for applications in process engineering. Their structural properties lead to low pressure drop and enhanced heat and mass transport as compared to conventional packed beds. Over the past years, the potential advantages of these new structures have been the topic in numerous investigations. However, only a few publications mention or take into consideration how the sponge packings are fitted into the respective apparatus. Using solid sponges as catalyst supports in the partial oxidation of o-xylene, this present contribution demonstrates the impact of the fitting procedure of sponges on the resulting process behaviour such as conversion and heat transfer.
Vanadia/titania catalyst particles were made by flame-spray
pyrolysis
and deposited onto ceramic sponge monoliths either by direct deposition
of the flame-made particles or by a dip-coating technique. In the
partial oxidation of o-xylene, the influence of the
coating thickness and porosity on the catalytic performance was investigated.
It was found that the highly porous coatings obtained by direct deposition
exhibit insufficient heat transfer properties, while dip-coated layers
are prone to internal mass transfer limitations if a certain thickness
of the coating is exceeded. In the absence of transport limitations,
kinetic experiments were carried out to derive a reaction network
and to develop a quantitative kinetic model. The resulting model describes
well the influences of reactant concentrations and temperature on
the product distributions in the oxidation of o-xylene
to phthalic anhydride over the novel flame-made catalyst and can be
used for reactor simulations.
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