Three different gas–liquid–solid reactor configurations have been used to investigate the performance of a P-doped NiMo/Al2O3 catalyst in the hydrodesulfurization of dibenzothiophene. The commonly used millipacked bed reactor with 250–500 μm catalyst particles diluted with 125 μm inert particles, a micropacked bed reactor with 55–90 μm catalyst particles, and a slurry reactor with 150–250 μm catalyst particles were used in the catalyst performance testing program. It appeared that the inherently small particle size in the packed beds causes the hydrodynamics to be dramatically different compared to the industrially applied trickle-bed reactors. For particles smaller than typically 2 mm the capillary forces predominate over the viscous and gravitational forces, in sharp contrast to large-scale industrial reactors. Since the gas flow follows preferential pathways through beds consisting of small particles, the poor radial dispersion of the gaseous components can cause mass-transport limitations, even for a rather slow reaction such as the hydrodesulfurization (HDS) of dibenzothiophene, as a result of the strong inhibition by the reaction product H2S. An adapted criterion is proposed for estimation of the contribution of poor radial dispersion in catalyst performance testing.

Figure 4. Characterization of red mud and red mud promoted with 2wt% of Ka fter reaction at 350 8C, 30 bar,and 50 hT OS:a)XRD results of iron-containing phaseso fsamples beforeand after catalytic reaction (PDF 01-089-0596, PDF 04-012-7038,a nd PDF 04-014-4562 diffractogramsw ere used for hematite, magnetite,a nd iron carbidep hases, respectively). b) 308-508 2q region of samples before and after catalytic reaction. c) XPS analysis results of samples before and after catalyticreaction.

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