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Catalyst Performance Testing in Multiphase Systems: Implications of Using Small Catalyst Particles in Hydrodesulfurization

Alsolami, Bandar H., Berger, Rob J., Makkee, Michiel, Moulijn, Jacob A.
Industrial & Engineering Chemistry Research 2013 v.52 no.26 pp. 9069-9085
catalysts, chemistry, engineering, hydrodynamics, hydrogen sulfide, particle size, slurries
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.