Effect of Coke and Metal Deposition on Catalyst Deactivation at Early Stages of Resid Hydrodesulfurization Operation

The hydrodesulfurization reaction with two kinds of atmospheric residues was carried out over three kinds of catalysts with different mean pore diameters to obtain catalysts with different deposited amounts of coke and metal on their surfaces. Elemental analysis and physical properties were carried out to elucidate the effects of coke and metal depositions on catalyst deactivation at an early stage of the reaction. Coke density (ρc) and metal density (ρm) calculated from the mean pore diameter determined by mercury porosimetry were independent of the kind of catalyst used, and operation time, were 1.25 and 2.50g/cm3, respectively. These results indicate that the effect on the decrease in pore volume of coke deposition was almost double to that of the metal deposition. Furthermore, accumulative thicknesses of coke (λc) and metal (λm) on the pore of the catalyst were calculated from decrease in pore diameter, based on the assumption that the pore was simply composed of uniform cylinder. Accumulative thicknesses were different with different kinds of catalyst used and they decreased more, the smaller the surface areas. The initial deactivation constant (α1) was directly related to the accumulative thickness of coke and metal. Moreover, it was found that the effect of the coke deposition accumulative thickness on reduction of pore diameter was almost triple to that of metal deposition. The catalyst deactivation on the SOR (start of run) in the hydrodesulfurization reaction was mainly responsible for the deposition of coke on the catalyst.