Activity and Stability of Zinc and Phosphorus Modified NiMo/Al2O3 Catalyst for Residue Hydrodesulfurization

Conversion of heavy oil to added-value lighter fractions is very important. One conversion method is hydrotreatment of heavier residues in the hydroprocessing unit followed by cracking in the FCC or RFCC unit. However, if heavier residues are treated with the same catalyst under the same process conditions, the sulfur contents in the product oil will increase, so higher temperatures will be required to maintain constant sulfur in the product oil. This higher temperature also results in shorter catalyst life. This study developed zinc and phosphorus modified NiMo/Al2O3 catalyst which is resistant to deactivation by coke deposition. The effect of zinc on the suppression of deactivation rate was remarkable in the catalyst containing phosphorus in this study. IR spectroscopy showed that the coexistence of zinc with phosphorus inhibited the increase of acidic hydroxyls and the addition of phosphorus increased acidic alumina hydroxyls, leading to lower coke deposition on the zinc and phosphorus modified NiMo/Al2O3 catalyst. Zinc and phosphorus modified NiMo/Al2O3 catalyst also showed less deactivation and higher hydrodesulfurization activity in the middle period of the bench plant test. These results were well-consistent with catalyst performance in the commercial plant.