Studies on the rejuvenation of spent catalysts: effectiveness and selectivity in the removal of foulant metals from spent hydroprocessing catalysts in coked and decoked forms

Two routes were used to rejuvenate spent residue hydroprocessing catalysts by leaching foulant metals. In the first, deoiled spent catalyst containing coke and deposited metals in sulfide form was chemically treated to remove the metal foulants. In the second, deoiled spent catalyst was decoked by controlled combustion of coke and the resultant coke-free catalyst containing metals in oxide form was subjected to leaching. Oxalic acid, a chelating agent which is able to form soluble metal complexes, was used for metal leaching in both routes. The influence of adding an oxidizing agent such as H₂O₂ to oxalic acid in particular its effect on the leaching efficiency was examined in both routes. The spent and treated catalysts were characterized and the improvements in surface area, pore volume and hydrodesulphurization-activity of the catalysts were compared. The selectivity for leaching of the major metal foulant (vanadium) was better, and activity recovery was higher for the catalyst rejuvenated by metal leaching prior to decoking.