Production of improved catalyst-type particles using length and density grading

A process for treating a spent hydrotreating catalyst supported on a refractory metal oxide support comprising shaped, generally cylindrical, regular geometric particles having substantially the same diameter, varying length and an L/D greater than one, said spent catalyst particles having carbonaceous and metallic deposits resulting from a hydrocarbon feedstock;

• passing said spent catalyst particles to a stripping zone in which volatilizable hydrocarbons are stripped from said withdrawn spent particles to render said catalyst particles free-flowing;
• passing said free-flowing catalyst particles to a length grading zone comprising a rotating cylindrical drum having inwardly opening indentations in a cylindrical wall thereof, said indentions having a transverse diameter L.sub.1 in the range of 0.8 to about 24 millimeters;
• rotating said drum about a longitudinal axis thereof at a speed sufficient to entrap in the indentations and convey catalyst particles having a length below L.sub.1 and an L/D greater than one upwardly to a height permitting the catalyst particles to fall into a fixed upwardly opening trough, while retaining catalyst particles having a length above L.sub.1 and an L/D greater than one in a bottom portion of said drum;
• conveying the catalyst particles in the trough out a first outlet;
• whereby said catalyst particles with a length less than L.sub.1 are separated from the desired catalyst particles which have a length greater than L.sub.1 ;
• said particles having a length greater than L.sub.1 comprising lightly contaminated particles and more heavily contaminated catalyst particles;
• and
• passing said catalyst particles from said bottom portion of said drum to a density grading zone in which lightly metals contaminated catalyst particles become suspended in a gas above more heavily metals contaminated catalyst particles, said more heavily contaminated catalyst particles being caused to move upwardly along an inclined, vibrating surface and are thereafter collected at a first density grading zone outlet, said lightly contaminated catalyst particles contacting a lower portion of said vibrating surface and are collected at a second density grading zone outlet;
• and
• passing said lightly contaminated catalyst particles to a regeneration zone in which carbonaceous deposits are removed from said lightly contaminated catalyst particles by oxidation in the presence of an oxygen-containing gas to produce regenerated catalyst particles which are lightly contaminated with metals.