Metal Reclamation from Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 296

separated by passage through granules of crystallized KCl. Finally, VCl 4 was recovered from
the residual gases by condensation at 60 ◦ C. The process is particularly applicable for the
recovery of Mo, V, and Al present in spent hydroprocessing catalysts. The recovery of Mo, V,
and Al exceeded 90 wt.% in the process. The nickel and cobalt chlorides, which are also
formed, are generally not volatile at the process conditions and they remain in the solid
residue within the column. Their recovery can be effected, for example, by forming an
aqueous solution with subsequent precipitation of the corresponding hydrates or the
carbonates.
Yoshida et al. [664] reported that metals, such as V and Ni, present in the spent residue
hydrotreating catalysts can be recovered by chlorination without subjecting the catalyst to
prior oxidation to remove coke and sulfur. The metals (V and Ni) present in the form of
sulfides are converted to chlorides on chlorination with a chlorinating agent (e.g. Cl 2 , HCl,
CCl 4 ,S 2 Cl 2 ) at a temperature below 600 ◦ C. Vanadium forms VCl 4 which is volatile while
nickel forms the non-volatile NiCl 2. Vanadium tetrachloride can be recovered from the gas
stream by condensation and nickel chloride can be recovered from the solid residue by solvent
extraction. Welsh et al. [665] used the mixture of gaseous chlorine, hydrogen chloride, and
water vapor for chlorination of the metals present in spent catalysts at temperatures in the
range 200-400 ◦ C. The Mo and V were volatilized as oxychlorides and aluminium is
volatilized as chloride. The metal chloride vapors were absorbed in an aqueous hydrochloric
acid solution at temperatures between about 20 and 70 ◦ C. Ni and Co in the spent catalyst were
converted to water-soluble chlorides.
The application of anhydrous chlorination technique for recovery of valuable metals from
spent hydroprocessing catalysts was investigated in more detail by Jong et al. [636] for US
Bureau of Mines. The chlorination studies were carried out in a batch fluidized bed reactor
(diameter, 1.25 and length 48 ) made of Vycor heat resistant glass. The chlorinator was
connected to a primary condenser and receiver, and then to the exhaust outlet ( Fig. 11.19 ). The
exhaust outlet was connected to a bubbler containing H 2 SO 4 to prevent backflow of air into the
reactor. Three types of spent catalysts (NiMo/Al 2 O 3 , NiW/Al 2 O 3 , and CoMo/Al 2 O 3 ) were
used in their experiments. Vanadium was not present in these catalysts. The catalysts were
heated in a flow of N 2 at 400 ◦ C for 30min to remove moisture from the catalyst before
starting chlorination. Since chlorination of metal oxide requires a reductant, such as carbon or
CO, waste catalysts containing more than 6.7 wt.% carbon, were chlorinated with only
Cl 2 +N 2 or Cl 2 +N 2 and air; other waste catalysts were chlorinated with Cl 2 +N 2 and CO or
Cl 2 +N 2 , CO and CO 2 . Chlorination was carried out at 450 ◦ C for 30min to separate volatile
MoO 2 Cl 2 or WO 2 Cl 2 from less volatile NiCl 2 or CoCl 2 , and AlCl 3 . The MoO 2 Cl 2 or WO 2 Cl 2
was hydrolyzed to recover MoO 3 or WO 3 as a final product. Hydrolysis recovered 65 to
84 wt.% of Mo and 90 wt.% of W. The chlorinated spent charge was leached with water. The
leach liquor was purified with an NH 4 OH-NH 4 Cl solution to precipitate Al and other metal
impurities. The Ni and Co were recovered by solvent extraction. The Ni or Co was precipitated