New Catalysts from Spent Catalysts - Spent Hydroprocessing Catalysts - page 244

Table 9.5: Metal content of acid extraction solutions [From ref. 531 . Reprinted with permission].

Metal Concentration (ppm)

Oxalic acid Citric acid

Fe 20 2650

Mo 167 1530

Ni 111 15000

V 18000 21000

activity to convert paraffins to aromatics. With this catalyst, the octane number of the
paraffinic naphtha increased from 55 to almost 87 at 81% yield. The catalyst prepared from the
citric acid extraction liquor contained mainly V, Ni and Fe. A high cracking and
dehydrogenation activity of this catalyst was attributed to the presence of Ni. This catalyst
gave high yields of H 2 , coke and light olefins at the expense of aromatics in products.

Cronauer and Bjorklund [532] developed a process for producing fresh molybdenum
containing catalysts by depositing molybdenum removed from a spent hydrotreating catalyst
that contained Mo, Co or Ni and Al 2 O 3 together with some other minor elements such as
silicon, iron, and Ti. The spent catalyst was first decoked and sulfided and then treated with
anhydrous gaseous hydrogen chloride at temperatures in the range 400 ◦ Cto575 ◦ C. The
molybdenum was removed from the spent catalyst as molybdenum oxychloride while the
other metals such as Co, Ni, Fe, Ti and the supporting Al 2 O 3 or SiO 2 were not affected during
chlorination. The vaporized molybdenum oxychlorides was deposited onto a fresh alumina
support in the presence of air. The performances of the prepared catalyst for promoting
hydrotreating or other reactions were not reported in this study.

A pure MoO 3 suitable for catalyst preparation could be obtained from spent hydroprocessing
catalysts using a radiation-thermal treatment [533-536] . The method is based on the
observation that active metals in spent hydroprocessing catalysts behaved differently under
irradiation by a 1.2 MeV fast electron beam. For example, in the spent NiMo/Al 2 O 3 catalyst,
the Mo-containing phases are selectively destroyed, whereas Ni-containing species are
preserved. As a consequence, the sublimation of Mo as MoO 3 is significantly enhanced.
Similar observations were also made for the spent CoMo/Al 2 O 3 catalysts. Potential options for
utilization of the Mo free catalysts, i.e., Ni/Al 2 O 3 and Co/Al 2 O 3 catalysts have not been
explored. It is believed that these materials may be suitable for some catalytic applications.
However, the method would have to be cost-effective to attract any commercial
interests.