New Catalysts from Spent Catalysts - Spent Hydroprocessing Catalysts - page 251

to partially replace cement. Su et al. [552] reported that spent FCC catalyst could substitute up
to 15% of cement content in the mortar without sacrificing the quality of concrete. In fact, the
substituted concrete was found to show a greater compressive strength than that without
substitution [106] . In another study, Su et al. [557] showed that spent catalyst can replace up to
10% of fine aggregate (sand) in cement mortars without decreasing the mortar strength.
Pacewska et al. [555] studied the mechanism of interaction of waste FCC catalysts with
Portland cement and reported that spent catalyst had pozzolanic properties and its pozzolanic
activity depended on its grain size. Addition of the spent catalyst favorably modified the
porous structure of the concrete, increased its comprehensive strength, density and reduced
water absorption. It was also found that in the presence of the aluminosilicate material of the
spent catalyst, the Ca(OH) 2 content decreased in the cement pastes due to pozzolanic reaction
[558,559] . The surface area of the hydrated paste became higher and the mean pore diameter
decreased as compared to reference sample prepared without mixing the spent catalyst.

Conventional spent hydroprocessing catalysts supported on -alumina may require some

pretreatment to attain suitable cementitious properties before they can be used in cement and
concrete industry. However, the advances in hydroprocessing catalysis indicate on the growing
consumption of catalysts which are supported on acidic supports. In their properties, these
supports (e.g., amorphous silica-alumina, zeolites, etc.) approach FCC catalysts. The increased
use of the modified hydroprocessing catalysts is dictated by the steady increase in the supply
of heavy crude requiring hydrocracking step to be converted to primary liquids. It is well
established that hydrocracking is aided by acidic supports. Currently, such catalysts are used
for dewaxing paraffinic feeds to prepare middle distillate fuels or lube base oil from
conventional crudes. Similar catalysts have been used for upgrading primary liquids and waxes
from Fischer-Tropsch synthesis. Of course, bifunctional catalysts containing noble metals
(e.g., Pt and Pd) could only be considered after most of the noble metal was recovered from
spent dewaxing catalysts.

9.4.2 Waste Water Treatment Agents

Preparation of a waste water treating agent of superior quality from spent FCC catalysts has
been reported in a process developed by Sanga and Nishimura in Japan [560] . The process
involves alkali treatment of waste catalyst (zeolite) grains arising from the fluidized bed
catalytic cracking units. Cation exchange property similar to that of fresh zeolites imparted to
the catalyst by this treatment. Use of spent cracking catalysts (zeolites) containing V, Fe, Ni,
copper and/or carbon for biological treatment of waste water from municipal and industrial
sources is reported in a US patent [561] . In this process, the waste cracking catalyst is
combined with activated sludge and the waste water is contacted with the sludge at conditions
at which biological oxidation takes place. The presence of inorganic oxides (from the spent
catalyst) in the sludge increased the rate of biological oxidation. Preparation of the active