Environmental and Safety Aspects of Spent Hydroprocessing Catalysts - Spent Hydroprocessing Catalysts - page 108

Table 5.4: Properties of spent catalysts treated in N 2 at 350 ◦ C [From ref. 331 . Reprinted with
permission].

Analysis (wt.%) Catalyst A Catalyst B

Loss on heating 15 1

Carbon 18 . 50 7 . 64

Hydrogen 1 . 31 0 . 46

Nitrogen 0 . 38 0 . 14

Sulfur 5 . 62 6 . 09

H/C 0 . 75 0 . 72

N/C 0 . 018 0 . 016

sample ignites, is taken as the flash point. A flash point occurring at low temperatures would
indicate that spent catalyst was not adequately de-oiled and dried. Therefore, potential for
ignition of such spent catalyst would be high.

5.2.1 Exposure to Air

A number of the reactions releasing toxic species and those which generate heat occur during
the exposure of spent catalyst to air alone and/or in the presence of water. Both organic (coke)
and inorganic portions of spent catalysts are involved, although in rather different ways. It
should be noted, that for most part, these reactions proceeds at very low rates. Therefore, their
effect may only be evident after a prolonged exposure.

5.2.1.1 Reactions of Air with Coke

On exposure to air, the flammability and ignitability of spent catalysts are of primary concern.
As it was indicated above, a spent catalyst may ignite if a sufficient vapor pressure of
flammable gases builds up over its surface. The flammable gases may include H 2 and volatile
hydrocarbons entrapped in the coke. As it was suggested earlier, the flammability can be
minimized by spent catalyst pretreatment, e.g., de-oiling and drying by flashing in H 2 followed
by inert gases. The actions that may be taken on the refinery site with the aim to minimize
hazardous nature of spent catalysts were discussed above.

Figure 5.4 [331] shows TPO of differently pretreated spent catalyst A and catalyst B. The
properties of these catalysts, after being treated in N 2 at 350 ◦ C, are shown in Table 5.4 .A
large difference in the loss on heating between these catalysts should be noted. Curve 1 depicts
the behavior of catalyst A (as received) during the temperature programmed pyrolysis (TPP) in
N 2 , whereas curve 3 the same catalyst during the TPO in 2% O 2 . It is evident from curve 3 that
the sufficient vapor pressure of the combustible volatile matter was developed already at