Regeneration - Spent Hydroprocessing Catalysts - page 161

Figure 6.26: Effect of O 2 concentration in regeneration gas on temperature runway in four zones
of fixed bed (solid symbols for tetrahydrofuran [THF] extracted catalyst) [From refs 419 and
420 . Reprinted with permission].

of spent catalyst was 350 ◦ C. From this correlation, it can be estimated that the O 2
concentration of about 4 vol.% can ensure the temperature excursion to less than 500 ◦ C. Thus,
according to Figs 6.17 and 6.22 [401,367,368] , in order to achieve a high recovery of catalyst
activity, the temperature of regeneration should not exceed 500 ◦ C.

The correlation in Fig. 6.26 [420] is applicable to a specific spent catalyst, i.e., it cannot be
applied generally. This is confirmed by the results in Fig. 6.25 [419] . The temperature profiles
in Figs 6.25 and 6.27 were obtained for catalyst A and catalyst B, respectively. The properties
of these catalysts are given in Table 6.9 . The temperature excursion in air for the much more
coke deposited catalyst B was lower compared with that for catalyst A. This can be attributed
to a much smaller surface area of catalyst B, which allowed only an external chemically

Table 6.9: Composition of coke (wt.%) on spent catalysts [From ref. 419 . Reprinted with
permission].

Catalyst A Catalyst B

Carbon 7 . 2 26 . 2

Hydrogen 0 . 8 3 . 5

H/C 1 . 3 1 . 6

Nitrogen 0 . 40 0 . 27

Sulfur 7 . 13 5 . 48