Regeneration - Spent Hydroprocessing Catalysts - page 129

Figure 6.5: Formation of SO 2 and CO 2 during temperature programmed oxidation (TPO) of
spent catalyst [From ref. 369 . Reprinted with permission].
temperature region coincides with the formation of CO 2 and can be almost certainly attributed
to the oxidation of organic sulfur in coke. The catalysts in Fig. 6.5 [369] were crushed to
100-200mesh before TPO experiments to minimize the interference of diffusion. The trends
observed in Fig. 6.5 are in agreement with the studies published by Zeuthen et al. [370,371] .
Matsushita et al. [240] evaluated the spent catalysts from the study of Hauser et al. [238,239]
using the TPO technique. The spent catalysts were used for hydroprocessing the atmospheric
residue derived from a Kuwait crude. They were taken at different stages on stream during the
same operation. The TPO profiles ( Fig. 6.6 ) revealed the two maxima of CO 2 formation, i.e.,
one at about 573 K and the other at about 700 K. These maxima were attributed to the
oxidation of a “soft” coke and a “hard” coke, respectively. It should be noted that in the study
of Seki and Yoshimoto [208] , the “hard” coke was defined as toluene insoluble portion of
coke. The “hard” coke studied by Hauser et al. [239] was much more refractory and was
adsorbed strongly on the catalyst surface. In its structure, the “soft” coke in the Hauser et al.
[238] study may approach the structure of the toluene insolubles portion of coke formed