Environmental Engineering Reference
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Figure 6.18: Effect of regeneration temperature on surface area and pore volume of catalyst
[From ref. 401 . Reprinted with permission].
was not yet completed. Above 400 C, the loss of surface area and pore volume may be
attributed to a gradual sintering of the catalyst. This is confirmed by the results in Fig. 6.19
[401] showing a gradual collapse of microporosity with increasing temperature of
regeneration. According to one observation [13] , only a relatively short excursion of
temperature during regeneration resulted in a significant damage to catalyst material.
The O 2 concentration in the oxidizing medium is the key parameter for controlling regeneration
temperature. Thus, as Fig. 6.20 [401] shows, the complete surface area recovery was achieved
using 5% O 2 gas. The surface area decreased with further increase in O 2 concentration. These
experiments were conducted at 400 C. However, at higher O 2 concentrations, the actual
temperature of particles was almost certainly higher than 400 C [13] . Therefore, sintering of
catalyst could not be prevented. The O 2 supply to the regenerator can also be increased by
increasing the flow of oxidizing medium. Figure 6.21 [401] indicates that there is an optimal
flow rate ensuring the highest recovery of surface area. An increase in the flow rate beyond the
optimum decreased the surface area recovery. In practical situation, damages to catalyst
properties in air can be minimized by employing an efficient excess heat withdrawing system.
The results in Table 6.5 [331] were obtained to compare two extreme regeneration conditions,
i.e., the first involving 2% O 2 in N 2 and the second involving air. The spent CoMo/Al 2 O 3 and
NiMo/Al 2 O 3 catalysts contained about 8 and 20 wt.% of coke, respectively. For both catalysts,
the surface area recovery in air approached only 40% of that for the fresh catalysts. A high
 
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