Environmental Engineering Reference
In-Depth Information
Figure 6.30: Formation of CO during temperature-programmed heating in flow of CO
2
; catalyst
A (NiMo/Al
2
O
3
) and catalyst C (CoMo/Al
2
O
3
) [From ref.
425
. Reprinted with permission].
CO
2
concentration from 10 to 100%. In this figure, the carbon content of the catalyst A and
catalyst C was about 19 and 3 wt.%, respectively.
According to
Fig. 6.29
, similar trends may also be observed when CO
2
was replaced by H
2
O
as the gasification reactant. This was indeed confirmed during the gasification of coke in steam
[426]
. Moreover, there is one patent
[427]
describing steam regeneration. According to this
patent, after being washed (de-oiled), the spent catalyst was contacted with steam between 540
and 680
◦
C. Apparently, after 2 to 5 h contact with steam, the catalyst was ready for reuse.
However, details of the composition and structure of spent catalysts could not be verified.
Also, for some catalysts, steaming may enhance sintering of active phase.
6.3.2 Regeneration with Nitrogen Oxides
Thermodynamic evidence (
Fig. 6.29
) indicates significant driving forces for the removal of
carbon using nitrogen oxides (N
2
O, NO, and NO
2
) via the following general
