86
Different routes are explored for making the promoted catalyst. The most successful
and simplest route involved the exchange of either the calcined zeolite or, preferably, the almost finished spray-dried catalyst with an exchangeable form of Pt
(300–800 ppm), such as the Pt(NH 3 ) 4
2+
cation [52]. The first actual commercial
demonstration was done in a TCC unit at Husky Oil in Salt Lake City in 1974 [53].
The test was successful, complete CO combustion was observed, and 4 wt% increase
in conversion was obtained due to higher reaction temperature. After this trial,
W. R. Grace’s Davison division began manufacturing Pt-promoted catalysts under
agreement with Mobil and several other refiners utilized the CO combustion
promoter.
It has been observed that the use of platinum-based CO promoters encourage the
formation of NO x gasses in some FCC regenerators. This led to the development of
nonplatinum CO promoters. In cases where platinum-based promoters were
observed to cause increased NOx emissions in flue gasses, the use of nonplatinum
CO promoters with comparable levels of CO oxidation was preferred.
By 1979, the use of CO combustion promoters became quite common. Addition
of CO combustion promoter can be at regular intervals (two times a day 1–2 kg
additive per ton) or as and when required. The catalyst additive practice paved the
way to new development in catalyst addition systems, and several new technologies
and additives were explored.
5.4.2 NO x Reduction Additives
Nitrogen oxides (NO, N 2 O, NO 2 ) are photochemically active gasses, which contribute to the greenhouse effect and acid rains. They are also pungent in odor and cause
chronic respiratory illnesses. Generally, NO x is a pollutant related to transport; however, flue gasses from FCC units processing heavily contaminated (non-hydrotreated)
feeds also contain a significant amount of NO x . In a complete combustion regenerator, around 5% of the organic nitrogen content of the hydrocarbon feed, ends up as
NO x . With more stringent environmental regulations, it is in the best interest of
refiners to monitor the flue gas compositions and rectify any deviation to the laiddown regulations caused by pollutants, especially SO x and NO x.
It is relatively easier for refiners to use NO x reduction additives compared to
modifying their existing flue gas treatment facilities. Addition of NO x reduction
additives to the catalyst inventory requires no changes or modifications and is quite
flexible in terms of the amount required for the degree of NO x reduction (Fig. 15).
The basic principle behind NO x reduction is selectively reducing nitrogen oxides
to nitrogen. The catalyst is modified by a copper, zinc, or a rare-earth element with
oxygen trapping capabilities. The reduction of NO by CO in the presence of oxygen
using additive with iridium supported on Ce-promoted alumina showed up to 40%
oxygen excess in the feed (e.g., 0.7% vol. in the feed in the conditions they used);
the activity in NO reduction and at the same time CO oxidation are quite high but
decrease, increasing oxygen excess to 100% [55].
A. R. Khande et al.
Different routes are explored for making the promoted catalyst. The most successful
and simplest route involved the exchange of either the calcined zeolite or, preferably, the almost finished spray-dried catalyst with an exchangeable form of Pt
(300–800 ppm), such as the Pt(NH 3 ) 4
2+
cation [52]. The first actual commercial
demonstration was done in a TCC unit at Husky Oil in Salt Lake City in 1974 [53].
The test was successful, complete CO combustion was observed, and 4 wt% increase
in conversion was obtained due to higher reaction temperature. After this trial,
W. R. Grace’s Davison division began manufacturing Pt-promoted catalysts under
agreement with Mobil and several other refiners utilized the CO combustion
promoter.
It has been observed that the use of platinum-based CO promoters encourage the
formation of NO x gasses in some FCC regenerators. This led to the development of
nonplatinum CO promoters. In cases where platinum-based promoters were
observed to cause increased NOx emissions in flue gasses, the use of nonplatinum
CO promoters with comparable levels of CO oxidation was preferred.
By 1979, the use of CO combustion promoters became quite common. Addition
of CO combustion promoter can be at regular intervals (two times a day 1–2 kg
additive per ton) or as and when required. The catalyst additive practice paved the
way to new development in catalyst addition systems, and several new technologies
and additives were explored.
5.4.2 NO x Reduction Additives
Nitrogen oxides (NO, N 2 O, NO 2 ) are photochemically active gasses, which contribute to the greenhouse effect and acid rains. They are also pungent in odor and cause
chronic respiratory illnesses. Generally, NO x is a pollutant related to transport; however, flue gasses from FCC units processing heavily contaminated (non-hydrotreated)
feeds also contain a significant amount of NO x . In a complete combustion regenerator, around 5% of the organic nitrogen content of the hydrocarbon feed, ends up as
NO x . With more stringent environmental regulations, it is in the best interest of
refiners to monitor the flue gas compositions and rectify any deviation to the laiddown regulations caused by pollutants, especially SO x and NO x.
It is relatively easier for refiners to use NO x reduction additives compared to
modifying their existing flue gas treatment facilities. Addition of NO x reduction
additives to the catalyst inventory requires no changes or modifications and is quite
flexible in terms of the amount required for the degree of NO x reduction (Fig. 15).
The basic principle behind NO x reduction is selectively reducing nitrogen oxides
to nitrogen. The catalyst is modified by a copper, zinc, or a rare-earth element with
oxygen trapping capabilities. The reduction of NO by CO in the presence of oxygen
using additive with iridium supported on Ce-promoted alumina showed up to 40%
oxygen excess in the feed (e.g., 0.7% vol. in the feed in the conditions they used);
the activity in NO reduction and at the same time CO oxidation are quite high but
decrease, increasing oxygen excess to 100% [55].
A. R. Khande et al.