Page 77 - Fluid Catalytic Cracking Handbook

FCC Feed Characterization 55

The word "basic" denotes molecules that react with acids. Basic
nitrogen compounds will neutralize acid sites on the catalyst. This
causes a temporary loss of catalyst activity and a drop in unit con-
version (Figure 2-7). However, nitrogen is a temporary poison. The
burning of nitrogen in the regenerator restores the activity of
the catalyst. In the regenerator, about 70% to 90% of the nitrogen in
the coke is converted to elemental nitrogen. The remaining nitrogen is
converted to nitrogen oxides (NO X). The NO x leaves the unit with the
flue gas.
Catalyst poisoning from the presence of basic nitrogen in the FCC
feedstock is significant and, unfortunately, very little attention is often
given to the deleterious effects of basic nitrogen. Virtually all the basic
nitrogen ends up in coke. As shown in Figure 2-7, about 1 vol% of
the FCC gasoline is lost for each 100 ppm of basic nitrogen in the
feedstock. To compensate for nitrogen poisoning, the reactor temperature
is raised. A catalyst with high zeolite content and an active matrix Is
also recommended.
For some refiners, hydrotreating the feed may be an appropriate
economical approach. Except for most of the California crudes and a

r
82 —

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C
o
76
1
C 74
o
o
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70
5C)0 1000 1500 2000
Total Nitrogen, ppm

Figure 2-7. Effect of FCC feed nitrogen on unit conversion.