Page 222 - Fluid Catalytic Cracking Handbook

190 Fluid Catalytic Cracking Handbook

3, Aniline Point. Feeds with a higher aniline point are less
aromatic and more paraffinic. The higher the aniline point, the
lower the octane.
4. Sodium. Additive sodium reduces unit conversion and lowers
octane (Figure 6-4).
C. Catalyst
1. Rare Earth. Increasing the amount of rare earth oxide (REO)
on the zeolite decreases the octane (Figure 6-5).
2. Unit Cell Size. Decreasing the unit cell size increases octane
(Figure 6-6).
3. Matrix Activity. Increasing the catalyst matrix activity increases
the octane.
4. Coke on the Regenerated Catalyst. Increasing the amount
of coke on the regenerated catalyst lowers its activity and
increases octane.

Benzene. Most of the benzene in the gasoline pool comes from
reformate. Reformate, the high-octane blending component from a
reformer unit, comprises about 30 vol% of the gasoline pool. Depend-
ing on the reformer feedstock and severity, reformate contains 3 vol%
to 5 vol% benzene.
FCC gasoline contains 0.5 to 1.3 vol% benzene. Since it accounts
for about 35 vol% of the gasoline pool, it is important to know what
affects the cat cracker gasoline benzene levels. The benzene content
in the FCC gasoline can be reduced by:
• Short contact time in the riser and in the reactor dilute phase
• Lower cat-to-oil ratio and lower reactor temperature
• A catalyst with less hydrogen transfer

Sulfur. The major source of sulfur in the gasoline pool comes from
FCC gasoline. Sulfur in FCC gasoline is a strong function of the feed
sulfur content (Figure 6-7). Hydrotreating the FCC feedstock reduces
sulfur in the feedstock and, consequently, in the gasoline (Figure 6-8).
Other factors that can lower sulfur content are:
• Lower gasoline end point (see Figure 6-9)
• Lower reactor temperature (see Figure 6-10)
• Increased matrix activity of the catalyst
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