Page 63 - Fluid Catalytic Cracking Handbook

FCC Feed Characterization 41

Nevertheless, these correlations are very practical tools for tracking
unit performance and for troubleshooting. They are also important in
process design and catalyst research.
The two primary factors that affect feed quality are:
* Hydrocarbon Classification
* Impurities

HYDROCARBON CLASSIFICATION

The hydrocarbon types in the FCC feed are broadly classified as
paraffins, olefins, naphthenes, and aromatics (PONA),

Paraffins

Paraffins are straight or branched chain hydrocarbons having the
chemical formula C nH 2n+2. The name of each member ends with -ane;
examples are propane, isopentane, and normal heptane (Figure 2-1).
In general, FCC feeds are predominately paraffinic. The paraffinic
carbon content is typically between 50 wt% and 65 wt% of the total
feed. Paraffinic stocks are easy to crack and normally yield the greatest
amount of total liquid products. They make the most gasoline and the
least fuel gas, but also the lowest octane number.

H
7 ? ? 7 f f
H— <p — C — C— H H— C — C — C — C— - H
H H H H H I H
H— T— H
PROPANE j
(C 3H 8) H

ISOPENTANE
(C S H 12 )
HHH T

H H H H H H H

NORMAL HEPTANE
(C 7 H 16 )
Figure 2-1. Examples of paraffins.