Page 220 - Fluid Catalytic Cracking Handbook

188 Fluid Catalytic Cracking Handbook

The key components affecting FCC gasoline quality are octane,
benzene, and sulfur and are discussed in the following sections.

Octane. An octane number is a quantitative measure of a fuel
mixture's resistance to "knocking." The octane number of a particular
sample is measured against a standard blend of n-heptane, which has
zero octane, and iso-octane, which has 100 octane. The percent of iso-
octane that produces the same "knock" intensity as the sample is
reported as the octane number.
Two octane numbers are routinely used to simulate engine per-
formance: the research octane number (RON) simulates gasoline
performance under low severity (@600 rpm and 120°F (49°C) air
temperature), whereas the motor octane number (MON) reflects more
severe conditions (@900 rpm and 300°F (149°C) air temperature). At
the pump, road octane, which is the average of RON and MON,
is reported.
Factors affecting gasoline octane are:
A. Operating Conditions
1. Reactor Temperature. As a rule, an increase of 18°F (10°C)
in the reactor temperature increases the RON by 1.0 and MON
by 0.4. However, the MON contribution comes from the
aromatic content of the heavy end. Therefore, at high severity,
the MON response to the reactor temperature can be greater
than 0.4 number per 18°F.
2. Gasoline End Point, The effect of gasoline end point on its
octane number depends on the feedstock quality and severity
of the operation. At low severity, lowering the end point of a
paraffinic feedstock may not impact the octane number; how-
ever, reducing gasoline end point produced from a naphthenic
or an aromatic feedstock will lower the octane.
3. Gasoline Reid Vapor Pressure (RVP). The RVP of the gasoline
is controlled by adding C 4's, which increase octane. As a rule,
the RON and MON gain 0.3 and 0.2 numbers for a 1.5 psi
(10.3 K p) increase in RVP.
B. Feed Quality
1. °API Gravity, The higher the °API gravity, the more paraffins
in the feed and the lower the octane (Figure 6-3).
2. K Factor. The higher the K factor, the lower the octane.