Page 133 - Fluid Catalytic Cracking Handbook

108 Fluid Catalytic Cracking Handbook

of the E-cat is directly related to the alumina content of the fresh
catalyst. When changing catalyst grades, the alumina level of the E-
cat is often used to determine the percent of new catalyst in the unit.

Sodium (Na)

The sodium in the E-cat is the sum of sodium added with the feed
and sodium on the fresh catalyst. A number of catalyst suppliers report
sodium as soda (Na 2O). Sodium deactivates the catalyst acid sites and
causes collapse of the zeolite crystal structure. Sodium can also reduce
the gasoline octane, as discussed earlier,

Nickel (Ni), Vanadium (V), Iron (Fe), Copper (Cu)

These metals, when deposited on the E-cat catalyst, increase coke
and gas-making tendencies of the catalyst. They cause dehydrogenation
reactions, which increase hydrogen production and decrease gasoline
yields. Vanadium can also destroy the zeolite activity and thus lead
to lower conversion. The deleterious effects of these metals also
depend on the regenerator temperature: the rate of deactivation of a
metal-laden catalyst increases as the regenerator temperature increases.
These contaminates originate largely from the heavy (1,050+ °F/
566+ °C), high-molecular weight fraction of the FCC feed. The
quantity of these metals on the E-cat is determined by their levels in
the feedstock and the catalyst addition rate. Essentially, all these metals
in the feed are deposited on the catalyst. Most of the iron on the E-
cat comes from metal scale from piping and from the fresh catalyst.
Metals content of the E-cat can be determined fairly accurately by
conducting a metals balance around the unit:
Metals in - Metals out = Metals Accumulated

This is a first order differential equation. Its solution is:

M e = A + [M 0 - A] x e- Ca X ^

Where:

M e = E-cat Metals Content, ppm
A = (W x M f)/C a
W = Feed rate, Ib/day
M f = Feed Metals, ppm