In the case of the Girard Point 1232 iron excursion
mentioned above, a combination of increased fresh
catalyst and good quality PCAT additions was used to
combat the negative effects of iron poisoning. To
overcome equipment limitations, PES worked with Grace
to increase the capacity of its catalyst loading system. It is
important to work closely with the fresh catalyst and
PCAT suppliers to develop the best flushing plan for each
respective unit. Several factors such as catalyst
selectivities, catalyst activity and unit limitations should
be considered to ensure a successful recovery while
maximising product yields.
Catalyst selection
Multiple unit objectives and
constraints had to be considered
when Grace chose the optimum
catalyst for the 1232 unit. Chief
among these was metals tolerance.
As noted throughout, overcoming
the effects of contaminant iron
and calcium were key factors. As
high levels of resid were
commonly processed, coke-
selective bottoms cracking was
essential. Moreover, catalyst
fluidisation was critical for this
older FCC unit with long
standpipes.
Pore size distribution
considerations
The importance of pore size in FCC
catalysts to selectively crack resid
fractions while avoiding diffusion
limitations is well known.
5
Catalysts that have a high level of
mesoporosity, in the 100 - 600 Å
range as measured by mercury (Hg)
porosimetry, are able to selectively
crack heavy hydrocarbons that
might ordinarily be coke
precursors.
Equally important is the
minimisation of sub-optimal
micropores of less than 100 Å
diameter. Cracking that occurs in
micropores is severely diffusion
limited, leading to excessive yield
of coke and gas. As shown in Figure
5, MIDAS® catalysts have a
substantial advantage over the
base catalyst in use at PES in both
mesoporosity and low level of
micropores.
Resid cracking involves the
destruction of complex, metals-
laden hydrocarbons. The design
of the MIDAS® Gold FCC catalyst
for the 1232 unit took into
account the need to resist the deleterious effects of
nickel (Ni) and vanadium (V), as well as iron and calcium
in the feed.
In combination with the selective bottoms cracking
matrix component present in MIDAS®Gold, additional
components were included in the formulation to
selectively react with Ni to form a nickel aluminate, which
is drawn away from the catalyst active surface and retards
dehydrogenation reactions caused by Ni on equilibrium
catalyst. These reactions are primarily related to
formation of hydrogen and coke.
The zeolite chosen for use in the PES 1232 unit
application has an appropriate degree of rare earth
stabilisation to protect the zeolite against attack by
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