Page 148 - Fluid Catalytic Cracking Handbook

FCC Catalysts 123

caused by nickel are often reduced by 40% to 60%. This is evidenced
by a sharp decline in dry gas and hydrogen yield.
Nickel passivation is generally economically attractive when the
nickel content of the E-cat is greater than 1,000 ppm. The Phillips
Petroleum secondary antimony patent position is due to expire in late
1999, At that time, antimony passivation can become economically
attractive at a lower nickel level than 1,000 ppm.
The antimony solution should be added in proportion to the amount
of nickel present in the feed. The optimum dosage normally cor-
responds to an antimony-to-nickel ratio of 0.3 to 0.5 on the E-cat.
Antimony's retention efficiency on the catalyst is in the range of 75%
to 85% without the recycling of slurry oil to the riser. If slurry recycle
is being practiced, the retention efficiency is usually greater than 90%.
Any antimony not deposited on the circulating catalyst ends up in the
decanted oil and the catalyst fines from the regenerator. It is often a
good practice to discontinue antimony injection about one month prior
to a scheduled unit shutdown to make sure the exposure to catalyst
dust containing antimony is reduced to a minimum when wearing a
half-faced respirator.

SUMMARY

The introduction of zeolite into the FCC catalyst in the early 1960s
was one of the most significant developments in the field of cat
cracking. The zeolite greatly improved selectivity of the catalyst,
resulting in higher gasoline yields and indirectly allowing refiners to
process more feed to the unit. With the introduction of reformulated
gasoline, new formulations in FCC catalyst will again help refiners
meet new requirements in gasoline quality.
Since there are over 120 different FCC catalyst formulations in the
market today, it is important that the refinery personnel involved in
cat cracker operations have some fundamental understanding of catalyst
technology. This knowledge is useful in areas such as proper trouble-
shooting and customizing a catalyst that would match the refiner's
needs. The additive technology will be expanding in coming years.
The need to produce reformulated gasoline will increase demand for
the shape-selective zeolite, such as ZSM-5. The pressure from environ-
mental agencies to reduce SO X and NO X will further increase the
demand for additives that reduce emissions.