QUESTIONS AND ANSWERS

I.FLUID CATALYTIC CRACKING:               www.wissenschaftler-avh.in

B.CATALYST/ADDITIVES(Contd.)

Q-36: What are the COMMON TOOLS and ANALYSES which are useful for the maintenance of 
Catalyst properties in FCC?

A-36:



                                    Maintenance  of  Catalyst  Properties

Maintenance of catalyst activity is critical to optimized FCC operation and profitability.
The loss of yield, conversion and selectivity can be acute if catalyst contaminants and
Microactivity  are not sustained at appropriate levels. Effective catalyst management must
be practiced to minimize delta coke and dry gas yields.

Fresh catalyst  microactivity (MAT) is determined by the proprietary components and
formulations of the supply companies. In the U.S., FCC catalyst is primarily supplied by
3 vendors; Grace Davison, Engelhard and Akzo. Each can custom formulate a catalyst
to meet the specific processing goals of the refiner. In general, this falls into three
categories; maximum gasoline, maximum octane or maximum octane-barrels of gasoline.
However, each unique catalyst’s performance is negatively affected by the accumulation
of contaminants absorbed from the feed oil in the Reaction Riser. The primary
contaminants are nickel and vanadium and to a lesser degree, sodium and iron.
Increasing concentrations of these additive contaminants function to shift the reaction
mechanisms  to those less desirable to the FCC processing  goals

 The main negative aspects of nickel accumulation are:

• Deposits on catalyst surface with minimal migration

• Catalyzes undesirable dehydrogenation reactions and coke

• Slightly decreases equilibrium MAT

• Increases delta coke and decreases catalyst circulation rate and cat-to-oil ratio,
leading to lower conversion, lower gasoline yield, lower gasoline selectivity, and
lower total liquid yield. Fuel gas yield and olefinicity of liquid products will be
increased.

The main negative aspects of vanadium accumulation are: 

• Migrates to the active zeolite components and destroys them

• Decreases equilibrium MAT

• Slightly catalyzes undesirable dehydrogenation reactions and coke

• Decreased MAT leads to lower gasoline and LPG liquid yields, lower gasoline
selectivity, and lower total liquid yield.

Overall, high catalyst contaminant concentrations are always unfavorable as they result in
gasoline and LPG product yield decreases with corresponding increases in Light Cycle
Oil (LCO), Slurry, Dry Gas and Coke. Whether by reaction mechanism or zeolite
destruction, delta coke increases with a resultant increase in Regenerator temperatures,
loss of catalyst circulation rate and loss of cat-to-oil. Stripper operation may also be
affected due to increased heavier, hydrocarbon undercarry.


Although each FCC is unique, certain common tools and analyses are useful
 to maintain the proper activity and contaminant levels. These include

• Routine laboratory analysis of feed contaminant concentrations to allow variation
of catalyst addition/withdrawal strategies

• Weekly Equilibrium Catalyst analysis by the FCC supplier to determine trends in
Contaminant  concentrations and impact on MAT and surface areas

• Survey and review of Regenerator temperatures to assess shifts related to
Changing  MAT or contaminants Solve the Five Most Common FCC Problems

• Frequent computation and review of heat and material balances and key
Performance  indicators. These would include coke yield, delta coke, air-to-coke
ratio, catalyst circulation rate, cat-to-oil ratio, conversion, gasoline yield, gasoline
selectivity,  gasoline octane or olefinicity,  total liquid yield, total dry gas yield, dry
gas SCFB, dry gas hydrogen concentration, and dry gas hydrogen to methane
ratio
.
• Injection of nickel or vanadium  passivation  additives to counteract metals effects.
Increasing steam or injection of sour lift gas into the Riser may also have a slight
Benefit  to decreasing nickel and vanadium effects

• Optimized catalyst addition and withdrawal program to maintain a desirable range
of contaminant concentrations.  The necessary fresh catalyst additions are based on
 feed total  Ni+V concentration to arrive at an equilibrium metals  concentration on the
 catalyst in the inventory.