1. Conversion Process: Catalytic cracking Hydrocracking Thermal cracking
Coking
Solvent De-asphalting

2. (5) Catalytic cracking
Convert heavy hydrocarbon fractions from vacuum distillation into a mixture of more useful products
Feedstock undergoes a chemical breakdown, under controlled heat ( oC) and pressure, in the presence of a catalyst
(5) Catalytic cracking
Effective catalyst: small pellets of silica, alumina or magnesia and nowadays zeolite
Principle reaction: Dehydrogenation of aromatics or naphthenes, which can then add side chains in place of some of the hydrogen attached to the ring of carbons

3. Catalytic cracking: products
Primary goal to make gasoline & diesel
Minimize the production of heavy fuel oil
Light ends contain large amounts of olefins
» Good for chemical feedstock
» Can recover chemical grade propylene & ethylene
» Propylene, butylene, & C5 olefins can be alkylated for higher yields of high-octane gasoline

4. Catalytic cracking
REGENERATOR
REACTOR
RISER
Catalytic cracking is the most important and widely used refinery process for converting heavy oils into more valuable gasoline and lighter products.
The cracking process produces carbon (coke) which remains on the catalyst particle and rapidly lowers its activity. To maintain the catalyst activity at a useful level, it is necessary to regenerate the catalyst by burning off this coke with air.
As a result, the catalyst is continuously moved from reactor to regenerator and back to reactor.
The cracking reaction is endothermic and the regeneration reaction exothermic.

5. Catalytic cracking
REGENERATOR
REACTOR
RISER
The catalytic-cracking processes can be classified into;
Moving-bed unit (like, Thermafor catalytic cracking (TCC))
Fluidized-bed unit (like, fluid catalytic cracker (FCC))
The hot oil feed is contacted with the catalyst in either the feed riser line or the reactor. As the cracking reaction progresses, the catalyst is progressively deactivated by the formation of coke on the surface of the catalyst. The catalyst and hydrocarbon vapors are separated mechanically, and oil remaining on the catalyst is removed by steam stripping before the catalyst enters the regenerator. The oil vapors are taken overhead to a fractionation tower for separation into streams having the desired boiling ranges.

6. Catalytic cracking
REGENERATOR
REACTOR
RISER
The spent catalyst flows into the regenerator and is reactivated by burning off the coke deposits with air.
Regenerator temperatures are carefully controlled to prevent catalyst deactivation by overheating.
This is done by controlling the air flow to give a desired CO2/CO ratio in the exit flue gases or the desired temperature in the regenerator.
The flue gas and catalyst are separated by cyclone separators and electrostatic
precipitators.
The catalyst in some units is steam-stripped as it leaves the regenerator to remove adsorbed oxygen before the catalyst is contacted with the oil feed.

8. Catalytic cracking
Two basic types of FCC units in use today are the ‘‘side-by-side’’ type, where the reactor and regenerator are separate vessels adjacent to each other, and the stacked type, where the reactor is mounted on top of the regenerator.
side-by-side FCC units
stacked type FCC units

9. FCC Process FCCU feed is preheated to 650oF and is fed into the riser
The ratio of catalyst: oil = 4:1 to 9:1 by weight.
Residence time of the gas < 5 seconds
The vapor generated by the cracking process lifts the catalyst up the riser. The vapor velocity at the base of the riser is about 6 m/s and increases to over 20 m/s at the riser exit.
FCC Process
REACTOR
REGENERATOR
FCCU feed is preheated to 650oF and is fed into the riser
Contains hot catalyst from the regenerator
RISER

10. A spent catalyst is withdrawn from the bottom of reactors and stripped with steam to vaporize the hydrocarbons remaining on the surface
Stripping removes most of the hydrocarbon vapors which are entrained between the particles of catalyst
FCC Process
REACTOR
It is desirable to separate the vapor and catalyst as quickly as possible to prevent overcracking of the desired products.
REGENERATOR
RISER

12. Catalytic cracking
The FCC process employs a catalyst in the form of very fine particles [average particle size about 70 micrometers (microns)] which behave as a fluid when aerated with a vapor. The fluidized catalyst is circulated continuously between the reaction zone and the regeneration zone and acts as a vehicle to transfer heat from the regenerator to the oil feed and reactor.
REGENERATOR
REACTOR
RISER

13. Catalyst Characteristics of good catalyst:
- ability to produce desirable product and not coke
- selective to valuable products, eg high octane gasoline is desirable,
- stable so it does not deactivate at the high temperature levels in regenerators.
- resistant to contamination

14. Catalyst
Three classes:
acid-treated natural aluminosilicates
amorphous synthetic silica-alumina combinations
crystalline synthetic silica-alumina catalyst called zeolite or molecular sieves

17. Makeup of a catalyst particle

18. Advantage of using zeolite as catalyst
Higher activity
Higher gasoline yield
Gasoline contains more paraffinic and aromatic HC
Lower coke yield
Increased isobutane production
Higher conversion without overcracking

19. What deactivates FCC catalyst
Conditions in the Regenerator:
temperature, water, time
Impurities/Poisons in the FCC feed:
Va, Ni, Fe, Cu
Temporary Poisons:
Nitrogen, Carbon on catalyst surface – lowers catalyst activity