petroleum refining

1. CHAPTER 5c
HYDROCRACKING

3. CHAPTER 5c - OUTLINE
HYDROCRACKING
I. Principles
II. Hydrocracking reaction
III.Feed preparation
IV.Process requirements
V. Hydrocracking Catalyst

4. HISTORY
• Hydrocracking is the conversion of higher boiling
point petroleum fractions to gasoline and jet
fuels in the presence of a catalyst.
• Hydrocracking process was commercially
developed in 1927 by I.G. Farben in Germany for
conversion of lignite (rarely black coal) to
gasoline.
• Esso and Chevron applied this process later in
USA.
• Due to importance of this process, it has been
heavily researched and modified in petroleum
industry.

5. PRINCIPLES
• Hydrogenation – oldest catalytic processes used in
petroleum refining.
• Why hydrocracking?
WHY?
demand of
petroleum
products
By-product
hydrogen
at low cost
Environmental
concern
• Demand shifted to high
ratios of gasoline and jet
fuel compared with the
usages of diesel fuel and
home heating oils.
• By-product hydrogen at
low cost and in large
amounts has become
available from catalytic
reforming operations
• Environmental concern
limiting sulfur and
aromatic compound
concentrations in motor
fuels have increased.

6. ADVANTAGES OF HYDROCRACKING
• Hydrocracking is one of the most versatile process,
which facilitate product balance with the market
demand.
Improved gasoline
pool octane numbers

7. MODERN REFINERY
• Catalytic cracking (FCC) & hydrocracking work as a
team.
• FCC takes more easily cracked paraffinic gas oils as
charge stocks, while hydrocracker is capable of using
aromatics and cycle oils and coker distillates as feed
(these compounds resist FCC)
• Cycle oils and aromatics formed in FCC make
satisfactory feedstock for hydrocracking.
• Middle distillate and even light crude oil can be used
in hydrocracking.

8. FEEDSTOCK
• Typical hydrocracker feedstock is shown below
• LCGO = light coker gas oil
• LCO = light cycle oil (produced in FCC, high in aromatics
and sulfur)
• HCGO = heavy coker gas oil

9. HYDROCRACKING PROCESSES
• There are a number of hydrocracking processes
available for licensing.
• These processes are fixed bed catalytic processes,
in which liquid is moving downward and gas is
moving upward/downward.
• The process employs either single stage or two
stage hydrocracking.
• The temperature and pressure may vary with the
age of catalyst, desired products and the
properties of feedstock.

10. HYDROCRACKING PROCESSES
PROCESS COMPANY
Unicracking UOP
GOFining EXXON Research & Eng
Ultracracking British Pet.Amoco
Shell Shell Development Center
BASF-IFB Badische Anilin, IFP
Unibon UOP, LLC
Isomax Chevron, UOP, LLC
There are other processes such as LC-Fining,
which are not based on fixed bed reactors.
(expanded bed reactor with continuous on
stream addition and withdrawal of catalyst)

11. HYDROCRACKING OBJECTIVE
REMOVE FEED
CONTAMINANTS
NITROGEN
SULFURMETALS
CONVERT
LOW VALUE
GAS OILS TO
VALUABLE
PRODUCTS
NAPHTHA
MIDDLE
DISTILLATES
ULTRA
CLEAN LUBE
BASE
STOCKS

12. PRIMARY PROCESS TECHNIQUE
Hydrogenation in fixed
hydrotreating catalyst
bed to improve H/C
ratios & remove feed
contaminants
Followed by one or more reactors
with fixed hydrocracking catalyst
beds to dealkylate aromatic rings,
open naphthene rings &
hydrocrack parafin chains

13. HYDROCRACKING BFD

14. HYDROCRACKING PROCESS FLOW
Fresh feed is mixed with H2 and recycle
gas (high in H2 content) and passed
through a heater to the first reactor
Feed that high in sulfur & nitrogen a
guard reactor is employed to convert
sulfur to H2S and N2 to NH3 ( to protect
precious catalyst in the following
reactor)
HC reactors are operated at high temp
to produce materials with boiling point
below 400 F

15. HYDROCRACKING PROCESS FLOW
Reactor gaseous effluent goes tru
heat exchangers and a high pressure
separator where the H2 rich gases are
separated and recycled to the first
stage.
Liquid product from the reactor is sent to a
distillation column where C4 and lighter gases
are taken off and the jet fuel, naphta and
diesel fuel streams are removed as liquid side
streams
Distillation bottom product is sent back
to hydrocracker

16. REACTIONS
• Hundreds of simultaneous chemical reactions
occuring in hydrocracking
Assumption – mechanism of hydrocracking
is that of FCC with hydrogen superimposed
In FCC, the C-C
bond is broken
Hydrogenation –
H2 is added to
C=C
Cracking –
endothermic
reaction
Hydrogenation –
exothermic
reaction

17. MAIN CHEMICAL REACTIONS
CATALYTIC
CRACKING
of heavy
hydrocarbons
into lighter
unsaturated
hydrocarbons
SATURATION
of the newly
formed
hydrocarbons
with
hydrogen
HYDRO
CRACKING

18. HYDROCRACKING REACTIONS
CRACKING & HYDROGENATION AS BELOW – the
scission of a C-C followed by hydrogenation

19. HYDROCRACKING REACTIONS
Aromatics
which are
difficult to
process in FCCU
are converted
to useful
products in
Hydrocrackers

21. • Cracking provides olefins for hydrogenation and
hydrogenation provides heat for cracking.
• Overall reaction provides excess of heat as
hydrogenation produces much larger heat than
the heat required for cracking operation.
• Therefore, the process is exothermic and
quenching (rapid cooling) is achieved by injection
cold hydrogen into the reactor and apply other
means of heat transfer
• Isomerization is another type of reaction, which
occurs in hydrocracking.
HYDROCRACKING REACTIONS

22. CATALYSTS
• Hydrocracking catalyst are dual functional
(having metallic and acidic sites) promoting
cracking and hydrogenation.
Cracking
Hydrogenation –
unsaturated
hydrocarbons
Hydrogenation of
aromatic
compounds
Hydrogenolysis of
naphthenic
structure

23. CATALYST SITE FUCNTIONS
Cracking is promoted by
metallic sites of catalyst
Acid sites transform the
alkenes formed into ions
Hydrogenation reactions also
occurs on metallic sites
Both metallic and acidic sites
take part in the 4th reactions
To minimize coke
formation a
proper balance
must be achieved
with the two sites
on the catalyst,
depends on the
conditions of the
operation

24. HYDROCRACKING CATALYSTS
• Generally a crystalline silica alumina base.
• Catalysts susceptible to sulfur poisoning if
hydrogen sulfide is present in large quantities.
• Catalysts not affected by ammonia.
• Sometimes necessary to remove moisture to
protect the catalyst.
• Catalyst deactivate and coke does form even with
hydrogen present.
• Hydrocarbons require periodic regeneration of
the fixed bed catalyst systems.