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Unit 3. Hydroconversion
Assistant lecturers
Belinskaya Nataliya Sergeevna
Kirgina Maria Vladimirovna
2
Название темы
Hydroconversion
Introduction
Hydroconversion is a term used to describe all different processes in which
hydrocarbon reacts with hydrogen.
hydrotreating
hydrocracking
The term hydrotreating is used to describe the process of the removal of
sulphur, nitrogen and metal impurities in the feedstock by hydrogen in the
presence of a catalyst.
Hydrocracking is the process of catalytic cracking of feedstock to products
with lower boiling points by reacting them with hydrogen.
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating
Objectives of hydrotreating
Removing impurities, such as sulphur, nitrogen and oxygen for the
control of a final product specification or for the preparation of feed for
further processing
Removal of metals, usually in a separate guard catalytic reactor when
the organo-metallic compounds are hydrogenated and decomposed,
resulting in metal deposition on the catalyst pores
Saturation of olefins and their unstable compounds
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Название темы
Hydroconversion. Hydrotreating
Role of Hydrotreating
Figure 1. Role of hydrotreating (HT) in the refinery
Meeting finished product
specification
Kerosene, gas oil and lube oil
desulphurization
Olefin saturation for stability
improvement
Nitrogen removal
De-aromatization for kerosene
to improve cetane number
Feed preparation for downstream
units
Naphtha is hydrotreated for
removal of metal and sulphur
Sulphur, metal, polyaromatics
removal from vacuum gas oil
to be used as fluid catalytic
cracking feed
Pretreatment of hydrocracking
feed to reduce sulphur,
nitrogen and aromatics
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating Chemistry
Desulphurization
a. Mercaptanes: RSH + H2 → RH + H2S
b. Sulphides: R2S + 2H2 → 2RH + H2S
c. Disulphides: (RS)2 + 3H2 → 2RH + 2H2S
d. Thiophenes:
Denitrogenation
a. Pyrrole: C4H4NH + 4H2 → C4H10 + NH3
b. Pyridine: C5H5N + 5H2 → C5H12 + NH3
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating Chemistry
Deoxidation
a. Phenol: C6H5OH + H2 → C6H6 + H2O
b. Peroxides: C7H13OOH + 3H2 → C7H16 + 2H2O
Hydrogenation of chlorides RCl + H2 → RH + HCl
Hydrogenation of olefins C5H10 + H2 → C5H12
Hydrogenation of aromatics
C6H6 + 3H2 → Cyclohexane
Naphthalene + H2 → Tetraline
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating Chemistry
Hydrogenation of organo-metallic compounds and deposition of
metals
Coke formation by the chemical condensation of polynuclear radicals
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Название темы
Hydroconversion. Hydrotreating
Termodynamics of Hydrotreating
Hydrotreating reactions are highly exothermic and reversible.
Olefin hydrogenation is usually complete.
Aromatic hydrogenation reaction can reach equilibrium under certain
condition.
Hydrodesulphurization can be carried out easier than denitrogenation.
Aromatic saturation is the most difficult reaction.
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating Catalysts
The hydrotreating catalyst is a porous alumina matrix impregnated
with combinations of cobalt (Co), nickel (Ni), molybdenum (Mo) and
tungsten (W).
The catalysts mainly have pores with a surface area of (200–300 m2/g).
Co-Mo
desulphurization of
straight run
petroleum fractions
Ni-Mo
is chosen when higher activity
is required for the saturation
of polynuclear aromatic
compounds or for the removal
of nitrogen and refractory
sulphur compounds
Ni-W
is chosen only when
very high activity
aromatic saturation
is required
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating Catalysts
Table 1. Reactivity of hydrotreating catalysts
Cobalt–molybdenum (Co–Mo) and nickel–molybdenum (Ni–Mo)
catalysts
resist poisoning
are the most universally applied catalysts for hydrodesulphurization
of feedstocks ranging from naphtha to residue
promote both demetallization and desulphurization
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Название темы
Hydroconversion. Hydrotreating
Hydrotreating Processes
Figure 2. The main elements of a hydrotreating process
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Название темы
Hydroconversion. Hydrotreating
Naphtha Hydrotreating
Figure 3. Naphtha hydrotreating process
13
Название темы
Hydroconversion. Hydrotreating
Middle Distillates Hydrotreating
Figure 4. Diesel fuel hydrotreating unit
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Название темы
Hydroconversion. Hydrotreating
Atmospheric Residue Desulphurization
Figure 5. Atmospheric residue desulphurization process
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Название темы
Hydroconversion. Hydrotreating
Operating Conditions Increasing hydrogen partial pressure improves the removal of sulphur and nitrogen
compounds and reduces coke formation.
Higher temperatures will increase the reaction rate constant and improve the kinetics.
Excessive temperatures will lead to thermal cracking and coke formation.
High space velocity results in low conversion, low hydrogen consumption and low coke
formation.
Table 2. Process parameters for hydrotreating different feedstocks
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Название темы
Hydroconversion. Hydrocracking
Hydrocracking
Hydrocracking is a catalytic hydrogenation process
in which high molecular weight feedstock is converted and hydrogenated
to lower molecular weight products.
Hydrogenation removes impurities
in the feed such as
sulphur, nitrogen and metals.
Cracking will break bonds,
and the resulting unsaturated products
are consequently hydrogenated into
stable compounds.
17
Название темы
Hydroconversion. Hydrocracking
Role of Hydrocracking
in the Refinery
Figure 6. Role of the hydrocracker in
the refinery
Hydrocracking is mainly used
to produce middle distillates of
low sulphur content such as
kerosene and diesel.
If mild hydrocracking is used, a
low sulphur fuel oil can be
produced.
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Название темы
Hydroconversion. Hydrocracking
Feed and Products
Table 3. Typical feedstock and products
FCC – fluid catalytic cracking, LCO – light gas oil, HCO – heavy gas oil
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Название темы
Hydroconversion. Hydrocracking
Hydrocracking Chemistry
Alkane hydrocracking
Hydrodealkylation
Ring opening
20
Название темы
Hydroconversion. Hydrocracking
Hydrocracking Chemistry
Hydroisomerization
Polynuclear aromatics hydrocracking
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Название темы
Hydroconversion. Hydrocracking
Hydrocracking Catalysts Classification of hydrocracking catalyst
Table 4. Bifunctional catalyst strength for hydrogenation and cracking
x represents order of strength
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Название темы
Hydroconversion. Hydrocracking
Thermodynamics of Hydrocracking
Aromatic hydrogenation
Paraffin hydrocracking
Naphthenes hydrocracking
Aromatic hydrodealkylation
exothermic reactions
Careful control of the fixed bed
temperature is required.
This is usually done by
gaseous quenches in the reactor
catalyst partitioning of the bed
Table 5. Heat of reaction
23
Название темы
Hydroconversion. Hydrocracking
Hydrocracking Processes
The following factors can affect operation (product quality), yield
(quantity), and the total economics of the process:
Process configuration
Catalyst type
Operating condition
One stage (once-through or recycle)
Two stages
Conversion level
Maximization of certain product
Product quality
Catalyst cycle
Partial hydrogen pressure
Liquid hourly space velocity
Feed/hydrogen recycle ratio
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Название темы
Hydroconversion. Hydrocracking
Hydrocracking Process Configuration
Figure 7. Simplified flow diagram of one-stage hydrocracking process with and without recycle
Is used for light feed with once through or recycle process
A conversion of 40–80% of the feed can be achieved
This configuration can be used to maximize a diesel product
It employs an amorphous catalyst
25
Название темы
Hydroconversion. Hydrocracking
Hydrocracking Process Configuration
Figure 8. Conventional two-stage hydrocracker
The hydrocracking catalyst in the first stage has a high hydrogenation/acidity ratio,
causing sulphur and nitrogen removal
In the second reactor, the catalyst used is of a low hydrogenation/acidity ratio in which
naphtha production is maximized
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Название темы
Hydroconversion. Hydrocracking
Hydrocracking Process Configuration
Figure 9. Main reactions in two-stage hydrocracking
27
Название темы
Hydroconversion. Hydrocracking
Hydrocracking Severity
1. Conventional hydrocracking
2. Mild hydrocracking the process is run at less severe operating conditions similar to desulphurization
(hydrotreating) conditions
a one-stage reactor without recycle is used in mild hydrocracking
the production of a high yield of fuel oil and savings of hydrogen
Table 6. Comparison of operating conditions of mild hydrocracking, hydrotreating and
conventional hydrocracking
28
Название темы
Hydroconversion. Catalytic Dewaxing
Catalytic Dewaxing
Catalytic dewaxing is a particular hydrocracking process used to
improve cold flow properties of middle distillates and lubricants by
cracking normal paraffins.
Dewaxing can be achieved by isomerization. Isoparaffins have lower
melting points than normal paraffins.
The properties targeted for improvement are
pour point and viscosity of middle distillates and lubricants
the cloud point of diesel fuel
the freeze point of jet fuel
29
Название темы
Hydroconversion. Catalytic Dewaxing
Catalytic Dewaxing
A single-stage, once through hydrocracking process can be used for
catalytic dewaxing, with or without hydrotreating, depending on the
sulphur and nitrogen content of the feedstock.
The catalytic process is carried out as a trickle bed reactor over a
bifunctional zeolite catalyst under hydrogen flow.
A non-noble metal (e.g. nickel) supported on a medium-pore zeolite,
such as ZSM-5 can be used.
30
Название темы
Hydroconversion
Issues for Self-study and Revision
Fahim M.A., Sahhhaf T.A., Elkilani A.S. Fundamentals of Petroleum Refining: – First Edition. –
Elsivier. – 2010. – 485 p. Hydrotreating pp. 153-171
Hydrocracking pp. 180-192
Meyers Robert A. (ed.) Handbook of petroleum refining processes. 3-rd edition. McGraw-Hill
Professional. – 2003. – 847 p.
Isocracking-hydrocracking for superior fuels and lubes production pp. 317-336