1. Crude oil Treatment process
Hydrotreatment
Sulfur recovery
Amine recovery

4. Hydrotreatment Catalyst
Solid consisting of a base alumina impregnated with metal oxides
Pellets shaped as cylindrical or pills
HDS: Co-Mb (hydrodesulfurization (HDS )
HDS, HDN and aromatics: Ni-Mb
(Hydrodenitrogenation (HDN )

5. Metals Removal
Lead, mercury, arsenic, silicon, nickel, vanadium, sodium
Decompose in reactor and deactivate catalyst
Cannot be removed by regeneration

6. Lead poisoning effect on catalyst activity

7. Arsenic poisoning effect on catalyst activity

8. Sodium poisoning effect on catalyst activity

9. Ease of hydroprocessing reactions

10. PROCESS VARIABLES
The principal operating variables are temperature, hydrogen partial pressure, and space velocity.
Increasing temperature and hydrogen partial pressure increases sulfur and nitrogen removal and hydrogen consumption.
Increasing pressure also increases hydrogen saturation and reduces coke formation.
Increasing space velocity reduces conversion, hydrogen consumption, and coke formation.
Although increasing temperature improves sulfur and nitrogen removal, excessive temperatures must be avoided because of the increased coke formation.

11. PROCESS VARIABLES
Typical ranges of process variables in hydrotreating operations are

12. Sulfur recovery
Hydrogen sulphide (H2S) created from hydrotreating is a toxic gas that needs further treatment
The usual process involves two steps:
1. Removal of the hydrogen sulphide gas from the hydrocarbon stream.
2. Conversion of hydrogen sulphide to elemental sulphur.
Solvent extraction: using diethanolamine (DEA) dissolved in water separates the H2S gas from the process stream (DEA should be recover)
The DEA and hydrogen mixture is then heated at a low pressure and the dissolved H2S is released as a concentrated gas stream which is sent to another plant for conversion into sulphur (SRU)

13. Chemistry
Conversion of the concentrated H2S gas into sulphur occurs in two stages:
Thermal reaction in furnace
Catalyst reaction in the reactor
As the reaction products are cooled the sulphur drops out of the reaction vessel in a molten state. Sulphur can be stored and shipped in either a molten or solid state.

14. The Claus Process
The overall reaction that takes place in the SRU is known as the Claus Reaction and can be represented by the following equation:    
1.  Thermal Reaction:
1/3 of the H2S in the acid gas stream is partially oxidised to sulphur dioxide in the Muffle Furnace to produce a 2:1 molar ratio of H2S to SO2.
3H2S + 3/2 O2  SO2 + H2O + 2H2S DH = kJ/mol H2S
This reaction occurs at ~1100oC and the energy released is used to generate steam in a waste heat boiler.
2. Catalytic Reaction: The remaining 2/3 of the H2S is reacted over a catalyst with SO2 produced in (1) to form elemental sulphur.
2H2S + SO2  3S + 2H2O DH = -31 kJ/mol H2S
Thermal and catalytic reactions are Reversible reactions
Thermodynamic Equilibrium

15. Thermodynamic Equilibrium
There are 2 regions of high conversion of H2S to elemental sulphur
High Temperatures – thermal reaction
Low Temperatures – catalytic reaction
Often the Claus process is kinetically limited due to residence time and mixing issues, especially in the burner in the Muffle Furnace
Activated alumina (Al2O3) – (Co-Mb)
Average life in a refinery SRU is 3-5 years

16. Incineration or Further Treatment
Claus Process
H2S O2
Muffle Furnace
925 – 1300 C
Thermal Reaction
Waste Heat Boiler
HP Steam – 3400kPa
Catalytic Reaction
Reactor)s)
170 – 350 C
Sulphur Condenser
LP Steam – 345kPag
Liquid Sulphur
Incineration or Further Treatment

17. Claus Process Acid Gas Produced in the Amine Regenerators
(Major components of acid gas: H2S, CO2, light HC

18. COS and CS2
Formation
The presence of CO2 and HC in the feed gases to the Claus plant gives rise to carbonyl sulphide (COS) and carbon disulphide (CS2) in the Muffle Furnace and Waste Heat Boiler
If these compounds are not hydrolysed back to H2S they will proceed through the catalytic reactors unreacted
This results in reduced sulphur conversion and decreased SRU efficiency.

19. COS and CS2 COS and CS2 Destruction
The hydrolysis reactions can be written as:
COS + H2O  CO2 + H2S
CS H2O  CO H2S
Hydrolysis is favoured by high temperatures (>310C)
The ability of the catalyst to carry out the COS/CS2 hydrolysis reactions depends on:
1.         the catalyst formulation
2.         the operating temperatures in the first reactor
3.         the state of deactivation of the catalyst
Destruction
The hydrolysis reactions can be written as:
COS + H2O  CO2 + H2S
CS H2O  CO H2S
Hydrolysis is favoured by high temperatures (>310C)
The ability of the catalyst to carry out the COS/CS2 hydrolysis reactions depends on:
1.         the catalyst formulation
2.         the operating temperatures in the first reactor
3.         the state of deactivation of the catalyst
Alternative: SCOT Process

20. SRU Efficiency
Sulphur recovery efficiency is a measure of the percentage of sulphur present in SRU feed as H2S, that is converted and recovered as liquid elemental sulphur.
Recovery = SPRODUCED/SFEED(as H2S)

21. End of lecture