Crude oil Treatment process Hydrotreatment Amine recovery

Hydrotreater BP-UK

Hydrotreatment What is hydrotreatment? It is a process to catalytically stabilize and/or remove undesirable elements from products or feedstocks by reacting them with hydrogen.  Stabilization usually involves converting unsaturated hydrocarbons such as olefins to paraffins. Undesirable elements removed by hydrotreating include sulfur, nitrogen, oxygen, halides, and metals.

Difference between Hydrotreating and Hydrocracking Hydrotreating and hydrocracking both can be called Hydroprocessing

PROCESS VARIABLES The principal operating variables are temperature, hydrogen partial pressure, and space velocity. Liquid Hourly Space Velocity (LHSV)= Volumetric flow rate/volume Weight Hourly Space Velocity (WHSV)= Mass flow rate/catalyst mass Increasing temperature and hydrogen partial pressure increases sulfur and nitrogen removal and hydrogen consumption. Increasing hydrogen partial 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.

PROCESS VARIABLES Typical ranges of process variables in hydrotreating operations are

Hydrotreatent Reactions Convert Organic S to Hydrogen Sulfide Convert Organic N to Ammonia Convert Organic O to Water Convert Organic halides to Hydrogen Halides Saturate Olefins Saturate Aromatics Remove Metals

Desulfurization Increasing Difficulty

Denitrogenation Denitrogenation is usually more complex than desulfurization.

Oxygen Removal

Olefin Saturation Olefins are unstable components and they polymerize in presence of oxygen Olefin saturation is very rapid and exothermic reaction

Aromatic Saturation Aromatics present as 1, 2, 3 or more rings structure Aromatic saturation is a stepwise reaction Aromatic saturation is an exothermic reaction

Aromatic Saturation

Halide Removal

Metals Removal Lead, mercury, arsenic, silicon, nickel, vanadium, sodium Compounds that contain metals decompose in reactor and deactivate catalyst The metal deposited on catalyst cannot be removed by regeneration

Lead poisoning effect on catalyst activity

Arsenic poisoning effect on catalyst activity

Sodium poisoning effect on catalyst activity

Ease of hydrotreatment reactions

Guard Reactor

Hydrotreatment Catalyst Solid consisting of a base alumina impregnated with metal oxides Pellets shaped as cylindrical or pills For Desulfurization, Co-Mb catalyst is used For Desulfurization, Denitrogenation and Aromatic saturation, Ni-Mb catalyst is used

Sulfur recovery Hydrogen sulfide created from hydrotreating is a toxic gas that needs further treatment Solvent extraction: using diethanolamine (DEA) dissolved in water separates the H2S gas from the process stream (DEA should be recovered) 34

H2S separation_ Amine Unit 35

DEA Chemistry DEA: weak organic base to absorb acid gases of H2S and CO2 from gas streams. Chemical Structure: DEA = [HO(CH2)2]2 - NH C2H4OH \ N - H / The reaction of DEA with H2S and CO2 are equilibrium reactions: H2S: R2NH + H2S ⇋ R2NH2SH CO2: 2R2NH + H2O + CO2 ⇋ (R2NH2)2CO3 where R = HO(CH2)2 Absorption Absorption is favoured by high pressures and low temperatures 36

Amine Regeneration Regeneration is favoured: low P and high T Acid gas components are boiled out of the amine solution The required heat input to the reboiler: Sensible heat required to bring the rich amine from the inlet temperature (~95°C) to the column base temperature (~127°C)  Heat of reaction to desorb the acid gas components.   Heat of vapourisation to generate sufficient water vapour within the column to strip the acid gas components in the amine Need to ensure that temperatures are maintained below 130°C to prevent amine degradation and subsequent amine corrosion 37

DEA Properties Amine Strength: Amine Loading: Ideally 25-27wt% DEA Higher amine concentrations = higher regenerator boiling temperatures and increased corrosion rates Lower amine concentrations = higher circulation rates and thus increase energy requirements for pumping and regeneration Amine Loading: Amine Loading = mol (H2S) + mol (CO2) mol (DEA) Target is an amine loading of 0.3 – 0.5 mol/mol 38

End of Chapter Nine