Hydrotreatments

Question 1

In what form are the impurities extracted in HDT units ?

Answer 1

• H2S
• H2O
• NH3
• Metals trapped in catalyst
• Unsaturated compounds are hydrogenated

Question 2

Under what form is sulfur found in light and intermediate cuts ?

Answer 2

Mainly mercaptants (RSH), sulfides (RSR) and thiophenic compounds (S in unsaturated cycle)

Question 3

Under what form is sulfur found in gasoil and residue ?

Answer 3

Mainlybenzothiophenic and dibenzothiophenic compounds (S in unsaturated cycle with one or two other aromatic cycles)

Question 4

Why don’t we like sulfur ?

Answer 4

• It produces pollutants SO2 and SO3
• It’s a source of corrosion
• It smells bad
• It’s a poison for catalyst

Question 5

Why don’t we like nitrogen in crude ?

Answer 5

• It’s a basic compound that can poison catalysts (with acidic function)
• It’s more difficult to extract than S

Question 6

In which cuts are metals mostly present ?

Answer 6

Vaccum residue (asphaltenes)

Question 7

How are residues treated to remove impurities ?

Answer 7

Hydrodemetallization

Question 8

Why is hydrodemetallization a complex and costly process ?

Answer 8

• Very high pressure (200 bar)
• Large amount of catalyst (because we trap the metal in the catalyst)
• We need new technologies to remove the catalyst when it’s saturated with metal

Question 9

Which conditions promote hydrotreatment reactions ?

Answer 9

• Increase of T

- Increase of P

Question 10

What is the range of T for HDT units in a refinery ?

Answer 10

From 300°C (light cuts) to 400 (heavy cuts)

Question 11

What is the range of P for HDT units in a refinery ?

Answer 11

From 20 bar (light cuts) up to 200 bar (residue)

Question 12

What characterizes hydrotreatment reactions ?

Answer 12

• ExoT
• H2 consumers
• Induce coke formation
• Can increase cetane of 3 to 4 points

Question 13

What are the two typical combination of metals in HDT catalyst ?

Answer 13

• Cobalt/Molybdene for S

- Nickel/Molybdene for N and hydrogenation

Question 14

What is the typical amount of catalyst needed depending on the cut (for 100 t/h of feed) ?

Answer 14

• Light cut : 30 t
• Gasoil : 75 t
• VGO : 200 t
• Vaccuum residue : 300 t

Question 15

Why do we need more catalyst for heavy feeds ?

Answer 15

The heavier the feed, the harder it is to treat, the more residence time we need and therefore the bigger the reactor and the more catalyst we need

Question 16

What kind of HDT for fuel gas, LPG and naphtha ?

Answer 16

HDT to remove S, N and olefins

Question 17

What kind of HDT for kerosene ?

Answer 17

Sweetening to remove mercaptants

Question 18

What kind of HDT for gasoil ?

Answer 18

HDS

Question 19

What kind of HDT for VGO ?

Answer 19

HDT to remove sulfur and hydrogenation of aromatics

Question 20

What kind of HDT for vacuum residue ?

Answer 20

HDM + HDT to remove sulfur

Question 21

What can we do to limit exoT in gasoli HDS ?

Answer 21

Quench with cold H2 in the reactor to limit exoT to 15°C

Question 22

What arethe typical T and P in a gasoil HDS ?

Answer 22

T = 360 and P = 60 bar

Question 23

What are the separation units after an HDS unit ?

Answer 23

• HP separator to remove H2 (55 bar)
• LP separator to remove H2S (10 bar)
• Gasoil stripper to recover wild naphtha
• Vacuum dryer after stripper to recover Gasoil

Question 24

What are the two kinds of loading in HDS ?

Answer 24

Sock vs Dense loading

Question 25

How much do we gain with dense loading ?

Answer 25

We can have 15 to 20% more catalyst