Catalytic Cracking Processes

Question 1

What are the properties of the catalyst for the FCC ?

Answer 1

• Fine powder catalyst

- Acidic alumina-silica

Question 2

What are FCC catalyst made of ?

Answer 2

FCC catalysts use a blend of amorphous and crystallized silica-alumina called zeolite or molecular sieves

Question 3

What are the different types of molecular sieves ?

Answer 3

A type, X and Y types

Question 4

What is the type of molecular sieves used for FCC catalyst ?

Answer 4

Y type

Question 5

What is the difference between A and X and Y sieves type ?

Answer 5

• A-sieves have small windows and are used for drying and separation
• X and Y sieves have larger windows to allow large molecules to enter and react

Question 6

What is the composition of the FCC catalyst ?

Answer 6

• 10-50 % zeolite (acidic function)

- the rest is amorphous silica-alumina

Question 7

What is the average diameter of an FCC catalyst ?

Answer 7

60-65 microns

Question 8

What are the operating conditions in the FCC ?

Answer 8

• T : 520 to 540°C
• P : 2 to 3 bar
• FCC catalyst

Question 9

What are the possible feeds for the FCC ?

Answer 9

• VGO from vacuum distillation
• Vacuum residue with low metal content
• VGO from visbreaker …

Question 10

What is the cycle occuring in the FCC ?

Answer 10

• The feed reacts with the catalyst
• The spent catalyst is sent to the regenerator
• The coke is burnt in the regenerator
• The hot regenerated catalyst is sent back to react with the feed

Question 11

What is the catalyst circulation in the FCC ?

Answer 11

From 10 to 30 t/min

Question 12

What is the part of coke on the used catalyst ?

Answer 12

Around 1 wt%

Question 13

How is the catalyst flow controlled in the FCC ?

Answer 13

The catalyst flows naturally -> no flowmeter or control valve

Question 14

In which part of the reactor does the reaction occur in a FCC ?

Answer 14

In the riser

Question 15

How long does the cracking last in an FCC ?

Answer 15

Several seconds

Question 16

What is the temperature range in the regenerator of the FCC ?

Answer 16

700 to 750°C

Question 17

What measure is taken to recover the particles of catalyst in the FCC ?

Answer 17

Cyclones in the reactor and the regenerator

Question 18

How are the products separated after the FCC ?

Answer 18

There is a fractionation column

Question 19

What is the tehcnology that enables to better control the temperature rise in the FCC during coke burning ?

Answer 19

R2R : 1 reactor and 2 regenerators

Question 20

What are the products of the FCC ?

Answer 20

• Fuel gas (C2 + H2S)
• C3 cut
• C4 cut
• Cracked naphthas = FCC gasoline
• LCO
• Heavy cuts

Question 21

What is the yield of the gas cut in the FCC ?

Answer 21

3 to 5%

Question 22

What is the yield of the C3 cut in the FCC ?

Answer 22

5 to 9 %

Question 23

What are the components found in the C3 cut of the FCC ?

Answer 23

Propane and Propylene (70%)

Question 24

What is the yield of the C4 cut in the FCC ?

Answer 24

6 to 12 %

Question 25

What are the components found in the C4 cut of the FCC ?

Answer 25

- n-butane - isobutane - butenes - isobutene

Question 26

What are the reactants and products of the alkylation unit ?

Answer 26

- Reactants : isobutane + butenes | - Products : isooctanes

Question 27

What are the operating conditions of the alkylation unit ?

Answer 27

- 30°C (HF)or 10°C (H2SO4) - P = 12 bar - Catalyst (liquid acid)

Question 28

What is the octane number of the alkylate ?

Answer 28

RON : 94 to 97 | MON : 92 to 95

Question 29

Where is the alkylation unit located in a refinery ?

Answer 29

Usually close to FCC

Question 30

What are the advantages of the alkylation unit ?

Answer 30

- Increased octane number | - Increased production of automotive fuel bases

Question 31

What are the reactants to make MTBE and ETBE ?

Answer 31

- methanol + isobutene -> MTBE | - ethanol + isobutene -> ETBE

Question 32

What are the operating conditions for the MTBE/ETBE reaction ?

Answer 32

- T = 80°C - P = 20 bar - Catalyst : acid resins

Question 33

What is the usual yield of FCC gasoline ?

Answer 33

40 to 50 %

Question 34

What is the octane number of the FCC gasoline ?

Answer 34

RON : 92-93 | MON : 79-80

Question 35

Why are we limited to add FCC gasoline in the final product ?

Answer 35

- sulfur content (100 to 1500 ppm) | - olefin content (usually 30% vol for a max of 18%)

Question 36

How can we solve the problem of sulfur content in FCC gasoline ?

Answer 36

- HDT of FCC feed | - Desulfurization of FCC gasoline

Question 37

What is the usual yield of LCO in the FCC unit ?

Answer 37

15 to 25 %

Question 38

What is the problem with LCO for gas oil pool ?

Answer 38

High aromatic content -> low cetane

Question 39

What is the usual yield of HCO in the FCC ?

Answer 39

6 to 10 %