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TU2 - Refining and Gas Processes > Catalytic Cracking Processes > Flashcards

Catalytic Cracking Processes Flashcards

1
Q

What are the properties of the catalyst for the FCC ?

A
  • Fine powder catalyst

- Acidic alumina-silica

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2
Q

What are FCC catalyst made of ?

A

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

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3
Q

What are the different types of molecular sieves ?

A

A type, X and Y types

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4
Q

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

A

Y type

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5
Q

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

A
  • 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
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6
Q

What is the composition of the FCC catalyst ?

A
  • 10-50 % zeolite (acidic function)

- the rest is amorphous silica-alumina

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7
Q

What is the average diameter of an FCC catalyst ?

A

60-65 microns

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8
Q

What are the operating conditions in the FCC ?

A
  • T : 520 to 540°C
  • P : 2 to 3 bar
  • FCC catalyst
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9
Q

What are the possible feeds for the FCC ?

A
  • VGO from vacuum distillation
  • Vacuum residue with low metal content
  • VGO from visbreaker …
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10
Q

What is the cycle occuring in the FCC ?

A
  • 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
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11
Q

What is the catalyst circulation in the FCC ?

A

From 10 to 30 t/min

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12
Q

What is the part of coke on the used catalyst ?

A

Around 1 wt%

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13
Q

How is the catalyst flow controlled in the FCC ?

A

The catalyst flows naturally -> no flowmeter or control valve

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14
Q

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

A

In the riser

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15
Q

How long does the cracking last in an FCC ?

A

Several seconds

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16
Q

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

A

700 to 750°C

17
Q

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

A

Cyclones in the reactor and the regenerator

18
Q

How are the products separated after the FCC ?

A

There is a fractionation column

19
Q

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

A

R2R : 1 reactor and 2 regenerators

20
Q

What are the products of the FCC ?

A
  • Fuel gas (C2 + H2S)
  • C3 cut
  • C4 cut
  • Cracked naphthas = FCC gasoline
  • LCO
  • Heavy cuts
21
Q

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

A

3 to 5%

22
Q

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

A

5 to 9 %

23
Q

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

A

Propane and Propylene (70%)

24
Q

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

A

6 to 12 %

25
Q

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

A
  • n-butane
  • isobutane
  • butenes
  • isobutene
26
Q

What are the reactants and products of the alkylation unit ?

A
  • Reactants : isobutane + butenes

- Products : isooctanes

27
Q

What are the operating conditions of the alkylation unit ?

A
  • 30°C (HF)or 10°C (H2SO4)
  • P = 12 bar
  • Catalyst (liquid acid)
28
Q

What is the octane number of the alkylate ?

A

RON : 94 to 97

MON : 92 to 95

29
Q

Where is the alkylation unit located in a refinery ?

A

Usually close to FCC

30
Q

What are the advantages of the alkylation unit ?

A
  • Increased octane number

- Increased production of automotive fuel bases

31
Q

What are the reactants to make MTBE and ETBE ?

A
  • methanol + isobutene -> MTBE

- ethanol + isobutene -> ETBE

32
Q

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

A
  • T = 80°C
  • P = 20 bar
  • Catalyst : acid resins
33
Q

What is the usual yield of FCC gasoline ?

A

40 to 50 %

34
Q

What is the octane number of the FCC gasoline ?

A

RON : 92-93

MON : 79-80

35
Q

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

A
  • sulfur content (100 to 1500 ppm)

- olefin content (usually 30% vol for a max of 18%)

36
Q

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

A
  • HDT of FCC feed

- Desulfurization of FCC gasoline

37
Q

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

A

15 to 25 %

38
Q

What is the problem with LCO for gas oil pool ?

A

High aromatic content -> low cetane

39
Q

What is the usual yield of HCO in the FCC ?

A

6 to 10 %

TU2 - Refining and Gas Processes (14 decks)

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