Catalytic Cracking Processes Flashcards
What are the properties of the catalyst for the FCC ?
- Fine powder catalyst
- Acidic alumina-silica
What are FCC catalyst made of ?
FCC catalysts use a blend of amorphous and crystallized silica-alumina called zeolite or molecular sieves
What are the different types of molecular sieves ?
A type, X and Y types
What is the type of molecular sieves used for FCC catalyst ?
Y type
What is the difference between A and X and Y sieves type ?
- 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
What is the composition of the FCC catalyst ?
- 10-50 % zeolite (acidic function)
- the rest is amorphous silica-alumina
What is the average diameter of an FCC catalyst ?
60-65 microns
What are the operating conditions in the FCC ?
- T : 520 to 540°C
- P : 2 to 3 bar
- FCC catalyst
What are the possible feeds for the FCC ?
- VGO from vacuum distillation
- Vacuum residue with low metal content
- VGO from visbreaker …
What is the cycle occuring in the FCC ?
- 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
What is the catalyst circulation in the FCC ?
From 10 to 30 t/min
What is the part of coke on the used catalyst ?
Around 1 wt%
How is the catalyst flow controlled in the FCC ?
The catalyst flows naturally -> no flowmeter or control valve
In which part of the reactor does the reaction occur in a FCC ?
In the riser
How long does the cracking last in an FCC ?
Several seconds
What is the temperature range in the regenerator of the FCC ?
700 to 750°C
What measure is taken to recover the particles of catalyst in the FCC ?
Cyclones in the reactor and the regenerator
How are the products separated after the FCC ?
There is a fractionation column
What is the tehcnology that enables to better control the temperature rise in the FCC during coke burning ?
R2R : 1 reactor and 2 regenerators
What are the products of the FCC ?
- Fuel gas (C2 + H2S)
- C3 cut
- C4 cut
- Cracked naphthas = FCC gasoline
- LCO
- Heavy cuts
What is the yield of the gas cut in the FCC ?
3 to 5%
What is the yield of the C3 cut in the FCC ?
5 to 9 %
What are the components found in the C3 cut of the FCC ?
Propane and Propylene (70%)
What is the yield of the C4 cut in the FCC ?
6 to 12 %
What are the components found in the C4 cut of the FCC ?
- n-butane
- isobutane
- butenes
- isobutene
What are the reactants and products of the alkylation unit ?
- Reactants : isobutane + butenes
- Products : isooctanes
What are the operating conditions of the alkylation unit ?
- 30°C (HF)or 10°C (H2SO4)
- P = 12 bar
- Catalyst (liquid acid)
What is the octane number of the alkylate ?
RON : 94 to 97
MON : 92 to 95
Where is the alkylation unit located in a refinery ?
Usually close to FCC
What are the advantages of the alkylation unit ?
- Increased octane number
- Increased production of automotive fuel bases
What are the reactants to make MTBE and ETBE ?
- methanol + isobutene -> MTBE
- ethanol + isobutene -> ETBE
What are the operating conditions for the MTBE/ETBE reaction ?
- T = 80°C
- P = 20 bar
- Catalyst : acid resins
What is the usual yield of FCC gasoline ?
40 to 50 %
What is the octane number of the FCC gasoline ?
RON : 92-93
MON : 79-80
Why are we limited to add FCC gasoline in the final product ?
- sulfur content (100 to 1500 ppm)
- olefin content (usually 30% vol for a max of 18%)
How can we solve the problem of sulfur content in FCC gasoline ?
- HDT of FCC feed
- Desulfurization of FCC gasoline
What is the usual yield of LCO in the FCC unit ?
15 to 25 %
What is the problem with LCO for gas oil pool ?
High aromatic content -> low cetane
What is the usual yield of HCO in the FCC ?
6 to 10 %
