This document discusses steam cracking, the dominant process for producing olefins like ethylene and propylene. Steam cracking involves the thermal decomposition of hydrocarbon feedstocks in the absence of oxygen, breaking carbon-carbon and carbon-hydrogen bonds. The cracking occurs through either free radical or molecular reaction pathways and is affected by variables like temperature, pressure, and feedstock composition. The document focuses on pyrolysis reactions and mechanisms for cracking various petrochemical feedstocks including ethane, propane, n-butane, and naphtha.

1. CE4102
Petrochemical Processes
Rinaldi M Rachman S.T., M.S.
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2. CE4102
Petrochemical Processes
Learning Outcomes:
1. Cracking Reaction Principles
2. Operating Variables on Steam Cracking
3. Cracking Furnace
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Lecture 3
OLEFINS PRODUCTION Part 2: Steam Cracking

3. Petrochemical Processes
Thermal Cracking
▪ Dominate among routes to olefins production
▪ is the heart of Petrochemical Complex produces majorly ethylene (the king! of building blocks) and
propylene (the crown prince!)
▪ Principally PYROLISIS: thermal decomposition of hydrocarbon in an absence of oxygen.
▪ Bond breakage/scission: C-H & C-C
▪ C-C Scission produces paraffin and olefin:
▪ C-H scission produces olefin and H2:
▪ Thermodynamics profile:
▪ Endothermic: required high energy
▪ Favors: C-C scisson
▪ Favors (P&T): High Temperature and Lower Pressure (towards the increasing number or molecules)
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C(m+n)H2 m+n +2 → CmH2m + CnH2n+2
CpH2p+2 → CpH2p +H2
∆GT
0=75,200 − 142T [=] J/mol
∆GT
0=125,400 − 142T for p>4 [=] J/mol

4. Petrochemical Processes
Bond Dissociation Energy (BDE)
▪ Longer HC chain → Lower BDE → Lower Cracking Temperature
▪ Stability ORDER:
▪ Aromatics > Naphthenes > Diolefins > Olefins > Paraffins
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5. Petrochemical Processes
Thermal Cracking = Pyrolysis
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6. Petrochemical Processes
Free Radical Reaction Pathway
Free Radical Reaction STEPS
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7. Petrochemical Processes
Free Radical Reaction: INITIATION
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8. Free Radical Reaction: PROPAGATION
Petrochemical Processes 8

9. Petrochemical Processes
Free Radical Reaction: TERMINATION
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10. Petrochemical Processes
Molecular Reaction Pathway
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11. Petrochemical Processes
Molecular Scheme Reaction (cont'd)
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12. Petrochemical Processes
Pyrolysis Reactions
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13. Pyrolysis Reactions (cont'd)
Petrochemical Processes 13

14. 14
Variety of Feedstock
Petrochemical Processes

15. 15
Feed: H/C Ratio over Carbon Number
Petrochemical Processes

16. Petrochemical Processes 16
Pyrolysis of Gaseous Feedstock: Ethane

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Pyrolysis of Ethane
Partial List of Ethane Cracking Mechanisms
Petrochemical Processes

18. 18
Pyrolysis of Ethane (1)
Petrochemical Processes

19. Petrochemical Processes 19
Reaction Rate: Initiation Steps

20. Petrochemical Processes 20
Reaction Rate: Initiation Steps

21. Petrochemical Processes 21
Free Radicals Pyrolysis of Propane

22. Petrochemical Processes 22
Free Radicals Pyrolysis of n-butane

23. Petrochemical Processes 23
Pyrolysis of n-butane: Molecular Kinetics
Approximation

24. Petrochemical Processes 24
Pyrolysis of LIQ. Feedstock: Naphta
MOLECULAR SCHEME REACTION MECHANISM

25. Petrochemical Processes 25
Pyrolysis of LIQ. Feedstock: Naphta (cont'd)
FREE RADICAL REACTION MECHANISM

26. 2
OPERATING VARIABLES

27. Petrochemical Processes 27
Important Definition in Cracking