Page 151 - Fluid Catalytic Cracking Handbook

126 Fluid Catalytic Cracking Handbook

Table 4-1
Important Reactions Occurring in FCC

1. Cracking:
Paraffins cracked to olefins
and smaller paraffins

Olefins cracked to smaller olefins C 9H l8 -> C 4H 8 + C 5H 10
Aromatic side-chain scission ArC 10H 21 ArC 5H 9 C SH 1
Naphthenes (cyclo-paraffins)
cracked to olefins and smaller
ring compounds Cyclo-C 1oH 20 -> C 6H 12 C 4H 8
2. Isomerization:

Olefin bond shift 1-C 4H 8 -^ trans-2-C 4H 8
Normal olefins to iso-olefin n-C 5H 10 — > iso-C 5H 10
Normal paraffins to iso-paraffin n-C 4H 10 iso-C 4H lo

Cyclo-hexane to cyclo-pentane C 6H 12 + C 5H 9CH 3
3. Hydrogen Transfer: Naphthene + Olefin
-» Aromatic + Paraffin
Cyclo-aromatization

4. Trans-alkylation/Alkyl-group
Transfer C 6H 6 2C 6H 5CH 3

5. Cyclization of Olefins to
Naphthenes C 7H 14 -^ CH 3-cyclo-C 6H ii
6. Dehydrogenation n-C 8H 18 ~^ C 8 16 + H 2
H
7. Dealkylation lso-C 3H 7-C 6H 5 -» C 6H 6 -\. C 3H 6
C 3H 6
8. Condensation Ar-C 3H == CH 2 + R,CH = CHR 2
v AT Ar + 2H
7 jT\I

THERMAL CRACKING

Before the advent of the catalytic cracking process, thermal cracking
was the primary process available to convert low-value feedstocks into
lighter products. Refiners still use thermal processes, such as delayed
coking and visibreaking, for cracking of residual hydrocarbons.