1. No category

How ZSM-5 works in FCC
Tom Ventham, Bart de Graaf, Mehdi Allahverdi, Martin Evans & Paul Diddams
Abu Dhabi International Downstream 2015
History of ZSM-5
• 1983: First commercial application in Neste Oy TCC unit
− Composite catalyst containing REY and ZSM-5
− Achieved +4 gasoline RON increase
• Main objective of initial ZSM-5 applications: Octane
− ZSM-5 improves octane more rapidly than reducing UCS
− Less dry gas production than increased Riser temperature
• ZSM-5 also used to increase alkylation or ETBE feed
• 2015: maximum propylene FCC operation established
FCC Process Optimisation for max. C3=
• Increase conversion through operation severity:
−
−
−
−
Increase cracking temperature
Increase catalyst circulation (catalyst-to-oil ratio)
Increase Ecat activity
Improve feed quality
• Minimise hydrocarbon partial pressure
• Naphtha / butylene recycle
− Crack all potential propylene precursors out of gasoline
Catalyst changes for max. C3=
• Maximise catalytic β-scission relative to:
−
−
−
−
Thermal cracking
Dehydrogenation
Hydrogen transfer
Polymerization
• How to reduce Hydrogen Transfer reactions:
− Reduce Unit Cell Size
 Reducing fresh catalyst rare earth (RE) on Zeolite-Y
− Optimise fresh catalyst zeolite-to-matrix ratio
• Use high activity ZSM-5 containing additives
If successfully executed, >10wt% propylene
yield achievable from typical FCC
configuration
Gasoline cracking test: Ecat & ZSM-5
• Laboratory test: crack a gasoline stream over FCC catalyst:
− Typical FCC gasoline stream
− ACE unit testing
− First tested with typical FCC Ecat without ZSM-5, then same Ecat with ZSM-5
• Most significant shift:
− Δolefins & Δnaphthenes > Δparaffins & Δaromatics
Gasoline Feed
without ZSM-5
with ZSM-5
Paraffins
34.9
32.4
28.7
Olefins
31.5
14.1
-55%
11.0
-65%
Naphthenes
11.6
6.3
-46%
6.4
-45%
Aromatics
21.5
22.7
23.5
Total Gasoline
99.5
75.5
69.3
• ZSM-5 increases aromatics present in the final product
VGO cracking test: Ecat & ZSM-5
• This time VGO is cracked over Ecat and Ecat + 25% ZSM-5
− ACE test at 65 wt% conversion
− All yields reported on weight % feed basis
• ZSM-5 cracks gasoline into LPG:
without ZSM-5
with ZSM-5
Delta
LPG (wt%)
14.7
23.6
+8.9
Gasoline (wt%)
43.1
33.6
-9.5
• Is the increase in LPG equal to the change in gasoline olefins?
without ZSM-5
with ZSM-5
Delta
LPG (wt%)
14.7
23.6
+8.9
Gasoline olefins (wt%)
7.7
5.1
-2.6
VGO cracking test: Ecat & ZSM-5 (part II)
• Most significant shifts in gasoline yield:
− paraffins > olefins > naphthenes > aromatics
without ZSM-5
with ZSM-5
Delta
Paraffins (wt%)
17.2
11.5
-5.7
Olefins (wt%)
7.7
5.1
-2.6
4
3.6
-0.4
14.2
13.5
-0.7
Naphthenes (wt%)
Aromatics (wt%)
• Which paraffins are most impacted by ZSM-5?
without ZSM-5
with ZSM-5
Delta
Paraffins (wt%)
17.2
11.5
-5.7
n-Paraffins (wt%)
1.2
0.9
-0.3
i-Paraffins (wt%)
9.3
4.6
-4.7
SC Paraffins* (wt%)
6.7
6.0
-0.7
*SC Paraffins = Side-chain paraffins originating from aromatic cores
-51%
Zeolite in FCC: commercial example 2015
• Main catalyst used at a maximum propylene FCC unit
− Fresh catalyst contains 40% RE-USY (Zeolite-Y)
− Once equilibrated, 50% crystal retention (Silica-to-Alumina Ratio increases)
• ZSM-5 added at 30% of additions (40% crystal)
− Once equilibrated, 100% crystal retention (SAR increases)
• Zeolite ratio in FCC inventory:
− RE-USY:
− ZSM-5 :
70% * 40% * 50% = 14% (54%)
30% * 40% * 100% = 12% (46%)
• 46% of all zeolite in FCC inventory is ZSM-5 crystal!
How ZSM-5 Works in FCC
LPG Olefins
Product of beta-scission
Oligomerization
precursors
C3=, C4=
Aromatic
Transalkylation
Gasoline Range
Molecules
Olefin
Aromatization
Oligomers
Olefin
Isomerization
How ZSM-5 Works in FCC
LPG Olefins
Product of beta-scission
Oligomerization
precursors
C3=, C4=
Aromatic
Transalkylation
Gasoline Range
Molecules
Olefin
Aromatization
Oligomers
Olefin
Isomerization
How ZSM-5 Works in FCC
LPG Olefins
Product of beta-scission
Oligomerization
precursors
Aromatic
Transalkylation
Gasoline Range
Molecules
Olefin
Aromatization
Oligomers
wt% xylenes
Base
5% ZSM-5 25% ZSM-5
50% ZSM-5
Olefin 51
Isomerization
48
m-xylene
53
53
p-xylene
20
20
21
26
o-xylene
27
27
27
26
How ZSM-5 Works in FCC
LPG Olefins
Product of beta-scission
Oligomerization
precursors
Aromatic
Transalkylation
Gasoline Range
Molecules
Olefin
Aromatization
Gasoline cracking
Oligomers
Increase in
aromatic cores
over ZSM-5
Gasoline
without ZSM-5
with ZSM-5
Paraffins
34.9
32.4
28.7
Olefins
31.5
11.0
Naphthenes
Olefin14.1
11.6 Isomerization
6.3
Aromatics
21.5
22.7
23.5
Total Gasoline
99.5
75.5
69.3
6.4
How ZSM-5 Works in FCC
LPG Olefins
Product of beta-scission
Oligomerization
precursors
Aromatic
Transalkylation
Gasoline Range
Molecules
Olefin
Aromatization
Conversion, %
Oligomers
Olefin
Isomerization
How ZSM-5 Works in FCC
LPG Olefins
J. Mol. Catal 17 (1982) 161
Product of beta-scission
Oligomerization precursors
Aromatic
Transalkylation
Propylene
cracked
over ZSM-5
Carbon number 
Gasoline Range
Molecules
Olefin
Aromatization
Oligomers
Olefin
Isomerization
How ZSM-5 Works in FCC
LPG Olefins
Product of beta-scission
Oligomerization precursors
Aromatic
Transalkylation
Gasoline Range
Molecules
Olefin
Aromatization
Oligomers
Olefin
Isomerization
Reactions over RE-USY and ZSM-5
Δ Propylene: 7 wt%
Δ Butylenes: 3 wt%
-6wt%
-5wt%
Gasoline components (wt% of feed)
C4=
+3wt%
C3=
+7wt%
LPG components (wt% of feed)
Effect of ZSM-5 on LPG Olefins
Δ Gasoline Olefins: 5 wt%
Δ Gasoline Paraffins: 6 wt%
Conclusions - How ZSM-5 works in FCC
• ZSM-5 chemistry in FCC is still the same as when it was
first applied: ZSM-5 reacts with gasoline olefins
• As with gasoline olefins, LPG olefins are not just a final
product, they are intermediates that can undergo a wide
range of different reactions
• ZSM-5 is used nowadays in similar zeolite concentrations
to RE-USY in maximum propylene applications