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Transcript of Worms Be Cher
8/12/2019 Worms Be Cher
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Catalytic Reduction of Sulfur
in Fluid Catalytic Cracking
Rick Wormsbecher
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Collaborators
Ruizhong HuMichael Ziebarth
Wu-Cheng Cheng
Robert H. Harding
Xinjin Zhao
Terry Roberie
Ranjit Kumar
Thomas Albro
Robert Gatte
Grace Davison Laboratoire Catalyse et Spectrochimie,
CNRS, Université de CaenFabian Can
Francoise Maugé
Arnaud Travert
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Outline
• Review of fluid catalytic cracking.• Sulfur balance and sulfur cracking
chemistry.
• Catalytic reduction of sulfur by
Zn aluminate/alumina.
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Fluid Catalytic Cracking• Refinery process that “cracks” high molecular
weight hydrocarbons to lower molecularweight.
• Refinery process that provides ~50 % of all
transportation fuels indirectly.• Provides ~35 % of total gasoline pool directly
from FCC produced naphtha.
• ~80 % of the sulfur in gasolines comes fromthe FCC naphtha.
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Sulfur in Gasoline
• Sulfur compounds reversibly poison the autoemission catalysts, increasing NOx andhydrocarbon emission. SOx emissions aswell.
• World-wide regulations to limit the sulfurcontent of transportation fuels. – 10 - 30 ppm gasoline.
• Sulfur can be removed by hydrogenationchemistry. – Expensive.
– Lowers fuel quality.
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Fluid Catalytic Cracking Unit
Feedstock Air
Flue Gas
Products
RiserReactor
(~500 ºC)
Regenerator
(~725 ºC)
50, 000
barrels/day
400 tons
catalyst
inventory
Reaction is endothermic.
Catalyst circulates fromRiser to Regenerator.
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Carbon DistributionH2 ~0.05 %
C1 ~1.0 %
C2-C4 ~14-18 %
C5-C11 ~50 %
C12-C22 ~15-25 %
C22+ ~5-15 %
Coke ~3-10 %
Feed
MW ~330 g/mole
Flare
Flare
Petrochem
Naphtha
LCO
HCORegen
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Catalyst Consumption
• 0.25 – 0.75 #’s/barrel• About 300,000 tons catalyst/year world
wide, for about 300 refiners.
• Consumption depends on feedstock
quality, mainly irreversible poisoning by
vanadium
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FCC Catalysts
• 10 - 50 % Y type zeolite, usually USY• 0 - 13 % Rare earth on zeolite
• 0 - 80 % active silica/alumina matrix• 0 - 50 % binder and kaolin
• Single component or blends• Additives for olefins, SOx, NOx, CO
• SULFUR REDUCTION TECHNOLOGY
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Solid acid catalysis
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Zeolite Y structure
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Cracking is Catalyzed by Solid
Acid/Hydrocarbon Interactions
• Initiation: Hydride abstraction by a Lewis siteor carbocation ion formation by a Brønsted
site.
• Propagation: Through primarily β-scission.• Product selectivities governed by stability of
product and the precursor carbocation.
• Isomerization, alkylation occur readily
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Formation of carbocation
transition states
CH2
R
H
HZ+R CH
3
H
Z
R R'
H
H
L+ R CH3
H
HL
R
HZ+
HH
R
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Beta scission
R CH2 CH2 CH2 CH2 R'
H
Z
R C CH CH2 CH2 R'Z
H
H
CH2
R' C CH CH2 CH2 RZ
H
H
CH2
CH2 CH2 R'
H
Z
H
CH3 CH2 R
H
Z
β
Charge isomerization
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Hydride Transfer (simplified)
- C - C - C -H H H
H H+
Z
+ H - Cfeed Cfeed +
Z
+ saturate
Hydride abstraction
High Brønsted site density favors hydride transfer.
Catalysts can be tailored with high or low site density.
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Feedstocks
• “Average” feed ~ 1.0 wt. % Sulfur • “Average” feed MW ~ 300 gr/mole
• ~ one in ten feed molecules contain S• S content ranges from 0 - 4.5 %
S f CC
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Sulfur Balance in a FCC Unit
F
C
C
Feed Sulfur (~0.3%)
Saturated Sulfur Thiophenes
Benzothiophenes
Multi-ring Benzothiophenes
Fuel Gas, H2S 40%
Gasoline 5%
Light Cycle Oil15 %
Bottoms 35 %
Coke, SOx 5 %
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Sulfur Species in FCC Gasoline (by GCAED)
20 40 60 80 1001.7e5
1.8e5
1.9e5
2.0e5
2.1e5
2.2e5
2.3e5
2.4e5
2.5e5
2.6e5
2.7e5
2.8e5Sig. 2 in C:\HPCHEM\1\DATA\D51024A\012R0501.D
Time (min.)
Thiophene
Methylthiophene
THT
C2-Thiophene
Benzothiophene
Methylthiophenol
C2-thiophenol
Benzenethiol
C3-thiophenes
Me-THT
C2-THT
SH
R
S
S
R
S
R
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Reaction Pathways of Sulfur Species
in FCCSulfur Species in Feedstock Sulfur Species in FCC Gasoline
Multi-Ring Aromatic Thiophenes
Alkylbenzothiophenes
Alkylthiophenes
Alkyl Sulfides, Mercaptans
(Including cyclic sulfides)
H2S + DiOlefin or Olefin
?
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Reaction Chemistry of S Compounds(Which Feedstock Sulfur Species End Up in Gasoline?)
• Spike a low sulfur (0.3wt% S) base feedstock with model S
compounds (0.7% wt% S).
• Look for yield changes in Microactivity Testing
• Compounds tested:
Thiols (octanethiol)
Sulfides (di-n-butylsulfide)
Alkylthiophenes (n-hexylthiophene, n-decylthiophene) Alkylbenzothiophenes (3- and 5-methylbenzothiophene)
Alkyldibenzothiophene (1,10-dimethyldibenzothiophene)
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Delta Yields of Gasoline Range Sulfur
Base Feedstock Spiked with Model S Compounds (0.7% S)
0
200
400
600
800
1000
1200
S u l f u r ,
p p m
Gasoline Sulfur C2-Thiophene
and Lighter
C3-,C4-Thiophene
+ Thiophenols
Benzo-Thiophene
Octanethiol
DecylThiophene
3-MethylBenzothiophene
5-MethylBenzothiophene
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Delta Yields of Gasoline Range Sulfur Base Feedstock (2.8% S) Spiked with Dimethyldibenzothiophene
(0.45% S)
0
20
40
60
80
100
120
S u l f u r , p p
m
C2-
Thiophene
and Lighter
C3-, C4-
Thiophenes
Thio-phenols Benzo
thiophene
1,10 DiMethyl-DiBenzothiophene
Recombination of H S and diolefin
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DCR Testing: Polysulfide and diolefin addition to a low sulfur
feedstock
(1% S) Di-Olefin +
Base 2% Di-Olefin Polysul fide Polysul fide
Mercaptans, ppm 5.1 7.3 47.4 30.7
C0-C4 Thiophenes, ppm 44.4 50.7 68.0 145.9
BenzoThiophene, ppm 13.3 11.2 11.5 9.9
Recombination of H2S and diolefin
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Reaction Pathways of Sulfur Species in
FCCSulfur Species in Feedstock Sulfur Species in FCC Gasoline
Multi-Ring Aromatic Thiophenes Small amount to benzothiophene
Alkylbenzothiophenes Benzothiophene by dealkylation
Small amount to thiophenols
Alkylthiophenes Thiophenes by dealkylation
Small amount to benzothiophene
Alkyl Sulfides, Mercaptans Thiophenes by cyclization, aromatization
(Including cyclic sulfides)
H2S + DiOlefin Thiophenes
Hydride Transfer Controls
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Hydride Transfer Controls
Rate of Thiophenic Cracking
S
R
S
R H2S + Hydrocarbon
Hydride-Transfer
from feed
Very stable and
Not-so Lewis basic sulfur
Less stable and
More Lewis basic sulfur
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A Catalytic Approach
• Zn Aluminate on γ-alumina.
• Solid Lewis Acid.
• Used as an additive (~10 - 75%) with
FCC catalyst.• Reduces sulfur in gasoline by 20-45%
without affecting other yields.• Most of reduction occurs in light (C3-)
thiophenes.
Wh Z ?
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Why Zn?
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Zn(AlO2)2 on γ-Al2O3
• Nominal 17 % Zn(AlO2)2 83 % γ-Al2O3
• ~150 m2/gr surface area
• Nominal monolayer of zinc (10 % Zn) on
pseudo-boehmite
• Converted to aluminate at 500 °C
• Both Zn(AlO2)2 and γ-Al2O3 spinel
structures
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Lewis Acidity
• Zn(AlO2)2 and γ-Al2O3 have only Lewisacidity.
• Zn(AlO2)2 increases the Lewis acidity of
the γ-Al2O3.
• Use pyridine DRIFTS for acid type
determination.
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Alumina Lewis acid sites
Al Al
Strong Weak
Zn aluminate/alumina vs alumina
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2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
K
u b e l k a - M u n k
14501500155016001650
Wavenumbers (cm-1)
Alumina Only
10%Zn/Alumina
Strong Weak
Lewis Acid
Zn aluminate/alumina vs. alumina
Si l Additi A h
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Simple Additive Approach
600
650
700
750
800
850
900
950
64 65 66 67 68 69 70 71 72 73
Conversion, wt%
c u t g a s o l i n e s u l f u r
10%
20%
( Zn additive)
FCC base catalyst only
(No Optimization of Hydride Transfer & sulfur activity)
15 % reduction
REUSY and Zn aluminate/alumina
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REUSY and Zn aluminate/aluminaMAT at 525 °C. Feedstock contains 1% S.
- 95% GO-405% GSR-1
Std.Conv. Wt% 70 70
C/O 3.78 3.80
H2 0.05 0.05
C1+C2 1.74 1.73LPG 16.49 16.21
C5+Gaso 48.67 48.73
LCO 20.27 20.39
640+Btms 9.75 9.60
Coke W% Feed 2.90 3.09
mercaptans 0.57 0.15
thiophene 55.62 40.35
C1-thiophene 140.22 91.52
tetrahydrothiophene 31.85 10.91
C2-thiophene 151.97 102.06
C3-thiophene + thiophenol 72.91 67.06
C4-thiophene + C1, C2 thiophenol 55.10 57.09
benzothiophene 387.61 365.13
tot w/benzo 895.86 734.28
ex benzo 508.25 369.15
REUSY
%total S conv% ex benzo
18.027.4
REUSY + 5 % Zn
aluminate
Working hypothesis
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Working hypothesis
S
R
S
R
R-R + H2Sk 1
k 2
k 3
k1
Hydride Transfer Catalyst site density
k3 Zn/Alumina
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Fixed Bed Layered Studies
ZnAluminate
on top
Zn
Aluminateon bottommixed
Samples feed Samples
intermeadiates
Samples
products
feed
Sulfur Yields vs Zn Aluminate Location
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Sulfur Yields vs Zn Aluminate Location
FCC cat w/10% Zn Aluminate Feedstock Contains 1.7% S
0
50
100
150
200
250
300
Thiophene C1- Thiophene Tetrahydrothiophene C2- Thiophene C3- Thiophene +
Thiophenol
C4- Thiophene + C1,
C2 Thiophenol
s u l f u r / p p m
FCC Zn Aluminate ABOVE Zn Aluminate MIXED Zn Aluminate BELOW
Experimental : operando study at U.
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• Reactors :
– Classical catalytic reactor
– IR reactor cell :
Gas outlet : IR, GC and MS Gas analysis
Gas inlet
Ai r
cooling
Heater
IR
beam CaF2KBr
Sample(wafer)
Teflon
window
holder
Kalrez
O-ring
IRSurface
analysis
pe e ta ope a do study at U
of Caen
simultaneously : adsorbed speciesproducts of a reaction
Summary of pure compound
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Summary of pure compound
operando studies on Zn/alumina andneat alumina
• No reaction with thiophene.
• Tetrahydrothiophene readilydecomposes.
• Evidence that paired Lewis/Brønstedsites are the active sites. More work.
Reaction of tetrahydrothiophene over
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IR gas spectra during the reaction IR Chemigram
Consumption of THT ; Formation of 1,3-butadiene.
16001800Wavenumbers (cm-1)
A b s
0.04 A b s
0.04
1400
5
10
15
20
25
30
35
40
45
50
55
m i n
5
10
15
20
25
30
35
40
45
50
55
m i n
THT
1,3-Butadiene
I n t e n s i t y
10 20 30 40 50
Time (minutes)
1,3-Butadiene
THT
Work done at U. of Caen
Reaction of tetrahydrothiophene over
Zn/alumina at 723 ºK
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C4H8S
C4H6
H2S
Ionic current
t (min)
Mass spec analysis during reaction with tetrahydrothiophene
Maximize Sulfur Reduction Approach
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Maximize Sulfur Reduction Approach
65
85
105
125
145
165
185
205
225
245
60 62 64 66 68 70 72 74 76 78
Conversion, wt%
c u t g a s o l i n e s u l f u r
Control
(Optimize Hydride Transfer & sulfur activity)
Increase site density + Zn/alumina in blend
Further increase site density + Zn/alumina in blend
Deactivation of sulfur reduction activity
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%
C u t G a s o
l i n e S u l f u r R e d u c t i o
n
10%
15%
20%
25%
30%
35%
0 1 2 3 4 5 6 7Days
50% Zn/alulmina in blend
Deactivation Mechanism
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GSR 1.1 Day 7
GSR 1.1 day 2
GSR 1.1 Day 3GSR 1.1 Day 4
GSR 1.1 Day 5
GSR 1.1 Day 6
GSR 1.1 Day 1
15
20
25
30
35
40
45
50
K u b e l k a - M u n k
160016101620163016401650
Wavenumbers (cm-1)
1. Strong Lewis Acid 1625cm-1
2. Weak Lewis Acid 1616cm-1
% light sulfur reduction vs.
Strong/ weak Lewis si tes ratio
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Strong/ weak Lewis si tes ratio
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60
Strong vs. Lewis Acid site ratio
% l i g
h t c u t s
u l f u r r e d u c
t i o n
Na and SiO2 Poisoning of Zn/Al2O3
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GSR vs. Na
10
20
30
40
0 0.02 0.04 0.06 0.08 0.1
Na
% C
u t g a s o l i n e S
R e d u
c t i o n
GSR vs. SiO2
10
20
30
40
50
0.5 1 1.5 2 2.5
%SiO2
%
C
u t g
a s o l i n e
S
R
e d
u c t i o n
2 g 2 3
Summary
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y• Zn aluminate catalyzes the decompositon of
saturated sulfur species.
• Maximum sulfur reduction activity is achievedby the optimization of hydride transfer activityof the base FCC catalyst and use of Znaluminate up to 50 % reduction.
• Currently this technology is in over 40 unitsworld wide and is expected to double in 2006.
• New technology, that does not deactivate, is
in commercial trial with excellentperformance.