Catalytic Reduction of Sulfur in Fluid Catalytic Cracking
Rick Wormsbecher
Collaborators
Ruizhong HuMichael ZiebarthWu-Cheng ChengRobert H. HardingXinjin ZhaoTerry RoberieRanjit KumarThomas AlbroRobert Gatte
Grace Davison Laboratoire Catalyse et Spectrochimie, CNRS, Université de Caen
Fabian CanFrancoise MaugéArnaud Travert
Outline
• Review of fluid catalytic cracking.• Sulfur balance and sulfur cracking
chemistry.• Catalytic reduction of sulfur by
Zn aluminate/alumina.
Fluid Catalytic Cracking• Refinery process that “cracks” high molecular
weight hydrocarbons to lower molecular weight.
• 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 from the FCC naphtha.
Sulfur in Gasoline• Sulfur compounds reversibly poison the auto
emission catalysts, increasing NOx and hydrocarbon emission. SOx emissions as well.
• World-wide regulations to limit the sulfur content of transportation fuels.– 10 - 30 ppm gasoline.
• Sulfur can be removed by hydrogenation chemistry.– Expensive.– Lowers fuel quality.
Fluid Catalytic Cracking Unit
FeedstockAir
Flue Gas
Products
Riser Reactor(~500 ºC)
Regenerator(~725 ºC)
50, 000 barrels/day
400 tons catalyst inventory
Reaction is endothermic.
Catalyst circulates from Riser to Regenerator.
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
HCO
Regen
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
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
Solid acid catalysis
Zeolite Y structure
Cracking is Catalyzed by Solid Acid/Hydrocarbon Interactions• Initiation: Hydride abstraction by a Lewis site
or carbocation ion formation by a Brønstedsite.
• Propagation: Through primarily β-scission.• Product selectivities governed by stability of
product and the precursor carbocation.• Isomerization, alkylation occur readily
Formation of carbocation transition states
CH2
R
HHZ+ R CH3
H
Z
R R'
H
H
L+ R CH3
H
HL
R
HZ+
HH
R
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
ZH
CH3 CH2 R
H
Z
β
Charge isomerization
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.
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 %
Sulfur Balance in a FCC Unit
F
C
C
Feed Sulfur (~0.3%)Saturated SulfurThiophenes BenzothiophenesMulti-ring Benzothiophenes
Fuel Gas, H2S 40%
Gasoline 5%
Light Cycle Oil 15 %
Bottoms 35 %
Coke, SOx 5 %
Sulfur Species in FCC Gasoline (by GCAED)
20 40 60 80 1001.7e51.8e51.9e52.0e52.1e52.2e52.3e52.4e52.5e52.6e52.7e52.8e5
Sig. 2 in C:\HPCHEM\1\DATA\D51024A\012R0501.D
Time (min.)
ThiopheneMethylthiophene
THT
C2-Thiophene
Benzothiophene
Methylthiophenol
C2-thiophenol
Benzenethiol
C3-thiophenes
Me-THT
C2-THT
SHR
S
S
RS
R
Reaction Pathways of Sulfur Species in FCC
Sulfur Species in Feedstock Sulfur Species in FCC Gasoline
Multi-Ring Aromatic Thiophenes
Alkylbenzothiophenes
Alkylthiophenes
Alkyl Sulfides, Mercaptans(Including cyclic sulfides)
H2S + DiOlefin or Olefin
?
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)
Delta Yields of Gasoline Range SulfurBase Feedstock Spiked with Model S Compounds (0.7% S)
0
200
400
600
800
1000
1200
Sulfu
r, pp
m
Gasoline Sulfur C2-Thiopheneand Lighter
C3-,C4-Thiophene+ Thiophenols
Benzo-Thiophene
OctanethiolDecylThiophene3-MethylBenzothiophene5-MethylBenzothiophene
Delta Yields of Gasoline Range SulfurBase Feedstock (2.8% S) Spiked with Dimethyldibenzothiophene
(0.45% S)
0
20
40
60
80
100
120
Sulfu
r, pp
m
C2-Thiopheneand Lighter
C3-, C4-Thiophenes
Thio-phenols Benzo thiophene
1,10 DiMethyl-DiBenzothiophene
DCR Testing: Polysulfide and diolefin addition to a low sulfur feedstock
(1% S) Di-Olefin +Base 2% Di-Olefin Polysulfide Polysulfide
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
Reaction Pathways of Sulfur Species in FCC
Sulfur Species in Feedstock Sulfur Species in FCC Gasoline
Multi-Ring Aromatic Thiophenes Small amount to benzothiophene
Alkylbenzothiophenes Benzothiophene by dealkylationSmall amount to thiophenols
Alkylthiophenes Thiophenes by dealkylationSmall amount to benzothiophene
Alkyl Sulfides, Mercaptans Thiophenes by cyclization, aromatization(Including cyclic sulfides)
H2S + DiOlefin Thiophenes
Hydride Transfer Controls Rate of Thiophenic Cracking
S
R
S
RH2S + Hydrocarbon
Hydride-Transferfrom feed
Very stable andNot-so Lewis basic sulfur
Less stable andMore Lewis basic sulfur
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.
Why Zn?
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
Lewis Acidity
• Zn(AlO2)2 and γ-Al2O3 have only Lewis acidity.
• Zn(AlO2)2 increases the Lewis acidity of the γ-Al2O3.
• Use pyridine DRIFTS for acid type determination.
Probe Lewis and Bronsted Acid Sites by Pyridine-IR analysis
-20
-10
0
10
20
30
40
50
60
70
80
90
Kub
elka
-Mun
k
1450 1500 1550 1600 1650 Wavenumbers (cm-1)
ZSM-5
γ -Al2O3
N⇓M
N⇑H
N⇓M
Alumina Lewis acid sites
Al Al
Strong Weak
2
4
6
8
10
12
14
16
18
20
22
24
26
28
30
32
34
Kub
elka
-Mun
k
1450 1500 1550 1600 1650 Wavenumbers (cm-1)
Alumina Only
10%Zn/Alumina
Strong Weak
Lewis Acid
Zn aluminate/alumina vs. alumina
Simple Additive Approach
600
650
700
750
800
850
900
950
64 65 66 67 68 69 70 71 72 73
Conversion, wt%
cut g
asol
ine
sulfu
r
10%
20%
( Zn additive)
FCC base catalyst only
(No Optimization of Hydride Transfer & sulfur activity)
15 % reduction
REUSY and Zn aluminate/aluminaMAT at 525 °C. Feedstock contains 1% S.
- 95% GO-405% GSR-1
Std.Conv. Wt% 70 70C/O 3.78 3.80H2 0.05 0.05C1+C2 1.74 1.73LPG 16.49 16.21C5+Gaso 48.67 48.73LCO 20.27 20.39640+Btms 9.75 9.60Coke W% Feed 2.90 3.09
mercaptans 0.57 0.15thiophene 55.62 40.35C1-thiophene 140.22 91.52tetrahydrothiophene 31.85 10.91C2-thiophene 151.97 102.06C3-thiophene + thiophenol 72.91 67.06C4-thiophene + C1, C2 thiophenol 55.10 57.09benzothiophene 387.61 365.13
tot w/benzo 895.86 734.28ex benzo 508.25 369.15
REUSY
%total S conv% ex benzo
18.027.4
REUSY + 5 % Zn aluminate
Working hypothesis
S
R
S
R
R-R + H2Sk1
k2
k3
k1 Hydride Transfer Catalyst site density
k3 Zn/Alumina
Fixed Bed Layered Studies
Zn Aluminateon top
Zn Aluminateon bottommixed
Samples feed Samples intermeadiates
Samples products
feed
Sulfur Yields vs Zn Aluminate LocationFCC 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
sulfu
r/pp
m
FCC Zn Aluminate ABOVE Zn Aluminate MIXED Zn Aluminate BELOW
• Reactors :– Classical catalytic reactor– IR reactor cell :
Gas outlet : IR, GC and MS Gas analysis
Gas inlet
Aircooling
Heater
IRbeam CaF2
KBr
Sample(wafer)
Teflonwindowholder
KalrezO-ring
IRSurfaceanalysis
Experimental : operando study at U. of Caen
simultaneously : adsorbed speciesproducts of a reaction
Summary of pure compound operando studies on Zn/alumina and
neat alumina
• No reaction with thiophene. • Tetrahydrothiophene readily
decomposes.• Evidence that paired Lewis/Brønsted
sites are the active sites. More work.
IR gas spectra during the reaction IR Chemigram
Consumption of THT ; Formation of 1,3-butadiene.
1600 1800 Wavenumbers (cm-1)
Abs
0.04Abs
0.04
1400
510
1520
2530
3540
4550
55
min
510
1520
2530
3540
4550
55
min
THT
1,3-Butadiene
Inte
nsity
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
C4H8S
C4H6
H2S
Ionic current
t (min)
Mass spec analysis during reaction with tetrahydrothiophene
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%
cut g
asol
ine
sulfu
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%
Cut
Gas
olin
e Su
lfur R
educ
tion
10%
15%
20%
25%
30%
35%
0 1 2 3 4 5 6 7Days
50% Zn/alulmina in blend
Deactivation MechanismGSR 1.1 Day 7GSR 1.1 day 2GSR 1.1 Day 3GSR 1.1 Day 4GSR 1.1 Day 5GSR 1.1 Day 6GSR 1.1 Day 1
15
20
25
30
35
40
45
50
Kube
lka-
Mun
k
1600 1610 1620 1630 1640 1650
Wavenumbers (cm-1)
1. Strong Lewis Acid 1625cm-1
2. Weak Lewis Acid 1616cm-1
% light sulfur reduction vs.Strong/ weak Lewis sites 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
% li
ght c
ut s
ulfu
r red
uctio
n
GSR vs. Na
10
20
30
40
0 0.02 0.04 0.06 0.08 0.1Na
% C
ut g
asol
ine
S R
educ
tion
GSR vs. SiO2
10
20
30
40
50
0.5 1 1.5 2 2.5
%SiO2%
Cut
gas
olin
e S
Red
uctio
n
Na and SiO2 Poisoning of Zn/Al2O3
Summary• Zn aluminate catalyzes the decompositon of
saturated sulfur species.• Maximum sulfur reduction activity is achieved
by the optimization of hydride transfer activity of the base FCC catalyst and use of Zn aluminate up to 50 % reduction.
• Currently this technology is in over 40 units world wide and is expected to double in 2006.
• New technology, that does not deactivate, is in commercial trial with excellent performance.
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