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Catalytic Reduction of Sulfur

in Fluid Catalytic Cracking

Rick Wormsbecher



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



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 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.



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.



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.



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



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 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



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



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



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 %

S f CC



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 %



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



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

?



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 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



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



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



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



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



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 ?



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 Lewisacidity.

• Zn(AlO2)2 increases the Lewis acidity of

the γ-Al2O3.

• Use pyridine DRIFTS for acid type

determination.



Alumina Lewis acid sites

Al Al

Strong Weak

Zn aluminate/alumina vs alumina



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



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



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



Working hypothesis

S

R

S

R

R-R + H2Sk 1

k 2

k 3

k1

Hydride Transfer Catalyst site density

k3 Zn/Alumina



Fixed Bed Layered Studies

ZnAluminate

on top

Zn

Aluminateon bottommixed

Samples feed Samples

intermeadiates

Samples

products

feed

Sulfur Yields vs Zn Aluminate Location



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.



• 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



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



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



C4H8S

C4H6

H2S

Ionic current

t (min)

Mass spec analysis during reaction with tetrahydrothiophene

Maximize Sulfur Reduction Approach



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



%

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



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



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



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



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.

worms be cher

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