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.