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Chain Growth in Fischer-Tropsch:Cobalt versus Iron

Irving Wender, Yulong Zhang, Li Hou, and John Tierney

Department of Chemical and Petroleum EngineeringUniversity of Pittsburgh

CFFS Annual Meeting, Roanoke, WVAugust 1-4, 2004

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Outline

Driving forces Fischer-Tropsch plants

Fischer-Tropsch vs ethylene

polymerization

Comparison of FT on cobalt and iron

Conclusions

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Driving Forces

Monetizing stranded gas reserves

Technology improvements

EPA regulations for low S, clean fuels

High oil prices Seeking alternative fuel route for energy

security

Co-production of electricity and fuels inFutureGen

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Current GTL Situation

*Coal feedstock

Existing Plants

Owner/Developer Location Capacity (b/d) Process Start Date

BP Alaska 300 BP/Davy 2002PetroSA South Africa 30,000 Sasol 1992

SASOL I -III* South Africa 175,000 Sasol 1956-1982Shell Bintulu Bintulu 12,500 Shell SMDS 1993

Syntroleum Oklahoma 2 Syntroleum 1990

Commercial Scale Plants Under Development

SasolChevron Nigeria 34,000 Sasol 2005-2006

Sasol/Qatar Petr. Qatar 34,000 Sasol 2005Pilot Scale Under Construction or Development

Conoco Oklahoma 400 Conoco 2002JNOC Japan 7 N/A 2002Mossgas/Statoil South Africa 1,000 Statoil 2002Syntroleum/Marathon Oklahoma 70 Syntroleum 2003

Fe

ExxonMobil has signed a $7 billion deal to develop a 154,000 barrels per dayGTL project in Qatar, scheduled production in 2011

Shell signed a $5 billion, 140,000 barrels per day GTL project in Qatar,

scheduled production in 2009

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China: Coal to Liquids Planned

China signed a letter of intent with SASOLto build two coal-to-liquid fuel plants

Cost $6 billion, $3 billion each.

440 million barrels/year, 8 times as large

as Sasols current production, covers 60%of China current oil imports

Financial Times, June 28, 2004

David Dapice, YaleGlobal, July 15 2004

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COdissociatesat roomtemp.

CO dissociates at200-300 oC

Non-dissociativeadsorption of CO

Ethylenepolymerization

Catalysts

FT catalysts, metal carbides FT catalysts, metal

Activity of Metallic Elements inPeriodic Table

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Fischer-Tropsch vs Ethylene polymerization

Fischer-Tropsch and ethylene

polymerization both follow stepwise chaingrowth mechanism (Schultz-FloryDistribution) to form high molecular weighthydrocarbons with the same structure(polymethylene and HDPE)

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Molecular Weight Distribution of Polymethylene asCompared with Polyethylene (HDPE).

Pichler, H., and Bellstedt, F., Erdoelund Kohle, Erdgas, Petrochemie

vereinigt mit Brennstoff-Chemie26,560 (1973).Schulz, H., Chemierohst. Kohle, 334(1977).

Ru catalyst, 1000atm, 100-120oC

CH3-CH2-(CH2)n-CH2-CH3

Polymethylene and polyethylene have the same structure

Both follow Schultz-Flory distribution

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IR Spectra of polymethylene and Zieglers polyethylene

Polymethylene

Polyethylene (HDPE)

Schulz, H., Chemierohst. Kohle, 334 (1977).

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Chain Growth vs. Polymerization

Schultz-FloryAnderson-Schultz-FloryProductdistribution

Straight chain hydrocarbonsStraight chain hydrocarbonsProducts

Ethylene monomer addedMethylene (-CH2-) produced insitu by CO hydrogenation

Monomer

High molecular weight

polyethylene

Gasoline, diesel and wax,polymethylene

Productrange

Polymerization by stepwise

addition of ethylenemonomer

Chain growth (polymerization)

by stepwise addition ofmethylene monomer

Reaction

PolyethyleneFischer-Tropsch

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Cobalt vs Iron Although many metals have Fischer-Tropsch activity,

only cobalt and iron catalysts are in industrial use. Cobalt and iron share similarities in FT Very active

Produces broad range of straight chain hydrocarbons

Product distribution follows ASF equation Cobalt and iron are also quite different in many aspects

Cobalt is active as Co metal

Iron is active as Fe carbides

Products differ Response to probes differs

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Iron in the presence of alkali is very active

for the WGS Allows use of CO2 in the FT synthesis

CO2+3H2CO2 + H2 = CO + H2O rwgs

CO + 2H2 = -CH2-+ H2O FTCO2+3H2 = -CH2- +2H2O

Iron as WGS Catalyst

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Cobalt vs IronDifferences in Catalysts

Iron carbidesCobalt metalActive catalyst

SiO2, Al

2O

3as structural

stabilizers

Iron loading: >85% weight

Supports are necessary

SiO2, Al2O3, TiO2, ZrO2Cobalt loading: ~20% weight

Supports

Difficult to regenerateRegenerate by oxidation andreduction

Regeneration

CuNoble metals (Ru, Rh, Re, Pt)Promoters

Essential for activity and

chain growth

Decreases activityAlkali (K)

Iron ($252/t)Cobalt ($57,300/t)

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Cobalt vs IronReaction Conditions

2/32/1H2/CO

10-40 atm.Pressure is necessary foractivity and chain growth.

1-30 atm.High pressure tends to formCo2(CO)8.

Pressure

180-250 C in LTFT

300-350 C in HTFT200-250 CTemperature

IronCobalt

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Cobalt vs IronProducts

HighLowOxygenates

Moderate to highHighWaxes

CO2 and H2OH2OOxygen sink

More olefinsFewer olefinsOlefins

Less sensitive to reaction conditions.Alkali promoter greatly decreases CH4selectivity

Very sensitive to hightemperature andH2/CO ratio

CH4

IronCobaltSelectivity

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Cobalt vs IronResponse to Probes

Acetylene inhibits adsorption of CO on FT catalyst1

surfaces and Initiates reaction at low temperature (120oC)

IronCobalt

Yield oxygenates with ASFdistribution

Yield oxygenates onlywith one carbon morethan the probe

Acetylenes

Difficult to incorporateIncorporates easilyEthylene(Olefins)

Incorporates 100 times fasterthan ethylene.

CH3CH2OHCH3CHO + H2

CH3CHO -CH2- + CO + H2

Not incorporatedEthanol

(Alcohols)

R C CH +CO+H2 RCH2CH2CH2OH

1Jackson, S. D., Hussain, N., and Munro, S., J Chem Soc Faraday T94, 955 (1998).

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Evidence for Initiation of FT by addition of acetylenes

5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00 50.00 55.00 60.000

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

5000000

5500000

6000000

6500000

7000000

7500000

8000000

8500000

9000000

Time-->

AbundanceTIC: CO05103V.D

C6 C7 C8C9 C11 C12 C14 C16 C17

C18C10 C13 C15 C19

Ph-C3

Ph-C4

Ph-C5

Ph-C6

Ph-C7

Ph-C8

Ph-C9

Ph-C10

Ph-C11

Ph-C12

Ph-C13

Ph-C8-Ph

Ph-C5OH

C5

Straight chain substituted benzene

Co10Al90, T=220

o

C, P=100psi, H2/CO=2, 4-phenyl-1-butyne were added inpentane (10% in volume) with a flow rate of 2ml/h

CH2 CH2 C CH

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Initiation of Chain Growth at Lower Temperature

10.00 20.00 30.00 40.00 50.00 60.00

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

4500000

5000000

5500000

6000000

6500000

7000000

7500000

8000000

8500000

9000000

9500000

1e+07

1.05e+07

1.1e+07

1.15e+07

1.2e+07

1.25e+07

1.3e+07

Time-->

Abundance

TIC: CO05202N.D

pentane

Ph-C3

Ph-C2Ph-C1

Ph-C4

Ph-C5

Ph-C6

Ph-C7

Ph-C5OH

Ph-C8

Ph-C9

Ph-C10

Co10Al90, T=180

o

C, P=100psi, H2/CO=2, 4-phenyl-1-butyne were added inpentane (10% in volume) with a flow rate of 2ml/h

Ph-C8-Ph

Ph-C11

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Oxygenated products without/with acetylene addition

on Co and Fe catalysts

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

C2OH C3 C4 C5 C6 C7 C8 C9 C10

n

Yields(mg/h)

without acetylene

with acetylene

100Fe/4.4Si/1.25K, T=180oC,

P=300psi, H2/CO=1, 1% acetylene

0

0.5

1

1.5

2

2.5

3

C2OH C3 C4 C5 C6 C7 C8 C9 C10

n

Yields(mg/h) without acetylene

with acetylene

Co10Al90, T=180oC, P=300psi,

H2/CO=1, 1% acetylene

Iron catalyst

Cobalt catalyst

Addition of acetylene to ironincreases oxygenates viaSchultz-Flory chain growth.

Addition of acetylene to cobaltyields C3 oxygenates only byhydroformylation

C5 oxygenates are formed by

hydroformylation of the dimerof acetylene on cobalt

C3H5OH

C3H5OH

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ConclusionsCobalt and iron differ in many ways:

Co will be used with natural gas: GTL

Iron will be used with coal: CTL

Iron is a water gas shift catalyst so that H2 + CO2can yield FT products.

Cobalt metal is a strong hydrogenation catalyst

producing saturated chains; iron carbides, in thepresence of alkali, produces more olefins

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Conclusions Cobalt, although much more expensive than iron, is

used in smaller amounts and can be used forseveral years by regeneration (oxidation/reduction).

Iron, because of formation of carbides (contraction)and carbon deposition (expansion), tends to

disintegrate during operation.

Schultz-Flory distribution is not peculiar to FT. Itdescribes stepwise addition of a monomer to a

growing chain. Similarity to ethylene polymerizationadds evidence for chain growth by stepwiseincorporation of methylene (-CH2-) in FT

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Conclusions Acetylene initiates FT at more than 100C below

normal FT temperatures for both iron and cobalt

Addition of acetylene to iron yields oxygenatesvia ASF chain growth; addition of acetylene tocobalt yields only a single oxygenate via

hydroformylation. The oxidative tendency of iron is shown by the

easy incorporation of ethanol and other alcohols

Ethylene (olefins) incorporates easily into cobalt,but not into iron catalyzed FT products.

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AcknowledgementWe thank the Department of Energy for

financial support.

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Characteristics of FT Catalysts

Strong and dissociative adsorption of CO

Products follow ASF distribution; stepwise chaingrowth by addition of C1 monomers (-CH2-)

FT catalysts form full-blown metal carbonyls.

Optimum conditions of pressure and temperature forFT synthesis are close to conditions at which formationof metal carbonyl can be detected

H. Pichler in Advances in Catalysis (1952) IV, 272-341

Sensitive to sulfur compounds

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CO Adsorption Properties on

Transition Metals Fe, Mo and W can dissociate CO at room

temperature and readily form active carbides. Co, Ru, Ni and Rh adsorb CO associatively at

room temperature; dissociatively at elevated

temperatures, active for FT synthesis in themetal form.

Nondissociative adsorption of CO, methanol

synthesis catalysts (Cu, Pd)

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Schultz-Flory Distribution

Assumptions Stepwise chain growth

(polymerization) byaddition of monomer

Chain growth andtermination probability aresame for all intermediates

)1(2)1( = nn

nW