The Fischer-Tropsch Process and Its InfluenceJeremy May

Sept. 26, 2002

CH4

•History

•Applications

•Overview

•Synthesis Gas Production - coal and natural gas - biomass

•Mechanism

•Catalysts - Iron based - Cobalt based - Homogeneous

•Selectivity

•Effects of H2O

•Future Research Areas

Contents

•Reactors

1

History1902: Methane formed from H2 and CO mixtures over Ni (Sabatier and Senderens).

1923: Fischer and Tropsch report work with Co, Fe, and Ru; at high pressure hydrocarbons are formed.

1936: First four production plants in Germany. (200,000 tons » 700,000 tons in 1944 w/ 9 plants).

1950: 5,000 bpd plant in Brownsville, TX.

1950-53: Slurry phase reactor pilot unit developed.

mid 1950's: Decline in F-T plants due to discovery of oil in the Mideast.

1955: First Sasol plant comissioned in South Africa; it used Fe catalyst (1980 and 1983 saw two more plants).

1970-80's: Renewed interest due to energy crisis.

1990's: Continued interest fueled by 'stranded' oil reserves.

1992: Mossgas' plant uses Sasol technology and natural gas as carbon source.

1992-1993: Shell plant (13,000 bpd) uses Co catalyst and natural gas source.

1993: Sasol slurry phase reactor (2500 bpd) using Fe catalyst.

2002: Current oil prices >$30 per barrel

Bukur, D. B. and Sivaraj, C. Appl. Cat. A: Gen. 2002, 231, 201Dry, M. E. Cat. Today 2002, 71, 227

Applications

Jacobs, Das, Zhang, Li, Racoillet, Davis Appl. Cat. A: Gen. 2002, 233, 263Joubert, D and Tincul, I. Macromol. Symp. 2002, 178, 69Dry, M. E. Cat. Today 2002, 71, 227Rostrup-Neilsen, J. R. Cat. Today 2002, 71, 243Knottenbelt, C.Cat. Today 2002, 71, 227

•Low Molecular Weight (MW) hydrocarbons (C1-C4) - combustion fuels - olefins (products are 85% olefinated) useful for polymers and for ethylene copolymers - α-olefins as fine chemicals

•Medium MW hydrocarbons (C4-C13) - gasoline (poorer quality than that petrochemically derived) - lubricants - diesel fuel (higher quality than that petrochemically derived) major application - olefins (products are 70% olefinated) useful for α-olefins as fine chemicals

•High MW hydrocarbons (C13+) - waxes and parrafins - lubricants - can be hydrocracked to diesel fuel - olefins (products are 60% olefinated) useful for α-olefins as fine chemicals

•Reverse Fischer-Tropsch processes can be used to generate H2-rich gas for fuel cells

•Benefits: - no Nitrogenous compounds (greatly reduced NOx emissions) - no Sulfur compounds (no particulates) - cetane rating (energy stored) 75-90% higher than that required for petrochemical derived deseil fuel

2

Overview

Air Separation Oxygen

Natural Gas(CH4)

+Steam

SyngasGeneration CO + H2

Fischer-TropschSynthesis

Hydrocarbons+

H2O

F-T productsupgrading

Jet Fuel, Diesel Fuel,Lubricants, Naphtha,

etc.

Δ (steam)

Power PlantElectricity

Synthesis Gas Production• 60-70% of total cost• Natural gas (more efficient and cost effective) h as 20% CO2, coal (more abundant) has 50% CO2

• For Co catalysts optimal ratio CO/H2 is 2.15, used at low temperature to give linear waxes

• For Fe catalysts: - low temperature optimal ratio CO/H2 is 1.7 to give linear waxes - high temperature optimal ratio H2/(2CO + 3CO2) is 1.05 to give low MW hydrocarbons (high temp allows water-gas shift reaction)

CO + H2O CO2 + H2

• Gasification of coal.

Coal 600 °C Many Productsto be separated

removal of

some CO2, H2Ssyngas (11% methane, H2/CO = 1.8)

catalytic

reformationsyngas (H2/(2CO+3CO2) = 1.05)

Khodakov, Griboval-Constant, Bechara, Zholobenko J. of Catalysis 2002, 206, 230Steen, V. Cat. Today 2002, 71, 225Dry, M. E. Cat. Today 2002, 71, 227Rostrup-Neilsen, J. R. Cat. Today 2002, 71, 243Meguernes, Chapelle, Czernichowski High Temp. Mater. Processes 2001, 5, 363Czernichowski, A. Oil & Gas Sci. Tech. 2001, 56, 181

From Coal and Natural Gas

3

• Methane (natural gas) derivation

a) two stage reforming - leftover syngas from F-T synthesis can be recycled

b) non-catalytic partial oxidation of CH4 (1% CH4 left) - H2/CO ratio 1.7, so enriched with stream reformed recycled gas (H2O and hydrocarbons removed)

c) future reactors will operate more cheaply (fixed bed reactors demonstrated in 8000 t/y unit)

d) Syntroleum proposal would eliminate need for an oxygen plant (40% of cost)

• At research level synthesis gas is generated from O2 or H2O oxidation of CH4 (H2/CO = 2)

Synthesis Gas ProductionNatural Gas

Synthesis Gas ProductionFrom Biomass Integrated Gasification-Fischer Tropsch (BIG-FT)

• Require more advanced gas cleaning technologies.

• Efficiencies calculated at 33-40% for atmospheric gasification systems and 42-50% for pressurized gasification systems.

• Requires: - Drying (using heat from Fischer-Tropsch process) - Gasification (air blown or pressurized and at 900 °C) - Gas cleaning (150 °C, filtration, acid gasses removed) - Gas Compression to 25 bar - Water-gas shift (330 °C, CO2 converted to CO) - F-T synthesis (240 °C, Co catalyst, α = 0.95, 80% conversion) - Workup (separation and cracking of products)

Tijmensen, Faaij, Hamelinck, van Hardeveld Biomass & Bioenergy 2002, 23,129Chaudhari, Bej, Bakhshi, Dalai Energy & Fuels 2001, 15, 736

4

Fischer-Tropsch Reactors• F-T reaction is highly exothermic, so heat removal is important• More methane produced with increasing temperature

Tubular Fixed Bed Reactor Fluidized Bed Reactor Slurry reactor

• Simple design, but expensive to scale because of many small tubes.• Catalyst replacement difficult. (Fe needs replacement often, Co years)• Temperature and Pressure gradients.• High MW hydrocarbons & deisel

• Better heat and temp control.• Online catalyst amount variable.• Second generation experiences less catalyst erosion.• Products must be volatile.• Gasoline and α-olefins

• Most advanced reactor.• Highly active Co catalysts.• Catalyst can be finely divided.• Good temperature control.• Better longer chain selectivity.• Ease of online catalyst adjusting.• Potential High Capacity• Gaseous and wax products removed separately.• Filter a challenge.• Mathematical models are more difficult.• Lower cost

Dry, M. E. Cat. Today 2002, 71, 227

CO

C O

H2

HC OH

H2H2O

CH2

H2

CH3 H2CCH3

[H]

Mechanism of Reaction

• H2, CO, CO2, H2O, and O2 are present on the catalyst, CO and H2 at saturation.• H2 and H2O equilibrate through catalyst• Also can incorporate CH2N2

+

• Alkyl

n

n

nelim.

CO [H]: Mavrikakis, Bäumer, Freund, Nørskov Catal. Let. 2002, 81, 153Ndlovu, Phala, Hearshaaw-Timme, Beagly, Moss, Claeys, Steen Catal. Today 2002, 71, 343Shi, B. and Davis, B. H. Catal. Today 2000, 58, 255Shi, B. and Davis, B. H. Catal. Today 2001, 65, 95

Shi, Li, Keogh, Davis App. Catalysis A: Gen .2002, 229, 283Overview of both mechs: Overett, Hill, Moss Coord. Chem. Rev. 2000, 206, 581CH2N2: Loggenberg, Carlton, Copperthwaite, Hutchings J. Chem. Soc., Chem. Commun. 1987, 541

5

CH2 CH2 CH2

[H]

+

• Alkenyl

+

n

n

n

elim.

Quyoum, Berdini, Turner, Long, Maitlis J. of Catalysis 1998, 173, 355Mann, Turner, Quyoum, Marsih, Maitlis JACS 1999, 121, 6497Maitlis, P. M. and Turner, M. L. Catal. Today 2001, 65, 91

Mechanism of Reaction

• The isomerization step is heavily questioned.• Maitlis supports proposal with labeled ethylene studies

Catalyst Reduction

Activity/Selectivity

RuPdPtReCu

LiNaKRbZr

Ni

Fe

Co

Ru

SiO2

Al2O3

TiO2

Catalysts

Active Metals Cost Activity1 Methane formation

WGS activity

Very active; linear, high Cn, low temp

Very active; very expensive!

1000

50,000

250

Promoters

Rea

ctiv

ity

Supports

• Note that all catalyst formulations are poisoned by sulfur

Rea

ctiv

ity

(optimal)

Rea

ctiv

ity

Sele

ctiv

ity

50%of SiO2

HMS mol sieves

Carbon nanotubes

newly developedanduntested

100 Å optimal

Rh Impossible to use on industrial scale∞

6

CatalystsIron-based

• Most studied because of its extensive use in industry.• Generally preferred for coal-based syngas (low H2/CO ratio).• Preparation: - Fused (impregnated) iron oxide with promoters added during fusion - Sintered iron oxide - Precipitated iron oxide with coprecipitation of promoters. (more expensive and higher attrition)• Less stable than Cobalt both in catalytic activity and structural strength.• Relies greatly on both types of promoters for activity. - Reduction of iron oxides difficult without noble metal addition. - Alkali additives prevent attrition and increase activity to functional level. - K2O most common. Less olefin formation, but high chain propagation probability (α).• High temperature use: - Lower MW hydrocarbons. - More CH4 produced. - Can incorporate CO2 through water-gas shift reaction• Low temperature use: - Lower MW hydrocarbons. - Longer catalyst lifetime.• Most advance catalyst is Fe/Cu/K/SiO2 - 80-89 % C5+ - α = 0.92-0.95 - Syngas conversion of 80 % - Low attrition Krishnamoorthy, Li, Iglesia Cat. Lett. 2002, 80, 77

Mavrikakis, Bäumer, Freund, Nørskov Cat. Letters 2002, 81, 153Sun, Fujimoto, Toneyama, Tsubaki Fuel 2002, 81, 1583Bukur, D. B. and Sivaraj, C. Appl Cat. A: Gen. 2002, 231, 201Dry, M. E. Cat. Today 2002, 71, 227

CatalystsCobalt-based

• Incorporated into industry in last ten years.• Not as acive as rhodium or ruthenium, but available for industrial scale.• Preparation by Incipient Wetness Impregnation (IWI): - SiO2 + Co2NO3 (aq) - Dried - Co loading approximately 10 % - Ru precipitated or added via IWI (0.2% by total weight) - Dried - Reduced under CO/N2• Higher pore size of support increases reduction of Co to activate catalyst, as does Ru. - Reactant and product transport more rapid. - Catalyst more dispersed. - Better adsorption patterns of H2 and CO. - Prevents breakdown of catalyst - Reducibility and crystallite size increased.• Co only useful at lower temperatures, but that coincides with optimal reaction conditions. (but can't utilize water-gas shift reaction to react with CO2)• If exposure to air is necessary, catalyst can be "passified" with CO/H2 = 10. Catalyst activity is then recoverable by reduction after exposure to air.

Jacos, Das, Zhang, Li, Racoillet, Davis App. Cat. A: Gen 2002, 233, 263Li, Jacobs, Das, Davis App. Cat. A: Gen 2002, 233, 255Zhang, Toneyama, Tsubaki Chem. Comm. 2002, 1216Yin, Li, Zhong, Peng Chinese J. of Cat. 2002, 23, 118Khodakov, Griboval-Constant, Bechara, Zholobenko J. of Cat. 2002, 206, 230Hammache, Goodwin, Oukaci Cat. Today 2002, 71, 361Saib, Claeys, Steen Cat. Today 2002, 71, 395Tsubaki, Sun, Fujimoto J. of Cat. 2001, 199, 236

7

CH2N2

Os

Os

Os

N

SR

R'

H2C

Os

Os

Os

N

SR

R'

Rh Os

P

P

P

P

CH2

OCH2C

OC

H2C

CH2CH2N2Rh Os

P

P

P

P

COOCOC

OC

CH2N2Rh Os

P

P

P

P

H2C

OC

CO

HCCH2

CO

CO

Homogeneous Catalysts

• Rh/Os >> Ir/Ir > Rh/Ru = Ir/Ru• Rh/Os produces ethylene from bridging methylene intermediate• Rh/Ru and Ir/Ru produce ethylene, but not from bridging methylene intermediate

• Reactivity not thoroughly defined

Rowsell, Trepanier, Lam, McDonald, Cowie Organomet. 2002, 21, 3228Dell'Anna, Trepanier, McDonald, Cowie Organomet. 2001, 20, 88Trepanier, Sterenberg, McDonald, cowie JACS 1999, 121, 2613Torkelson, McDonald, Cowie JACS 1998, 120, 4047Kabir, Malik, Mandal, Mottaliv, Abedin, Rosenberg Organomet. 2002, 21, 2593

Selectivity• Anderson-Schultz-Flory distiribution - F-T viewed as a polymerization reaction: WR = (1-α)2nαn -1

where n = carbon #, Wn = weight fraction, and α = Chain growth probability

• Variables that affect distribution: - Temperature: lower T gives higher Cn, less branching, and fewer oxygenations - Feed gas composition - Pressure: for Co, higher P gives higher Cn. - Catalyst type - Promoters: alkali increase chain growth for Fe (Li > Na > K > Rb > none) - Support: SiO2 > TiO2 > AlO3 > nonewww.thecwcgroup.com/system/images/cwc/confsession/ 8731.3674075995-1023709105_27847.pdfDry, M. E. Cat. Today 2002, 71, 227

8

Effects of H2O

• Water can increase product MW by increasing the concentration of active "C" species relative to CO (at saturation) and H2, possibly by competing with H2. Thus, chain propagation is increased relative to hydrogenation. For this reason olefinicity is also increased. Kinetic arguments that the propagation/termination rate ratio and ["C"] have the largest influences support this observation. For alumina supports this trend is smaller or reversed. For TiO2 no effect is seen.

• Water can irreversibly deactivate catalyst at high pressures.

H2CR "C"[H]R

R

Bertole, Mims, Kiss J. of Catalysis 2002, 210, 84Li, Jacobs, Das, Davis Appl. Cat. A: Gen. 2002, 233, 255Zhang, Jacobs, Sparks, Dry, Davis Catal. Today 2002, 71, 411

Accelerated

xM + C MxC

2 CO CO2 + C (precipitates onto catalyst and deactivates)

Future Research Areas• Catalyst development: Heterogeneous and Homogeneous - Higher selectivity for larger MW hydrocarbons - Lower attrition rate - Slower deactivation - Selectivity for hydrogenation or olefination - Eliminate competing reactions Boudouard reaction

Carbide formation

• Reaction conditions: - Lower temperature - Easier removal of products - Supercritical fluid as solvent?

• Syngas synthesis - Lower cost - Widen selection of feedstock - Use CO2 - Unite with F-T process

*All above references apply

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