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Fischer-Tropsch Synthesis
Team #1Junghye Chang, Austin Hughes, Hannah Hunter, Yasmin Moez,
Jane Njihia, Brianna Sheard
Introduction and Background
[1] Mena Subiranas, A. & Schaub, G. (2009). Combining Fischer-Tropsch (FT) and Hydrocarbon Reactions under FT Reaction Conditions: Model Compound and Combined-Catalyst Studies. International Journal of Chemical Reactor Engineering, 7(1), pp. -. Retrieved 30 Jan. 2020, from doi:10.2202/1542-6580.2022[2] Zhang, Q.; Deng, W.; Wang, Y. Recent Advances in Understanding the Key Catalyst Factors for Fischer-Tropsch Synthesis. Journal of Energy Chemistry 2013, 22 (1), 27–38.
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What is Fischer-Tropsch Synthesis ?
Heterogeneous reaction process that converts synthesis gas (CO and H2) to hydrocarbons
(2n + 1) H2 + n CO → CnH2n+2 + n H2O
Why Fischer-Tropsch?
▪ Environmental demands▪ Technological developments▪ Decreasing fossil energy
resources
Introduction and Background
3
Benefits of Fischer-Tropsch
▪ Produces synthetic fuel of higher quality than conventional means
▪ Low-sulfur diesel fuel▪ Economic benefits
[1] Mena Subiranas, A. & Schaub, G. (2009). Combining Fischer-Tropsch (FT) and Hydrocarbon Reactions under FT Reaction Conditions: Model Compound and Combined-Catalyst Studies. International Journal of Chemical Reactor Engineering, 7(1), pp. -. Retrieved 30 Jan. 2020, from doi:10.2202/1542-6580.2022[3] Gruber, H.; Groß, P.; Rauch, R.; Reichhold, A.; Zweiler, R.; Aichernig, C.; Müller, S.; Ataimisch, N.; Hofbauer, H. Fischer-Tropsch Products from Biomass-Derived Syngas and Renewable Hydrogen. Biomass Conversion and Biorefinery 2019..
Schematic of biomass gasification using excess electricity, recycled CO2 and FTS to produce hydrocarbons
Main Points of Design Interest
▪ Exothermic, needs cooling to operate ▪ Gas to liquid (GTL) reaction involving
catalyzed adsorption- Metal catalysts are used
▪ Produces hydrocarbon molecules of various chain lengths
Reactors
4
Reactor Types
Operating Conditions
▪ High Temperature: 320 - 350 °C▪ Low Temperature: 220 - 250 °C▪ Pressure: Typically 2 - 3 MPa▪ Higher CO partial pressure → Longer carbon chains
[4] Steynberg, A. P., & Dry, M. E. (Eds.). (2004). Fischer-Tropsch Technology (Vol. 152). Elsevier.
Reactors
5
Advantages and Disadvantages
Slurry Phase
▪ + Highest diesel yield▪ + Easy to operate▪ - More downstream processing▪ - Lower overall CO conversion
Fluidized Bed (Sasol Advanced Synthol)
▪ + Higher capacity▪ + Highest gasoline and alkene yield▪ - High methane production▪ - Higher catalyst loading & losses
Diagram of slurry phase FT reactor. Slurry phase with Co catalyst is ideal for diesel production.
[4] Steynberg, A. P., & Dry, M. E. (Eds.). (2004). Fischer-Tropsch Technology (Vol. 152). Elsevier.
Catalysts
6[5] Abelló, S.; Montané, D. Exploring Iron-Based Multifunctional Catalysts for Fischer–Tropsch Synthesis: A Review. ChemSusChem 2011, 4 (11), 1538–1556. https://doi.org/10.1002/cssc.201100189.
Cobalt and Iron Catalyst Comparison
Cobalt Catalyst
Kinetics
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Iron Catalyst
Zimmer- man (1990)
Riedel(2003)
kFT(mol/s∙ kg∙ Pa)
8.58 1.77
EA,FT(kJ/mol)
86 72
aFT 4.8 33
bFT 0.33 2.7
kFT,240°C(mol/s∙ kg∙ Pa2)
1.26 x 10-12
kFT,220°C(mol/s∙ kg∙ Pa2)
8.85 x 10-13
EA,FT(kJ/mol)
92.7 - 94.5
aFT,240°C(Pa-1)
1.16 x 10-5
aFT,220°C(Pa-1)
2.23 x 10-5
[1] Subiranas, A. M., & Schaub, G. (2007). Combining Fischer-Tropsch (FT) and Hydrocarbon Reactions under FT Reaction Conditions -- Catalyst and Reactor Studies with Co or Fe and Pt/ZSM-5. International Journal of Chemical Reactor Engineering, 5(1), 11–12. doi: 10.2202/1542-6580.1522
Kinetic Rate Law Expression and Parameter Values
ASPEN
8[6] Pondini, M., & Ebert, M. (2013). Process synthesis and design of low temperature Fischer-Tropsch crude production from biomass derived syngas . Department of Energy and Environment, Division of Heat and Power Technology, CHalmers University of Technology.
Type of Reactor
▪ RStoich
▪ Simulates a Slurry Reactor with FT kinetics
Complications with Kinetics
▪ Large number of hydrocarbon products with a series of very complicated rate laws
Work Around from Literature
▪ Use one aggregate rate law equation in ASPEN Plus▪ Use probability distribution models in Excel to get actual
hydrocarbon product distribution
Integrating Fischer-Tropsch Synthesis into ASPEN
Examples and Applications
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Sasolburg, South Africa (Sasol)
▪ Fixed bed and slurry phase reactors with Fe catalyst▪ Leading producer of paraffin wax
Secunda, South Africa (Sasol)
▪ Fluidized bed reactors with Fe catalyst▪ Wider product spectrum → more complex separation
Sasol Secunda plant. Circulating fluidized bed reactors are seen on the right, and Advanced Synthol reactors on the left.
[4] Steynberg, A. P., & Dry, M. E. (Eds.). (2004). Fischer-Tropsch Technology (Vol. 152). Elsevier.