1. Fischer-Tropsch Reaction Kinetics
By: Matt Spielman, Hannah Ham, Yusuf Khan, Trey Crump

2. Fischer-Tropsch Introduction
The Fischer-Tropsch process is a set of reactions that converts carbon monoxide and hydrogen gas into liquid hydrocarbons
General reaction formula for alkane synthesis via FT reaction kinetics
(2n + 1)H2 + (n)CO → CnH2n+2+ (n)H2O
Diesel fuel synthesis reactants derived from natural gas, coal, and biomass
FT kinetics used worldwide in large scale gas-liquid and coal-liquid facilities

4. Reaction Mechanisms for FT synthesis
Mechanism 1 rejected due to unexpected behavior. Equilibrium constant for water increased with increasing temp but kinetic constant kch increased while absorption equilibrium constant for hydrogen decreased.
Mechanism 2 showed the same behavior
Image adapted from

5. Reaction Mechanisms for FT synthesis cont.
Mechanism 3 is valid if the effect of water on the FT reaction kinetics is removed. Assume that water does not adsorb strongly on the catalyst surface.
Mechanism 4 is invalid because the kinetic constant increased with temperature and absorption constant for H2CO decreased while the absorption constants of CO and water increased
Many other models exist but we will focus on M3 because it had R2 values of and when compared to experimental data in this study
Image adapted from

6. Kinetic Constant & Activation Energy
Lumped kinetic constant values
Kinetic constants each component extracted from the top table
M3 was found to yield the most physically significant result so was mainly focused on the statistical testing
Activation energy for M3 found to be 90 to 120 kJ/mol
Heat of adsorption of CO 70 to 185 kJ/mol
Heat of adsorption of H2 20 to 105 kJ/mol
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7. Formation of Alkanes & Side Reactions
(2n + 1)H2 + (n)CO → CnH2n+2+ (n)H2O
Alkenes:
(2n)H2 + (n)CO → CnH2n +(n)H2O
Alcohol:
(2n)H2 + (n)CO → CnH2n+2 + (n-1)H2O
Boudouard:
2CO → C+ CO2
Alkanes ideal formula of CnH2n+2 desired
Typically n ranges from 10-20
Produced alkanes are likely to be straight chain, used as diesel fuel
Alkane formation needs stronger hydrogenating catalyst than alkene
Reactions adapted from

8. H2/CO feed ratio
Reaction rate decreases slightly at lower H2/CO ratios
Significantly lower below 2 due to inhibition of CO2

9. Product Distribution
As feed ratio is increased selectivity to methane, light gases, and gasoline increases
Increasing feed ratio also decreases selectivity to diesel/wax

10. Effect of Temperature/Pressure
Increasing temperature increased the reaction rate constant (k)
Increasing feed pressure of CO increased the reaction rate, while increasing feed pressure of H2 decreased reaction rate.
Increasing CO feed pressure decreases water pressure in the reactor, while increasing H2 pressure increases water pressure in the reactor.
Water is a strong inhibitor on the catalyst and reduces reaction rate of FT reaction.

11. Catalysts Usually cobalt or iron based
Cobalt is used for natural gas, while iron is used for biomass and coal
Iron- biomass or coal, more water-gas-shift activity than cobalt
Ruthenium- very active, very expensive
Nickel- promotes methane formation, generally not desirable
Iron has more water-gas shift activity than cobalt, so it is better for biomass or coal feeds due to their low H2/CO ratio. Natural gas is more hydrogen rich so cobalt is used
Cobalt more expensive than iron, but operates at lower pressure and lasts longer, so costs offset.

12. Diesel Fuel Fischer-Tropsch processes produce a synthetic diesel fuel
Low sulfur-content fuel, less harmful to environment
As opposed to traditional petroleum-derived diesel

13. Conclusion
Mechanism 3 was valid when using the assumption that water does not adsorb strongly on the catalyst surface
Ideal formula of CnH2n+2 desired for diesel fuel. Typically n ranges from
Reaction rate decreases slightly at lower H2/CO ratios and it is significantly lower below a ratio of 2 due to inhibition of CO2
Increasing feed ratio increased selectivity to shorter chains
Increasing temperature increased the reaction rate constant
Increasing feed pressure of CO increased the reaction rate, while increasing
feed pressure of H2 decreased reaction rate.

14. Questions?

15. Reference Links
(pg.150)