1. Reaction Kinetics of Methanol Synthesis
Jill DeTroye, Brandon Hurn,
Kyle Ludwig, and Isaac Zaydens

2. Overview Review the Reactions Brief Introduction of Catalytic Kinetics
Discussion of Reaction Kinetics
Summary and Conclusions
Questions

3. Reactions Our proposed process reactions include:
Methane-Steam Reforming (MSR)
Water-Gas Shift (WGS)
Methane Oxidation (MO)
Methanol Synthesis (MS)

4. Reactions Reaction Name Reaction’s Chemical Formula
Methane Steam Reforming
CH4 + H2O CO + 3H2
Water Gas Shift
CO2 + H2O CO + H2
Methane Oxidation
CH4 + 2O CO2 + 2H2O
Methanol Synthesis #1 (Syngas)
CO + 2H CH3OH
Methanol Synthesis #2 (CO2)
CO2 + 3H CH3OH + H2O

5. Catalytic Reaction Rates
Homogeneous - Reactants/Catalysts in same phase
Heterogeneous - Reactants/Catalysts in different phase
Our purposes: Solid-Phase Catalyst w/ Gas/Vapor Phase Reactants
Adsorption Constants (generally K)
Rate Constants (generally k)
Partial Pressures (pi)

6. Methane Steam Reforming
Main process for the production
of syngas using nickel-alumina
catalysts
High ratio of steam to methane
Moderate temperature
Low/moderate pressure
Steam reforming on nickel-alumina catalysts is the main process for the production of synthesis gas.
The effect of temperature on methane conversion is a non-linear relationship between reaction rate constants and temperature. When methane conversion is low, methane conversion is proportional to contact time with the catalyst. This proportional trend is enhanced when the steam-to-methane ratio is increased. This indicates that the rate of methane conversion is proportional to the partial pressure of methane at low product concentrations, due to insignificant reverse reaction.
Lower temperatures are better because at higher temperatures, the selectivity for carbon monoxide decreases.
Steam reforming is very sensitive to pressure. High pressures enhance the forward reaction, but also drive the reverse reaction.
Picture shows the ratio of conversion at 300kPa to conversion at 120kPa at two temperatures. This shows that at these relatively low temperatures, the effect of pressure on the forward reaction is much greater than reverse reaction. Ultimately though, it indicates the decreased significance of effects from temperature and contact time due to a larger enhancement of the reverse reaction rates at high product concentrations.

7. Methane Steam Reforming

8. Steam Methane Reforming
Coefficients change depending
on temperature, pressure, and
steam-to-methane ratio
Rates use partial pressures,
typical of catalytic kinetics

9. Steam Methane Reforming

10. Steam Methane Reforming
LEFT: Effect of steam-to-methane ratio on initial methane disappearance rate
RIGHT: Effect of pressure on initial methane disappearance…
The initial methane disappearance rate increased slightly as pressure increased, which indicates that desorption of products is not the rate controlling step. It is more likely that surface reactions are rate controlling in steam reforming.

11. Steam Methane Reforming
Activation Energies, Adsorption Enthalpies, Pre-Exponential Factors
Use Arrhenius Equation

12. Water-Gas Shift Moderately exothermic K decreases with increasing T
Kinetically favored at high T, but Thermodynamically favored at low T
Catalyzed by metals and metal-oxides
ΔHfo = kJ/mol
The Water Gas Shift Reaction (WGSR) is a reaction traditionally used for the production of Hydrogen from synthesis gas which is further used for ammonia production in the fertilizer industry, petroleum refineries for a variety of operations and recently as fuel for power generation and transportation. The use of gasification for power generation has also increased the use of water gas shift reactors multifold.
Water gas shift reaction is a moderately exothermic reversible reaction and the equilibrium constant of the reaction decreases with increasing temperature.
The WGSR can be catalyzed by both metals and metal oxides

13. Water-Gas Shift Regenerative Mechanism Associative Mechanism
In the regenerative mechanism also known as the redox mechanism, the oxidation reduction cycle occurring on the catalyst surface is responsible for the reaction. In the redox mechanism it is proposed that the catalyst surface is oxidized by H2O, producing H2 as by product followed by reduction of surface to convert CO to CO2. The redox mechanism is used to explain the high temperature water gas shift reaction.
The associative mechanism is an adsorption - desorption model where the adsorbed species interact to form an adsorbed intermediate which then decomposes to form H2 and CO2. This is described using a Langmuir isotherm series of kinetic expressions.

14. Water-Gas Shift
Kinetic model parameters

15. Water-Gas Shift
Reaction rate based on Langmuir:

16. Methane Oxidation ΔGo= -801.06 kJ/mol ΔHfo= -802.64 kJ/mol
Highly exothermic - Increase in heat shifts reaction to the left
Pressure - No change

17. Methane Oxidation Figures adapted from Veldsink et al.
Excess Nitrogen and excess Oxygen

18. Methane Oxidation Catalyst: CuO-γ-Al2O3
k0 = 1.08 (kmol kgcat-1 Pa-1 s-1)
EA = 1.25 x 105 (J mol-1)
K02 = 1.2 x 10-2 (Pa-1)
KH2O = 1.2 x 10-2 (Pa-1)
KCO2 = 5.0 x 10-3 (Pa-1)
Faster catalyst deactivation at higher temperature and high water content (3%)

19. Methane Oxidation
Figures adapted from Veldsink et al.

20. Methane Oxidation Optimal operating conditions: pCH4≤ 6 kPa
pH2O≤ 8 kPa
pCO2≤ 20 kPa
0.06 kPa ≤ pCO2 ≤ 22 kPa
723 K ≤ T ≤ 923 K

21. Methanol Synthesis ΔHfo = -90.55 kJ/mol at 298K ΔGo = -25.34 kJ/mol
Exothermic: higher methanol yields are obtained at lower temperatures and higher pressures

22. Methanol Synthesis
ZnO/Cr2O3 catalyst with copper dispersed on the zinc-based catalysts.

23. Methanol Synthesis ΔHfo = -49.43 kJ/mol ΔGo = 3.30 kJ/mol
Exothermic: higher methanol yields are obtained at lower temperatures and higher pressures

24. Methanol Synthesis
ZnO/Cr2O3 catalyst with copper dispersed on the zinc-based catalysts

25. Sources
Hou, Kaihu, and Ronald Hughes. "The Kinetics of Methane Steam Reforming over a Ni/alpha-Al2O Catalyst." Chemical Engineering Journal 82 (2001): Web. 10 Feb
Smith, Byron, RJ, Muruganandam Loganathan, and Murthy S. Shantha. "A Review of the Water Gas Shift Reaction Kinetics." INTERNATIONAL JOURNAL OF CHEMICAL REACTOR ENGINEERING R4 8 (2010): Web. 10 Feb
Veldsink, J.W., G.F. Versteeg, and W.P.M. Van Swaaij. "Intrinsic Kinetics of the Oxidation of Methane Over an Industrial Copper(II) Oxide Catalyst on a Gamma-Alumina Support." The Chemical Engineering Journal 57 (1995): Print.
"Industrial Methanol from Syngas: Kinetic Study and Process Simulation : International Journal of Chemical Reactor Engineering." Industrial Methanol from Syngas: Kinetic Study and Process Simulation : International Journal of Chemical Reactor Engineering. N.p., 27 Aug Web. 12 Feb