1. Steam Reform and Water-Gas Shift Reaction Kinetics
By: Shira Rubin, Brandon Wallace, David Hans, Rachel Pennington, Ziad Fenis
Team #2

2. Introduction 9 million tons of hydrogen produced in U.S. per year
Hydrogen used to synthesize ammonia and methanol
Energy applications
Syngas (CO+ H2)
Hydrogen fuel cells
Reactant for Fischer-Tropsch reaction
Converting syngas to hydrocarbons

3. Hydrogen Production Electrolytic processes Water splitting
Biological processes
Bacteria producing hydrogen through biological processes
Thermochemical processes
Steam reforming
Dry reforming
Partial oxidation
Three diff types of processes to produce hydrogen. Biological process is still very new and being studied, barely really works right now. Water splitting is really in. we are focusing on thermochemical, specifically SR

4. Steam Reforming and Water Gas Shift
Overall:
High temperatures ( C)
Moderate pressures (3-25 bar)
Two reactions are normally done consecutively one right after the other to give the overall reaction. SR is endothermic, WGS is slightly exo. Both reactions need a catalyst

5. General mechanism of both reactions
General mechanism of both reactions. Exact mechanisms depend on the catalyst metal and are mostly theorized not actually proved. M is the metal catalyst, tons of diff types are currently used. Notice that diff catalysts are used for each SR and WGS and really is a two step process. In figure 2, its feed stock not specifically methane because can use biofuels that have other things like ethane in it as long as main ingredient is methane (biofuels are also cheaper but issues with side reactions and CO2 emissions).
Also adding extra water to WGS reaction bc pushing reaction forward since its reversable (Le Chateliers Principle). Also want to make sure CO is the limiting reagent so no emission of it whatsoever

6. Steam Reforming Endothermic Commercially Ni catalyst is used
Some use rhodium, ruthenium, platinum, palladium
Higher temperatures increase conversion yet increase carbon deposition which deactivates the catalyst
Moderate pressures showed good selectivity

7. Water Gas Shift (WGS) Slightly exothermic Highly reversible
Many different catalysts used and still being studied currently
Common ones used in industry are iron and chromium oxides
Current research into bimetallic catalysts
Very important bc reduces CO emissions and turns it into CO2. Not significantly affected by pressure since same moles on each side.
Currently catalysts that combine two or three diff metals are being used. These experiments showed them to be much better than just using one metal for the catalyst. Some examples are on the next slide

8. First table shows catalysts for SR
First table shows catalysts for SR. shows how bimetallics can give better conversion and S/C ratio. X is the conversion.
Second table is catalyts for WGS. notice the ones with high 99% conversion have some negative aspects like no increase in oxygen storage capacity (OSC) and have to think about catalyst regeneration also

9. WGS continued All about the catalyst
Low temperature (LT) shift catalysts: copper based
High temperature (HT) shift catalysts: iron oxide, chromium oxide
Many kinetic mechanisms for both HT and LT have been proposed
LT: associative
HT: redox
Commercially carried out in two adiabatic stages, first HT then LT with cooling in between to maintain inlet temp. Do this bc copper catalyst gets poisioned by sulphur compounds from the fuel (methane here) whereas iron catalysts wont get poisioned.
For HT, redox mechanism proposes that catalyst surface is first oxidized to form H2 then surface is reduced to turn CO to CO2.
Associative is the longer one with the * that refers to the catalyst surface and ads means adsorbed to catalyst. Notice how formic acid is proposed as the intermediate here.

10. Considerations Temperature
Arrhenius relationship. Equilibrium constant decreases with increasing T.
Thermodynamics favor low temperatures
Kinetics favor high temperatures
Reactor design
Completely depends on kinetics of reaction
Trade-off between thermo and kinetics. Hard to find an optimal temp for both (kinetically controlled at low temps, thermodynamically controlled at high temps).
Reactor design depends on the kinetics which depends on the catalyst. This is why so many people are trying to find the right kinetics using diff theories, bc if we understand them then we can optimize the process better

11. Langmuir-Hinshelwood Mechanism
Here is just one proposed mechanism, * indicates surface of the catalyst. Do a bunch of catalysis math to solve for r, need a rds though which again is just a theory

12. On slide before, showed the langmuir-hinshelwood one
On slide before, showed the langmuir-hinshelwood one. Now showing other typical interpretations of kinetics.
Notice they are dependant on concentration or partial pressures of compounds
Also the rate determining steps are unknown but tons have been proposed

13. Challenges Sulfur poisoning
Methane forms H2S in side reactions and poisons the catalyst
Carbon formation
Deposits on the catalyst covering the active site
Sintering
Lowers catalyst activity
Cost
Catalyst cost
Separation costs
Cost: can use a more expensive catalyst then have to do less separation or opposite. tradeoff

14. Conclusions
Steam reforming and the water gas shift reactions work together to create syngas
Syngas can be used to make hydrocarbons, methanol, ammonia and other important industrial chemicals
Kinetics depend on the catalyst used
Kinetics are theorized and not yet fully proven and accepted worldwide

15. Questions?

16. References
Smith R J, B., Loganathan, M. & Shantha, M. (2010). A Review of the Water Gas Shift Reaction Kinetics. International Journal of Chemical Reactor Engineering, 8(1), Retrieved 30 Jan. 2018, from doi: /
Liu, J. A. (2006). Kinetics, catalysis and mechanism of methane steam reforming. Worcester Polytechnic Institute.
LeValley, T. L., Richard, A. R., & Fan, M. (2014). The progress in water gas shift and steam reforming hydrogen production technologies–a review. international journal of hydrogen energy, 39(30),
“Hydrogen Production Processes.” Department of Energy, energy.gov/eere/fuelcells/hydrogen-production-processes.
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