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Kinetics & Catalysis of Methane Steam Reforming in SOFCs and Reformers

Kinetics & Catalysis of Methane Steam Reforming in SOFCs and Reformers. Caitlin A. Callaghan (PhD), James Liu (MS candidate), Ilie Fishtik, and Ravindra Datta. Alan Burke, Maria Medeiros, and Louis Carreiro. Fuel Cell Center Chemical Engineering Department Worcester Polytechnic Institute

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Kinetics & Catalysis of Methane Steam Reforming in SOFCs and Reformers

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  1. Kinetics & Catalysis of Methane Steam Reforming in SOFCs and Reformers Caitlin A. Callaghan (PhD), James Liu (MS candidate), Ilie Fishtik, and Ravindra Datta Alan Burke, Maria Medeiros, and Louis Carreiro Fuel Cell Center Chemical Engineering Department Worcester Polytechnic Institute Worcester, MA Naval Undersea Warfare Center Division Newport Newport, RI

  2. Methane Steam Reforming • Consists of three reversible overall reactions (OR): • Endothermic (reforming is favored by high temperature) • Exothermic (favors low temperature while pressure is unaffected) • Steam to Carbon ratio (P(H2O)/P(CH4) or S/C) around 3 are applied Rostrupnielsen J. R, Journal of Power Sources 105 (2002) 195-201

  3. Solid Oxide Fuel Cell Similar ORs and Chemistry

  4. Microkinetic & Graph Theoretic Approach • Develop Molecular Mechanisms • Predict Kinetics of Elementary Reactions (UBI-QEP or Ab Initio) • Draw Reaction Route (RR) Networks • Microkinetic Analysis of Network • Comparison with Experiment • Design of better Catalysts

  5. RR Graphs A RR graph may be viewed as several hikes through a mountain range: • Valleys are the energy levels of reactants and products • Elementary reaction is a hike from one valley to adjacent valley • Trek over a mountain pass represents overcoming the energy barrier

  6. s3 s4 s5 s3 s4 s1 s2 s5 OR RR Graph Topology Mechanism: A + B  C s1: A + S  A·S s2: B + S B·S s3: A·S + B·S  C·S + S s4: C·S  C + S s5: A·S + B·S  C + 2S Full Route A + B s1: A + S  A·S s2: B + S B·S s5: A·S + B·S  C + 2S OR: A + B  C s1 s2 s5 C Empty Route s3: A·S + B·S  C·S + S s4: C·S  C + S –s5: C + 2S  A·S + B·S OR: 0  0

  7. forward reaction rate net reaction rate reaction affinity Rate, Affinity & Resistance • DeDonder Relation: • Reaction Affinity: • Reaction Rate (Ohm’s Law): (conventional) RESISTANCE

  8. Electrical Analogy a b • Kirchhoff’s Current Law • Analogous to conservation of mass • Kirchhoff’s Voltage Law • Analogous to thermodynamic consistency • Ohm’s Law • Viewed in terms of the De Donder Relation e c d f g i h

  9. Example ofWGS Reaction

  10. Surface Energetics for Cu(111) Catalyst: Adsorption and Desorption Steps Activation energies: kcal/mol Pre-exponential factors: atm-1s-1 (ads/des) s-1 (surface)

  11. Constructing the RR Graph • Select the shortest MINIMALFR 1 s1 s2 s3 s15 s7 s18 s18 s7 s15 s3 s2 s1

  12. Constructing the RR Graph • Add the shortest MINIMAL ER to include all elementary reaction steps 2 s16 + s17 – s18 = 0 s5 + s9 – s4 = 0 s6 + s16 – s12 = 0 s8 + s16 – s14 = 0 s4 + s6 – s7 = 0 s5 + s8 – s7 = 0 s4 s6 s12 s1 s2 s3 s15 s7 s18 s9 s16 s5 s17 s8 s14 All but 3 steps included! s14 s17 s5 s16 s8 s9 s18 s7 s15 s3 s2 s1 s12 s6 s4

  13. Constructing the RR Graph 3 • Add remaining steps to fused RR graph s3 + s16 – s11 = 0 s6+s10–s3 = 0 s3+s13–s8 = 0   s4  s6 s12 s1 s2 s3 s15 s7 s18 s11 s9 s16 s5 s17 s8 s13 s14 s10 s10 s14 s13 s5 s17 s16 s8 s9 s11 s7 s18 s15 s3 s2 s1 s12 s6 s4

  14. Constructing the RR Graph • Balance the terminal nodes with the OR 4

  15. RR Network

  16. RR enumeration FR1: s1 + s2 + s3 + s7 + s15 + s18 = OR FR2: s1 + s2 + s7 + s11 + s15 + s17 = OR FR3: s1 + s2 + s3 + s4 + s6 + s15 + s18 = OR FR4: s1 + s2 + s3 + s5 + s8 + s15 + s18 = OR FR5: s1 + s2 + s4 + s6 + s11 + s15 + s17 = OR FR6: s1 + s2 + s3 + s4 + s12 + s15 + s17 = OR FR7: s1 + s2 + s3 + s5 + s14 + s15 + s17 = OR FR8: s1 + s2 + s3 + s7 + s15 + s16 + s17 = OR FR9: s1 + s2 + s5 + s8 + s11 + s15 + s17 = OR FR10: s1 + s2 + s7 + s8 – s13 + s15 + s18 = OR  FR250: s1 + s2 + s4 – s10 – 2s13 + 2s14 + s15 + 2s17 – s18 = OR FR251: s1 + s2 + s5 + 2s10 + 2s12 + s13 + s15 – 2s16 + s18 = OR FR252: s1 + s2 + s5 + 2s10 + 2s12 + s13 + s15 + 2s17 – s18 = OR ER1: s4 + s6 – s7 = 0 ER2: s4 – s5 – s9 = 0 ER3: s5 – s7 + s8 = 0 ER4: s6 – s8 + s9 = 0 ER5: s3 – s6 – s10 = 0 ER6: s3 – s8 + s13 = 0 ER7: s3 – s11 + s16 = 0 ER8: s6 – s12 + s16 = 0 ER9: s8 – s14 + s16 = 0 ER10: s9 + s12 – s14 = 0  ER115: s5 – s7 + s9 – s10 + s11 + s17 – s18 = 0 ER116: s4 – s7 – s10 – s13 + s14 + s17 – s18 = 0 ER117: s5 – s7 + s10 + s12 + s13 + s17 – s18 = 0

  17. 12 10 10 10 )) 8 10 1 - 6 10 R ( R + R ) 4 7 5 8 10 Resistance (rate(s R + R + R 7 5 8 2 10 0 10 R 15 1 6 10 -2 10 -4 10 10 10 273 373 473 573 673 773 873 )) Temperature (K) 1 - 5 10 R 3 Resistance (1/rate(s 0 10 R , R 1 5 1 7 R 2 -5 10 R 1 -10 10 273 373 473 573 673 773 873 Temperature (K) Quasi Equilibrium & RDS Simulations based on energetics of Cu(111)

  18. Reduced Rate Expression rOR = r8 + r10 + r15 where (OHS is the QSS species.)

  19. Cu(111) Fe(110) Ni(111) Simulation of Microkinetic Model

  20. Other Catalysts Pt Pd Rh Ru

  21. Example ofMSR Reaction

  22. Theoretical Thermodynamic Equilibrium Calculations Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

  23. S. Rakass, H. Oudghiri-Hassani, P. Rowntree and N. Abatzoglou Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland. Rakass, S. Journal of Power Sources xxx(2005) xxx-xxx

  24. Froment et al. Mechanism forMethane Steam Reforming s1: CH4 + S = CH4.S s2: H2O + S = O.S + H2 s3: CO.S = CO + S s4: CO2.S = CO2 + S s5: H.S + H.S = H2.S + S s6: H2.S = H2 + S s7: CH4.S + S = CH3.S + H.S s8: CH3.S + S = CH2.S + H.S s9: CH2.S + O.S = CH2O.S + S s10: CH2O.S + S = CHO.S + H.S s11: CHO.S + S = CO.S + H.S s12: CHO.S + O.S = CO2.S + H.S s13: CO.S + O.S = CO2.S + S Xu, J.; Froment, G. F. , AIChE Journal, 1989, 35, 88

  25. MSR RR Network OR1: -CH4 - H2O + CO + 3H2 = 0 OR2: -CH4 - 2H2O + CO2 + 4H2 = 0 OR3: -H2O - CO + CO2 + H2 = 0 OR4: -CH4 - CO2 + 2CO + 2H2 = 0

  26. Activities of Metals for Steam Reforming Rostrupnielsen J. R , Journal of Catalysis 144, 38-49 (1993)

  27. Ni Catalyst Ni ExperimentalResults Theoretical Equilibrium Calculations of MSR Roine, A. HSC Chemistry; Ver. 4.1 ed.; Outokumpu Research: Oy, Pori, Finland.

  28. Rhodium Catalyst

  29. Future Work • Combine both WGSR and MSR Network together • Determine promising catalyst candidates for reforming based upon RR graph theory. • Perform MSR and ATR studies

  30. Benefits to the Navy • Extend fundamental understanding of reaction mechanisms involved in logistics fuel reforming reactions • Gather data on air-independent autothermal fuel reformation with commercially available catalysts • Develop new catalytic solutions for undersea fuel processing • Develop relationship between ONR and WPI

  31. For more information…. WPI – Worcester, MA Caitlin Callaghan – caitlin@alum.wpi.edu, http://alum.wpi.edu/~caitlin James Liu – jliu0928@wpi.edu Ilie Fishtik – ifishtik@wpi.edu Ravindra Datta – rdatta@wpi.edu NUWC – Newport, RI Alan Burke - BurkeAA@Npt.NUWC.Navy.Mil

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