Experimentation and Application of Reaction Route Graph Theory for Mechanistic and Kinetic Analysis of Fuel Reforming Reactions - PowerPoint PPT Presentation

Loading...

PPT – Experimentation and Application of Reaction Route Graph Theory for Mechanistic and Kinetic Analysis of Fuel Reforming Reactions PowerPoint presentation | free to view - id: 733ed1-ZmJlZ



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Experimentation and Application of Reaction Route Graph Theory for Mechanistic and Kinetic Analysis of Fuel Reforming Reactions

Description:

Experimentation and Application of Reaction Route Graph Theory for Mechanistic and Kinetic Analysis of Fuel Reforming Reactions Caitlin A. Callaghan, Ilie Fishtik ... – PowerPoint PPT presentation

Number of Views:34
Avg rating:3.0/5.0

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Experimentation and Application of Reaction Route Graph Theory for Mechanistic and Kinetic Analysis of Fuel Reforming Reactions


1
Experimentation and Application of Reaction Route
Graph Theory for Mechanistic and Kinetic Analysis
of Fuel Reforming Reactions
Caitlin A. Callaghan, Ilie Fishtik, and Ravindra
Datta
  • Fuel Cell Center
  • Chemical Engineering Department
  • Worcester Polytechnic Institute
  • Worcester, MA

Alan Burke, Maria Medeiros, and Louis Carreiro
Naval Undersea Warfare Center Division
Newport Newport, RI
2
Introduction
  • Predicted elementary kinetics can provide
    reliable microkinetic models.
  • Reaction network analysis, developed by us, is a
    useful tool for reduction, simplification and
    rationalization of the microkinetic model.
  • Analogy between a reaction network and electrical
    network exists and provides a useful
    interpretation of kinetics and mechanism via
    Kirchhoffs Laws
  • Example the analysis of the WGS reaction
    mechanism

Callaghan, C. A., I. Fishtik, et al. (2003).
"An improved microkinetic model for the water gas
shift reaction on copper." Surf. Sci. 541 21.
3
Reaction Route Graph Theory
Ref. Fishtik, I., C. A. Callaghan, et al.
(2004). J. Phys. Chem. B 108 5671-5682.
Fishtik, I., C. A. Callaghan, et al. (2004). J.
Phys. Chem. B 108 5683-5697. Fishtik, I., C.
A. Callaghan, et al. (2005). J. Phys. Chem. B
109 2710-2722.
  • Powerful new tool in graphical and mathematical
    depiction of reaction mechanisms
  • New method for mechanistic and kinetic
    interpretation
  • RR graph differs from Reaction Graphs
  • Branches ? elementary reaction steps
  • Nodes ? multiple species, connectivity of
    elementary reaction steps
  • Reaction Route Analysis, Reduction and
    Simplification
  • Enumeration of direct reaction routes
  • Dominant reaction routes via network analysis
  • RDS, QSSA, MARI assumptions based on a rigorous
    De Donder affinity analysis
  • Derivation of explicit and accurate rate
    expressions for dominant reaction routes

4
RR Graphs
Stop
Start
  • 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

5
RR Graph Topology
  • Full Routes (FRs)
  • a RR in which the desired OR is produced
  • Empty Routes (ERs)
  • a RR in which a zero OR is produced (a cycle)
  • Intermediate Nodes (INs)
  • a node including ONLY the elementary reaction
    steps
  • Terminal Nodes (TNs)
  • a node including the OR in addition to the
    elementary reaction steps

6
Electrical Analogy
  • Kirchhoffs Current Law
  • Analogous to conservation of mass
  • Kirchhoffs Voltage Law
  • Analogous to thermodynamic consistency
  • Ohms Law
  • Viewed in terms of the De Donder Relation

7
The WGSR Mechanism
On Cu(111)
a - activation energies in kcal/mol (? ? 0
limit) estimated according to Shustorovich
Sellers (1998) and coinciding with the
estimations made in Ovesen, et al. (1996)
pre-exponential factors from Dumesic, et al.
(1993). b pre-exponential factors adjusted so
as to fit the thermodynamics of the overall
reaction The units of the pre-exponential
factors are Pa-1s-1 for adsorption/desorption
reactions and s-1 for surface reactions.
water gas shift reaction
8
Constructing the RR Graph
  1. Select the shortest MINIMAL FR

1
s1
s2
s14
s10
s3
s5
s5
s3
s10
s14
s2
s1
water gas shift reaction
9
Constructing the RR Graph
  1. Add the shortest MINIMAL ER to include all
    elementary reaction steps

2
s4 s6 s14 0
s7 s9 s10 0
s4 s11 s17 0
s4 s9 s15 0
s12 s15 s17 0
s7 s8 s12 0
s11
s17
s8
s12
s1
s2
s14
s10
s3
s5
s6
s7
s9
s4
Only s13 and s16 are left to be included
s15
s15
s6
s4
s9
s7
s5
s3
s10
s14
s2
s1
s12
s8
s17
s11
water gas shift reaction
10
Constructing the RR Graph
  1. Add remaining steps to fused RR graph

3
s12 s13 s16 0 s13 s14 s15 0
?
s11
?
s17
s8
s12
s1
s2
s14
s10
s3
s5
s6
s7
s9
s4
s15
s16
s13
s13
s16
s15
s6
s4
s9
s7
s5
s3
s10
s14
s2
s1
s12
s8
s17
s11
water gas shift reaction
11
Constructing the RR Graph
  1. Balance the terminal nodes with the OR

4
OR
s1
s2
s14
s10
s3
s5
s15
s11
s13
s8
s6
s7
s17
s9
s16
s12
s12
s4
s4
s17
s9
s16
s7
s6
s11
s8
s15
s13
s5
s3
s10
s14
s2
s1
OR
water gas shift reaction
12
Microkinetics
  • We may eliminate s13 and s16 from the RR graph
    they are not kinetically significant steps
  • This results in TWO symmetric sub-graphs we only
    need one

water gas shift reaction
13
Resistance Comparisons
Experimental Conditions Space time 1.80
s Feed COinlet 0.10 H2Oinlet 0.10 CO2
inlet 0.00 H2 inlet 0.00
water gas shift reaction
14
Network Reduction
15
Reduced Rate Expression
R7
R15
n6
R8
R11
R6
n2
n3
n5
n7
R10
Aoverall
Assume that OHS is the QSS species.
where
water gas shift reaction
16
Model vs. Experiment for WGS Reaction
Experimental Conditions Space time 1.80
s FEED COinlet 0.10 H2Oinlet 0.10 CO2
inlet 0.00 H2 inlet 0.00
water gas shift reaction
17
Energy Diagram
18
ULI Objectives
  • Elucidate the mechanism and kinetics of logistics
    fuel processing using a building block approach
    (i.e. CH4, C2H6 , JP-8)
  • In first 1-2 years, utilize theoretical and
    experimental research to methodically investigate
    reforming of methane on various catalysts
  • CH4 H2O ? CO 3H2 (MSR)
  • CH4 ½ O2 ? CO 2 H2 (CPOX)
  • CO H2O ? CO2 H2 (WGS)

19
Experimental Approach
  • Catalysts of interest Ni, Cu, Ru, Pt, CeO2, and
    commercially available catalysts for steam and
    autothermal reformation
  • Both integral and differential experiments used
    to study kinetics (Tmax 800 oC)
  • WPI (External reforming)
  • Test in-house fabricated catalysts
  • Methane steam and autothermal reformation
    reactions
  • NUWC (Internal External reforming)
  • Apparatus available at NUWC for internal
    reforming with SOFC button cell tests
  • Commercial catalyst testing external steam and
    autothermal reforming of methane

20
MSR/WGSR Apparatus
21
Objective Tasks
  • Theoretical Work

22
Objective Tasks
  • Experimental Work

23
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
About PowerShow.com