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Laboratory for Chemical Technology, Ghent University
http://www.lct.UGent.be
Exploring The Fundamentals In Catalytic Partial Oxidation Of Methane: The Interaction Between Diffusion And Reaction In
A Packed Bed Reactor
Songjun Liu; Ana Obradović; Joris W. Thybaut; Guy B. Marin
MaCKiE, Budapest, Hungary, May 26, 2017
1
Introduction
Aim: Study the diffusion-reaction interaction by
a packed bed reactor model:
• External and internal diffusions
• Surface and homogeneous reactions
Ho
mo
ge
ne
ous re
actio
ns
Syngas production route ∆𝑯𝟐𝟗𝟖𝟎 𝑲𝒋
𝒎𝒐𝒍
Steam reforming (SR): CH4 + H2O = CO + 3H2 206 CO + H2O = CO2 + H2 -41
Catalytic partial oxidation (CPO): • Direct route: CH4 + 0.5O2 = CO + 2H2 -38 • Indirect route: CH4 + 2O2 = CO2 + 2H2O -802 CH4 + H2O = CO + 3H2 206
Advantages of CPO:
• Autothermal operation
• High catalytic reaction rate:
• short residence time (1-10 ms)
• high throughput
• ideal H2/CO ratio: 2/1
High velocity
High reactivity
Limiting
MaCKiE, Budapest, Hungary, May 26, 2017
Outline
• Introduction
• Reactor model development
• Model validation & baseline case
• Reactor performance at various configurations
• Conclusion
• Acknowledgement
3
MaCKiE, Budapest, Hungary, May 26, 2017
Packed bed reactor model
4
Interstitial cylinder diameter:
MaCKiE, Budapest, Hungary, May 26, 2017
Pellet scale Reactor scale
Microkinetics:
CPO on Rhodium[2] :
6 gas species, 12 surface species,
36 reactions
CH4 Homogeneous combustion
(Reduced GRI30)[3] :
32 species, 196 reversible reactions
[1] Kechagiopoulos, Panagiotis N., Joris W. Thybaut, and Guy B. Marin. Industrial & Engineering Chemistry Research 53.5 (2013): 1825-1840.
[2] Dalle Nogare, D., Degenstein, N. J., Horn, R., Canu, P., & Schmidt, L. D. (2011). Journal of catalysis, 277(2), 134-148
[3] Gregory P. Smith, David M. Golden, Michael Frenklach, Nigel W. Moriarty, Boris Eiteneer, Mikhail Goldenberg, C. Thomas Bowman, Ronald K.
Hanson, Soonho Song, William C. Gardiner, Jr., Vitali V. Lissianski, and Zhiwei Qin http://www.me.berkeley.edu/gri_mech/
Assumptions:
• Sphere particles and cylindrical
tubes around particles
• No axial diffusion and conduction
• No pressure drop
• Ideal gas
Governing equations
5
𝜕𝐶𝑖,𝑔
𝜕𝑡= −
𝜕(𝑢𝑔𝐶𝑖,𝑔)
𝜕𝑧+𝐷𝑚,𝑖
𝑟
𝜕
𝜕𝑟𝑟𝜕𝐶𝑖,𝑔
𝜕𝑟+ 𝑅𝑖,𝑔
𝜕𝐶𝑖,𝑐
𝜕𝑡= −
𝐷𝑒,𝑖
𝜉2𝜕
𝜕𝜉𝜉2
𝜕𝐶𝑖,𝑐
𝜕𝜉+ 𝑎𝑐𝑅𝑖,𝑠 + 𝜀𝑐𝑅𝑖,𝑔
Interstitial phase: Convection, external diffusion, homogeneous reactions
Intraparticle phase: internal diffusion, homogeneous reactions, surface reactions
Surface intermediates:
𝜕𝜃𝑖,𝑠
𝜕𝑡=𝑅𝑖,𝑠
Γ
𝜃𝑖,𝑠 = 1
𝜕𝑇𝑠
𝜕𝑡= −
𝛼𝑒
𝜉2𝜕
𝜕𝜉𝜉2
𝜕𝑇𝑠
𝜕𝜉−
(𝜀𝑐 𝑅𝑖,𝑔𝐻𝑖,𝑔𝑁𝑠𝑝,𝑔𝑖 + 𝑎𝑐 𝑅𝑖,𝑠𝐻𝑖,𝑠)/(𝜌𝑠𝐶𝑝𝑠)
𝑁𝑠𝑝,𝑠𝑖
𝜕𝑇𝑔
𝜕𝑡= −
𝜕(𝑢𝑔𝑇𝑔)
𝜕𝑧+𝛼𝑔
𝑟
𝜕
𝜕𝑟𝑟𝜕𝑇𝑔
𝜕𝑟−
𝑅𝑖,𝑔𝐻𝑖,𝑔/(𝜌𝑔𝐶𝑝𝑔)𝑁𝑠𝑝,𝑔𝑖
𝑧 = 0 ∧ 0 < 𝑟 <𝑑𝑣
2 :
𝐶𝑖,𝑔 = 𝐶𝑖,0, 𝑇𝑔 = 𝑇0 𝑟 = 0 ∶
𝜕𝐶𝑖,𝑔
𝜕𝑟= 0,
𝜕𝑇𝑔
𝜕𝑟= 0
𝑟 =𝑑𝑣
2∶
0 = 𝑎𝑔𝐷𝑚,𝑖𝜕𝐶𝑖,𝑔
𝜕𝑟+ 𝑎𝑐𝐷𝑒,𝑖
𝜕𝐶𝑖,𝑐
𝜕𝜉
0 = 𝑎𝑔𝜆𝑔𝜕𝑇𝑔
𝜕𝑟+ 𝑎𝑐𝜆𝑒
𝜕𝑇𝑠
𝜕𝜉
𝜉 = 0 ∶
𝜕𝐶𝑖,𝑐
𝜕𝜉= 0,
𝜕𝑇𝑠
𝜕𝜉= 0
𝜉 =𝑑𝑝
2:
𝐶𝑖,𝑔 = 𝐶𝑖,𝑐 , 𝑇𝑔 = 𝑇𝑠
Boundary conditions:
MaCKiE, Budapest, Hungary, May 26, 2017
Solution
6
Pellet coordinate: Orthogonal collocation (for symmetry problem) Collocation points: >> interstitial : 6 >> intraparticle :11
Reactor coordinate: Backward difference 115 points unevenly distributed
MaCKiE, Budapest, Hungary, May 26, 2017
Outline
• Introduction
• Reactor model development
• Model validation & baseline case
• Reactor performance at various configurations
• Conclusion
• Acknowledgement
7
MaCKiE, Budapest, Hungary, May 26, 2017
Model validation & baseline case
8
Baseline conditions >> Inlet Temperature = 500 °C >> Pressure = 1 atm >> CH4/O2/N2 = 2/1/4 >> W/FCH4,0 = 0.774 kg s mol
-1, V/Ftot,0 = 1.73·10-4 m3 s mol-1
>> Catalyst diameter = 0.4 mm >> Catalyst density = 2280.0 kg/m3 >> Rh specific surface area = 0.2 m2/g >> Catalyst porosity/tortuosity = 0.4/4.0 >> Bed porosity = 0.42 (loose packing) >> Reactor length/diameter = 20mm/15mm
MaCKiE, Budapest, Hungary, May 26, 2017
Model validation
9 [1] Dalle Nogare, D., Degenstein, N. J., Horn, R., Canu, P., & Schmidt, L. D. (2011). Journal of catalysis, 277(2), 134-148.
Literature results: spatial profiles of experimental
and modeling compositions in foam reactor[1]
This work: Mole fractions profile along axial coordinate
(radial positon: center of interstitial phase)
Qualitatively validated
MaCKiE, Budapest, Hungary, May 26, 2017
10
MaCKiE, Budapest, Hungary, May 26, 2017
High solid conductivity
Temperature & mole fractions: reactants
Mole fractions: major products
11
High diffusivity
MaCKiE, Budapest, Hungary, May 26, 2017
Kinetically favorable:
Steam reforming, WGS
x CO2 reforming, reverse WGS
MaCKiE, Budapest, Hungary, May 26, 2017
Surface coverages
12
Mole fractions: Radicals
13
Conclusions for baseline case:
• strong diffusion limitations in both inter- and intra- particle phase
• Steam reforming is kinetically favored, CO2 consumption is kinetically unfavorable,
• homogeneous reactions are negligible at atmosphere pressure
MaCKiE, Budapest, Hungary, May 26, 2017
Outline
• Introduction
• Reactor model development
• Model validation & baseline case
• Reactor performance at various configurations
• Conclusion
• Acknowledgement
14
MaCKiE, Budapest, Hungary, May 26, 2017
Reactor performance
15
cases: 1. Increase reactivity Rh specific surface area: 0.2, 0.6, 1.0 m2/g 2. Increase particle diameter (increase diffusion distance) Catalyst particle diameter: 0.4, 0.8, 1.2 mm 3. Industrial condition Particle diameter: 1.2 mm Pressure: 10:5:30 bar
MaCKiE, Budapest, Hungary, May 26, 2017
16
Rh specific surface area: 0.2, 0.6, 1.0 m2/g
High loading:
Steam reforming: kinetics & transport
limited
Oxidation: transport limited
MaCKiE, Budapest, Hungary, May 26, 2017
H2/CO: 2.00 2.00 2.00
Rh specific surface area
17
MaCKiE, Budapest, Hungary, May 26, 2017
H2/CO: 2.00 1.93 1.80
Particle diameter: 0.4, 0.8, 1.2 mm bed porosity: 0.42, 0.44, 0.45
Interstitial tube diameter: 0.193, 0.419, 0.654 mm
Particle diameter
18
Particle diameter 1.2 mm Pressure: 10:5:30 bar
MaCKiE, Budapest, Hungary, May 26, 2017
H2/CO: 1.86 1.90 1.97 2.03 2.07
(1) A.Bitsch-Larson; R. Horn; L.D. Schmidt, Applied Catalysis A: General 348 (2008), 165–172.
High pressure
Conclusion
19
MaCKiE, Budapest, Hungary, May 26, 2017
1. An adiabatic packed bed reactor was developed and validated. Strong
diffusion limitations were confirmed in both inter- and intra-particle
phase
2. High catalyst loading has little impact on reactor performance in the
highly diffusion limited reactor.
3. The diffusion limitations are largely enhanced for larger particles, lower
the efficiency of catalytic bed.
4. Homogeneous combustion at elevated pressure changes the reaction
path, results in a more complicated coupling of homogeneous
reactions, mass and heat transfer and surface reactions.
Acknowledgement
20
MaCKiE, Budapest, Hungary, May 26, 2017
Thank you for your attention
European Research Council FP7/2007-2013/ERC
grant agreement n° 290793
China Scholarship Council
Laboratory for Chemical Technology
Ghent University
https://www.lct.ugent.be/
CPO on Rh kinetics
21
MaCKiE, Budapest, Hungary, May 26, 2017