Exploring The Fundamentals In Catalytic Partial Oxidation Of … · Exploring The Fundamentals In...

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

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Packed bed reactor model

4

Interstitial cylinder diameter:

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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

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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

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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

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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

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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

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MaCKiE, Budapest, Hungary, May 26, 2017

Reactor performance

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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

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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

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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

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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

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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

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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

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MaCKiE, Budapest, Hungary, May 26, 2017