Oxidative Coupling of Methane Spring Session - Traxxys

Design of Catalytic Membrane Reactor for Oxidative

Coupling of Methane

F. Gallucci

M. van Sint Annaland

Chemical Process Intensification – Department of Chemical

Engineering and Chemistry - TU/e – The Netherlands

Process Intensification PIN-NL, April 10, 2013

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Outline

• Introduction

• Design of catalytic membrane reactor

o Packed bed membrane reactor

o Hollow fiber catalytic membrane reactor

• Results

• Conclusions

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Motivation

• Ethylene production

• Highly reactive, intermediate product

Used for e.g. ethylene oxide, polyethylene, PVC,

Ethylbenzene

• Current: steam cracking of naphtha/ethane

Mostly oil-based, endothermic, energy intensive, high

temperature process (>850°C)

Alternative energy efficient production methods

• Production of ethylene from natural gas

Indirect conversion route (GTL)

Synthesis gas (CO, H2) via reforming

Fischer-Tropsch gives higher hydrocarbons

Direct conversion route

Oxidative coupling (OCM) to ethylene

from: http://www.exxonmobilchemical.com

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Introduction

• Ethylene production

• Production of ethylene from natural gas

Indirect conversion route (GTL)

Synthesis gas (CO, H2) via steam reforming of methane (SRM)

Fischer-Tropsch gives higher hydrocarbons

Direct conversion route

Oxidative coupling of methane (OCM) to ethylene

2 CH4 + O2 C2H4 + 2H2O

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Introduction contd…

• Production of ethylene via oxidative coupling of methane [OCM]

2 CH4 + O2 C2H4 + 2H2O

CH4 + 2O2 CO2 + 2H2O

C2H4 + 3O2 2CO2 + 2H2O

Typical conversion-selectivity

problem

• Highly exothermic

• Large methane recycle

• Maximum C2 yield < 30%

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Kinetics of OCM

• Reaction scheme

• Formation rates of C2H4, C2H6 and CO2 (primary reactions)

2O

2O2 2CO H O

2O2H

1 2

3

2 6 2C H H O4CH

2CO H

2O

2 4 C H 2H O

2 3

mol

m

mn

C C Or k T p ps

2 CH4 + ½ O2 C2H6 + H2O

n = 1.0

m = 0.352

CH4 + 2 O2 CO2 + 2 H2O

n = 0.587

m = 1

Distributive O2 feeding = membrane reactor

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Possible packed bed reactor configurations for OCM

CH4 + O2

cooling

CH4 + O2

CH4

O2

Pre mixed adiabatic: very low C2

yield for the high temperature and

O2 concentration

Pre mixed : low C2 yield at high O2

concentration

Distributive feeding: low C2 yield for

high temperature

CH4

O2

cooling

Distributive feeding with cooling

(Virtually isothermal):Highest yield

More complicated reactor design

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Novel Process Design

• Design a possible autothermal process in single multifunctional reactor

o Integration of exothermic OCM and endothermic steam reforming of methane (SRM) Htot = 0

o Advantages:

− Increase methane utilization/conversion

− OCM/SRM Ethylene/synthesis gas production

− Optimal heat integration

This presentation

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Integration of OCM and SRM

• CH4 + ½ O2 → ½ C2H4 + H2O ΔHr = -140 kJ/mol

• CH4 + 2 O2 → CO2 + 2 H2O ΔHr = -801 kJ/mol

• Combustion of ethane/ethylene

• CH4 + H2O 3 H2 + CO ΔHr = 226 kJ/mol

• Reforming of ethane/ethylene

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Outline

• Introduction




• Results

• Conclusions

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Integration on single catalyst particle

Final goal

• Levels of integrating OCM and SRM

o Multifunctional catalyst

o Thermal coupling

Particle scale Reactor scale

O2 O2

CH4

I II III IV

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Integration on single catalyst particle: Design

• Possible integration on single catalyst particle

Uniform catalyst layout Figure a non-selective highly exothermic process

Dual function catalyst Reforming activity in particle center (Figure b) and ocm activity

in outer layer of particle separated by inert porous layer (Figure c)

• Possible autothermal design

Requires calculation of

o SRM core diameter

o Thickness of ocm catalytic layer

o Thickness of inert layer

o Properties of inert layer (porosity and tortuosity)

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Possible process design

Integration of exothermic oxidative coupling and endothermic reforming of methane on

particle and reactor scale OCM

SRM

mole

r [m]

O2 c

on

cen

trati

on

0 R

PBMR

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Integration on particle scale

Influencing CH4 mole flux

to the particle centre

Preventing C2 mole flux to

the particle centre

r [m]

O2 c

on

cen

trati

on

0 R

Complete

conversion of

O2 at OCM layer

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Numerical model: Particle scale

Kinetics from:

OCM: Stansch, Z., Mleczko, L., Baerns, M.

(1997) I & ECR, 36(7), p-2568.

SRM: Nimaguchi and Kikuchi(1988). CES,

43(8), p-2295

• Intraparticle reaction model

• Optimize the catalyst particle

o Thickness of OCM catalytic layer

o Thickness of SRM catalytic layer

o Thickness of inert porous layer

o Diffusion properties viz. porosity and tortuosity

• Advantages: o Strong intraparticle concentration profiles o Beneficial for C2 selectivity o Vary rSRM: autothermal operation

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Integration on single catalyst particle

Results – influence on performance

• Methane consumption by dual function catalyst particle

• Influence on CH4 conversion

~50% increase (Vs. OCM)

• Reforming diffusion limited

SRM flow = f(XCH4)

Presence sufficient H2O

Proportional to e/t or dSRM

Input: XCH4 = 0.4; XO2 = 0.005; XH2O = 0.5, rSRM = 0.5mm,

rOCM = 0.5mm, rp = 1.5mm

0.0000 0.0005 0.0010 0.00150.0

0.5

1.0

1.5

2.0

2.5

3.0

InertSRM

e/t

e/t

C

H4

[x 1

0-6

mol/

s]

r [m]

e/t

OCM

S

RM

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Integration on single catalyst particle contd…

Results – COx production

• COx production

Large contribution of SRM

OCM contrib. low low pO2

• Reforming diffusion limited

Mainly CO production

WGS on OCM cat CO2

Strong decrease by dOCM

• Loss of C2 products by

reforming?

Input: XCH4 = 0.4; XO2 = 0.005; XH2O = 0.5, rSRM = 0.5mm,

rOCM = 0.5mm, rp = 1.5mm

0.0000 0.0005 0.0010 0.0015-0.5

0.0

0.5

1.0

1.5

2.0

CO2

[x 1

0-6

mol/

s]

r [m]

InertSRM OCM

CO

e/t

e/t

e/t

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• Losses of C2 to reforming core

Negligible (Maximum 3% ) at reactor inlet conditions

• What about the energy balance?

Input:

XCH4 = 0.4; XO2 = 0.005;

XH2O = 0.5, rSRM = 0.5mm,

rp = 1.5mm

0.0000 0.0005 0.0010 0.0015-0.1

0.0

0.1

0.2

0.3

0.4

0.5 InertSRM

e/t

e/t

C

2 [x

10-6

mol/

s]

r [m]

e/t

OCM

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• Results: Energy production OCM/SRM particle Vs only OCM particle

o Variation of e/tratio at constant rSRM:

• Distributed feeding of O2 Qtot < 0.3 W makes dual function catalysis possible

• Autothermal operation is possible e/t = 0.01-0.08

• Other options: Variation of rSRM, steam concentration

Input:

XCH4=0.4; XH2O=0.5

T = 800 C; P = 150kPa;

rOCM=0.25mm;

rSRM = 0.5mm

rp=1.5 mm

0.00 0.05 0.10 0.15-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

XO2

= 0.001

XO2

= 0.003

Qto

t, [

W]

e/t [-]

OCM OCM/SRM

XO2

= 0.005

Autothermal region

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Numerical model: Reactor scale

• Two cylindrical compartments separated by -Al2O3 membrane for O2

distribution

• Unsteady state heterogeneous reactor model coupled with intraparticle

reaction model

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Results: Only OCM: Distributed feed of O2

• Distributed feed of O2 (CH4/O2 = 4; Lr = 2m):

• Distributed oxygen feeding desirable

• Premixed Vs distributed feeding cooled mode T = 1000 C Vs 800 C

• Premixed Vs distributed feeding Improved C2 yield < 5-10% Vs 36%

• For OCM cooled reactor preferred with high yield of C2 (>36%)

0.0 0.5 1.0 1.5 2.00%

10%

20%

30%

40%

YC

2

[%

]

z [m]

Isothermal

Cooled

Adiabatic

0.0 0.5 1.0 1.5 2.0750

800

850

900

950

1000

T [

°C]

z [m]

Isothermal

Cooled

Adiabatic

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Results: Reactor scale for OCM/SRM

Results – comparison of dual function process with only OCM

Non-isothermal conditions:

XCH4 = 0.3; XH2O = 0.4, CH4/O2 = 4, rp = 1.5mm;

rOCM = 0.25mm

0.0 0.5 1.0 1.5 2.00

10

20

30

40

50

60

70

80

OCM adiabatic

C

H4

z [m]

rSRM

= 15 m

rSRM

= 20 m

rSRM

= 30 m

rSRM

= 40 m

OCM cooled

OCM adiabatic Vs rSRM = 20m

CH4 conversion:

• 55% Vs 62%

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Results – comparison of dual function process with only OCM


XCH4 = 0.3; XH2O = 0.4, CH4/O2 = 4, rp = 1.5mm;

rOCM = 0.25mm

OCM adiabatic Vs rSRM = 20m

CH4 conversion at optimum C2

Yield:

• CH4 conversion: 34% Vs 48%

• Max. C2 Yield: 18% Vs 17%

0.0 0.5 1.0 1.5 2.00

10

20

30

40

OCM adiabatic

YC

2

[%

]

z [m]

rSRM

= 15 m

rSRM

= 20 m

rSRM

= 30 m

rSRM

= 40 m

OCM cooled

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• Results: OCM/SRM particle Vs only OCM

o Influence on heat production


XCH4 = 0.3; XH2O = 0.4, CH4/O2 = 4, rp = 1.5mm;

rOCM = 0.25mm

• OCM (adiabatic mode) Vs OCM/SRM o Temperature decrease of 50-60 C

• rSRM = 20 m autothermal

operation possible at Lr = 1.2 m

Advantages:

• Increased CH4 conversion

• Nearly equal C2 production

at autothermal conditions

Disadvanges:

• Complicated and expensive

manufacturing of catalyst

0.0 0.5 1.0 1.5 2.0

700

800

900

1000

OCM adiabatic

T [C

]

z [m]

rSRM

= 15 m

rSRM

= 20 m

rSRM

= 30 m

rSRM

= 40 m

OCM cooled

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Research topics

Project goal

• Levels of integrating OCM and SRM

o Thermal combination on reactor scale

o Combining on particle scale

Particle scale Reactor scale

O2 O2

CH4

I II III IV

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Reactor concept

Thermal coupling of OCM and SRM

SRM

OCM

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Reactor concept

Oxidative coupling of methane

• Application of membrane reactor for OCM

o Uniform heat generation (driving force)

o Higher C2 selectivity and CH4 conversion

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Reactor concept

Temperature profiles in membrane reactor (OCM)

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Outline

• Introduction




• Results

• Conclusions

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Hollow fiber catalytic membrane reactor

• Hollow fiber dual function catalytic membrane reactor

o Core SRM

o Outer shell OCM

• Easier and less complicated manufacturing

SRM

OCM

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2-D reactor model

Hollow fiber model

Radial profiles

Reactor model

Hollow fiber model in

series Axial

profiles

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Cases

Only OCM Dual function

𝝏𝑪

𝝏𝒓=𝝏𝑻

𝝏𝒓= 𝟎

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Only OCM: Packed bed vs. Hollow fiber

• C2 Yield

o Isothermal: Packed bed (41%) > Hollow fiber (39%)

o Adiabatic: Packed bed (18%) < Hollow fiber (26%)

• Hollow fiber reactor better heat transfer effects

Hollow Fiber Reactor (Solid line) : Fixed bed reactor (dotted line)

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Hollow fiber: Dual function vs. only OCM

• C2 Yield:

o Isothermal: Dual function (29%) < only OCM (39%)

o Adiabatic: Dual function (29%) > only OCM (27%)

• Maximum yield: CH4 conversion is 64% Vs 41% (Dual function Vs

only OCM)

Dual function (Solid line) : Only OCM (dotted line)

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Conclusions

• OCM / SRM integration in single multifunctional reactor

o Reactor performance:

Hollow fiber catalytic membrane reactor > Packed bed membrane reactor

o Increased CH4 conversion compared to only OCM

o Simultaneous production of C2 and syngas without heat exchange

equipment

• Autothermal operation possible in both reactors

• The models presented here could be useful to provide the guidelines

for designing and improving the overall performance of the process

• Outlook

Experimental demonstration

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Acknowledgments

• Collaborations

Prof. dr. Ir. Leon Lefferts (University of Twente, Netherlands)

VITO (Belgium)

Tecnalia (Spain)

BIC (Russia)

Financial support from NWO/ASPECT

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Thank you [email protected]

[email protected]

Documents

Oxidative Coupling of Methane Spring Session - Traxxys