Oxidative Coupling of Methane : a heterogeneously

Methusalem M2dcR2 Advisory board meeting, Ghent, 19/06/2012

Oxidative Coupling of Methane : a heterogeneously catalysed gas phase reactionVaios I. Alexiadis*, Panagiotis N. Kechagiopoulos*, Joris W. Thybaut* and Guy B. Marin*

http://www.lct.UGent.be E-mail : Vaios.Alexiadis@UGent.be

*Laboratory for Chemical TechnologyKrijgslaan 281 (S5), 9000 Ghent, Belgium

Acknowledgement : This work was supported bythe Long Term Structural Methusalem Funding by the Flemish Government.

European Research Institute of Catalysis

� Oxidative Coupling of Methane (OCM) is one of the most attractive methods to utilize natural gas as chemical feedstock for the production of higher hydrocarbons.

� OCM process occurs through a mechanism in which catalytic reactions interact with gas phase reactions.

� CH3● radicals, produced on the catalyst surface, either couple in the gas phase to produce the desired C2

hydrocarbons or are oxidized forming undesired carbon oxides.

� CH3● radicals are highly reactive. In order to account for the irreducible mass transport limitations, an one-dimensional heterogeneous reactor model is employed (coordinate z), which distinguishes between a solid-intraparticle phase (coordinate ξ) and a fluid-interstitial phase (coordinate r).

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EXP_CH4

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Figure 1. Parity diagrams for CH4, C2H6, C2H4, CO, CO2 and lumped C2 products. The depicted results are in molar fractions, %. Experimental results derived from RUB.

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Figure 2. Reactants conversion and products selectivity vs. space time at different temperatures. Experimental results derived from RUB.Experimental conditions : P =190 KPa, CH4/O2, feed = 4 and 80 % N2 dilution.

C1. ∗⇔∗+ OO 222

C2. ∗+•⇔∗+ OHCHOCH 34

C3. ∗+•⇔∗+ OHHCOHC 3242

C4. ∗+•⇔∗+ OHHCOHC 5262

C5. ∗+∗⇔∗ OOHOH 22

C6. ∗+⇔∗ OHOH 22

C7. ∗⇔∗+• OCHOCH 33

C8. ∗+∗⇔∗+∗ OHOCHOOCH 23

C9. ∗+∗⇔∗+∗ OHCHOOOCH 2

C10. ∗+∗⇔∗+∗ OHCOOCHO

C11. ∗+∗⇔∗+∗ 2COOCO

C12. ∗⇔∗+ COCO

C13. ∗⇔∗+ 22 COCO

C14. ∗⇔∗+ OHCOHC 4242

C15. ∗+∗⇔∗+∗ OHOHCOOHC 3242

C16. ∗+∗⇔∗+∗ CHOOCHOOHC 232

C17. ∗+⇔∗+• OHHCOHC 4252

C17. ∗+⇔∗+• OHOCHOOCH 23

C19. ∗+•⇔∗+ OHCHOOOCH 2

C20. ∗+⇔∗+• OHCOOCHO

C21. ∗+•⇔∗+ OHHOH 2

C22. ∗+•⇔∗+ OHHOOOH 222

C23. ∗+⇔∗+• OHOOHO 22

C24. ∗+•⇔+∗• OOHHO2

C25. ∗+•⇔∗+ OHOHOOH 2

C26. ∗+•⇔∗+• OHOOOH

Pressure (kPa) 190.0

Temperature (K) 980.0 – 1180.0

CH4/O2, feed (molCH4 molO2-1) 2.0 – 4.0

W/Ftot (mg s nml-1) 2.0 – 11.0

Ftot (nml s-1) 7.0

N2 dilution (%) 80.0 – 90.0

Radius of catalyst pellet (m) 1.0 10-4

Length of catalyst bed (m) 1.5 10-2

Catalyst 1%Sr/La2O3

Surface area (m2 kg-1) 2000.0

Porosity (mg3 mc

-3) 0.27

Density (kg m-3) 2300.0

SiC dilution weight (kg) 1.0 10-3

� The microkinetic model contains 39 reversible gas phase reactions (adopted from Chen et al.) and 26 reversible catalytic reactions; 24 gas phase and 11 surface species are involved.

� Gas phase reactions couple with the catalytic reactions via the reactor model equations.

� 25 catalyst descriptors are incorporated in the microkinetic model.

Catalytic reactions networkSimulated reaction conditions and catalyst

properties derived from RUB experiments

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C2H4 selectivity

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C2 selectivity

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Figure 3. Reactants conversion, C2 selectivity and yield vs. CH4 / O2, feed at different space times. Operating conditions : P =190 KPa, T = 1065 K and 80 % N2 dilution.

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Figure 4. Yield of C2 products, %, vs. catalyst descriptors. Operating conditions : P=190 KPa, T=1065 K, CH4/O2,feed = 3, W/Ftot= 9 mg s nml-1 and 80% N2 dilution.

This set of catalytic reactions is coupled to the gas-phase branched-chain reaction network shown in Table 1 via the reactor model equations presented in Section 2.1. This set of catalytic reactions is coupled to the gas-phase branched-chain reaction network shown in Table 1 via the reactor model equations presented in Section 2.1.