Influence of potassium on Pt-catalysts in steam reforming of methane and ethane.

0.0E+00 1.0E-05 2.0E-05 3.0E-05 0.74 1.2 1.7 2.2 Ethane concentration (v%) co nv ers ion ra te (mo l/(g.s)) 0.0E+00 1.0E-05 2.0E-05 3.0E-05 0.74 1.2 1.7 2.2 Ethane concentration (v%) co nversio n rate (m ol /(g. s) 0 100 200 300 Temperature (°C) TC D

K

T=70°C

Combine the exothermic oxidative coupling of methane and highly exothermic combustion (side) reactions with the endothermic processes of methane steam and dry reforming. Convert methane to ethylene and synthesis gas (CO and H2) in one multifunctional reactor in an autothermal process

INTRODUCTION

AIM OF THE PROJECT

e-mail:P.O.Graf@utwente.nl

Patrick Graf, Barbara Mojet and Leon Lefferts

Influence of potassium on Pt-catalysts in steam

reforming of methane & ethane

Influence of potassium on Pt-catalysts in steam

reforming of methane & ethane

Financial support ACTS-NWO Project No. 053.62.008 (ASPECT) is gratefully acknowledged

CONCLUSIONS

C H

C

C O , H

1

2

2

4

3

Involved reactions are shown in the scheme: 1. Oxidative coupling of methane leads to

ethane and ethylene (C2)

2. Side combustion reactions of methane and C2 yield H2O and CO2

3. H2O and CO2can react with remaining

methane to synthesis gas (CO & H2) via

steam and dry reforming

4. Main challenge: suppress steam/dry reforming of ethane and ethylene to avoid complete reaction to synthesis gas

OBJECTIVE

• Influence relative steam reforming rates of CH4and C2H6by potassium addition

• Explain effect of potassium on methane/ethane competition

MIXTURE OF METHANE & ETHANE ON PT-YSZ

CO DESORPTION IN TPD & FTIR

EXPERIMENTAL

ƒ1 wt% Pt on Yttrium stabilized zirconia (YSZ)

ƒUnmodified versus potassium modified

ƒEqual metal loading & preparation

ƒT = 700°C, H2O = 12 vol% (H/C ratio >1)

ƒEthane concentration varied from 0.7 to 2.2vol.%, methane constant: 7.7 vol.%

ƒPotassium influences relative reaction rates of C2H6& CH4on Pt/YSZ ƒCompetition between both components is prevented through weaker

adsorption on potassium modified catalysts

K

No K

Pt-YSZ without K

¾Strong influence of components to each other: Increase in ethane concentration ⇒less methane converted

¾Higher concentrations: low rate for both components K modified Pt-YSZ

¾Methane almost unaffected by ethane addition

¾Ethane reaction rate indicates first order behaviour

¾Variation in methane concentration (not shown) shows similar trends: first order in methane, ethane unaffected

¾Methane and ethane react more independently

CH

C

H

ƒCO used as probe molecule for adsorption strength of methane and ethane

ƒPotassium decreases CO desorption temperature, indicating weaker adsorption

ƒResults confirmed in FTIR experiments for linear Pt-CO adsorption

ƒAssuming Langmuir Hinshelwood kinetics, weak adsorption of both methane and ethane explains non-competitive behaviour on potassium modified catalysts:

4 4 4 6 2 6 2 4 4 6 2 6 2 4 4 4 4 4

1

,

1

p

K

p

K

p

K

p

K

p

K

p

K

=

⇒

<<

+

+

=

θ

θ

No K

T=130°C

p

kK

r

k

r

θ

θ

θ

=

=

ƒMethane reaction rate dependent only on methane partial pressure, independent of ethane partial pressure:

2000 2050 2100 2150 2200 Wavenumber (cm-1) A.U . 2083 30°C 98°C 90°C 82°C

K

CH

= 7.7 vol.%