7/27/2019 Hydrogen From SMR 1

1/2

OXIDATIVE STEAM REFORMING OF METHANE IN

MICROCHANNEL REACTORS

Mustafa Karakaya, Eyup Simsek, Ahmet K. Avci, Z. Ilsen Onsan

Department of Chemical Engineering, Bogazici University, Bebek 34342,

Istanbul, Turkey

Summary

Oxidative Steam Reforming (OSR) of methane to synthesis gas over -Al2O3 supported

bimetallic 0.2wt%Pt-2wt%Rh catalyst was investigated in coated and packed microchannel

reactors. Methane conversion and CO selectivity in product were investigated in terms of

reaction temperature, molar steam-to-carbon (S:C) and oxygen-to-carbon (O2:C) ratios, and

contact time over two catalyst geometries. It was found that the coated microchannel reactor,

which gives higher CO selectivity is more preferable than the packed microchannel reactor.

Keywords

Microchannel reactor, oxidative steam reforming, methane, bimetallic Pt-RhIntroduction

Syngas (CO+H2) is an important feedstock in

industrial chemicals production processes such as

Fischer-Tropsch and methanol syntheses. Oxidative

steam reforming (OSR), which is a combination of

endothermic steam reforming and exothermic total

oxidation, is a major route for producing syngas

from hydrocarbon-based fuels. While combustion

of part of the fuel facilitates steam reforming, it

might also lead to hot-spot formation in industrial

reactors, which, in turn, causes deactivation of the

Ni-based catalyst generally used. Hot spots during

OSR can be eliminated by using Rh- or Pt-based

catalysts [1].

Emerging microchannel technology can be another

option for the solution of the problem described

above. With their characteristic channel dimensionsbetween 10 and 1000 m, microchannels provide

enhanced heat transfer rates that are a few orders of

magnitude greater than those possible with

conventional reactors [2]; therefore, heat generated

locally can rapidly be spread over the entire

domain, and nearly isothermal operating conditions

can be guaranteed. Moreover, due to reduced mass

transfer limitations owing to micrometer channel

dimensions, the reactions can be carried out in the

kinetic regime.

The aim of this work is to assess the methane OSR

performances of two typical microchannel reactor

configurations wall-coated and packed that are

operated under identical conditions in a wide range

of parameter values including residence time,

reaction temperature, inlet steam-to-carbon (S:C)

and oxygen-to-carbon (O2:C) molar ratios.

Experimental

Oxidative steam reforming runs on the bimetallic

0.2wt%Pt-2wt%Rh dispersed on a suitable porous

-Al2O3 support. Powdered catalyst is prepared by

incipient-to-wetness impregnation and then mixed

with water to form slurry which is coated on two

heat-treated FeCrAlY plates to give a catalyst

amount of 0.0107 g. The coated plates are then

inserted into an engineered steel housing such that

the space between the catalytic faces of the plates

forms a microchannel. In the packed configuration

(Fig. 1), the particulate catalyst is also prepared byincipient-to-wetness impregnation, and then filled

into the microchannel having the same flow-by

(void space+catalytic coating) volume. In this case,

two uncoated plates are inserted into the central

part of the housing and supported with a ceramic

wool plug. The resulting space forms a

microchannel, having dimensions of 0.75 mm x 4

mm x 20 mm (height x width x depth). This

microchannel is filled with a total amount of

0.0107 g of the particulate catalyst. The reactor is

placed inside a long quartz tube whose temperatureis kept constant by an electric furnace.

7/27/2019 Hydrogen From SMR 1

2/2

The effects of reaction temperature, contact time,

oxygen-to-carbon (O2:C), steam-to-carbon (S:C)

molar ratios are studied. The temperature is varied

at 50C increments between 500 and 650C. The

O2:C ratio with the specific values of 0.47, 0.54 and

0.63 is kept below the stoichiometric value of 2.The S:C ratio is varied between 0.5 and 3. Using N2

as balance, total flow rate and CH4 mole fraction

are kept constant at 210 cm3/min and 0.14,

respectively, except in testing the effect of contact

time (Wcat/FCH4,0) where contact times of 0.35, 0.41,

0.50 and 0.71 mg.min/cm3are used in both reactor

configurations.

Fig. 1. Top (left) and cross-sectional (right) views

of the packed microchannel configuration (1:

Engineered metal housing; 2: FeCrAlY plates; 3:

Packed catalyst; 4: Ceramic wool plug)

SEM-EDX characterization of the reduced catalyst

showed uniform distribution of metals across the

plate and no coke formation in both geometries.

Results and Discussion

Although increase in reaction temperature increases

CH4 conversion in both reactor configurations,

coated microchannel gives higher CH4 conversions

up to 600-625C, after which performances of

coated and packed reactor configurations are

similar (Fig. 2).

Fig. 2. Effect of temperature on CH4 conversion in

coated and packed microchannels (S:C=3.0,

O2:C=0.47)

Fig. 3. Effect of temperature on CO selectivity in

coated and packed microchannels (S:C=3.0,

O2:C=0.47)

Full oxygen conversion is achieved in all runs,

indicating that total oxidation is much faster than

steam reforming and that increasing temperature

only enhances the reforming conversion. Higher

temperatures lead to higher CO selectivity (moles

CO/(moles CO+moles CO2)) values (Fig. 3).

Comparing two catalyst geometries, lower CO

selectivity is obtained in packed microchannel

because water gas shift activity seems to suppress

the partial oxidation of methane. As for the effect

of O2:C ratio, total oxidation conversion increases

with increasing oxygen partial pressure, and the

amount of extra water produced increases steam

reforming conversion, which, however, also

decreases the CO selectivity (Fig. 3).

Acknowledgement

Financial support provided by Bogazici University

projects BAP-09HA506D and BAP 6349, and

TUBA-GEBIP support to Ahmet K. Avci are

acknowledged.

References

[1] K. Tomishige, S. Kanazawa, K. Suzuki, M.

Asadullah, M. Sato, K. Ikushima, K.

Kunimori, Effective heat supply from

combustion to reforming in methane

reforming with CO2 and O2: comparison

between Ni and Pt catalysts, Appl. Catal. A

Gen. 233 (2002) 35- 44.

[2] L. Kiwi-Minsker, A Renken, Microstructured

reactors for catalytic reactions, Catal. Today,

110 (2005) 2-14.