22P029-P
Dry Reforming of methane using atmospheric pressure non-thermal plasma
大気圧非平衡プラズマを用いたメタンのドライリフォーミング
Takamasa Okada, Masahiro Iwata, Akira Yonesu and Nobuya Hayashi
岡田隆昌, 岩田将裕，米須 章，林 信哉
University of the Ryukyus
1, Senbaru, Nishihara, Nakagami, Okinawa 903-0213, Japan
琉球大学 〒903-0213 沖縄県中頭郡西原町千原1番地
Saga University
1, Honjyo, Saga, 840-8502, Japan
佐賀大学 〒840-8502 佐賀県佐賀市本庄町1番地
Dry reforming of methane was investigated using atmospheric pressure non-thermal plasma generated by
the microwave discharge. Analysis of optical emission spectra and FTIR spectra indicated that methaneand carbon dioxide could be decomposed and converted into hydrogen and carbon monoxide in the plasma.
Acetylene was also detected as the hydrocarbon compounds in the product gases. The experimental results
shown that the H2/CO ratio can be controlled by adjusting the CH4/CO2 ratio in the gas feed.

1. Introduction
Dry reforming is utilized in producing hydrogenand carbon monoxide from methane with carbon
dioxide. The synthesis gas, a mixture of hydrogenand carbon monoxide, is an important intermediate
for various synthesizing chemicals. Therefore,
several techniques were proposed to the dry
reforming of methane, such as catalysis conversion,
plasma conversion and combination of catalyst andplasma [1-4]. Plasma chemical conversion iseffective methods for the dry reforming of methane.
The objective of this work is to investigate the dry
reforming of methane using atmospheric pressure
non-thermal plasma generated by our self-designed
microwave discharge system.
2. Experimental
Experimental apparatus is illustrated in Fig. 1(a).
The experiment was performed in a stainless steel
cylindrical chamber, which contains stainless steel
pipe surrounding a quartz discharge pipe (20mminner diameter) placed along the chamber axis. Aslit (60mm length, 5mm width) was arranged oneach aluminum pipe as shown in Fig. 1(b). The
length of the slit was chosen as half the wavelengthof the microwave. A gaseous mixture of CO2, andCH4 was mixed with Ar gas which was used as theplasma forming gas and fed to the quartz tube underatmospheric pressure. When the microwave isintroduced into the chamber through a waveguide,
non-thermal plasma is produced in the quarts tube.
The products after reaction were identifies by useof FTIR spectrometer (JASCO, FT/IR4000). The
exhaust gas from the microwave plasma wascollected at the end of quartz tube and analyzed by

FTIR spectrometer as shown in Fig. 1. The
emission spectra in the discharge region weremeasured with the multi-channel monochrometer(Ocean Optics HR2000CG-UV-NIR), spectral
resolution 0.75nm, and spectral range 200-1000nm.
Optical emission is collected along the radial
position through a view port on the side of thechamber using a lens-optical fiber combination.
(a)Microwave

Waveguide

Quartz tube

ShieldGas

Stainless steel chamber Antenna
Gas
Monochrometer

FTIR
Spectrometer

(b)
60mm

Slit

5mm

Quartz tube

Fig.1. Schematic diagram of experimental set-up

3. Results and discussion
3.1. Product by the plasma conversion
The typical FTIR spectra after the plasma
processing and the typical optical emission spectra
are shown in Fig. 2 and Fig. 3, respectively. The
experiment were worked at conditions of Ar flow
rates 6.0 ml/min, CH4 flow rates 0.07 ml/min,
CO2 flow rates 0.08 ml/min and microwave power80.16

70.14

60.12

50.10

hydrogen

40.08

30.06

carbon monoxide

20.04

10.02

0

Absorbance[arb.units]

0.12

0.00
0.5

0.7

CO

0.1

Absorbance of CO [abs units]

way. This result indicates that the H2/CO ratio of
the synthesis gas can be controlled by adjusting theCH4/CO2 ratio in the gas feed.
Generally, it is required for various H2/CO ratiosof the synthesis gas to synthesize different chemicalproducts.
Emission intensity ratio H2 /Ar900W.
We can confirm that methane and carbon dioxide
can be converted into hydrogen and carbon
monoxide by atmospheric non-thermal plasma
processing from Fig. 2 and Fig. 3. Moreover,acetylene (C2H2) was also detected as thehydrocarbon compounds in the tail gas as shown inFig. 2. The optical emission spectra (Fig. 3) indicatethat hydrogen atom (H) and hydrocarbon (CH) also
exist in the plasma. Thus, the production ofacetylene by the plasma is considered as follows.
CH4→CH3+H
CH3→CH2+H
CH2→CH+H ⇒ 2CH→C2H2

0.9

1.1

1.3

1.5

Reactants ratio CO2 /CH4

CO2CH4CH4C2H2H2O

H2O

0-0.011000

2000

3000

4000

Wavenumber[cm-1]

Fig.2. FTIR spectra of CH4 + CO2 plasma

Intensity[a.u.]

15000

C2C2 swan band

0200

0.05
0.04
0.03
0.02
0.01
0.00
0.5

0.7

0.9

1.1

1.3

1.5

Reactants ratio CO2 /CH410000

5000

Absorbance of C 2 H2 [abs units]

0.05

Fig.4. Effect of reaction CO2/CH4 ratio on
productions of H2 and CO

CH400

Fig.5. Effect of reaction CO2/CH4 ratio on
production of C2H2H
H2600

Ar800

1000

Wavelength[nm]Fig.3. Optical emission spectra of CH4 + CO2 plasma

3.2. Effect of CO2/CH4 ratio on conversion
Effect of the reactants ratio (CO2/CH4) on
conversion was investigated. The productions ofhydrogen, carbon monoxide and acetylene wereinvestigated under the experiment condition of Ar
flow rates 6.0 ml/min, methane flow rates 0.07
ml/min and microwave power 900W. The reactants
ratio was operated by changing carbon dioxide flowrates. The result is shown in Fig. 4 and Fig. 5.
From these Figure, we can see that the productionof carbon monoxide increased with increasing thereactants ratio (CO2/CH4), but the production ofhydrogen and acetylene changed in the opposite

4. Conclusions
Dry reforming of methane has been investigatedusing atmospheric pressure non-thermal plasma.
The process is effective in converting methaneand carbon dioxide into synthesis gas. The main
products were hydrogen, carbon monoxide andacetylene. It is found that the H2/CO of thesynthesis gas can be controlled by the CH4/CO2
ratio in the gas feed.
References[1] Jing Lu and Zhenhua Li: J Natur Gas Chem. 19(2010) 375.
[2] Zhang X, Wang B W, Liu Y W and Xu G H: Chin. J.
Chem. Eng. 17 (2009) 625.
[3] M Jasinski, M Dors and J Mizeraczyk: J. PowerSources. 181 (2008) 41.
[4] N. Hayashi, T. Yamakawa and S. Baba: Vacuum 80(2006) 1299.