reforming ch4

8/10/2019 Reforming CH4

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CO2reforming of CH4by atmospheric pressure glow

discharge plasma: A high conversion ability5

Daihong Li, Xiang Li, Meigui Bai, Xumei Tao, Shuyong Shang,Xiaoyan Dai, Yongxiang Yin*

School of Chemical Engineering, Sichuan University, Chengdu 610065, Sichuan, China

a r t i c l e i n f o

Article history:

Received 2 September 2008

Received in revised form

16 October 2008

Accepted 16 October 2008

Available online 25 November 2008

Keywords:

Plasma

Methane

Carbon dioxide

Syngas

Conversion ability

a b s t r a c t

CO2reforming of CH4to syngas has been investigated by a special designed plasma reactor

of atmospheric pressure glow discharge. High conversion of CH4, CO2, and high selectivity

of CO, H2, as well as high conversion ability are carried out. The experiment is operated in

wider parameter region, such as CH4/CO2 from 3/7 to 6/4, input power from 49.50 W to

88.40 W and total feed flux from 360 mL/min to 4000 mL/min. The highest conversion of

CH4and CO2is 98.52% and 90.30%, respectively. Under the experimental conditions of CH4/

CO2rate at 4/6, input power at 69.85 W and total feed flux at 2200 mL/min, the conversion

ability achieves a maximum of 12.21 mmol/kJ with the conversion of CH 4and CO2is 60.97%

and 49.91%, the selectivity of H2 and CO is 89.30% and 72.58%, H2/CO rate is 1.5, respec-

tively. This process has advantages of relatively large treatment and high conversion

ability, which is a benefit from a special designed plasma reactor.

2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights

reserved.

1. Introduction

The reaction of CO2 reforming of CH4 to syngas is widely

researched for great benefit to both environment and

economy. This conversion would not only reduce the atmo-

spheric emissions of CO2 and the consumption of CH4, but also

meet the special requirement in many synthesis processes

with its proper rate of H/C. Several technologies were

proposed to CO2 and CH4 conversion, such as catalysis

conversion [115], plasma conversion [1628] and combination

of catalyst and plasma[2934].

In the catalytic reforming of CO2and CH4, carbon deposi-

tion, leading to the deactivation of catalysts, was an intrac-

table problem. Therefore, a lot of efforts including addition

of promoters[17], selection of the supports[810], changes

in preparation conditions [11,12] and studies of reaction

mechanism[1315]were paid for seeking catalysts that have

good anti-carbon deposition performance.

Plasma process offers a unique way to induce gas phase

reaction, which is utilized in many chemical reactions. Several

plasma methods were employed to convert CO2 and CH4, such

as thermal plasma (TP)[16], dielectric barrier discharge (DBD)

[1720], corona discharge (CD) [2124], AC arc discharge (AD)

[25] and glow discharge (GD) [26]. Plasma processshowed to be

a fast conversion and easy realization, its conversion ability

still needed to be improved for future commercial use, though

some researchers attempted to combine catalyst and plasma

in CO2and CH4reforming system[2934]in recent years.

In this paper, CO2 reforming of CH4 to syngas by atmo-

spheric pressure glow discharge plasma is studied. With its

special characteristic of electron density, electron energies,

plasma temperature lower than thermal plasma, higher than

5 The project was supported by the National Natural Science Foundation of China (No.10475060).* Corresponding author.

E-mail address:[email protected](Y. Yin).

A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c om / l o c a t e / h e

0360-3199/$ see front matter 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

doi:10.1016/j.ijhydene.2008.10.053

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 4 ( 2 0 0 9 ) 3 0 8 3 1 3
mailto:[email protected]://www.elsevier.com/locate/hehttp://www.elsevier.com/locate/hemailto:[email protected]


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nonthermal plasma such as DBD and corona discharge, aswell as feed gases (CO2 and CH4) served as direct discharge

gas, atmospheric pressure glow discharge plasma process

brings out a high conversion ability, which is several times

higher than that of other discharge plasmas before.

2. Experiment

2.1. Plasma apparatus

Fig. 1 shows the schematic configuration of the plasma

reactor. An inside stainless steel stick with the outer diameter

of 8 mm is connected to the high voltage supply and thecoaxial iron crust with the inner diameter of 30 mm serves as

the grounded electrode. The stainless steel stick has an

ellipse-like discharge tip. An iron plate with a hole of 3 mm

diameter in the center is located at the contracted exit with

the inner diameter of 10 mm. The discharge zone is formed

within a gap of 7 mm between the stainless steel stick and the

iron plate. Two electrodes are separated by nonconductor.

As shown inFig. 2, 50 Hz AC high voltage is connected on

a booster. Adjusting booster, the voltage from the transformer

of 1:500 is applied on two electrodes. By the impedance of

transformer with high transformation ratio, a stable atmo-

spheric pressure discharge mode is achieved without any

added ballast element.The voltage information between the two electrodes is

from a potentiometer of 10 MU (R3)/100 kU (R2), and the

discharge current information in the circuit is from a resis-

tance of 100U (R1). All the measurements are made by a digital

oscilloscope (RIGOL DS5022M). The details of the measure-

ment are shown inFig. 2.

The principle and characteristic of discharge in this

experiment are similar to our previous studies[35]. When ac

voltage is risen to about 7000 V (mean-root-square value), the

gas between two electrodes are broken. After breaking, due to

the negative feedback of impedance of transformer, the

voltage on the generator automatically falls down to several

hundred volts, when a stable discharge is maintained. A

typical VI characteristic for stable discharge is shown inFig. 3. As a result, the discharge current increases with

increasing the voltage from booster, while the voltage

between two electrodes almost keeps at 500 V. Because the

discharge has this typical characteristic and operates at

atmospheric pressure, we call it atmospheric pressure glow

discharge. This kind of plasma reactor has a special charac-

teristic of electron temperature, electron density, plasma gas

temperature which are about 2.5 eV, 3.5 1012/cm3, 900 K,

Fig. 1 Schematic configuration of the plasma reactor.

Fig. 2 Sketch of measure circuit for voltage and current in

the discharge experiment.

0.08

0.10

0.12

0.14

0.16

0.18

400 450 500 550 600

Discharge voltage(V)

current(A)

Fig. 3 Diagram of the VI characteristic discharge

P[1 atm, discharge gas: CH4and CO2.

Fig. 4 Schematic diagram of experimental process 1.CH4;

2. CO2; 3. needle valve; 4. rotormeter; 5. mixer; 6. plasma

reactor; 7. cold trap; 8. bubble meter; 9. electrical source;

and 10. GC7900.

i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 4 ( 2 0 0 9 ) 3 0 8 3 1 3 309


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respectively. And also can keep the feed gas absolutely pass

through the discharge space.

2.2. Experimental system and analysis

The schematic diagram of experimental process is shown in

Fig. 4. The system is assembled with four major parts: a feedgas system, a plasma reactor, AC high voltage power supply,

and a gas analysis system. The feed and products are

measured by a bubble meter and analyzed by a gas chro-

matographic (GC7900) equipped with a thermal conductivity

detector (TCD). TDX-01 is used in GC column, the column

temperature is 100 C, the TCD current is 30 mA, and the flow

rate of the carrying gas (Ar) is 25 mL/min.

2.3. Calculations

By gas chromatographic analysis, it is found that the products

consisted of H2, CO, CH4, CO2and H2O. After reaction, there isstill a little carbon powder left in the reactor. According to the

analysis of the products, the overall conversions and selec-

tivity are defined as

CH4conversion (%) (moles of CH4converted/moles of CH4introduced) 100%

CO2conversion (%) (moles of CO2converted/moles of CO2introduced) 100%

H2selectivity (%) [moles of H2produced/(2moles of

CH4converted)] 100%

CO selectivity (%) [moles of CO produced/(moles of CH4convertedmoles of CO2converted)] 100%

H2/COmoles of H2produced/moles of CO produced.

Conversion ability shows the energy efficiency of CO2reforming of CH4by plasma. It is defined as:

E (mmol/kJ) (millimoles of CH4and CO2converted per

second) 1000/(input power on plasma reactor).

3. Results and discussions

3.1. Effects of CH4/CO2 rate on reaction

In the experiments, the discharge gas is composed of CH4and

CO2. Keeping CH4CO2total flow flux of 1000 mL/min, input

power of 68.95 W, the effect of CH4/CO2 rate on reaction is

investigated by varying the CH4/CO2rate from 3/7 to 6/4. The

results are shown inFig. 5.

In the experiment, When the CH4/CO2rate is from 3/7 to 6/

4, the discharge could be obtained steadily for a long time. But

when the rate reaches at 7/3, serious carbon deposition on

electrodes affects the discharge stability. As shown inFig. 5,

with the CH4/CO2 mole rate increases from 3/7 to 6/4, the

0

10

20

30

40

50

60

70

80

90

100

3 : 7 4 : 6 5 : 5 6 : 4

CH4/CO2

CH4 CO2

0

10

20

30

40

50

60

70

80

90

100

3 : 7 4 : 6 5 : 5 6 : 4

CH4/CO2

H2 CO

Conversion(

)

Selectivity(

)

a b

0

0.2

0.4

0.6

0.8

1

1.2

1.4

3 : 7 4 : 6 5 : 5 6 : 4

CH4/CO2

H2/CO

c

Fig. 5 Effects of CH4/CO2rate on reaction (a) Conversion of CH4and CO2; (b) Selectivity of H2and CO; (c) H2/CO mole rate. The

input power is 68.95 W and total feed flux is 1000 mL/min.



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conversion of CH4decreases from 94.61% to 87.47% while that

of CO2increases from 77.62% to 87.48%, the selectivity of H2increases from 72.80% to 87.53% while that of CO decreases

from 88.87% to 68.90%, and H2/CO mole rate increases from

1.00 to 1.28, respectively. These could be interpreted by

amount of O atoms. The lower the CH4/CO2rate is, the more O

atoms are in excess, which conduces to the reactions of

COCO and H2OH2O, the higher CO selectivity andlower H2electivity is obtained. Vice versa, the similar analysis

is for the results gotten at higher CH4/CO2rate.

Concerning about CO selectivity and carbon deposition, it

would be better to choose the CH4/CO2ratio in the range less

than5/5. In the following investigation CH4/CO2 4/6 is chosen.

3.2. Effects of feed flux treated per power

Define V F/P. F isthe total feedfluxof H2 and CO2 (mL/min); P

is the power on plasma reactor (W). V is an important

parameter to express the feed flux treated per power (W).

Experiments are conducted by keeping CH4/CO2 rate of 4/6,

varying the V from 5 mL/min/W to 60 mL/min/W. The exper-

imental results are shown inFig. 6.

As shown inFig. 6, the conversion of CH4and CO2decrease

from 96.68% to 13.49% and from 87.40% to 9.67%, respectively.

For an increasingV implied the average energy obtained by

each molecule is reduced. The selectivity of H2increases from

76.33% to 98.60% while that of CO decreases from 85.71% to

54.50% and H2/CO mole rate increases from 0.99 to 2.52 with V

increases from 5 mL/min/W to 60 mL/min/W. Thats because

the larger feed flux treated per power is, the lower the

temperature of reaction system is, which prevents H2 and C

atoms from further oxidation. Yunhua Li [36] analyzed

thermodynamic equilibrium of CO2 reforming of methane, theresults also showed that coke elimination should be done by

increasing the reaction temperatures.

3.3. Conversion ability

Conversion ability is important because it expresses the

economic value of the process.Fig. 7shows conversion abili-

ties of all the experiments investigated. It is interesting that

the optimal conversion ability locates at the region of

V 20w40 mL/min/W, where the conversion abilities are all

bigger than 10 mmol/kJ.

0

10

20

30

40

50

60

70

80

90

100

5 10 15 20 25 30 35 40 45 50 55 60

(mL/min/W)

CH4 CO2

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

5 10 15 20 25 30 35 40 45 50 55 60

(mL/min/W)

H2/CO

0

10

20

30

40

50

60

70

80

90

100

5 10 15 20 25 30 35 40 45 50 55 60

(mL/min/W)

H2 CO

Selectivity(

)

Conversion(

)

Fig. 6 Effects of feed flux treated per power. (a) Conversion of CH4and CO2; (b) Selectivity of H2and CO; (c) H2/CO mole rate

vs.V. The experimental condition: CH4/CO2rate 4/6, input power 49.5w88.4 W, feed flux 360w4000 mL/min.

0

2

4

6

8

10

12

14

5 10 15 20 25 30 35 40 45 50 55 60

(mL/min/W)

E(m

mol/kJ

Fig. 7 Conversion abilities on various V.



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Conversion abilities in this work are much higher than

plasma reactions. A comparison is shown inTable 1.

4. Summary and conclusions

In this work, CO2reforming of CH4to syngas has been inves-

tigated using atmospheric pressure glow discharge plasma.

Some conclusions can be given as following:

1. The process is effective in converting CH4 and CO2 into

syngas. The products are simple, including H2, CO, and

a small amount of H2O. The highest conversion of CH4and

CO2 is 98.52% and 90.30%, respectively, and the highest

conversion ability is 12.21 mmol/kJ.

2. Both the CH4/CO2 rate and the V (feed flux treated per

power) influence CH4and CO2conversions and H2and CO

selectivity. Proper H2/CO rate could be gained by modu-

lating the CH4/CO2rate and V.

3. Compared with other plasma process, the plasma used in

present experiment has advantages of larger treatment and

higher conversion ability. It benefits from its special

characteristic.

r e f e r e n c e s

[1] Seok SH, Choi SH, Park ED, Han SH, Lee JS. Mn-promoted Ni/Al2O3catalysts for stable carbon dioxide reforming of

methane. Journal of Catalysis 2002;209(1):615.[2] Valentini A, Carreno NLV, Probst LFD, Probst LFD, Filho PNL,Schreiner WH, et al. Role of vanadium in Ni:Al2O3catalystsfor carbon dioxide reforming of methane. Applied CatalysisA 2003;255(2):21120.

[3] Chen HW, Wang CY, Yu CH, Tseng LT, Liao PH. Carbondioxide reforming of methane reaction catalyzed by stablenickel copper catalysts. Catalysis Today 2004;97(23):17380.

[4] Martinez R, Romero E, Guimon C, Bilbao R. CO2reforming ofmethane over coprecipitated NiAl catalysts modified withlanthanum. Applied Catalysis A 2004;274(12):13949.

[5] Jozwiak WK, Nowosielska M, Rynkowski J. Reforming ofmethane with carbon dioxide over supported bimetalliccatalysts containing Ni and noble metal I. Characterizationand activity of SiO2supported NiRh catalysts. Applied

Catalysis A 2005;280(2):23344.

[6] Nimwattanakul W, Luengnaruemitchai A, Jitkamka S.Potential of Ni supported on clinoptilolite catalysts forcarbon dioxide reforming of methane. International Journalof Hydrogen Energy 2006;31(1):93100.

[7] Supaporn T, Apichai T, Chairut S, Sarayut Y. Synthesis gasproduction from dry reforming of methane over Ni/Al2O3stabilized by ZrO2. International Journal of Hydrogen Energy2008;33(3):9919.

[8] Verykios XE. Catalytic dry reforming of natural gas for theproduction of chemicals and hydrogen. International Journalof Hydrogen Energy 2003;28(10):104563.

[9] Souza MDMVM, Clave L, Dubois V, Perez CACP, Scmal M.Activation of supported nickel catalysts for carbon dioxidereforming of methane.AppliedCatalysis A 2004;272(12):1339.

[10] Pompeo F, Nichio NN, Ferretti OA, Resasco D. Study of Nicatalysts on different supports to obtain synthesis gas.International Journal of Hydrogen Energy 2005;30(1314):1399405.

[11] Liu GH, Chu W, Long HL, Dai XY, Yin YX. A novel reductionmethod for Ni/gAl2O3catalyst by a high frequency coldplasma jet at atmospheric pressure. Chinese Journal ofCatalysis 2007;28(7):5824.

[12] Liu GH, Li YL, Chu W, Shi XY, Dai XY, Yin YX. Plasma-assisted preparation of Ni/SiO2catalyst using atmospherichigh frequency cold plasma jet. Catalysis Communications2008;9(6):108791.

[13] Tsang SC, Claridge JB, Green MLH. Recent advances in theconversion of methane to synthesis gas. Catalysis Today1995;23(1):315.

[14] Wang SB, Lu GQ. Carbon dioxide reforming of methane toproduce synthesis gas over metal-supported catalysts: stateof the art. Energy Fuels 1996;10(4):896904.

[15] Li DH, Xi M, Tao XM, Shi XY, Dai XY, Yin YX. TPD Studies onNi/gAl2O3 catalysts reduced by atmosphere plasma.Chinese Journal of Catalysis 2008;29(3):28791.

[16] Fincke JR, Anderson RP, Hyde T, Detering BA, Wright R,Bewley RL, et al. Plasma thermal conversion to acetylene.Plasma Chemistry and Plasma Processing 2002;22(1):10536.

[17] Zhou LM, Xue B, Kogelschatz U, Eliasson B. NonequilibriumPlasma reforming of greenhouse gases to synthesis gas.Energy Fuels 1998;12(6):11919.

[18] Zhang YP, Li Y, Wang Y, Liu CJ, Eliasson B. Plasma methaneconversion in the presence of carbon dioxide usingdielectric-barrier discharges. Fuel Processing Technology2003;83(13):1019.

[19] Li Y, Xu GH, Liu CJ, Eliasson B, Xue BZ. Co-generation ofsyngas and higher hydrocarbons from CO2and CH4usingdielectric-barrier discharge: effect of electrode materials.Energy Fuels 2001;15(2):299302.

[20] Li Y, Liu CJ, Eliasson B, Wang Y. Synthesis of oxygenates and

higher hydrocarbons directly from methane and carbon

Table 1 Comparison of specific energy with different plasmas.

Plasma Feed flux (mL/min) P (W) Conversion (%) Selectivity (%) E (mmol/kJ) Refs.

CH4 CO2 H2 CO

Ac dielectric barrier 500 500 40 20 88.5 0.18 [17]

Dielectric barrier discharge 60 100 64.3 43.1 32.2 0.26 [18]

Pulsed corona plasma 25 42 63.7 60.2 62.6 0.26 [21]

Ac arc 75 30 88.9 53.2 81.5 0.15 [25]

Radio-frequency plasma 2920PPS 100 30.6 31.8 23.9 22.1 0.68 [27]

Radio-frequency plasma 10.3 kPPS 200 36.2 65.9 57.8 85.9 2.4 [28]

Thermal plasma

and catalyst

3.67 104 9.6 103 88.28 76.05 72.48 89.06 2.3 [33]

Present experiment 2.2 103 69.85 60.97 49.91 89.30 72.58 12.21 This paper



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dioxide using dielectric-barrier discharges: productdistribution. Energy Fuels 2002;16(4):86470.

[21] Dai B, Zhang XL, Gong WM, He R. Study on the methanecoupling under pulse corona plasma by using CO2as oxidant.Plasma Science and Technology 2000;2(6):57780.

[22] Li MW, Xu GH, Tian YL, Chen L, Fu HF. Carbon dioxidereforming of methane using dc corona discharge plasmareaction. Journal of Physical Chemistry A 2004;108(10):168793.

[23] Le H, Lobban LL, Mallinson RG. Some temperature effects onstability and carbon formation in low temperature ac plasmaconversion of methane. Catalysis Today 2004;89(1-2):1520.

[24] Zhao GB, John S, Zhang JJ, Wang LN, Muknahallipatna S,Hamann JC, et al. Methane conversion in pulsed coronadischarge reactors. The Chemical Engineering Journal 2006;125(2):6779.

[25] Huang A, Xia GG, Wang JY, Suib SL, Hayashi Y, Matsumoto H.CO2reforming of CH4by atmospheric pressure ac dischargeplasmas. Journal of Catalysis 2000;189(2):34959.

[26] Chen Q, Dai W, Tao XM, Yu H, Dai XY, Yin YX. CO 2reformingof CH4by atmospheric pressure abnormal glow plasma.Plasma Science and Technology 2006;8(2):1814.

[27] Yao SL, Ouyang F, Nakayama A, Suzuki E, Okumoto M,Mizuno A. Oxidative coupling and reforming of methane

with carbon dioxide using a high-frequency pulsed plasma.Energy Fuels 2000;14(4):9104.

[28] Yao SL, Okumoto M, Nakayama A, Suzuki E. Plasmareforming and coupling of methane with carbon dioxide.Energy Fuels 2001;15(5):12959.

[29] Jiang T, Li Y, Liu CJ, Xu GH, Eliasson B, Xue BZ.Plasma methane conversion using dielectric-barrierdischarges with zeolite A. Catalysis Today 2002;72(34):22935.

[30] Zhang XL, Zhu AM, Liu ZF, Li XH, Gong WM. Catalytic activityof metal and metal-oxide catalysts in oxidative coupling ofCH4with CO2under pulse corona plasma. Chinese Journal ofCatalysis 2003;24(10):7256.

[31] Song HK, Choi JW, Sung HY, Lee H, Na BK. Synthesis gasproduction via dielectric barrier discharge over Ni/gAl2O3catalyst. Catalysis Today 2004;89(12):2733.

[32] Cheng DG, Zhu XL, Ben YH, He F, Cui L, Liu CJ. Carbondioxide reforming of methane over Ni/Al2O3treatedwith glow discharge plasma. Catalysis Today 2006;115(14):20510.

[33] Tao XM, Qi FW, Yin YX, Dai XY. CO2reforming of CH4bycombination of thermal plasma and catalyst. International

Journal of Hydrogen Energy 2008;33(4):12625.[34] Fidalgo B, Dominguez A, Pis JJ, Menendez JA. Microwave-

assisted dry reforming of methane. International Journal ofHydrogen Energy 2008;33(15):433744.

[35] Li X, Tang JC, Dai XY, Yin YX. Study of atmospheric pressureabnormal glow discharge. Plasma Science and Technology

2008;10(2):1858.[36] Li YH, Wang YQ, Zhang XW, Mi ZT. Thermodynamic

analysis of auto thermal steam and CO2reforming ofmethane. International Journal of Hydrogen Energy 2008;33(10):250714.


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