22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Oxidative and wet reforming of methane by means of packed-bed dielectric
barrier discharge reactor
A.M. Montoro-Damas1, A. Gómez-Ramírez1, V.J. Rico1, M.A. Rodríguez2, A.R. González-Elipe1 and J. Cotrino1,3
1
2
Institute of Material Science (ICMS), Seville, Spain
Institute of Ceramics and Glass (ICV), Madrid, Spain
3
University of Seville, Spain
Abstract: Plasma reforming of methane has been investigated in a packed bed DBD
reactor in order to find the optimum working parameters that maximize both the reaction
yield and the energy efficiency of the process at low-level power. Wet and oxidative
processes were studied, together with the influence of working parameters such as dielectric
barrier thickness, size of ferroelectric pellets, operating frequency or size of the electrode.
Keywords: dielectric barrier discharge, packed bed reactor, reforming of methane, energy
efficiency
1. Introduction
Reforming of hydrocarbons by means of dielectric
barrier discharge (DBD) plasmas has proved to be one of
the most versatile and powerful plasma methods either in
the presence or in the absence of catalysts [1]. Although
there is a high number of contributions reporting the
feasibility of the plasma reforming process by DBD
plasma [2, 3] improving its energetic performance at low
power consumption has not received an equivalent
attention. In this work, a systematic study of the energy
efficiency for methane reforming has been carried out by
changing working parameters such as gap between
electrodes, size of the ferroelectric pellets, operating
frequency or size of the active electrode.
2. Experimental setup
A scheme of the employed reactor is presented in
Fig. 1. It consists of a parallel plate packed-bed DBD
reactor [4] filled with PZT (lead zirconate titanate)
pellets. The distance between the upper and the bottom
electrode could be varied from 3 mm to 10 mm, and two
types of pellet diameter distributions – ranging either
from 0.5 mm to 2 mm or from 2 mm to 3 mm – were
utilized. The whole system was kept at 130 ºC to avoid
any condensation of water in the system. The reactants
were introduced in the plasma region through a tube
placed in the centre of the grounded electrode, while both
products and unreacted compounds got out from the
plasma zone through the sides of the inter-electrode gap
as represented in Fig. 1.
The energetic efficiency η of the plasma reaction [2] is
given by Eq. 1, where E is the energy consumed in the
process, and LHV (H 2 ) and LHV (CH 4 ) are the lower
heating values for hydrogen and methane, respectively.
The energy efficiency has also been determined by means
of the parameter L defined in Eq. 2, where V 298K is the
number of litres of H 2 produced at 298 K and one bar.
This parameter is very adequate to study the energy
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Fig. 1. Sketch of the DBD reactor utilized in the present
work. The dielectric barrier is formed by PZT pellets, and
the gas flow path is indicated by arrowed lines.
efficiency for hydrogen production when we are
comparing different mixtures of reactants, because it
directly accounts for the energy required to obtain the
product of interest.
We determined the power consumption by measuring
the area inside the corresponding Lissajous figure, i.e.,
Q-V diagrams, which are obtained by recording, with an
oscilloscope, the alternate voltage applied to the active
electrode and the current circulating through the system.
3. Results
In the course of the present investigation, we varied
systematically the frequency of the applied voltage.
Firstly, a set of experiments of wet reforming were
carried out, according to the reaction Eq. 3. We
introduced a stoichiometric proportion of the reactants,
i.e., H 2 O:CH 4 = 2:1, with flows of 4.76 cm3/min for
methane and 9 cm3/min for water. Fig. 2 shows that,
independently of the gap distance between electrodes, the
amount of reformed methane increases with the applied
frequency, whereas the parameter L decreases. The
calculation of the LHV efficiency, η, revealed that it
decreases as well, exactly in the same way as L. In terms
of the percentage of reformed methane, we can see in
Fig. 2 that the thickest barrier provides the best results.
On the contrary, if we are interested in reducing the
energy costs of hydrogen production, we should choose
1
the thinnest barrier.
Fig. 2. Percentage of CH 4 conversion and energy
efficiency – measured in litres of hydrogen produced per
kWh – as a function of frequency. Empty triangles and
circle/cross points represent data for experiments with
double total gas flow.
Top: 3 mm gap between
electrodes. Bottom: 10 mm gap between electrodes.
did not affect to the Q-V plot, while increasing the pellet
size led to a minimal reduction of the area within the
curve, i.e., the power consumption lowers under these
conditions.
4. Conclusions
Wet and oxidative reforming of methane in a packedbed DBD reactor filled with PZT pellets has been studied.
The versatility of the reactor allowed us to change
working parameters such as the barrier thickness and the
active electrode size. A systematic analysis for different
gap distances between electrodes revealed that, while the
percentage of methane conversion increases with
frequency, the energy efficiency decreases. These results
were obtained for the two reactant mixtures. However,
although we found a similar behaviour by the two kinds
of reforming process, higher values of methane
conversion and energy efficiency were achieved for the
oxidative process. The effect of doubling the total flow
was tested in the case of wet reforming, and it led to a
higher hydrogen production at the same energy cost.
Finally, wet reforming experiments reducing the area of
the active electrode or increasing the pellet size originated
a more energetically efficient reaction.
5. Acknowledgements
The effect of doubling the reactant flow at a given
We thank the Junta de Andalucia (Project P12-FQMfrequency was also explored and the obtained illustrated 2265, University of Seville) and Spanish Ministry of
in Fig. 2. It can be seen that increasing the flow rate Science and Innovation (Project Recupera2020-2.2.3,
decreases the methane conversion slightly, but increases Spanish National Research Council) for financial support.
the energy efficiency significantly. This result is a
consequence of a higher net hydrogen production at the 6. References
[1] H.L. Chen, H.M. Lee, S.H. Chen, Y. Chao and
same energy cost.
M.B. Chang. Appl. Catal. B: Environm., 85, 1-2
The influence of working parameters such as the size of
(2008)
the active electrode or the ferroelectric pellets has been
studied as well. The energy efficiency is higher for small [2] G. Petitpas, J.-D. Rollier, A. Darmon, J. GonzalezAguilar, R. Metkemeijer and L. Fulcheri. Int. J.
electrodes and for bigger pellets. The first configuration
Hydrogen Energy, 32, 14 (2007)
result indicates that the plasma discharge is also activating
the back reaction Eq. 3. Therefore, optimizing the [3] B. Sarmiento, J.J. Brey, I.G. Viera, A.R. GonzálezElipe, J. Cotrino and V.J. Rico. J. Power Sources,
residence time of reactants in the plasma zone would
169, 1 (2007)
contribute to increase the energy efficiency of the system.
A higher efficiency with bigger pellets suggests the [4] H.L. Chen, H.M. Lee, S.H. Chen and M.B. Chang.
Ind. Engng. Chem. Res., 47, 7 (2008)
existence of a critical space between pellets to effectively
sustain the plasma.
Other type of experiments investigated in this work 7. Equations
consisted of the oxidative reforming of methane
flows of 1.2 cm3/min η ( H 2 + CO ) produced × LHV ( H 2 ) ×100
according to Eq. 4. O 2 and CH 4 =
(1)
3
and 10.8 cm /min, respectively, were introduced in the
E + ( CH 4 )injected × LHV ( CH 4 )
reactor. The analysis of the results, i.e., methane
conversion and energetic efficiencies η and L, depicted a
V
(2)
L = 298K
tendency similar to that obtained in the wet reforming
E
process. Nevertheless, for this reactant mixture, these two
magnitudes had significantly higher values, thus
CH 4 + H 2O → CO + 3H 2 ( ∆H 0 =
+206 kJ mol−1 ) (3)
sustaining the use of the reactant mixture CH 4 /O 2 for
reforming of methane.
(4)
−36 kJ mol−1 )
CH 4 + O2 → 2CO + 4 H 2 ( ∆H 0 =
As stated in Section 2, we obtained the Lissajous figure
for all the performed experiments. In this regard, it is
worth mentioning that doubling the total flow of reactants
2
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