22nd International Symposium on Plasma Chemistry
July 5-10, 2015; Antwerp, Belgium
Pulsed corona-induced CO 2 methanation
W.F.L.M. Hoeben, E.J.M. van Heesch, F.J.C.M. Beckers, W. Boekhoven and A.J.M. Pemen
Department of Electrical Engineering, Electrical Energy Systems group, Eindhoven University of Technology, Den
Dolech 2, 5612 AZ Eindhoven, the Netherlands
Abstract: CO 2 methanation has been observed by application of pulsed corona discharges
in a CO 2 atmosphere over a deionized water film. At 46 kJ/L energy density,
approximately 440 ppm CH 4 has been observed at a production efficiency near 398 pmol/J.
Nickel-based corona wires seems to strongly promote the plasma-induced CO 2 methanation
process.
Keywords: CO 2 , methanation, non-thermal plasma, plasma catalysis, DSRD pulse source
1. Introduction
Exclusively reserving fossil hydrocarbons for synthesis
of life sustaining chemicals (e.g., pharmaceuticals, crop
protection and food conservation agents, garments)
prevents preliminary depletion of precious organic carbon
sources through energy generation. An immense world
reserve of inorganic carbon is stored in both the
atmosphere as carbon dioxide and in oceans as
carbonates. CO 2 back conversion thus is of great interest
[1-3] but at the same time attractive only, if the required
energy originates from sustainable energy sources.
The direct conversion of carbon dioxide to methane has
been studied using pulsed corona discharges in a carbon
dioxide atmosphere over a deionized water film. CH 4
formation is assumed to proceed via the precursors CO
and H 2 , produced from plasma-induced dissociation of
CO 2 and H 2 O, respectively. Although experiments have
been performed without direct use of catalytic materials,
d-metal catalytic activity of the corona wires seems to
play an important role in CO 2 methanation.
2. Experiments
Under ambient conditions, nanosecond-risetime 65 kV
high voltage pulses of 100 ns pulse duration from a driftstep-recovery-diode (DSRD) based pulse source [4] have
been applied to a capacitive electrode configuration in a
reactor with gas flow recycling, see Fig. 1. Typical
voltage & current oscillograms are given in Fig. 2.
The gas phase composition has been monitored using a
gas chromatograph - flame ionization detector - mass
spectrometer (Shimadzu QP2010p GC-FID-MS) and also
a gas chromatograph with Thermal Conductivity Detector
and MTN-assisted Flame Ionization Detector (Shimadzu
GC2010p GC-TCD-MTN-FID). Experiments have been
performed using both Nikrothal 80 and stainless corona
wires.
The GC-FID-MS with dedicated separation
column is used to identify gas phase products, especially
possibly complex organics. The GC-TCD-MTN-FID
instrument focusses on simple permanent gases, with
increased sensitivity for CO and CO 2 using the
CO x -converting MTN unit in combination with the FID.
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Fig. 1. Pulsed corona reactor with gas infrastructure.
Fig. 2. Typical voltage & current oscillograms recorded
at energy density 46 kJ/L, with derived pulse energy.
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3. Results
Initial CO 2 methanation experiments have been
performed using Nikrothal 80 corona wires. The GCFID-MS chromatograms represented by Fig. 3 indicate
the formation of CH 4 as a function of the energy density,
adjusted up to 46 kJ/L where about 440 ppm CH 4 has
been detected. CH 4 production is confirmed by the mass
spectrometer Total Ion Current chromatograms given by
Fig. 4. The CH 4 production efficiency is approximately
3.98E-10 mol/J.
Fig. 3. Top: GC-Total Ion Current chromatograms with
peaks CO ~ 3.4 min, O 2 ~ 3.5 min, CH 4 ~ 3.6 min,
CO 2 ~ 4.0 min, H 2 O ~ 12.5 min. Bottom: GC-Flame
Ionization Detector chromatograms with CH 4 peak
~ 3.6 min. GC-FID-MS data as a function of the energy
density.
Fig. 4. GC-Total Ion Current chromatograms with m/z
values recorded at 46 kJ/L. Arrows indicate CH 4 .
Further evidence has been obtained with experiments
using the same pulse source and reactor, the latter now
equipped with stainless steel corona wires. Gas phase
analysis has been performed using both diagnostic tools.
Applied energy densities have been 90-359 kJ/L. The
formation of O 2 , CO and H 2 is illustrated by the
GC-TCD-MTN-FID chromatograms in Fig. 5. Again
CH 4 has been detected, but levels have appeared to be
sub-ppm now, while the applied energy density has been
much higher than before. Observed CO 2 conversion
levels are high i.e. up to 64%. CO 2 conversion efficiency
values are approximately 90 - 143 eV/molecule.
Fig. 5.
Top: GC-Flame Ionization Detector
chromatograms indicating the formation of CO ~ 4.8 min
and CH 4 ~ 7.5 min and conversion of CO 2 ~ 9.6 min.
Bottom:
GC-Thermal
Conductivity
Detector
chromatograms primarily indicating the formation of
H 2 ~ 2.8 min, O 2 ~ 4.0 min, CO ~ 4.7 min and the
conversion of CO 2 ~ 9.5 min.
4. Discussion
It is remarkable that the plasma-induced CO 2
methanation using Nikrothal corona wires is much more
effective than that achieved with stainless steel based
wires. Nikrothal appears to be an austenitic nickelchromium alloy (19 - 21% Ni), where nickel as d-metal
catalytic material exhibits specific methane yielding CO
hydrogenation potential [5].
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Although proof of principle has been provided for
plasma-driven CO 2 methanation, the observed energy
efficiency of approximately 398 pmol/J is still poor.
However, improvement seems feasible by application of a
dedicated nickel-based catalyst, sub-nanosecond rise time
pulsed corona discharges [6] and tuning of the plasma
spatial & energy distribution [7].
Concluding, a topic of special interest is the release of
CO 2 from its major source seawater [8]. Preliminary
experiments prove the plasma-induced desorption of CO 2
from 200 g seawater (origin: North Sea). Fig. 6 shows
GC-TCD-MTN-FID chromatograms of the gas phase
after 0, 30 and 60 min of pulsed corona operation using
the same settings as before. Prior to the tests, the reactor
has been thoroughly flushed with synthetic air 4.8, being
CO 2 free. Observed CO 2 quantities are about 529 ppm at
maximum. In addition to CO 2 desorption, the formation
of some CO has been observed due to plasma-induced
dissociation of CO 2 .
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Fig. 6. GC chromatograms of the gas phase over plasma
exposed seawater, as a function of the exposure time.
Top: GC-Flame Ionization Detector chromatograms
indicating CO ~ 4.9 min and CO 2 ~ 10.2 min. Bottom:
GC-Thermal Conductivity chromatograms indicating
O 2 ~ 3.7 min, N 2 ~ 3.8 min, CO 2 ~ 10.1 min.
5. References
[1] W. Wang, S. Wang, X. Ma and J. Gong. Chem.
Soc. Rev., 40, 3703-3727 (2011)
[2] E. Jwa, H. Lee, S.B. Lee, M.Y.S. Fuel Proc.
Technol., 108, 8993 (2013)
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