Ethanol conversion in glow and barrier discharges
The efficiency of ethanol conversion in glow and barrier discharges is analyzed. It is found that for a given power the ethanol conversion is more efficient in glow discharge. This is caused by the principal difference in the way of generation of active atoms and radicals in both types of discharges...
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| Zitieren: | Ethanol conversion in glow and barrier discharges / D.S. Levko, A.N. Tsymbaluk, V.V. Kolgan // Вопросы атомной науки и техники. — 2014. — № 6. — С. 212-214. — Бібліогр.: 10 назв. — англ. |
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irk-123456789-819502015-05-23T03:01:53Z Ethanol conversion in glow and barrier discharges Levko, D.S. Tsymbaluk, A.N. Kolgan, V.V. Низкотемпературная плазма и плазменные технологии The efficiency of ethanol conversion in glow and barrier discharges is analyzed. It is found that for a given power the ethanol conversion is more efficient in glow discharge. This is caused by the principal difference in the way of generation of active atoms and radicals in both types of discharges. In addition, the main channels leading to the generation and quenching of H₂ and CO are studied. The method to increase the efficiency is proposed. Анализируется эффективность преобразования этанола в тлеющем и барьерном разрядах. Обнаружено, что при заданной мощности преобразование этанола является более эффективным в тлеющем разряде. Это обусловлено различием в способе генерации активных атомов и радикалов в обоих типах разрядов. Также изучаются основные каналы, ведущие к генерации и тушению молекул Н₂ и СО. Предложен способ по повышению эффективности конверсии этанола в барьерном разряде. Аналізується ефективність перетворення етанолу в тліючому і бар'єрному розрядах. Виявлено, що при заданій потужності перетворення етанолу є ефективнішим у тліючому розряді. Це обумовлено розходженням у способі генерації активних атомів і радикалів в обох типах розрядів. Також, вивчаються основні канали, що ведуть до генерації та гасіння молекул Н₂ і СО. Пропонується спосіб щодо підвищення ефективності конверсії етанолу в бар’єрному розряді. 2014 Article Ethanol conversion in glow and barrier discharges / D.S. Levko, A.N. Tsymbaluk, V.V. Kolgan // Вопросы атомной науки и техники. — 2014. — № 6. — С. 212-214. — Бібліогр.: 10 назв. — англ. 1562-6016 PACS: 52.65.-y, 52.80.-s http://dspace.nbuv.gov.ua/handle/123456789/81950 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии |
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Низкотемпературная плазма и плазменные технологии Низкотемпературная плазма и плазменные технологии Levko, D.S. Tsymbaluk, A.N. Kolgan, V.V. Ethanol conversion in glow and barrier discharges Вопросы атомной науки и техники |
| description |
The efficiency of ethanol conversion in glow and barrier discharges is analyzed. It is found that for a given power the ethanol conversion is more efficient in glow discharge. This is caused by the principal difference in the way of generation of active atoms and radicals in both types of discharges. In addition, the main channels leading to the generation and quenching of H₂ and CO are studied. The method to increase the efficiency is proposed. |
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Article |
| author |
Levko, D.S. Tsymbaluk, A.N. Kolgan, V.V. |
| author_facet |
Levko, D.S. Tsymbaluk, A.N. Kolgan, V.V. |
| author_sort |
Levko, D.S. |
| title |
Ethanol conversion in glow and barrier discharges |
| title_short |
Ethanol conversion in glow and barrier discharges |
| title_full |
Ethanol conversion in glow and barrier discharges |
| title_fullStr |
Ethanol conversion in glow and barrier discharges |
| title_full_unstemmed |
Ethanol conversion in glow and barrier discharges |
| title_sort |
ethanol conversion in glow and barrier discharges |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2014 |
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Низкотемпературная плазма и плазменные технологии |
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http://dspace.nbuv.gov.ua/handle/123456789/81950 |
| citation_txt |
Ethanol conversion in glow and barrier discharges / D.S. Levko, A.N. Tsymbaluk, V.V. Kolgan // Вопросы атомной науки и техники. — 2014. — № 6. — С. 212-214. — Бібліогр.: 10 назв. — англ. |
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Вопросы атомной науки и техники |
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AT levkods ethanolconversioninglowandbarrierdischarges AT tsymbalukan ethanolconversioninglowandbarrierdischarges AT kolganvv ethanolconversioninglowandbarrierdischarges |
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2025-07-06T07:44:18Z |
| last_indexed |
2025-07-06T07:44:18Z |
| _version_ |
1836882711002742784 |
| fulltext |
ISSN 1562-6016. ВАНТ. 2014. №6(94)
212 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2014, №6. Series: Plasma Physics (20), p. 212-214.
ETHANOL CONVERSION IN GLOW AND BARRIER DISCHARGES
D.S. Levko
1
, A.N. Tsymbaluk
2
, V.V. Kolgan
3
1
LAPLACE (Laboratoire Plasma et Conversion d’Energie), Universite de Toulouse, UPS,
INPT Toulouse, France;
2
East Ukrainian National University name Vladimir Dal, Lugansk, Ukraine;
3
Taras Shevchenko National University of Kyiv, Ukraine
E-mail: dima.levko@gmail.com
The efficiency of ethanol conversion in glow and barrier discharges is analyzed. It is found that for a given
power the ethanol conversion is more efficient in glow discharge. This is caused by the principal difference in the
way of generation of active atoms and radicals in both types of discharges. In addition, the main channels leading to
the generation and quenching of H2 and CO are studied. The method to increase the efficiency is proposed.
PACS: 52.65.-y, 52.80.-s
INTRODUCTION
Nowadays, mixture of molecular hydrogen H2 and
carbon monoxide CO (further, syn-gas) is used for the
synthesis of different chemicals [1], is used as an
intermediate reagent for the liquid fuel generation [2] as
well as it is proposed using as an alternative fuel [3].
One of the efficient ways of syn-gas production is its
generation from the ethanol in non-equilibrium plasmas
of electrical discharges in plasma-chemical reactors of
different types [3, 4]. The choice of non-equilibrium
plasma is caused by more efficient use of electrical
power [4-6]. The main types of discharges for the
generation of non-equilibrium plasma are glow
discharge (GD), dielectric barrier discharge (DBD),
high-frequency and microwave discharges. Both GD
and DBD are widely used discharges for the generation
of syn-gas. For instance, DBD was studied
experimentally in [7], while GD was studied in [8]. The
comparison between these two papers shows that for the
same power GD allows obtaining larger density of syn-
gas. Also, in accordance with [4] DBD has smaller
energy efficiency in comparison with other discharges.
The difference between these discharges requires
detailed study.
The aim of the present paper is the comparison of
efficiency of the ethanol conversion in DBD and GD.
For this purpose the global (zero-dimensional) model is
used. It is assumed in this model that the initial
component content of the gas mixture is identical for
both discharges. Also, the power introduced in the
discharge is also assumed to be the same.
1. PHYSICAL MODEL
In order to study the plasma kinetics in both
discharges the model developed in [10] is used. The gas
mixture consists of argon (typical density ~10
19
cm
-3
),
ethanol (~10
18
cm
-3
) and water (~10
18
cm
-3
). Argon is
used as a buffer gas. Its admixture increases the average
electron energy, which results in the increase in the rates
of electron-molecular reactions. In addition, since argon
is a rare gas it does not participate in chemical reactions.
This simplifies the analysis of the obtained results.
It is assumed that DBD is the sequence of discharges
which temporal duration is 15 ns (power-on stage). At
this stage one obtains the electric current through the
cathode-anode gap. These discharges are separated by
the intervals when the power is turned off (power-off
stage). The frequency of discharges is 18 kHz. In the
opposite, in GD the power is introduced in the discharge
continuously. In order to compare DBD and GD the
calculations are carried out for the time during which
the same energy is spent.
The following assumptions are made in the model:
1) electrical power introduced in the discharge is
averaged over the entire discharge volume; 2) electric
field in the discharge is homogeneous and is constant in
time; 3) discharge plasma column is homogeneous; 4)
temperature of the gas mixture is constant and equal to
400 K. Such choice of the gas temperature is caused by
the fact that usually ethanol is converted in overheated
mixture. The gas pressure is atmospheric.
2. NUMERICAL MODEL
Numerical modeling includes the following steps: 1)
calculation of the electron energy distribution function
(EEDF) with the accounting for elastic and non-elastic
electron-neutral collisions (with argon, ethanol and
water); 2) numerical solution of the system of kinetic
equations in zero-dimensional approximation. Kinetic
mechanism includes 30 species (C2H5OH, O2, H2O, H2,
CO, CH4, CH3CHO etc), 43 electron-molecular
reactions and 130 chemical reactions. The rate
coefficients of latter processes are taken from NIST
database (for details see [10]).
The following system of kinetic equations is solved
numerically:
...lj
lj,
ijl
j
jijei
i NNkNkS
dt
dN
. (1)
Here Ni, Nj, Nl are the densities of molecules and
radicals, kij, kiml are the rate coefficients of chemical
reactions for i
th
component of gas mixture, and Sei are
the rates of electron-molecular reactions. The method to
define Sei as well as the list of these reactions is detailed
in [10]. In GD Sei are calculated at each time step, while
in DBD they are calculated only during the power-on
stage. Otherwise, Sei are assumed equal to zero.
ISSN 1562-6016. ВАНТ. 2014. №6(94) 213
3. RESULTS
The simulation results have shown that in both
discharges the main channel of H2 generation is the
reaction between ethanol and hydrogen atoms:
С2Н5ОН + Н → С2Н5О + Н2. (2)
However, as it is shown in Fig. 1, the density of H2
is 4 orders of magnitude larger in GD than in DBD. This
indicates on the larger efficiency of GD.
Fig. 1. Temporal evolution of the H2 density in glow and
dielectric barrier discharges
The variation of ethanol density during the
simulations can be neglected in comparison with the
variation of densities of active species. Therefore, in
further analysis the density of С2Н5ОН is assumed
constant. Keeping constant the ethanol density in
reaction (2) one concludes that the difference in
efficiency of DBD and GD is explained by the different
dynamics of H density in both discharges. The latter is
caused by the different temporal duration of reaction of
H generation. The simulation results have shown that
during the discharge the main reaction of H generation
is the ethanol dissociation by the electron impact:
С2Н5ОН + е → С2Н5О + Н + е. (3)
In DBD this reaction works only during 15 ns, i.e.
during the power-on stage. Between subsequent
discharges the mixture is not affected by the discharge.
Since the gas temperature is small the rate coefficients
of thermo-dissociation reactions are small. Therefore,
active species are not generated during the power-off
stage. These species very fast (during a few
microseconds) recombine generating stable molecules
(Fig. 2). Figs. 2,a,b show the comparison between the
time evolution of H density in GD and DBD. One can
see that in GD the density of H grows during ≈1 µs until
it reaches the saturation level (~10
13
cm
-3
).
Fig. 1 shows that at this stage the density of H2 also
grows. Since the time duration of one current pulse in
DBD is only 15 ns, the power is turned off before the
density of H reaches the steady-state value. It reaches
much smaller value of ~10
10
cm
-3
. This results in the
substantial difference between rates of reaction (2)
obtained in DBD and GD. As a consequence, one
obtains different efficiency of syn-gas generation in
these discharges. In addition, one can conclude from
Fig. 2 that in DBD each consequent discharge acts on
the mixture which is free from active species. That is,
reaction (2) starts with some time delay.
Fig. 2. Temporal evolution of the densities of Н, О and
ОН (a) in the initial moment of time, and (b) at later
times
Another important component of syn-gas is the
carbon monoxide CO. Fig. 3 shows its temporal
evolution obtained for both discharges.
Fig. 3. Temporal evolution of the CO density in glow
and dielectric barrier discharges
214 ISSN 1562-6016. ВАНТ. 2014. №6(94)
One can see that again the efficiency of CO
generation is higher in GD. Analysis of the plasma
kinetics has shown that CO is mainly generated in the
following reactions:
СН3СО + М → СН3 + СО + М, (4)
НСО + О2 → СО + НО2, (5)
where M is the third body (in the present model it is
H2O or C2H5OH). Radicals СН3СО and НСО are
generated efficiently only during the discharge (or the
power-on stage of DBD). During the power-off stage
these radicals are quenched. Thus, in analogy with H2,
the difference in efficiency of CO generation in DBD
and GD is explained by different ways of power
introduction in the discharge.
CONCLUSIONS
Thus, one can conclude that the ethanol conversion
in DBD occurs only during short current pulses having
temporal duration of 15 ns. As a consequence, the
efficiency of ethanol conversion is higher in GD than in
DBD for the same initial conditions and the same power
introduced in the discharge. From this point of view the
use of GD for the generation of H2/CO mixture is more
profitable. This result is in qualitative agreement with
the results presented in [7, 8].
The disadvantage of pulsed discharge can be
removed by the increase in the frequency of discharge
pulses. As was obtained above, the main channel of H
quenching is the reaction (2), which leads to the
generation of H2. The rate coefficient of this reaction at
gas temperature of 400 K is ≈2.4×10
-14
cm
-3
·s
-1
.
Assuming that the largest density of H in DBD is
≈2×10
10
cm
-3
one estimates the rate of (2) as
≈7×10
15
cm
3
s
-1
. The estimation of time during which the
density of H decreases by the order of magnitude gives
≈1 µs. Thus, it is possible to increase the efficiency of
ethanol conversion in DBD, if one increases the
frequency of the pulses up to 1 MHz. This will occur
because each subsequent discharge will act on the
mixture containing enough active atoms and radicals.
However, the majority of dielectrics are damaged at
high frequency due to capacitive currents. Therefore, it
seems promising to replace DBD by high-frequency and
microwave discharges. For these discharges the
frequency 1 MHz and higher is standard. Moreover, for
these discharges high frequencies are supported easily at
atmospheric pressure. In the opposite, different
instabilities develop in glow discharges at these
conditions.
REFERENCES
1. Synthesis gas combustion: Fundamentals and
Applications / Edited by Tim C. Lieuwen, Taylor &
Francis Group, 2010.
2. M. Irfan, M. Usman, K. Kusakabe // Energy. 2011.
v. 36, p. 12-40.
3. B.-J. Zhong, Q.-T. Yang, F. Yang // Combustion and
Flame. 2010, v. 157, p. 2005-2007.
4. G. Petitpas, J.-D. Rollier, A. Darmon, et al. // Int.
Journal of Hydrogen Energy. 2007, v. 32, p. 2848-2867.
5. O. Aubry, A.C. Met Khacef, J.M. Cormier // Chem.
Eng. J. 2005, v. 106, p. 241.
6. A. Yanguas-Gil, J.L. Hueso, J. Cotrino, A. Caballero,
A.R Gonzalez-Elipe // Appl. Phys. Lett. 2004, v. 85,
p. 4004.
7. Wang Baowei, Lu. Yijun, Xu . Zhang, Hu. Shuanghui
// Journal of Natural Gas Chemistry. 2011, v. 20,
p. 151-154.
8. V.Ya. Chernyak, S.V. Olszewski, V.V. Yukhymenko,
et al // IEEE Trans. Plasma Science. 2008, v. 36,
p. 2933-2939.
9. A.I. Schedrin, D.S. Levko, V.Ya. Chernyak,
V.V. Yukhymenko, V.V. Naymov // Letters in GETF.
2008, v. 88, p. 107-110.
10. D.S. Levko, A.N. Tsymbaluk, A.I. Schedrin //
Plasma Physics. 2012, v. 38, p. 991-1000
Article received 26.10.2014
КОНВЕРСИЯ ЭТАНОЛА В ТЛЕЮЩЕМ И БАРЬЕРНОМ РАЗРЯДАХ
Д.С. Левко, А.Н. Цымбалюк, В.В. Колган
Анализируется эффективность преобразования этанола в тлеющем и барьерном разрядах. Обнаружено,
что при заданной мощности преобразование этанола является более эффективным в тлеющем разряде. Это
обусловлено различием в способе генерации активных атомов и радикалов в обоих типах разрядов. Также
изучаются основные каналы, ведущие к генерации и тушению молекул Н2 и СО. Предложен способ по
повышению эффективности конверсии этанола в барьерном разряде.
КОНВЕРСІЯ ЕТАНОЛУ У ТЛІЮЧОМУ ТА БАР’ЄРНОМ РОЗРЯДАХ
Д.С. Левко, А.M. Цимбалюк, В.В. Колган
Аналізується ефективність перетворення етанолу в тліючому і бар'єрному розрядах. Виявлено, що при
заданій потужності перетворення етанолу є ефективнішим у тліючому розряді. Це обумовлено
розходженням у способі генерації активних атомів і радикалів в обох типах розрядів. Також, вивчаються
основні канали, що ведуть до генерації та гасіння молекул Н2 і СО. Пропонується спосіб щодо підвищення
ефективності конверсії етанолу в бар’єрному розряді.
|