Decomposition of aqueous solution of acetic acid under the action of atmospheric-pressure dielectric barrier discharge in oxygen

Article abstract of DOI:10.1134/S1070427212010144

Decomposition of an aqueous solution of acetic acid under the action of an atmospheric-pressure dielectric barrier discharge in oxygen in a flow-through reactor was studied. A mechanism of chemical reactions is suggested, which describes the decomposition of the acid and formation of the reaction products observed.

Full text of DOI:10.1134/S1070427212010144

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2012, Vol. 85, No. 1, pp. 71−75. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © E.S. Bobkova, A.A. Isakina, V.I. Grinevich, V.V. Rybkin, 2012, published in Zhurnal Prikladnoi Khimii, 2012, Vol. 85, No. 1, pp. 75−79.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Decomposition of Aqueous Solution of Acetic Acid
under the Action of Atmospheric-Pressure Dielectric Barrier
Discharge in Oxygen
E. S. Bobkova, A. A. Isakina, V. I. Grinevich, and V. V. Rybkin
Ivanovo State University of Chemical Engineering, Ivanovo, Russia
Received December 3, 2010
Abstract—Decomposition of an aqueous solution of acetic acid under the action of an atmospheric-pressure
dielectric barrier discharge in oxygen in a flow-through reactor was studied. A mechanism of chemical reactions
is suggested, which describes the decomposition of the acid and formation of the reaction products observed.
DOI: 10.1134/S1070427212010144
The problem of water treatment to bring its quality to
the potable water level is one of the most topical issues.
The commonly used methods of water purification,
such as chlorination, ozonation, UV irradiation, are
comparatively expensive and fail to always provide
the required efficiency [1]. That is why purification
techniques based on high-energy chemical methods,
radiative, photochemical, and plasmochemical have
been intensively studied recently [2, 3]. In fact, the
ozonation and UV irradiation are processes of this kind
because both ozone and UV light are produced by some
gas discharge.
full decomposition of the main substance, they will
determine the purification quality. However, data of
this kind cannot be found in the overwhelming majority
of known reports and the efficiency of a particular
type of treatment is judged from the decrease in the
concentration of the main organic contaminant [8]. Only
in [5, 7, 9], it was noted that carboxylic acids accumulate
in the course of time in aqueous solutions in destruction
of phenol and its oxy derivatives.
In this study, we examined the decomposition of an
aqueous solution of acetic acid in a DBD in order to find
whether it is possible and advisable to use the discharge
both in removal of the acid itself and in processes in
which the acid is a reaction product.
The energy efficiency of these methods is poor
because they use only a small part of opportunities
furnished by a discharge, which yields a large number
of active species capable of effective decomposition of
organic impurities. These are radicals, excited atoms
and molecules, electrons, and ions. Their use requires
a special organization of the process because, as a rule,
these species are short-lived. Therefore, various kinds of
gas discharges that are in direct contact with a solution
being processed are promising.
EXPERIMENTAL
The experimental installation was described in
detail in [7]. The reactor for DBD generation had the
form of a vertical Pyrex tube with an outer diameter of
12 mm and wall thickness of 1.7 mm, which served as
the dielectric barrier for the discharge. An aluminum
alloy electrode with a diameter of 8 mm was coaxially
mounted within the tube. The electrode was coated
with a hydrophilic glass fabric with a thickness of
about 1 mm. The discharge zone length L was 12 cm.
A solution was introduced through radial orifices in the
upper part of the internal electrode and flowed down
A large number of designs of this kind have been
developed. For example, these are the corona discharge
burning over the surface of a solution [4], dc discharge in
a fluid [5], pulsed streamer discharge in solution [6], and
dielectric barrier discharge (DBD) [7]. Decomposition
products are of particular interest because, even upon
71

72
BOBKOVA et al.
BaCl2·2H2O + 2NH4OH + 2CO2
in the film mode over the surface of the glass fabric
under the gravity force. The volumetric flow rate of the
solution was controlled, with the time τL of its residence
with the discharge zone varied approximately from 2 to
12 s. The value of τL was calculated by
→ Ba(HCO3)2 + NH4Cl + 2H2O,
Ba(HCO3)2 + BaCl2·2H2O + 2NH4OH
→ 2BaCO3↓ + 2NH4Cl + 4H2O,
τL = πDhL/Q,
BaCO3 + 2HCl → BaCl2 + CO2↑ + H2O,
HCl + NaOH → NaCl + H2O.
where D is the diameter of the glass fabric coating; h,
thickness of the solution film; and Q, volumetric flow
rate of the solution.
A sample of an ammonia solution of BaCl2 through
which CO2 was passed was boiled on a water bath
to provide complete precipitation of BaCO3. The
precipitate was filtered off and dissolved in a certain
amount of hydrochloric acid. The excess amount of the
acid was titrated with sodium hydroxide.
The solution film thickness was estimated using the
expression valid for a smooth laminar flow in the gravity
force field [10]:
h = {(3ν/g)[Q/(πD)]}1/3
,
where ν is the kinematic viscosity, and g, the gravitational
constant.
Figure 1 shows how the concentration of acetic acid
and degree of its decomposition depend on the time
of residence of the solution with the discharge zone.
The degree of decomposition, obtained in this case, is
fairly high (~70%). It is noteworthy that a ~14% degree
of decomposition of the acid was achieved in [14] in
a similar reactor, with air used as the plasma-forming
gas. The fact that the degree of decomposition reaches
saturation means that either the process is limited by the
generation rates of active species, or there occur inverse
reactions that form the acid from its interaction products.
The second hypothesis seems to be more substantiated
for the following reasons.
A 16-kV mains-frequency voltage was applied
between the internal electrode and an aluminum foil
electrode deposited onto the outer tube. Under these
conditions, the discharge current was 0.56 mA, and
the specific power introduced into the discharge,
0.93 W cm–3. Technical-grade oxygen (99.8%) served
as the plasma-forming gas with a flow rate of 3.2 cm3
s–1. The oxygen was delivered in the direction opposite
to that of the solution. The initial concentration of the
acid solution was 55 × 10–6 M.
After the stationary process mode was attained, the
gas leaving the reaction zone was passed during a fixed
time through an absorbing vessel or through a bed of a
GTT catalyst which effectively converts carbon mon-
oxide molecules to carbon dioxide [11]. The absorbing
solution was filled with distilled water or an ammonia
solution of barium chloride. The resulting solutions and
the discharge-treated solution were analyzed. The con-
tent of acetic acid was found from the optical density at
the absorption peak of colored solutions (λ = 400 nm)
produced by the reaction of the acid with ammonium
meta-vanadate [12]. The optical density was measured
with a Hitachi U-2001 spectrophotometer (Japan). The
aldehyde concentration was measured by the photolumi-
nescent method. A luminescing compound was formed
by the reaction of the aldehyde with 1,3-cyclohexanedi-
one in the presence of ammonium ions. A Flyuorat-02
fluorimeter (Russia) was used. The CO2 concentration
in the gas phase was determined using the following
scheme of reactions [13]:
The specific action of the electric discharge on the
α, %
τ, s
Fig. 1. Concentration c of acetic acid and degree α of its
decomposition vs. the time τ of residence between the solution
and the discharge zone.
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DECOMPOSITION OF AQUEOUS SOLUTION OF ACETIC ACID
73
solution consists in that its surface is bombarded with
high-energy particles. In particular, the cathode potential
drops in atmospheric-pressure discharges reach several
hundred electronvolts [15]. Therefore, it would be
expected that the discharge must have an effect similar to
that produced on water by radiation [16], i.e., formation
found from the initial portion of the kinetic curve (Fig. 1
at τL → 0), was 2.4 × 10–5 M s–1. Consequently, formation
of active species cannot be the rate-determining factor
for decomposition of the acid and its regeneration
reactions
·
·СН2–(С=О)–ОН + H → СН3–(С=О)–ОН,
СН3–(C=O)· + ·ОН → СН3–(С=О)–ОН
of OH, H·, and O· radicals as primary active species.
Just this assumption was made in studies concerned
with the decomposition of phenol in a streamer corona
reactor [6] and formation of hydrogen peroxide in a dc
discharge with an electrolyte cathode [17]. Primary
active species are formed in the following reactions:
may occur.
Let us evaluate the rate constant of the reaction
·
between OH radicals and the acid. Among their loss
reactions, reaction (1) has the maximum rate constant of
5.5 × 1010 M–1 s–1 [6]. Equating the rate of this reaction
to the rate of radical formation, we obtain [·OH] =
4.9 × 10–8 M. Apparently, this value is the upper-bound
estimate. Taking the experimental value of the acid
decomposition rate and assuming that the acid reacts
with ·OH radicals, we find that the rate constant of this
reaction is 9 × 106 M–1 s–1. In view of the fact that the
value of this constant is the lower-bound estimate, it is
in good agreement with the constant of 1.6 × 107 M–1
s–1, obtained in [19]. Because the same species are
involved in both initiation and inverse reactions, a 100%
decomposition, observed for phenols [7], is hardly
expected in the case under consideration.
H2O + discharge → ·OH + H· and H2 + O·.
The first of these reactions is more probable because
of the lower energy expenditure.
The radicals formed interact with each other to give
both molecular and radical products:
H· + H· → H2,
O· + ·OH → O2 + H·,
·OH + ·OH → H2O + ·O,
·OH + ·OH → H2O2.
(1)
The main transformation product of the acid is the
aldehyde in the liquid phase (Fig. 2), and CO2 and CO
molecules in the gas phase (Fig. 3). The aldehyde and
acid molecules hardly pass into the gas phase (Fig. 4).
The concentration ratio between CO2 and CO molecules
is approximately 1 : 1. Consequently, one molecule
each of CO2 and CO must be formed from a molecule
of the acid, which requires that the bond between the
methyl and carboxy groups should be ruptured. With
consideration for the initiation reactions written above,
this may occur as a result of the following possible
reactions:
Thus, the ·OH, O·, and H· radicals are active species
capable of interacting with the acid. The following
reactions are energetically possible:
СН3–(С=О)–ОН + О → ·СН2–(С=О)–ОН + ·OH, (2)
СН3–(С=О)–ОН + ·ОН → ·СН2–(С=О)–ОН + H2О, (3)
СН3–(С=О)–ОН + Н → ·СН2–(С=О)–ОН + H2,
СН3–(С=О)–ОН + ·ОН → СН3–(C=O)· + H2O2.
(4)
(5)
Let as estimate the formation rates of the H· and
·OH radicals. According to [18], the yield of H· and
·OH radicals per mole of electrons under the action of
discharge is approximately 10. At a discharge current
of 0.56 mA, this gives a total formation rate of radicals
of 5.8 × 10–8 mol s–1. Taking the time of contact with
the solution to be, for the sake of certainty, τL = 2 s and
having calculated the solution volume being treated, V =
0.46 × 10–3 l, we find that the formation rate of radicals
is 1.4 × 10–4 M s–1. The decomposition rate of the acid,
·СН2–(С=О)–ОН + О → ·ОСН2–(С=О)–ОН,
·ОСН2–(С=О)–ОН → ·(C=O)–OH + СН2O,
·(C=O)–OH + ·OH → H2CO3 → H2O + CO2,
СН2O + OH → H·CO + H2O,
H·CO + OH → CO + H2O.
The acetaldehyde can be formed by the scheme
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74
BOBKOVA et al.
СН3–(С=О)–ОН + ·ОН → СН3–(C=O)· + H2O2,
СН3–(C=O)· + H → СН3–(C=O)H.
Calculations of the amount of carbon in the products
and in the undecomposed acid demonstrated that at
contact durations of 3, 4, and 5.5 s its contents are 80,
86, and 96%, respectively, relative to the content of
carbon contained in the starting acid. Despite that the
difference from 100% is within the balance calculation
error (~20%), the systematic improvement of the
balance with increasing contact duration suggests that
an additional product, undetected by the methods used,
is formed at a short contact duration. The concentration
of this product must exceedingly strongly depend on the
contact duration. Possibly, the product of this kind could
be methanol formed by the scheme
τ, s
Fig. 2. Concentration c of acetic aldehyde in solution vs. the
time τ of residence between the solution and the discharge
zone.
СН3–(C=O)· + О → СН3 + СО2,
·
СН3 + ·ОН → СН3ОН.
·
A similar scheme, but with H atoms involved, could
yield methane. However, methane must give carbon
oxides in the gas phase, which would be detected in the
balance.
CONCLUSIONS
τ, s
(1) The transformation of an aqueous solution of
acetic acid by active species formed under the action
of an atmospheric-pressure dielectric barrier discharge
on water was studied. It was shown that the conversion
of the acid reaches a value of 70%, with the main
conversion products being CO2 and CO molecules in the
gas phase and acetaldehyde in the liquid phase.
Fig. 3. Concentration c of carbon(II) oxide in the gas phase vs.
the time τ of residence between the solution and the discharge
zone. (1) Without a catalyst and (2) with a catalyst.
(2) It was suggested the fundamental aspects of
formation of acetic acid decomposition products are
common to monobasic carboxylic acids.
(3) It was found that, in destruction of an aqueous
solution of acetic acid, not only oxidation occurs in the
aqueous solution, but also reduction of acetic acid and
products of its decomposition.
REFERENCES
τ, s
1. Trapido, M., Munter, R., and Veressinina, Y., Proc. Int.
Conf. Int. Ozone Association of the European-African-
Asian-Australasian Group in Conjunction with Acwatech,
Moscow, 1998, May 26–28, pp. 519–523.
Fig. 4. Concentration c of (1) acetic aldehyde and (2) acetic
acid in the gas phase vs. the time τ of residence between the
solution and the discharge zone. (1) Without a catalyst and (2)
with a catalyst.
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DECOMPOSITION OF AQUEOUS SOLUTION OF ACETIC ACID
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2. Pikaev, A.K., Khim. Vysok., Energ., 2000, vol. 34, no. 2,
12. Lur’e, Yu.Yu., Analiticheskaya khimiya promyshlennykh
stochnykh vod (Analytical Chemistry of Industrial
Wastewater), Moscow: Khimiya, 1984.
pp. 83–102.
3. Lerouge, S., Fozza, A.C., Wertheimer, M.R., et al.,
13. Hillebrand, W.F. and Lundell, G.E.F., Applied Inorganic
Analysis, John Wiley & Sons Inc., New York; Chapman
& Hall Ltd, London, 1953, 2nd ed.
Plasmas Polymers, 2000, vol. 5, no. 1, pp. 31–46.
4. Grabowski, L.R., Van Veldhuizen, E.M., Pemen, A.J.,
and Rutgers, W.R., Plasma Chem. Plasma Proc., 2006,
vol. 26, no. 4, pp. 3–17.
14. Ognier, S., Iya-sou, D., Fourmond, C., and Cavadias, S.,
Plasma Chem. Plasma Proc., 2009, vol. 29, no. 4,
pp. 261–273.
5. Jinzhang Gao, Yongjun Lin, Wu Yang, et al,. Plasma
Sources Sci. Technol., 2003, vol. 12, pp. 533–538.
15. Titov, V.A., Rybkin, V.V., Maximov, A.I., and Choi, H.S.,
Plasma Chem. Plasma Proc., 2005, vol. 25, no. 5,
pp. 503–518.
6. Grymonpre, D.R., Sharma, A.K., Finney, W.C., and
Locke, B.R., Chem. Eng. J., 2001, vol. 82, pp. 189–207.
7. Bubnov, A.G., Burova, E.Yu., Grinevich, V.I., et al.,
16. Pikaev, A.K., Kabakchi, S.A., and Makarov, I.E.,
Vysokotemperaturnyi radioliz vody i vodnykh rastvorov
(High-Temperature Radiolysis of Water and Aqueous
Solutions), Moscow: Energoatomizdat, 1988.
Plasma Chem. Plasma Proc., 2006, vol. 26, no. 1, pp. 19–
30.
8. Malik, M.A., Plasma Chem. Plasma Proc., 2010, vol. 30,
no. 1, pp. 21–31.
17. Chumadova, E.S., Shikova, T.G., Rybkin, V.V., and
Titov, V.A., Izv. Vyssh. Uchebn. Zaved., Khim. Khim.
Tekhnol., 2008, vol. 51, no. 11, pp. 29–32.
9. Bubnov, A.G., Burova, E.Yu., Grinevich, V.I., et al.,
Plasma Chem. Plasma Proc., 2007, vol. 27, no. 2,
pp. 177–187.
18. Gangal, U., Srivastava, M., and Sen Gupta, S.K., Plasma
Chem. Plasma Proc., 2010, vol. 30, no. 2, pp. 299–310.
10. Bird, R.B., Stewart, W.E., and Lightfoot, E.N., Transport
Phenomena, New York: Wiley, 1960, p. 37.
19. Karpel Vel Leitner, N. and Dore, M., J. Photochem.
Photobiol. A. Chem., 1996, vol. 99, nos. 2–3, pp. 137–
143.
11. Egorova, G.V., Voblikova, V.A., Tkachenko, S.N., et al.,
Zh. Fiz. Khim., 2003, vol. 77, no. 11, pp. 1966–1971.
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