The oxidation of chlorine ions under the joint action of ozone and permanganate ions

Article abstract of DOI:10.1134/S0036024406040121

The oxidation of chlorine ions in the system O₃ + MnO ₄ ^- + H⁺ + Cl^- with the formation of Cl₂ in the gas phase was studied. The phenomenon of transfer catalysis of the reaction between O₃ and Cl^- by the MnO ₄ ^- ion was observed (the products of the reduction of MnO ₄ ^- by the chlorine ion are oxidized by ozone to recover MnO ₄ ^- ). The rate of the formation of Cl₂ in the O₃ + MnO ₄ ^- + H⁺ + Cl ^- system was higher than the sum of the corresponding rates in the oxidation of Cl^- by O₃ and MnO ₄ ^- separately. A scheme explaining the trends observed experimentally for the formation of Cl₂ and changes in MnO ₄ ^- concentration was suggested. The formation of MnO ₄ ^- in the oxidation of Mn³⁺ with ozone in acid media was studied. Pleiades Publishing, Inc., 2006.

Full text of DOI:10.1134/S0036024406040121

ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 4, pp. 557–561. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.V. Levanov, I.V. Kuskov, E.E. Antipenko, V.V. Lunin, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 4, pp. 653–657.
CHEMICAL KINETICS
AND CATALYSIS
The Oxidation of Chlorine Ions under the Joint Action of Ozone
and Permanganate Ions
A. V. Levanov, I. V. Kuskov, E. E. Antipenko, and V. V. Lunin
Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119899 Russia
E-mail: levanov@kge.msu.ru
Received June 15, 2005
–
4
+
–
Abstract—The oxidation of chlorine ions in the system é + MnO + H + Cl with the formation of Cl in
3
2
–
the gas phase was studied. The phenomenon of transfer catalysis of the reaction between O and Cl by the
3
–
–
MnO ion was observed (the products of the reduction of MnO by the chlorine ion are oxidized by ozone to
4
4
–
4
–
4
+
–
recover MnO ). The rate of the formation of Cl in the é + MnO + H + Cl system was higher than the
2
3
–
4
–
sum of the corresponding rates in the oxidation of Cl by O and MnO separately. A scheme explaining the
3
–
trends observed experimentally for the formation of Cl and changes in MnO concentration was suggested.
2
4
–
3
+
The formation of MnO in the oxidation of Mn with ozone in acid media was studied.
4
DOI: 10.1134/S0036024406040121
INTRODUCTION
ducted on a unit described earlier [2]. In all experi-
ments, the flow rate of ozonized oxygen was 21 l/h, and
The shortcoming of ozone as an oxidizer is its low
reactivity toward certain substances. The permanganate
ion can interact with many compounds inactive with
the concentration of ozone in the gas entering the reac-
3
tor (C ) was 10.0 g/m , unless otherwise specified.
O3
respect to ozone. It was, however, shown in [1] and this The solutions studied contained 0.01–0.08 M HCl and
work (see below) that ozone can, in acid solutions, oxi- NaCl, [HCl] + [NaCl] = 1 M and 0–1.0 mM KMnO . In
4
dize low-oxidation-degree manganese compounds
all experiments, the total ionic strength of solutions and
–
4
–
4
formed in the reduction of MnO back to MnO . For concentration of chlorine ions were 1 M. The solutions
–
were prepared from distilled water, hydrochloric acid
of os. ch. (special purity) grade, sodium chloride of kh.
ch. (chemically pure) grade, and pharmaceutical potas-
sium permanganate.
this reason, joint use of MnO and é in acid media
4
3
may offer promise for the oxidation of substrates that
weakly interact with ozone.
The chlorine ion is an example of substrates inert
with respect to ozone. The interaction é + Cl is of
We measured the rate of chlorine liberation from the
–
3
dn
interest for various processes where ozone is used and
the presence of chlorine ions is possible. In addition,
revealing the conditions under which the rate of the
1
Cl2
reactor per unit reaction solution volume - -- --------- -- (fur-
V dt
ther “chlorine release rate”) and the concentration of
–
reaction between é and Cl increases can contribute to
–
3
MnO in the solution. The permanganate ion has a light
4
developing general methods for increasing the reactiv-
ity of ozone toward inert substrates.
–1
–1
absorption maximum at 525 nm (ε525 = 2300 å cm ),
and its concentration was determined by optical density
measurements at this wavelength. The absorption spec-
tra were recorded on an Agilent 8453 UV-Vis spectro-
photometer.
The purpose of this work was to study the oxidation
–
+
–
of chlorine ions in the é + MnO + H + Cl system
3
4
with the formation of Cl in the gas phase and the influ-
2
ence of significant experimental factors (acidity and the
concentration of permanganate ions) on the rate of
releasing chlorine.
The chlorine release rate was measured after a sta-
–
tionary concentration of MnO in the reaction solution
4
was established. The amount of Cl in outgoing gases
2
EXPERIMENTAL
was determined by photometric iodometry. A detailed
description of the procedure for determining Cl in a
2
–
–
The reaction between é , MnO , and Cl was per-
3
4
mixture of gases containing ozone can be found in our
formed in a bubbler at ~20°ë. Experiments were con- work [3]. As a result, we obtained the time t depen-
5
57

5
58
LEVANOV et al.
(
dnCl2/dt)/V, µmol/(l min)
(dnCl2/dt)/V, µmol/(l min)
70
1
1
1
80
40
00
1
2
1
2
5
3
1
0
0
0
0
6
2
0
0
0.4
0.8
–
[
MnO ], mM
4
3
Fig. 2. Dependences of chlorine formation rate on the sta-
–
4
tionary concentration of MnO in the reaction solution.
The initial solution contained 0.4 M HCl, 0.6 M NaCl, and
0
0.4
0.8
H ], M
potassium permanganate; (1) experimental data for the
+
[
–
+
–
é −MnO –H –Cl system and (2) calculated sum of chlo-
3
4
–
rine formation rates in the oxidation of Cl by ozone and
permanganate ion separately.
Fig. 1. Dependences of the rate of chlorine formation on
reaction solution acidity. The sum of the concentrations of
HCl and NaCl in reaction solutions is 1 M, the stationary
–
+
concentrations of MnO are 1.0 mM ([H ] = 0.01 M),
4
ity of the rates of formation and consumption of man-
ganese compounds in various degrees of oxidation was
established because of constant concentrations of the
+
+
0
0
.96 mM ([H ] = 0.2 M), 0.93 mM ([H ] = 0.4 M),
+
+
.78 mM ([H ] = 0.6 M), and 0.85 mM ([H ] = 0.8 å);
–
+
–
–
(
1) experimental data on the é –MnO –H –Cl system,
3
4
oxidizer (ozone) and reducing agent (Cl ) in the reaction
(
2) calculated sum of chlorine formation rates in the oxida-
solution. The chlorine release rate was time-independent
under approximately stationary conditions.
–
tion of Cl by ozone and permanganate ion separately, and
+
–
(3) experimental data on the é –H –Cl system.
3
RESULTS AND DISCUSSION
–
dence of the amount of chlorine nCl2 formed in the
When ozone interacts with acid solutions of Cl , the
presence of permanganate ions in the reaction solution
considerably accelerates chlorine release (Figs. 1, 2).
reactor; the dependence was rectilinear. The chlorine
dn
1
Cl2
–
4
release rate - -- --------- -- was determined as the slope of the
Changes in the concentration of MnO in the reac-
V dt
–
tion solution. Both é and MnO can oxidize chlorine
linear dependence of nCl2 on t per unit reaction solution
volume V. So far, the experimental procedure was sim- ions in the é
ilar to that used in [2].
3
4
–
4
+
–
–MnO
–H –Cl system. Ozone is sup-
3
plied into the reactor at a constant rate substantially
higher than the rate of its decay as a result of various
chemical reactions in the solution. It can therefore be
expected that a stationary concentration of ozone is
established in the reactor. Conversely, permanganate
ions are contained in the reaction system in a limited
amount and are used in the oxidation of chlorine ions.
An approximately stationary regime, when the con-
centrations of the reagents in the reaction solution and
chlorine in outgoing gases remained virtually constant,
was established during measurements. The regime was
stationary because, first, ozone was supplied into the
reaction system from the outside at a constant rate, sec-
–
+
In order to characterize the processes responsible for
ond, the concentrations of Cl and H in the reaction
–
4
+
–
solution were virtually equal to their initial concentra- the liberation of Cl in the é –MnO –H –Cl system, it
2
3
–
4
tions (the experimental conditions were selected such
is important to know how the concentration of MnO
changes during the reaction. According to Fig. 3, the
concentration of MnO first decreases and then reaches
–
that the rates of Cl oxidation and Cl formation were
2
–
+
fairly small and the consumption of Cl and H during
measurements could be ignored), and, third, the equal-
–
4
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 4 2006

THE OXIDATION OF CHLORINE IONS UNDER THE JOINT ACTION OF OZONE
559
–
a stationary value. The dependence of the stationary
concentration of permanganate ions on experimental
[
0
MnO ], må
.6
4
conditions is presented in the table. The ratio between
1
–
the stationary and initial MnO concentrations does
4
not depend on the initial concentration of permangan-
ate ions; it decreases as solution acidity increases and
2
0
.4
increases as the concentration of ozone grows. It fol-
–
4
+
–
3
lows that, in the é –MnO –H –Cl system along with
3
the consumption of permanganate ions in the oxidation
–
of chlorine ions, MnO is regenerated by ozone from
4
0
.2
the products of its reduction. Note that small amounts
20
40
60
t, min
of hydrated MnO precipitates are formed at low reac-
2
tion solution acidity.
–
4
3+
Fig. 3. Dependences of the concentration of MnO in reac-
The oxidation of Mn with ozone. The final product
of the reduction of permanganate ions with chlorine
ions in an acid medium at ~20°C is Mn(III) compounds
tion solutions on the duration of experiments. The initial
–
4
−
solution composition: [MnO ]0 = 0.56 mM; [Cl ] = 1 å;
[
4]. We therefore studied the products formed in the
+
and [H ] = (1) 0.4 M, (2) 0.6 M, and (3) 0.8 M.
interaction of trivalent manganese ions with ozone and
3
+
the kinetics of this interaction. The interaction of Mn
–
4
with é was conducted in a bubbler at ~20°ë in sulfuric
+
–
3
é + MnO + H + Cl system decreases as solution
3
acid solutions. The initial solutions contained 0.5, 1, or
acidity grows (see table).
3
+
2
M H SO and 1 mM Mn . Ozonized oxygen was sup-
2 4
plied into the reactor at a rate of 21 l/h, and the concen-
A scheme of processes responsible for the formation
–
4
+
–
tration of ozone at the entrance to the reactor was of Cl . The release of chlorine in the é –MnO –H –Cl
2
3
3
1
0.0 g/m .
system occurs as a result of two parallel reactions,
–
4
3
+
–
We found that the oxidation of Mn with ozone including, first, the interaction of MnO with Cl
–
–
4
gave MnO . All trivalent manganese was converted
4
accompanied by the regeneration of MnO in the reac-
into permanganate ions in 1 and 2 M H SO . In 0.5 M
–
2
4
tion between ozone and the products of MnO reduction
4
3
+
H SO , only 27 mol % of Mn was converted into
2
4
–
–
and, second, the reaction between Cl and é without
permanganate ion participation. The kinetics of the reac-
tion between Cl and é in acid media (the é −H –Cl
3
MnO , and the rest was oxidized to Mn(IV) and pre-
4
–
+
–
cipitated as hydrated MnO2.
3
3
system) was studied in detail in our work [2].
The kinetics of the reaction was controlled spectro-
photometrically by measuring the intensity of absorp-
We suggest the following scheme of interrelated
–
tion of MnO in the reaction solution. The overwhelm-
–
–
4
processes of the interaction of MnO with Cl and
4
ing majority of ozone reactions with various substrates
follow second-order kinetics and are first-order in the
–
regeneration of MnO with ozone that occur in the
4
substrate and é [5]. The effective rate constant for the
–
4
3
+
–
é + MnO + H + Cl system:
3
3
+
reaction between Mn and é was therefore calculated
3
–
4
–
by the equation
ånO + Cl
Mn(V) + Cl2,
Mn(III) + Cl2,
(1)
(2)
–
Mn(V) + Cl–
d[MnO ]
4
3
+
-
--------------------- = k [Mn ][O ].
eff 3
dt
The concentration of ozone in H SO solutions was Ratios between stationary and initial concentrations of per-
2
4
–
4
–
4
–
4
estimated using the data obtained by us in [6]. The manganate ions ([MnO ] /[MnO ] ) in the O –MnO –
effective constant values are given below:
∞
0
3
+
–
H –Cl system under various experimental conditions
cO3 , g/m3 [H ], M [MnO ] , mM [MnO ] /[MnO ]
+
–
4
–
4
–
4
[
H SO ], M
0.5
1.0
2.0
2
4
0
∞
0
keff, l/(mol min)
~2500
1350
630
1
0.0
10.0
0.0
0.4
0.4
0.6
0.8
0.8
0.11
0.56
0.56
0.56
0.56
0.93
0.93
0.78
0.53
0.85
3
+
It follows that the rate of the reaction of Mn with
1
é substantially decreases as the concentration of the
3
acid increases. This is in agreement with the observa-
tion that the stationary concentration of MnO in the
10.0
40
–
4
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 4 2006

5
60
LEVANOV et al.
Mn(III) + O3
Mn(V) + O3
Mn(V) + é ,
(3)
R [Mn(V)] = R [Mn(III)] .
(7)
2
2
∞
3
∞
–
ånO + é .
(4) The concentrations in the stationary state are denoted
by subscript ∞.
4
2
The scheme is based on the data on permanganate ion
–
In our experiments, the chlorine formation rate was
measured under stationary conditions. Chlorine is
+
–
concentration changes in the é –MnO –H –Cl sys-
tem, data on the interaction of é with Mn (see formed in reactions (1) and (2) and in the reaction
above), and data on the kinetics of interaction between between Cl and é without permanganate ion partici-
3
4
3
+
3
–
3
–
4
pation. The following equation therefore follows from
the above scheme for the experimentally determined
chlorine release rate:
–
MnO and Cl in acid media (see our work [4]). The
scheme only includes the main processes that lead to
the formation of Cl and, in particular, ignores the for-
2
mation of hydrated MnO precipitates at low acidities.
2
dn
dn
Cl2
1
Cl2
–
–
4 ∞
–
- -- --------- --
= (O , Cl ) + R [MnO ]
-----------
3
1
According to [4], the reaction between MnO and
Cl in acid media involves two steps (steps (1) and (2)
4
V dt
Vdt
R [Mn(V)] .
(8)
–
+
2
∞
in the scheme given above). The reagent concentration
dependence of the rate at stage (1) is given by the equa-
tion
dn
Cl
2
–
Here, --------- -- (O , Cl ) is the rate of chlorine formation
3
–
4
+
2
–
2
Vdt
w = k [MnO ][H ] [Cl ] ,
1
1
–
from Cl under the action of ozone only. This rate can
(5)
4
4
be calculated using our data from [2]. Its dependence
k = 0.098 l /(mol min) [4].
1
on acidity is shown in Fig. 1 (curve 3 was obtained in
At stage (1), permanganate ions are consumed, and one calculations based on the data from [2] and symbols are
–
4
–
4
the experimental values). Using (6) to describe
Cl molecule per MnO ion is formed; MnO is
2
–
reduced to manganese compounds containing manga- [Mn(V)] through [MnO ] measured experimentally
∞
4
∞
nese in the oxidation degree intermediate between +7
and +3. Supposedly, Mn(V) is formed: this is our work-
yields
ing hypothesis. At stage (2), the second Cl molecule
2
dn
dn
–
1
Cl2
Cl
–
–
2
and Mn(III), which is the final MnO reduction prod- - -- --------- -- = --------- -- (O , Cl ) + R [MnO ] {1 + R /R }.(9)
4
3
1
4
∞
2
4
V dt
Vdt
uct, are formed. It was shown in [4] that it was Mn(III)
that was the final product of the reaction between
–
4
dn
dn
Cl
2
–
1
Cl
2
–
MnO and Cl in acid media at room temperature.
Here, the - -- --------- -- , --------- -- (O , Cl ), and R values are
3 1
V dt
Vdt
–
4
The regeneration of MnO
from the products of its
known (R is calculated by (5)), and we can therefore
1
reduction is described by stages (3) and (4).As has been
calculate the ratio between the specific rates R /R in
each experiment. We found that this ratio was R /R ≈
2
4
shown above, the oxidation of Mn(III) with ozone does
2
4
–
3
indeed produce MnO .
4
1.8 (at cO3 = 10 g/m ) in all experiments. The chlorine
It is assumed that reactions (1)–(4) are first order in formation rates calculated by (9) with the use of the
the concentrations of the corresponding manganese
dn
Cl
2
–
compounds. This is substantiated by the observation ratio R /R = 1.8 and the known --------- -- (O , Cl ) and R
2
4
3
1
Vdt
values are shown in Figs. 1 and 2 (solid lines 1).
–
4
that the ratio between the stationary and initial MnO
–
+
–
concentrations in the é –MnO –H –Cl system does According to these figures, (9) is in agreement with the
3
4
–
4
rates of chlorine formation observed experimentally.
Equation (9) was obtained within the framework of
Scheme (1)–(4), according to which the reduction of
not depend on the initial concentration of MnO (see
table). The rate w of stage i is then equal to the product
i
of the specific rate R by the concentration of the corre-
–
4
–
i
MnO to Mn(III) and the oxidation of Mn(III) to
sponding Mn compound. For instance, for reaction (1),
–
4
MnO proceed via the same intermediate compound.
+
2
– 2
4
we have w = R [MnO ], where R = k [H ] [Cl ] and
1
1
1
1
The conclusion that the consumption and regeneration
4
4
k = 0.098 l /(mol min).
–
–
4
1
+
–
of MnO in the é –MnO –H –Cl system involves the
4
3
As has been mentioned above, stationary regime is
established in the reactor as time passes. The rates of
formation and consumption of manganese compounds
in various oxidation states are then equal, that is,
same intermediate compound is substantiated by the
possibility of correctly describing the experimental
chlorine release rates with the use of Eq. (9).
–
4
The opposite suggestion that the reduction of MnO
and oxidation of Mn(III) proceed via different interme-
–
4
R [MnO ] = R [Mn(V)] ,
(6)
1
∞
4
∞
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 4 2006

THE OXIDATION OF CHLORINE IONS UNDER THE JOINT ACTION OF OZONE
561
diate compounds is at variance with the experimental
data. The rate of chlorine formation would then be
dn dn
ACKNOWLEDGMENTS
This work was financially supported by the Russian
Foundation for Basic Research (project no. 04-03-
32915) and the “State Program for Support of Leading
Scientific Schools” (project NSh no. 1275.2003.3).
1
Cl2
Cl2
–
–
-
-- --------- -- = --------- -- (O , Cl ) + 2R [MnO ] . Here, all the
3 1 ∞
4
V dt
Vdt
values on the right-hand side are known from experi-
ment or can be calculated. The rates of chlorine forma-
tion calculated this way (they are shown by dashed
lines in Figs. 1, 2, curves 2) noticeably differ from the
experimental values.
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1
2
To summarize, we for the first time studied the for-
mation of chlorine in the oxidation of chlorine ions
–
under the joint action of O and MnO in acid media.
3
4
–
Transfer catalysis of the reaction between O and Cl by
3
(
5), 439 (2003)].
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–
–
MnO ions was observed; the latter react with Cl to
4
produce chlorine and are reduced to manganese com-
pounds in low oxidation degrees. These compounds are
5. J. Hoigné, H. Bader, W. R. Haag, and J. Staehelin, Water
–
Res. 19 (8), 993 (1985).
oxidized back to MnO by O . Compared with the
4
3
6
7
. A. V. Levanov, I. V. Kuskov, K. B. Koiaidarova, et al.,
Kinet. Katal. (in press).
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138 (2005)].
other systems studied by us [2, 6, 7], this one is charac-
terized by the highest rate of chlorine ion oxidation.
The permanganate ion can be used as a catalyst of
ozone reactions with inactive substrates.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY Vol. 80 No. 4 2006