Decomposition Characteristics of Benzene, Toluene and Xylene in
an
Atmospheric DC Corona discharge
Kohji Nagao1, Takahiro Sakamoto1, Kohki Satoh1,2 and Hidenori Itoh1
1 Department
of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran, Hokkaido 050-8585,
Japan
2 Center of Environmental Science and Disaster Mitigation for Advanced Research, Muroran Institute of Technology,
1. Introduction
2.
Experimental
apparatus
and
Muroran, Hokkaido 050-8585, Japan
Recently, a large volume of exhaust gas containing environmental pollutants is emitted
from factories, automobiles etc., and this causes major environmental issues.
conditions
¾ Electrode
• A multi-needle electrode, which consists of thirteen
Email : [email protected]
stainless-steel needles (55 mm length and 4 mm
[1]
0
50
PRTR
(Pollutant
Release
and250
Transfer
Register) data in 2005
100
150
200
300
toluene (41%)
xylene (26%)
¾ Toluene (C6H5CH3) and xylene (C6H4(CH3)2)
are emitted to the environment in the largest
volume.
ethlbenzene
methylene chloride
poly oxyethylene = alkyl ether
p-dichlorobenzene
benzene (4%)
0
50
100
150
200
emission volume [kt/year]
250
300
¾ The emission volume of benzene (C6H6) is
less than those of toluene and xylene, but it
has carcinogenicity and teratogenicity.
¾ Discharge chamber
• The cylindrical discharge chamber is made of
stainless-steel, with 197 mm inner diameter and
300 mm height.
¾ Applied voltage
¾ Environmental pollutants, such as benzene, toluene and xylene, must be removed or decomposed
at the source.
¾ Development of effective removal techniques for the pollutants is required.
¾ Objective
diameter) and a plane electrode, made of stainless
steel (80 mm diameter) are placed in a cylindrical
discharge chamber.
• The distance between the multi-needle electrode
and the plane electrode is fixed at 35 mm.
Approaches to decompose environmental pollutants
using discharge plasmas have attracted attention.
We clarify the decomposition characteristics of benzene, toluene and xylene in an atmospheric DC corona
discharge in nitrogen-oxygen mixture gas. Particularly, we examine the by-products of benzene, toluene
and xylene in an atmospheric DC corona discharge and the concentration variations of benzene, toluene
and xylene.
[1] Ministry of the Environment：The compendium of PRTR data on 2005 (released in 2007).
• A positive DC high voltage 25 ~ 27 kV is applied
to the multi-needle electrode, generating a streamer
corona discharge.
¾ Gas condition
• Nitrogen-oxygen mixture gas is used as a background gas, and its mixture ratio is N2:O2
= 80:20 %.
• Initial gas pressure in the chamber and the concentration of benzene, toluene and xylene
are respectively 1013 hPa (atmospheric pressure) and 300 ppm.
¾ Concentration measurement
• Concentrations of benzene, toluene, xylene and by-products are measured by a Fourier
Transform Infrared Spectrophotometer (Shimadzu, FTIR- 8900) equipped with a gas cell
(Infrared Analysis, 10PA), which has optical path length of 10 m.
¾ Measurement of voltage and current
• Applied voltage is measured by high-voltage probe (Tektronix P6015A).
• Discharge current is measured every second through the monitor of the DC power supply
(Max-Electronics, LS40-10R1).
3. Results and discussion
(1) Infrared absorbance spectra (in N2-O2 mixture gas containing C6H6)
3.0
3.0
(3) Formulation of the concentration variation
for benzene, toluene and xylene
¾ Red, blue and
2
2.0
2.0
green
points
respectively
100
8
C6H6
1.0
1.0
the
6
¾ represent
Lines
indicate
4
concentration
optimum fittings
0.0
0.0
variations
of
3.0
3.0
O3
of
the
2
benzene,
toluene
HCOOH
¾
The
concentrations
concentration
CO2
N2O
HCN
CO
10
and
xylene almost
as a
2
2.0
2.0
decrease
variations.
8
CO2
6
function with
of the
linearly
the
C2H2
CO
4
input energy.
1.0
1.0
input
energy,
¾ The concentration
2
namely,
these
variation
C
(
ε
) is
0.0
0.0
decreases as
represented
1
4000
3500
3000
2500
2000
1500
1000
500
800
700
600
500
exponentially
with
0
10
20
30
40
50
60
70
-1
-1
ε
)
=
C
exp(
αε
),
C
(
wavenumber [cm ]
wavenumber [cm ]
0
input energy [kJ]
the input
is the
where,
C0 energy.
‡ Before discharge
‡ After discharge (input energy : 20 kJ, discharge time : 60 min)
initial
-1), bend (667 cm-1)
CO
:
anti
str
(2349
cm
2
α
∆α
concentration, ε is
CH str
: 3068 cm-1
CO
: 2220 ~ 2050 cm-1
C
H
0.043
6
C6H65CH
0.125
0.082
the input energy
CH bend
: 1038, 673 cm-1
HCOOH : C=O str (1770 cm-1), C-O str (1105 cm-1)
3
C6H4(CH3)2
0.237
0.194
-1)
1
benzene
toluene
(C
)the
(C63H
) 4(CH3)2)
C
H
:
CH
bend
(730
cm
and
α
is
6Hxylene
6(C
6H5CH
ring
deform
:
1435
cm
2xylene
2 todischarge
¾
¾
Only
The
CO
Similar
concentrations
,
the
CO,
by
concentration
HCOOH,
products
of
of
C
are
benzene,
CO,
of
H
produced
CO
and
HCOOH,
increases
HCN
toluene
in
are
the
C
and
found
monotonously
corona
H
and
HCN
be
decrease
produced
once
with
in
the
monot
increase
N
by
input
O
the
onously
mixture
decomposition
with
energy
the
with
gas
;
therefore,
input
with
the
of
electrical
toluene
energy,
benzen
CO
and
and
is
e.
input
found
xylene.
then
energy,
to
they
be
¾
A
red
red,
dashed
blue
line
and
The
points
are
Considering
that
the
¾
The
It
is
likely
α
value
that
for
α
benzene,
represents
α
value
toluene
the
for
cleavage
xylene
and
xylene
is
rate
the
are
of
largest
0.043
the
benzene
in
(
α
the
),
0.125
three
ring,
concentrations
The corona
concentration
Cnitrogen-oxygen
(ε) is represented asmixture
¾ The concentrations
of benzene,
and
xylene
decrease
with
thexylene
input
energy
monotonously.
2
2 characteristics
2
2
2 benzene,
2 toluene
2toluene
2-1)
2 an
B variation
B
(2) Concentration
variations
of
toluene,
xylene
and
by
products
Decomposition
of
benzene,
and
in
atmospheric
DC
discharge
in
HCN
:
bend
(712
cm
damping
are
shown.
atend
and
gaseous
the
to
decrease
energy
end
product
required
; ,therefore,
inHCOOH,
tothe
decompose
these
corona
areH
discharge.
regarded
xylene
intermediate
and
products.
that
for ~toluene
is-1, the
second.
that
for
toluene
the -second,
probably
is
green
optimum
that
points
benzene,
fitting
show
approximately
αdischarge.
and
represents
0.237
(=the
αXC),is
dissociation
respectively,
rateitand
ofismethyl
the
deviations
groups.
of
the
(and
-1, 1340
T )∆α
N2HCN
O isasthe
:smallest,
2260
~ 2170
cmby
1200ofcm
O3: anti
str (1042and
cm-1xylene
)
ε
)
exp[
(0.043+0.093
n
)
ε
],
C
(
CO,
C
and
are
found
to
be
products
benzene,
toluene
in
the
corona
¾
CO
0
2
2 2
gas
coefficient
ofa
toluene and
xylene are∆α
decomposed
by the
cleavage
of
the
benzene
expressed
by
damping
coefficients
from αB are
0.082
(∆αthe
=αofT-damping
α
) and
are shown.
T
B
where,
ntoisdethe
numberatof
methyl
group
in
one
molecular
¾ CO2 is gaseous end product, and CO, HCOOH, C2H2 and HCN are regarded as intermediate products, which
tend
composed
the
sufficient
input
energy.
substances.
methyl
coefficients.
straight
= α Xcoefficients
- αline,B ) of.
0ring. and1 by9the 4dissociation
( ∆ of α
X groups.
of benzene, toluene and xylene.
¾ The concentrations of benzene, toluene and xylene decrease exponentially with the input energy.
toluene
αbenzene,
= 0.043+0.093
n,
where,
and
and 0.043xylene,
¾ Benzene, toluene and xylene are decomposed by the cleavage of benzene ring and by the dissociation of methyl groups.
0.093
n are and
the
respectively,
¾ The concentration variation of benzene, toluene and xylene with the input energy C(ε) is represented as C(ε) = C0exp[-(0.043+0.093n)ε].
coefficients
of
orange and light
benzene
ring
blue bars represent
cleavage
and,
α
and
∆α
B
dissociation
respectively.
of
methyl
groups,
respectively.
4. Conclusions
C6H6
C6H6
C6H6
C6H5CH3
C6H4(CH3)2
concentration [ppm]
absorbance [a.u.]
without discharge
with discharge (20 kJ)