Transcript O 2 + O → O 3

Decoloration characteristics of organic dye in an aqueous solution
by a pulsed-discharge plasma
Shin
1
Ikoma ,
1
Miyazaki ,
Yasushi
Kohki
1,2
Satoh ,
and Hidenori
1
Itoh
1Department
of Electrical and Electronic Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Japan
2Center of Environmental Science and Disaster Mitigation for Advanced Research, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Japan
E-mail : [email protected]
APPARATUS & CONDITIONS
INTRODUCTION
 Electrode : A multi-needle electrode and a
water bath electrode
 Background
• A multi-needle electrode:
Various methods and techniques to reduce environmental pollutants like dioxin, toluene, trichloroethylene,
etc. have been developed. Advanced Oxidation Processes (AOPs)[1], such as ozone-UV oxidation, photo
catalytic oxidation, pulsed-discharge etc., have been used as effective methods for purifying polluted water.
1, 4, 37 and 55 stainless-steel needles are
arranged on a stainless-steel plate.
• A water bath electrode:

A water bath made of stainless-steel, which has
the dimensions of 119mm inner diameter and
12mm depth, is placed under the multi-needle
electrode.
 The water bath electrode is earthed.
Pulsed discharge
 The hazardous substances can be directly decomposed by the collision with high
energy electrons[1].
A mixture of effects causing decomposition of the
hazardous substances is
expected by using pulseddischarge plasma.
 The species which have high oxidation potential, such as OH, O, O3 etc., are
produced by a pulsed-discharge plasma generated above a water surface[2], and
that the species can dissolve into the water, reacting with substances in the water.
 UV radiation may contribute to the decomposition of the hazardous
substances[1][2].
• Gap length:

 Discharge chamber :
• A cylindical discharge chamber is made of
acrylic resin (140mm inner diameter, 100mm
height and 1.5L volume).
 Objective
 H.V. pulse generator:
We generated a pulsed-discharge plasma above test liquid (containing low concentration of
methylene blue) and investigated the decomposition characteristics of methylene blue by the plasma
exposure.
 Recent works (Decomposition of methylene blue by using pulsed-discharge plasma)
 Pawlat et
investigated the effects of the pulse repetition rate and gas flow rate on the decomposition
characteristics of methylene blue.
 Georgescu et
• Initial concentration : 10ppm
• Weight : 70g
 Background gas : N2 (99.99%)，O2 (99.5%) and Ar(99.99%)
reported that the O3 contributes to the decomposition of methylene blue.
• Mixture ratios are N2(or Ar) : O2 =100:0, 90:10, 80:20, 60:40, 40:60, 20:80, 10:90 and 0:100
 Concentration measurements of methylene blue :
Influence of electrode configuration on the decomposition characteristics
• The test liquid is exposed to the pulsed discharge for 60min, and the temporal variation in concentration of methylene blue,
O3 and NOx are measured.
• Concentration of methylene blue mesured by absorption photometry using 650nm laser and Photonic Multi-Channel
Analyzer (PMA).
 The number of needles (1, 4, 37 and 55)
Influences of background-gas composition on the decomposition characteristics
 N2(or Ar):O2=100:0，90:10，80:20，60:40，40:60，20:80，10:90 and 0:100
[1] M.A.Malik et al.:Plasma Sourse Sci. Technol. 10 (2001) 82.
[2] P.Lukes et al.:J. Phys. D: Appl. Phys. 38 (2005) 409.
• A high-voltage pulse, generated by a blumlein
pulse-generator, is applied to the multi-needle
electrode.
• The coaxial transmission lines are charged at
+14.14kV.
• Pulse repetition rate is 20pps (pulses per second).
 Substitution of polluted water : A aqueous methylene blue solution
al.[3]
al.[4]
A distance between the tip of multi-needle
electrode and the surface of the test liquid is
fixed at 4mm.
C16H18ClN3S･3H2O
 Mesurement of voltage and current
• Applied voltage and discharge current are measured by high voltage probe (Tektronix, P6015A) and digital oscilloscope
(Yokogawa, DL1620).
[3] J.Pawlat et al.:Acta Physica Slovaca 55 (2005) 479.
[4] N.Georgescu et al.:Proceedings of GD 2006 F05 (2006) 497.
RESULTS & DISCUSSION
(2) Influence of electrode configuration on methylene blue decomposition
(1) The characteristics of an applied HV
pulse
Vg
Ig
100
0
0
-10
-50
80
decomposition rate [%]
50
10
current [A]
voltage [kV]
20
-20
-30
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
-100
5.0
4.5
time [s]
electric power [MW]
1needle
100
O3 concentration [ppm]
30
10
2.0
1.5
1.0
60
1needle
4needles
37needles
55needles
40
0.5
0.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
8
6
O3
4
1
4
37
 Maximum values of discharge-voltage,
discharge-current and electrical power are
respectively -20kV, -70A and 1.5MW.
 Pulse width is 500ns.
10
20
30
40
50
60
70
 Filamental discharges from the needle tip reach the water surface,

The O3 contributes to the decomposition
of methylene blue.
and the discharges split into several branches, then some of them
reach the water bath electrode.
Methylene blue can be decomposed by OH radicals generated by the
reaction between electrons and H2O vapour.
55 and 37 needles
＞ 4
In the case of 1needle
[needles]
 Input energy per pulse is 0.7J.
Methylene blue can be decomposed by
H2O + e → OH + H
OH radicals.
 O3 produced with the high concentration, O3 contributes to the
(3) Influence of the background-gas composition (N2-O2) on methylene blue decomposition
Methylene blue decomposition rate after 15min plasma exposure
decomposition of methylene blue.
(4) Influence of the background-gas composition (ArO2) on methylene blue decomposition
100
60
40
20
20
30
40
50
60
98%
68%
40～65%
O and O3 contribute to
the decomposition of
methylene blue.
OH radicals produced
by the reaction between
N2 exited in metastable
state and H2O.
O2 + O → O 3
H2O + e → OH + H
0
10
in N2-O2 mixture
O2 + e → 2O + e
1needle
d=4mm
0
in pure N2
70
operation energy density [J/(g･ppm)]
＞
N2(A) +H2O →
＞
OH + N2 +H
H2O + e → OH + H
N 2 (A) : N 2 ( A3  u )
The decomposition rate
decreases due to the
production of NOx.
O2 + e → 2O + e
O2 + O → O3
N2(A) +H2O →
OH + N2 +H
H2O + e → OH + H
N2 [%]
80
60
40
20
0
100
80
NO+NO2
80
60
60
40
O3
NO2
NO
40
20
20
0
0
10
20
30
40
Low oxygen
50
O2 [%]
60
70
80
90
High oxygen
NOx production processes
120
0
100
O3 & NOx concentration [ppm]
decomposition rate [%]
100
100
Following reactions can be induced by the Low oxygen concentration（NO production）････
pulsed-discharge plasma with the background  N produced by the reaction (4), leads NO
production reactions in (5) and (6).
gas consisting of N2 and O2[1,2,5,6].
 NO produced by the reaction between N2
O2 + e → 2O + e
････(1)
molecules exited in metastable state and O, as
O2 + O → O3
････(2)
shown in (7).
N2(A) +H2O → OH + N2 +H ････(3)
High oxygen concentration (NO2 production)････
N2 + e → N + N + e
････(4)
 NO production reactions shown in (5), (6) and
N + O → NO
････(5)
(7) are activated, and they are consumed for
NO2 productions shown in (8) and (9).
N + O3 → NO + O2
････(6)
N2(A) + O → NO + N
････(7)
The decomposition rate decreases due to the
NO + O → NO2
････(8)
consumption of O, O3 and N2(A) by NOx
NO + O3 → NO2 + O2
････(9)
production.
100
100
decomposition rate [%]
N2:O2=100:0
N2:O2=90:10
N2:O2=80:20
N2:O2=60:40
N2:O2=40:60
N2:O2=20:80
N2:O2=10:90
N2:O2=0:100
in pure O2
Ar [%]
90
80
70
60
50
40
30
20
10
120
100
80
80
60
60
40
40
20
20
0
0
10
20
30
40
50
60
70
80
90
0
100
O2 [%]
 O3 concentration increases in proportional to the increase of the
O2 concentration.
In N2-O2 mixture, NOx production inhibits O3 generation.
 The decomposition rate of methylene blue is nearly-constant
with O3 concentration decreases at the same time.
Excited molecules of Ar may contribute Methylene blue
decomposition.
Exited molecules of Ar (Ar*)
• OH radicals produced by the reaction between Ar exited in
metastable state and H2O vapour.
H2O + Ar* → OH + H + Ar
• Exited molecules of Ar can decompose the benzen rings[7].
[5] C.Mavroyannis et al.:Can. J. Chem., 39 (1961) 1601.
[6] O.Eichwald et al.:J. Appl. Phys. 82 (1997) 4781.
[7] N.Goto et al.: IEEJ Trans., FM, 126 (2006) 321.
CONCLUSIONS
We investigated the decomposition characteristics of aqueous methylene blue solution, by pulsed discharge, with the different electrode configuration and composition of the background gas.




0
O3concentration [ppm]
decomposition rate [%]
80
OH
1 and 4 needles
O2 + e → 2O + e
O2 + O → O3
80
The decomposition rate
1 ＞ 37
O3
55
Decomposition rate of methylene blue
increases monotonously with the increase
of O3 concentration except for 1needle.
operation energy density [J/(g･ppm)]
55 ＞
O3
OH
number of needlles
0
0
OH
O3
2
5.0
time [s]
OH
0
d=4mm
N2:O2=80:20
20
55needles
Methylene blue decomposition rate tends to increase when the number of needle-electrodes increases, except for the case of 1needle.
In pure O2, O3 produced with the highest concentration (120ppm), and the O3 contributes to the decomposition of methylene blue.
In pure N2, slight increase in the decomposition rate can be made by the contribution of OH radicals, produced by the reaction between N2 molecules exited in metastable state and H2O vapour.
In N2-O2 mixture, the decomposition rate of methylene blue decreases due to the decomposition of O3 by NO and N and the inhibition of O3 generation by NOx production.