1. Decomposition Characteristics of Acetone in an Atmospheric DC
Corona discharge
Takahiro Sakamoto1, Kohki Satoh1,2 and Hidenori Itoh1
1 Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran, Hokkaido , Japan
2 Center of Environmental Science and Disaster Mitigation for Advanced Research, Muroran Institute of Technology, Muroran, Hokkaido , Japan
1. Introduction
2. Experimental apparatus and conditions
Background
Electrode : a multi-needle and a plane
・ Thirteen stainless-steel needles (55mm length and
4mm diameter) are mounted on a metal holder to
form the multi-needle electrode.
・ The plane electrode made of stainless-steel is 80mm
diameter.
・ Gap length is 35mm.
・ Volatile Organic Compounds (VOCs) has a possibility of the generating suspended matter
　(SPM) and photochemical oxidant.
Development of Effective removal techniques of VOCs are required.
We focus on acetone, which is an organic solvent used for semiconductor cleaning etc., has an affect on the malfunction of bloods and central nervous system.
Discharge chamber : a stainless cylinder
・ 197mm inner diameter and 300mm height
Approaches to decompose VOCs using discharge plasmas has attracted attention.
Applied voltage : +26kV DC
・ A positive DC high voltage around 26kV is applied to the multi-needle
electrode, generating a streamer corona discharge.
Objective
We clarify the decomposition process of acetone by an atmospheric DC corona discharge in nitrogen-oxygen mixture at atmospheric pressure.
We examine the influence of oxygen concentration in a background gas on decomposition characteristics of acetone in the corona discharge, from the detailed investigation of mass balance for carbon atoms, the yield and selectivity of CO2 [1].
Initial concentration of acetone : 200ppm
Background gas and gas pressure : nitrogen-oxygen mixture and 1013hPa
・ Mixture rates are N2/O2 = 80/20, 85/15, 90/10, 98/2.0 and 99.8/0.2 (%).
・ Atmospheric pressure (1013hPa)
Concentration measurements of acetone and by-products : by Infrared spectroscopy
・ The concentration is measured by a Fourier Transform Infrared Spectrophotometer (Shimadzu, FTIR-8900) with a gas cell (Infrared Analysis
Inc., 10PA), which optical path length is 10m.
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.
[1] Hyun-Ha Kim et al. : Appl. Catal. B: Environ. 56(2005)213.
3. Results and discussion
(1) Infrared absorbance spectra (at N2/O2 = 98/2.0%)
(3) Mass balance for carbon atoms
The number of carbon atoms (in ppm)
before discharge
Cin acetone =
Concentration of acetone ×
The number of carbon atoms in an acetone molecule(3)
Cin each by-product =
Concentration of each by-product ×
The number of carbon atoms in each by-product molecule(1)
N2/O2 = 80/20(%)
N2/O2 = 90/10(%)
N2/O2 = 95/5.0(%)
after discharge
(22.0kJ)
After discharge (input energy : 60kJ)
N2/O2 = 98/2.0(%)
N2/O2 = 99.8/0.2(%)
　　CH4 : deg-str(3019cm-1)
　　CO2 : anti str(2349cm-1), bend(667cm-1)
　　N2O : 2170～2260cm-1, 1206～1320cm-1
　　CO : 2050～2220cm-1
HCOOH : C-O str(1105cm-1)
O3 : anti str(1042cm-1)
HCN : bend(712cm-1)　
are shown.
Before discharge
　　CH3 d-str : 3019cm C-C str 　 : 1216cm-1
　　C=O str 　 : 1731cm CH3 rock : 981cm-1
　　CH3 d-derom : 1435cm C=O ip-bend : 530cm-1
　　CH3 s-derom : 1364cm-1
　 are shown.
・ The upper border lines of CO2 are the total amount of
carbon atoms in the gas phase.
・ The maximum value of the longitudinal axes are the
total amount of carbon atoms in the discharge chamber.
CH4, CO2, CO, HCOOH and HCN are found to be produced by the decomposition of acetone.
Oxygen concentration
・ high, then the number of carbon atoms converted to CO increases
・ low, then the number of carbon atoms converted to CH4 increases
Namely, decomposition process of acetone can be shown as follows,
H2O can be produced in the corona discharge, but we can not deduce the concentration of H2O properly, so that it can not be discussed here.
(2) Concentration variations of acetone and by-products
・ High oxygen concentration :
・ Low oxygen concentration :
CH4
CH3COCH3 CO
CO2
CH3COCH3
CO2 CO
Deposition
・ The summation of carbon atoms contained in the by-products, which correspond to the upper border line for CO2, is smaller than number of carbon atoms initially contained in acetone.
・ The difference shows the number of carbon atoms contained in the deposits on the electrodes and walls.
・ Percentage of deposited carbon atoms at input energy of 60kJ,
25.5% at N2/O2 = 80/20(%)
24.8% at N2/O2 = 90/10(%)
20.7% at N2/O2 = 95/5.0(%)
17.8% at N2/O2 = 98/2.0(%)
8.21% at N2/O2 = 99.8/0.2(%)
・ When oxygen concentration is low, the carbon atoms contained in
deposits on the plane electrode and the wall of the discharge
chamber decreases.
(4) Yield and selectivity of COX (at input energy of 60kJ)
The COX yield (YCOx) and selectivity (SCOx) [1] are calculated by following equations,
where, [acetone], [CO] and [CO2] are the concentrations of each molecule, and [acetone]0 is the initial concentration of acetone.
The concentration of acetone decreases with input energy, and it decreases to 0 ppm at approximately 40kJ.
・ The oxygen concentration in the background gas does not influence on the acetone decomposition.
The CO2 yield and selectivity
: When the oxygen concentration increases, YCO2
and SCO2 tend to decrease.
The concentrations of CO, CH4, HCOOH and HCN once increase with the input energy, and then they tend to decrease ; therefore, these are regarded as intermediate products.
The CO yield and selectivity
: YCO2 and SCO2 are independent of the oxygen
concentration.
・ The concentration of CO is high when oxygen concentration is high.
・ The concentration of CH4, HCOOH and HCN are low when oxygen concentration is high.
In the viewpoint of VOCs-removal applications, the preferable gaseous end product is known to be CO2 [2].
The concentrations of CO2 increases monotonously with the input energy ; therefore,CO2 is found to be a gaseous end product in the corona discharge.
[2] Hyun-Ha Kim et al. : J. Inst. Electrostat. Jpn. 29 1(2005)32
It is found that high CO2-yield is achieved at the low oxygen concentration.
4. Conclusions
Decomposition characteristics of acetone using the atmospheric DC corona discharge in the background gas of nitrogen-oxygen mixture
CO2, CO, CH4, HCOOH and HCN are found to be by-products of acetone in the corona discharge.
CO, CH4, HCOOH and HCN are regarded as intermediate products, which tend to decomposed at sufficient input energy, and CO2 is gaseous end product.
Acetone is chiefly inverted to CO2 via CO at high oxygen concentration and via CO and CH4 at low oxygen concentration.
The oxygen concentration in the background gas does not influence on the acetone decomposition.
The carbon atoms contained in deposits on the plane electrode and the wall of the discharge chamber decreases
when the oxygen concentration decreases.
The CO2 yield and selectivity have tendencies to increase with decreasing the oxygen concentration.