corona-discharge treatment of gaseous benzene, toluene and
TRANSCRIPT
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C6H4(CH3)2
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FAH
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HCOOH
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Corona-discharge treatment of gaseous benzene, toluene and xylene
at atmospheric pressure
Kohji Nagao1, Kohki Satoh1,2 and Hidenori Itoh1
1 Graduate school of Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan2 Center of Environmental Science and Disaster Mitigation for Advanced Research, Muroran Institute of Technology, Muroran 050-8585, Japan
Email : [email protected]
2. Experimental apparatus and conditions
Discharge chamber
• The cylindrical discharge chamber is made of
stainless-steel, with 197 mm inner diameter and
300 mm height.
Applied voltage
• A positive DC high voltage (20 ~ 28 kV) is applied
to the multi-needle electrode, generating a streamer
corona discharge.
Electrodes
• A multi-needle electrode, which consists of thirteen
stainless-steel needles (55 mm length and 4 mm
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.
Gas conditions
• Nitrogen-oxygen mixture is used as a background gas, and the mixture ratio is N2:O2 = 80:20 %.
• Initial gas pressure in the chamber is 1013 hPa (atmospheric pressure), and initial concentrations of benzene, toluene and xylene are 300 ppm.
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.
Measurement of voltage and current
• Applied voltage is measured by a high-voltage probe (Tektronix P6015A).
• Discharge current is calculated by voltage drop across a non-inductive resistance (1 kW), which is connected between the plane electrode and
the earth.
1. Introduction
Objective
We investigate the decomposition characteristics of benzene, toluene and xylene in an atmospheric DC
corona discharge. Concentration variations of benzene, toluene, xylene and by-products are measured by
infrared spectroscopy, and then the decomposition processes of benzene, toluene and xylene is examined.
Recently, various kinds of VOCs (volatile organic compounds) contained in exhaust gas
from factories, automobiles, etc., cause major environmental issues.
Toluene (C6H5CH3) and xylene (C6H4(CH3)2)
are emitted to the environment in the largest
volume.
toluene (41%)xylene (26%)
benzene (4%) The emission volume of benzene (C6H6) is
less than those of toluene and xylene, but it
has carcinogenicity and teratogenicity.
PRTR (Pollutant Release and Transfer Register) data in 2007[1]
ethlbenzene
methylene chloride
poly oxyethylene = alkyl ether
p-dichlorobenzene
[1] Ministry of the Environment of japan：The compendium of PRTR data on 2007 (released in 2009).
benzene (C6H6) toluene (C6H5CH3) xylene (C6H4(CH3)2)
Approaches to decompose VOCs
using discharge plasmas have
attracted attention.
Decomposition processes of benzene, toluene and xylene in nitrogen-oxygen mixture gas in an atmospheric DC corona discharge are investigated.
CO2, CO, HCOOH, formic anhydride (FAH), C2H2, HCN, maleic anhydride and glyoxal are produced from benzene in the atmospheric DC corona discharge.
Acetic formic anhydride (AFAH), peroxyacethyl nitrate, CH4, HCHO, CH3COOH and methyl glyoxal are produced from only toluene and xylene.
Concentrations of benzene, toluene and xylene decrease monotonously with the increase of input energy.
Benzene, toluene and xylene are chiefly converted to CO2 via CO, HCOOH, FAH and AFAH by the atmospheric DC corona discharge.
Some of carbon atoms containing in benzene, toluene and xylene are deposited on the electrodes and the wall of the discharge chamber.
3. Results and discussion
4. Conclusions
(3) Mass balance for carbon atoms
The total number of carbon atoms, which is presented as the top line of stacked graph, decreases
monotonously with the increase of input energy, and then becomes constant.
×number of carbon atoms in each of gaseous molecules concentration [ppm]
The number of carbon atoms [ppmC]
C6H6 C6H5CH3 C6H4(CH3)2
CO2 is a gaseous end product, and the other products are intermediate products.
(2) Concentration variations of benzene, toluene, xylene and major by-products
Concentrations of benzene, toluene and xylene decrease with the increase of input energy.
CO2, CO, HCOOH, FAH and AFAH are major by-products from benzene, toluene and xylene.
(4) Decomposition processes of benzene, toluene and xylene
Benzene, toluene and xylene are chiefly
converted to CO2 via CO, HCOOH, FAH and
AFAH by the atmospheric DC corona
discharge.
The some of carbon atoms are deposited on the
electrodes and the wall of the discharge
chamber.
(1) Infrared absorbance spectra
CO2, CO, HCOOH, formic anhydride and acetic formic anhydride are produced from toluene.
By-products from xylene are the same as those from toluene.
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with discharge (10 kJ)
C6H5CH3
after separation
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without discharge
with discharge (10 kJ)
C6H6
after separation
CO2, CO, HCOOH and formic anhydride are produced from benzene.
O3 and N2O are produced from the background gas.
C6H6
CO2CO
HCOOHN2O O3
C6H6
CO2
C6H6
formic anhydride (FAH)
C6H5CH3
C6H5CH3
C6H5CH3
CO2CO
N2O O3 CO2HCOOH
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FAH50
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AFAH
This leads that the some of carbon atoms containing in benzene, toluene and xylene are deposited on
the electrodes and the wall of the discharge chamber.
C6H6
C6H5CH3
C6H4(CH3)2only C6H5CH3 and C6H4(CH3)2
AFAH
FAH
HCOOH
CO
CO2
fragments or by-products deposit
FAHacetic formic anhydride (AFAH)
CH4
HCHO
CH3COOH
methyl glyoxal
peroxyacetyl nitrate
AFAHCO2
CO
HCOOH
FAH
maleic anhydride
glyoxal
C6H6
C2H2
HCN
minor products
By-products from benzene, toluene and xylene
C6H4(CH3)2C6H5CH3