Large volume treatment of formaldehyde using atomosphericmicroplasma
Kazuo Shimizu , Masaki Kanamori , and Marius Blajan
Innovation and Joint Research Center, Shizuoka University, 3-5-1 Jyouhoku, Hamamatsu, 432-8561, Japan, E-mail：shimizu@cjr.shizuoka.ac.jp

1.Introduction

4. Results and discussion

Recently, Indoor Air Quality (IAQ) is recognized as
an important factor of houses and buildings. This
point of view emerged since Sick-building syndrome(SBS) has become a worldwide issue.
In this paper, decompositon of HCHO was carriedout by using atmospheric microplasma at highvolume flow rate in order to confirm theeffectiveness of microplasma for large volumetreatment.

4.１Formaldehyde decomposition
The concentration of HCHO was estimated by theDNPH method using the HPLC. The initial HCHO
concentration was set to about 1.25 mg/m3(1 ppm)
which is about 10 times higher than the regulated
value in Japan.

Fig.7 Byproduct analysis by the FT-IR(wavenumber: 950-1200 [cm-1]).

2. Atmospheric microplasma

Table.1 Byproduct concentration.

Fig.4 HCHO removal ratio versus discharge
time for various gas flow rates.
Fig.4 shows the results of the HCHO
decomposition using microplasma. Removal ratio ofHCHO (αHCHO) was calculated by the equation
below.

VD [kV]NOx [ppm]

N2O [ppm]

CO [ppm]

0.6

0.6

0.6

1.2

0.8

7.4

2.4

8.2

1.0

24.0

9.1

10.5

Table.1 shows the byproduct concentrations.
Byproduct concentrations increase with the increaseof discharge voltage. CO concentration exceeded 10ppm. This could be because some CO2 wasdissociated by electron collision. CO derives mostly
from the decomposition of HCHO.

4.3 Smell Analysis
Fig.1 Schematic image of microplasma
electrode.
Atmospheric microplasma is a kind of dielectricbarrier discharge which has a discharge gap in theorder of micro meters. A schematic image of themiroplasma electrode is presented in Fig.1.

(ΔHCHO: Decreased amout of HCHO per 15 minutes.)
In order to compare the effectiveness with thesame condition, the decomposed amount of HCHOper 1m3 of circulated air (ηHCHO) was calculated by
the equation below.

minutes.)(⊿Q: Circulated volume of air per 15Fig.8 Smell similarity analysis of room air andozone by Fragrance Flavor Analyzer.

Fig.2 Image of microplasma during
discharge.
Two metal circular plates covered with dielectricmaterials are placed together with a spacer inbetween. By applying an alternative voltage,streamers generate to form glow-like plasma (Fig.2).

3. Experimental setup

Fig.5 HCHO removal amount per 1 m3 versus
discharge time for various gas flow rates.
Fig.5 shows ηHCHO during with the discharge time.
ηHCHO were higher with lower gas flow rates since
the exposure time in plasma decrease at higher flowrates.

4.2 Byproduct Analysis

A byproduct analysis is carried out by the FT-IR.
For this analysis, the initial concentration of HCHOis set to about 10 ppm, in order to make thespectrums larger for identification. The gas flow rate
was set to 2 L/min, and the humidity was set to 60%.
The discharge voltage was change between 0.6～
1.0 kV.
Figs.6 and 7 show the analysis results at different
wavenumber ranges.

Fig.3 Experimental setup
Fig.3 shows the experimental setup. This
microplasma reactor is placed inside a 1 m3 acrylic
cube. The fan flows the surrounding air through theelectrode at a flow rate of 0.1~0.5 m3/min. A neontransformer was used as the power source formicroplasma. Its maximum output voltage was 1.3
kV at a frequency of 25 kHz.

Fig.6 Byproduct analysis by the FT-IR(wavenumber: 2080-2300 [cm-1])
From the analysis results, carbon dioxide, carbon
monoxide, and nitrous oxide were discovered as
byproducts without humidity.

Fig.9 Smell similarity nalysis of HCHO before
and after microplasma Treatment.
The smell similarity of room air and ozone ispresented in Fig. 8, and the similarity of HCHO
before and after microplasma treatment is shown inFig. 9.

5. Conclusion
In this study, treatment of 1 ppm of formaldehyde
in a 1m3 cube with large volume flow rate (0.10～0.50 m3/min) was confirmed by atmosphericmicroplasma. The following conclusions wereobtained by the series of experiments.
(1) A removal ratio of 70% was achieve at adischarge voltage of 1.0 kV, discharge power
20W, gas flow rate 0.50 m3/min and discharge
time of 60 min.
(2) Removed amount of formaldehyde per 1 m3 wascalculated for various gas flow rates. About 70μg/m3 was obtained for gas flow rate of 0.10m3/min.
(3) Byproduct analysis was carried out with the FTIR. N2O, CO, and HCOOH were found as
byproducts, when initial concentration of HCHO
was set to 10 ppm.
(4)Smell analysis was carried out with the Fragrance
Flavor Analyzer. Smell similarity has changed
after microplasma treatment, and it is mainly thesmell of remaining ozone.