22P069-P
Characteristic of Water Plasmas Generated from O/W Emulsion
by DC Discharge under Atmospheric Pressure
O/Wエマルションを利用した大気圧直流放電による水プラズマの特性
Go Ohta, Sooseok Choi, and Takayuki Watanabe
太田 剛, 崔 秀錫, 渡辺隆行
Department of Environmental Chemistry and Engineering, Tokyo Institute of Technology
4259 G1-22, Nagatsuta, Yokohama, Kanagawa 226-8502, Japan
東京工業大学大学院総合理工学研究科 〒226-8502 横浜市緑区長津田町4259番地G1-22
O/W emulsion has been decomposed by a DC water plasma system. 1-Decanol emulsion used as a model
substance of water-insoluble organic compound was prepared with emulsifier of Tween60 for plasma
supporting gas. The water plasma torch was operated in different arc currents form 6 A to 8 A atatmospheric pressure. The main gases generated from the decomposition were H2, CO, and CO2. At arc
current of 8 A, the TOC value decreased from 3.40×10 4 mg/L to 1.18×102 mg/L, and over 99.6% of carbon
in the raw material was decomposed.

1. Introduction
Thermal plasmas have the following advantages:
high enthalpy to enhance reaction kinetics, highchemical reactivity, and control over oxidation orreduction atmospheres in accordance with required
chemical reactions. These advantages enable
thermal plasmas to treat the waste effectively [1-3].
Direct current (DC) water plasma torch generates
100%-water plasma by high temperature arc
discharge at atmospheric pressure. Therefore,
abundant O and OH radicals which promote waste
decomposition are produced in water plasma flame.
It is also a portable lightweight plasma generation
system that does not require additional plasma
forming gas supply and water cooling unit
Although some water-soluble organic materials
were investigated in the previous work [2,3],
treatment of water-insoluble materials has not been
tried. In the present work, the purpose is toinvestigate the decomposition characteristics ofoil-in-water (O/W) emulsion in the DC waterplasma system.
2. Experimental Setup
Emulsions are colloids made of two immiscible
fluids; one being dispersed in the other in thepresence of surface active agents. There are various
intermediate or consumer products consisting
wholly or partly of emulsions [4]. The emulsion
used in this study is a kind of O/W where oil
droplets are dispersed in water phase. It is
composed of H2O, 1-decanol and non-ionicsurfactant (Tween60). In the samples, the ratio of
1-decanol concentration was 0.1-0.5mol% and theratio of 1-decanol to Tween60 was 1.00 to 26.54 in
the mole ratio.

Schematic diagram of the atmospheric DC waterplasma system is shown in Fig. 1. The experimental
system consists of four parts: (1) water plasma
torch, (2) power supply, (3) condenser, and (4)treated liquid collector. Decomposition experiments
were conducted with the batch process as follow;
the emulsion fills water the reservoir of the torch,and then the arc is ignited. The emulsion is
evaporated spontaneously with the generation ofthermal plasma, and it decomposed in the discharge
region directly.
The produced gas and liquid from thedecomposition were separated by the condenser.
Gas phase treated material was analyzed by gas
chromatography (GC) equipped with a thermal
conductivity detector and a quadrupole mass
spectrometer (QMS). In addition, carbon
concentration in treated liquid was measured by atotal organic carbon (TOC) analyzer.

Fig. 1. Schematic diagram of the experimental setup.

55-10

H +-11+O

210C-12

H2O+Current: 8 A+CO2++CO

10-1310-14

Intensity [a.u.]

1010-10

H-11

10

2++

C-12H O

Current: 6 A+COCO+2+22+

O

10-13

1010-14

TotalEvaporation

4540
2015Gas10501020m/z [-]3040050

Fig. 2. Spectrum of produced gas of 0.5mol%
1-decanol emulsion at 6 A and 8 A.

61500

TOC [mg/L]

H2CO-1

10CO2-2

1010-3CH4-4TOC value of Produced Liquid [mg/L]

0.70.60.57
Arc Current [A]

890.5mol% 1-Decanol

0.5mol% 1-Decanol

0.8105Fig. 4. Effect of arc current on total evaporation
rate and gas generation rate.

0.9

Mole Fraction in Gas [-]0.5mol% 1-Decanol

50
Generation Rate [mg/s]

Intensity [a.u.]

10COCH

1000

4CO

2500

0567Arc Current [A]89Fig. 3. Effect of arc current on gas composition
generated from 0.5mol% 1-decanol emulsion.

3. Results and Discussion
Fig. 2 represented mass spectrum of the produced
gas from the decomposition with the arc current of
6 A and 8 A. H2, CO and CO2 were detected, and it
also indicates that there were no hydrocarbons
composed of more than two carbon atoms in theproduced gas. The intensities of each mass peak aresimilar though the different arc current wassupplied.
The produced gas composition was analyzed indetail with GC measurements as shown in Fig. 3.
Although CH4 was detected in the case of 7 A, itsconcentration is negligible. The mole fraction of H2
in the produced gas is more than 60%. As thecurrent increases, the concentration of H2 and CO2
gradually increase while CO decreases. However,those changes are very small due to the different
gas generation rate for arc current as shown Fig. 4.
The generated O and OH radicals from H2O in thewater plasma are increased with the increase of thearc current. However, the current increase also
leads to the enhancement of raw material
evaporation, generating more carbon sources from1-decanol at the same time. Consequentially, mole
fractions of CO and CO2 are not changed

5678Arc Current [A]9Fig. 5. Effect of arc current on TOC in the
produced liquid.

considerably, because of the contradiction
phenomena.
The amount of carbon in the treated liquid ispresented in Fig. 5. The TOC value decreased withincreasing arc current. At 8 A, the TOC value
decreased from 3.40×104 mg/L in raw material to
1.18×102 mg/L in treated liquid. Therefore, over
99.6% carbon in O/W emulsion was converted toCO, CO2, and soot.
4. Conclusion
1-Decanol O/W emulsion was used as a modelsubstance for treatment of water-insoluble organiccompound. Carbon sources in the raw material areeasily conversed to CO, CO2 and soot, and carbon
concentration in treated liquid is notably decreased.
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[2] Narengerile, et al.: Jpn. J. Appl. Phys. 50 (2011)
08JF13.
[3] Narengerile, et al.: Chem. Eng. J. 168 (2011) 985.
[4] T.N. Hunter: J. Adv. in Colloid and Interface Sci.
137 (2008) 57.