24pD04P
同軸型水素プラズマシャワー法を用いた二酸化炭素還元によるメタンの生成
Production of Methane by Carbon Dioxide Reduction Using a Coaxial Hydrogen
Plasma Shower Method
佐藤史明，飯塚哲
Fumiaki Sato，Satoru Iizuka
東北大学大学院工学研究科
Department of Electrical Engineering, Graduate School of Engineering, Tohoku University
1. Introduction
Today, emissions of carbon dioxide into theenvironment have been regarded as a serious causeof the global warming. For this reason, various
studies for carbon dioxide reduction have beenconducted all over the world. The purpose of thisstudy is to reduce the carbon dioxide efficiently byusing a hydrogen plasma to convert it to methane asa reusable organic compound. Here, potentialenergies of H* (10.20eV) and H2* (11.75eV) are sohigh that they can overcome potential energies ofCO2 (8.28eV) and CO (11.09eV) in their reduction
reactions.
Our group have studied fundamental propertiesof the conversion of carbon dioxide to methane byusing a hydrogen plasma [1]. In this report, theexperiment is conducted by changing the discharge
electrode configuration with magnets, discharge
current, and input gases flow rate.

production; γ (L/kWh).
Through the experiment, the gases mainly produced
were found to be CO and CH4. Dependences of CH4
yield and γ on input gas flow rate ratio H2/CO2 areshown in Figs.1 (a) and (b), respectively, with CO2
flow rate as a parameter. Here, the distance between
electrodes was 4.5 mm and the discharge current was
fixed at 0.7mA.

2. Experimental Apparatus and Methods
In this study, the apparatus is radially divided
into two (discharge and non-discharge) regions byorifices which make also a pressure difference.
Though we use two kinds of gases (hydrogen andcarbon dioxide), the discharge takes place only forhydrogen to prevent re-decomposition of theproduct of methane. H* and H2*, generated in thedischarge region, flow into the non-discharged
region like a shower to react with carbon dioxide
introduced into the non-discharge region. The
power supply provides a square-pulse voltage withrepetition frequency of 25 kHz. Cylindricalsamarium cobalt magnets are placed at both ends ofthe discharge region to confine hydrogen plasma.
All produced gases are sampled and analyzed by
FTIR, and finally evacuated by a scroll pump.

Fig.1 Input gas flow rate ratio dependence of(a) α×β/100 [%] and (b) γ [L/kWh].

3. Experimental Results
In the experiments, the following four items aredefined to evaluate the results. Decomposition ratioof CO2; α (%), CH4 selectivity; β (%), CH4 yield;
α×β/100 (%), and energy efficiency for CH4(a)(b)

In the case of H2/CO2 = 5, the value of α×β is
nearly constant (about 15%), but γ increases by
about 1.75 times when CO2 flow rate is changed
from 1 sccm to 2 sccm. From this result, it isthought that the discharge with large CO2 flow rateis effective for generating CH4 with less electricity
consumption.
4. Summary
Production of methane is investigated by carbon
dioxide reduction using a hydrogen plasma. Gases
produced were CO and CH4. From the results ofinput gases flow rate dependence, not onlyhydrogen flow rate but also total flow rate is a key
parameter to increase the energy efficiency for theCH4 production.
Reference[1] K. Arita, et al., 31th ICPIG, P1-104-pp.1-4(2013).