Conversion of CO2 to CH4 by a Pulsed Hydrogen Plasma Shower Method

Aims: To suppress the emission of CO2 to the environment and to save the consumption of fossil fuels, CO2 was converted to CH4 by a newly developed hydrogen shower method with a hydrogen pulse plasma.

Study Design: Research study.

Place and Duration of Study: This study was performed for 2013 - 2015 at Department of Electrical Engineering, Tohoku University, Sendai, Miyagi, Japan.

Methodology: The experiment was carried out in a small chamber which was divided into two parts by an orifice disc of 3-mm-thickness stainless plate with one 0.5-mm-diameter hole at the center. Hydrogen gas was supplied from the left part, where hydrogen radicals of H* and H2* were produced by a pulse discharge. Hydrogen radicals were supplied through the orifice from the left part to the right part as a hydrogen radical shower. Carbon dioxide was directly supplied to the right reaction part, where CO2 was able to collide with hydrogen radicals and as a result CH4 was produced.

Results: Dependences of CO2 decomposition ratio α, methane selectivity β, and energy efficiency γ on hydrogen flow rate, electrode distance, discharge tube diameter, applied voltage, electrode diameter, and gas feeding type were investigated. Methane was produced from carbon dioxide by using a hydrogen radical shower method. Methane was only organic species produced from CO2. Only CO was detected as non-organic by-product. It was found that the decomposition ratio α, methane selectivity β, and energy efficiency γ were α = 32%, β = 37%, and γ = 1.6 L/kWh, respectively, under optimized condition at the flow rate ratio of CO2: H2 = 1:2, gap distance of d = 6 mm, and input power of Pin = 4.6 W (1.2 kV, 3.8 mA) with a use of 6-mm-diameter electrode.

Conclusion: Energy efficiency in our case was fairly improved. Hydrogen radical shower method was very effective for the conversion of CO2 to CH4.