Paper PS-TuP29
Synthesis of Small Organic Molecules from a CO₂/CH₄ Mixture by Dielectric Barrier Discharge (DBD): Gas Composition and Power Effect

Tuesday, October 29, 2013, 6:00 pm, Room Hall B

Carbon dioxide is usually considered as an end-product in chemistry because of its high stability. Due to the high quantities of CO₂ produced, its conversion received more and more attention in the recent years [1]. The transformation of CO₂, with CH₄ as second reactant and using atmospheric plasma technology shows that in good conditions, both gases can be converted into valuable products [2-3].

The conversion of CO₂/CH₄ mixtures was performed using a dielectric barrier discharge atmospheric plasma using Argon as the main plasmagen gas. Gas Chromatography was used to determine the composition of the gas after plasma treatment and this treatment was carried out in a new type of reactor developed in the laboratory. We demonstrated that the synthesis of syngas (CO and H₂) and small organic molecules such as C₂H₆, C₂H₄ is totally possible in this type of discharge [Fig. 1].

The study is focused on the effect of the plasma parameters on the CO₂ and CH₄ conversion rate. The parameters which are evaluated in this work are the ratio of CO₂/CH₄ flow rates and the power supplied.

We demonstrated that the CO₂/CH₄ ratio in the mixture has an important impact on the conversion rate. However, there is no real interaction between active species of these two gases since oxygenated organic compounds have only been detected at trace amounts. Nevertheless, the absence of oxygen after CO₂/CH₄ plasma is always obtained, suggesting that atomic oxygen is consumed in a plasma which contains only a few quantity of CH₄.

On the other hand, the effect of the power was clearly visible, showing a linear increase for both the CO₂/CH₄ conversion rates and the production of syngas according to the supplied power [Fig. 2]. This suggests that the number of electrons circulating between the electrodes has a huge impact on the conversion rate.

The detection of emitting species generated in the plasma (such as CO₂⁺ and CO₂ from the Fox, Duffendack and Barker’s system, different peaks of H, OH, O…) was also carried out via optical emission spectroscopy (OES).

Finally, we observed a different effect of two plasmagen gases (Argon and Helium) on the conversion of CO₂ and CH₄. Indeed, the conversion of CH₄ is better when He is used as carrier gas compared to the use of Ar, whereas we observed an opposite effect for the conversion of CO₂.

[1] T. Sakakura, J-C. Choi and H. Yasuda, Chem. Rev. 107 (2007) 2365−2387

[2] X. Tao, M. Bai, X. Li, H. Long, S. Shang, Y. Yin and Xiaoyan Dai, Progress in Energy and Combustion Science 37 (2011) 113-124

[3] A-J. Zhang, A-M. Zhu, J. Guo, Y. Xu and C. Shi, Chemical Engineering Journal 156 (2010) 601–606