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| Discharge Characteristics and Reaction Performance of CH4 Reforming with CO2 in Dielectric Barrier Discharge with Segmented Electrodes |
| Sun Minjie, Fu Junhui, Liu Honglin, Mei Danhua, Fang Zhi |
| College of Electrical Engineering and Control Science Nanjing Tech University Nanjing 211816 China |
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Abstract CH4 reforming with CO2 is an effective way to convert the main two greenhouse gases (CO2 and CH4) into value-added chemicals. However, the traditional methods for this reaction have limitations in terms of operating conditions, reactant conversion and product selectivity, catalyst preparation and activity maintenance, due to its highly endothermic characteristics. Non-thermal plasma, as a novel molecule activation approach, has provided new routes for CH4 reforming with CO2. Dielectric barrier discharge (DBD) has attracted most attention for this process due to its simple structure, the potential plasma-catalysis synergy, and successful experience in industrial applications. The performance of this process is significantly affected by the reactor structure, and it has been demonstrated that using DBD with segmented electrodes is one approach to adjust the reactant conversion, product distribution and energy efficiency of this process, but the influence mechanism of the number of segmented electrodes and the distance between adjacent electrodes on the above performance parameters is still unclear. To deal with these issues, CH4 reforming with CO2 has been performed in DBD reactors with segmented electrodes. The discharge characteristics and the reaction performance are investigated in detail under different conditions (e.g., the number of segmented electrodes and the distance between adjacent electrodes).
The DBD reactors are self-designed with quartz tube, stainless-steel rod and mesh, which functions as the dielectric tube, high-voltage electrode and low-voltage electrode, respectively. The low-voltage electrode is grounded via a reference capacitor. In order to investigate their respective influences, the number of segmented electrodes is set as 1, 2, 3 and 4 when the total length of the low-voltage electrode is fixed at 120 mm; while the distance between adjacent electrodes is set as 10 mm, 20 mm, and 30 mm when the number of segmented electrodes is 2. A custom-built AC power source is used to drive the DBD reactors. The applied voltage, the total current and the voltage across the reference capacitor are respectively sampled by a Tektronix high-voltage probe, a Pearson current coil monitor and a Pintech differential probe, and saved using a Tektronix digital oscilloscope. The electrical characteristics are obtained by analyzing the voltage-current wave forms and the corresponding Lissajous figure. The temperature of the outer electrode is measured by a Fotric infrared thermometer. The discharge characteristics are discussed from the perspective of electrical characteristics and temperature characteristics. The reactants and gaseous products are analyzed by a Techcomp gas chromatography (GC). The reaction performance is evaluated by the parameters of reactant conversion, product yield and selectivity, and energy efficiency.
The following conclusions can be drawn: (1) Increasing the number of segmented electrodes or extending the distance between adjacent electrodes has little effect on the discharge duration time, but enhances the edge effect, which expands the discharge volume and shows obvious influence on the charge generation and transfer. There exists an optimum number of segmented electrodes that enables the DBD reactor to have the strongest capability of charge generation and transfer. (2) The outer surface of the DBD reactor shows the uniform temperature distribution when using the segmented electrodes, and no local high temperature areas are observed, which is beneficial to the long-term stability of reaction. With the combined effect of edge effect, residence time and charge generation and transfer ability, increasing the number of segmented electrodes or extending the distance between adjacent electrodes enhances the conversion of CO2 and CH4. (3) Increasing the number of segmented electrodes improves the yield and selectivity of H2 and CO, but has little effect on that of other products. While extending the distance between adjacent electrodes enhances the selectivity of C2H6, but has insignificant effect on that of H2, CO, and other hydrocarbons. (4) When the number of segmented electrodes is fixed at 2, extending the distance between adjacent electrodes decreases the discharge power and the capability of charge generation and transfer, but enlarges the discharge volume and increases the residence time of the reactant in the plasma reaction volume, which improve the possibility of collision between reactant molecules and reactive species, consequently promoting the plasma reaction and increasing the energy efficiency. The maximum total energy efficiency for converting reactants 0.334 mmol/kJ was obtained when the electrode spacing was 30 mm in the DBD reactor with 2 segmented external electrodes.
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Received: 29 December 2022
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2023, Vol. 38 
