Periodic Reporting for period 1 - GlidArc (Towards a fundamental understanding of a gliding arc discharge for the purpose of greenhouse gas conversion into value-added chemicals)
Reporting period: 2015-06-22 to 2017-06-21
The accuracy of the modelling results of plasma-based CO2 conversion critically depends on the accuracy of the assumed input data. This is especially true for the cross section of electron impact dissociation, but it is not clear from literature which excitation channels effectively lead to dissociation. Therefore, this work discusses the effect of different electron impact dissociation cross sections reported in literature on the calculated CO2 conversion, for a dielectric barrier discharge (DBD) and a microwave (MW) plasma. Our calculations indicate that the choice of this cross section is crucial for the DBD, where this process is the dominant mechanism for CO2 conversion. Comparison is made to experimental data to elucidate which cross section might be the most realistic. (See Fig.1). This work also provides important reference for modelling of the gliding arc and is published in .
2. Study on the effect of excited states and ion kinetics on the critical breakdown of hot CO2
Understanding the dielectric properties of a hot gas is required for various practical applications, including a gliding arc used for CO2 conversion. The gliding arc discharge reignites itself at the shortest electrode gap separation, where a residual warm environment facilitates the start of a new cycle. This work discusses some overlooked physics and clarifies inaccuracies in the evaluation of the effective ionization coefficients and the critical reduced breakdown electric field of CO2 at elevated temperature, considering the influence of excited states and ion kinetics. Our results indicate that the excited species lead to a greater population of high-energy electrons at higher gas temperature and this affects the Townsend rate coefficients, but the critical reduced breakdown electric field strength of CO2 is only affected when also properly accounting for the ion kinetics (See Fig.2). This work is published in and honorably recommended as a Featured article and selected as a LabTalk.
3. Study on gliding arc based CO2 conversion
In order to reduce the computation time, we developed a non-quasineutral plasma description which is firstly evaluated for reliability and applied to a one-dimensional as well as a two-dimensional gliding arc model (See Fig.3) and validated with experiments. Our calculated values of the electron number density in the plasma, the CO2 conversion and energy efficiency show reasonable agreement with the experiments, indicating that the model can provide a realistic picture of the plasma chemistry. As the model provides a realistic picture of the plasma behaviour, we use it first to investigate the plasma characteristics, which is necessary to understand the underlying mechanisms. Subsequently, we perform a chemical kinetics analysis, to investigate the different pathways for CO2 loss and formation. Based on the revealed discharge properties and the underlying CO2 plasma chemistry, the model allows us to propose solutions on how to further improve the CO2 conversion and energy efficiency by a gliding arc plasma. This work is published in:
S Kolev, S Sun, G Trenchev, W Z Wang, H Wang, 2016 Plasma Process. Polym. 14,1600110; W Z Wang, A Berthelot, S Kolev, X Tu, A Bogaerts, 2016 Plasma Sources Sci. Technol. 25, 065012;
A Bogaerts, A Berthelot, S Heijkers, S Kolev, R Snoeckx, S Sun, G Trenchev, K Van Laer and W Z Wang, 2017 Plasma Sources Sci. Technol. 26, 063001;
M Ramakers, G Trenchev, S Heijkers, W Z Wang and A Bogaerts, 2017 ChemSusChem 10, 2642-2652; W Z Wang, D H Mei, X Tu, A Bogaerts, 2017 Chem. Eng. J 330, 11–25.
4. Study on nitrogen fixation by gliding arc plasma
Gliding arc plasma also has great potential in nitrogen fixation, but little is known about the underlying mechanisms. Therefore, we developed a chemical kinetics model for a gliding arc reactor for nitrogen oxide synthesis. Experiments are carried out to validate the model. We use the model to investigate the reaction pathways for the formation and loss of NOx. The results indicate that vibrational excitation of N2 in the gliding arc contributes significantly to activating the N2 molecules, and leads to an energy efficient way of NOx production, compared to the thermal process. Based on the underlying chemistry, the model allows us to propose solutions on how to further improve the NOx formation by gliding arc technology. This work is published in and selected as very important paper, for the cover profile story and as cover figure of the journal (see Fig.4).