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Plasma chemical conversion of methane by pulsed electron beams and non-self-sustained discharges

Investigations of methane conversion in atmospheric-pressure mixtures of various composition and temperature, irradiated by pulsed nanosecond electron beams and non-self-sustained discharges initiated by electron beams, were carried out. It was shown that during direct conversion at room temperature, the energy cost of the conversion of one CH4 molecule (5.6 eV molecule−1) was commensurate with that obtained in the experiments with the use of continuous electron beam. The main products of direct conversion were hydrogen and ethylene. If a small amount of oxygen was present in the mixture, methanol was added to the conversion products, which in turn decomposed into CO, CO2 and H2O. The results of numerical simulations and experiments were basically the same. The use of a non-self-sustained discharge increased the degree of direct conversion of methane, but the energy cost of conversion also increased. The main products of carbon dioxide conversion of CH4 (dry reforming) under the action of pulsed electron beam at room temperature were CO, H2, C2H6, and carbon. Energy cost of conversion (12 eV molecule−1) was about two times higher than in the case of direct conversion of methane. However, the use of pulsed electron beam for dry reforming turned out to be energetically more efficient than the use of the most types of discharges. The main products of CH4 oxidative conversion by pulsed electron beam were H2, C2H6, and C2H4. At room temperature, the energy cost of methane conversion without a catalyst was 9 eV molecule−1, whereas the use of Ni catalyst resulted in a seven-fold increase, and the use of NaOH/CaO one—in a 14-fold increase in the conversion efficiency compared to irradiation without a catalyst. When the temperature of the catalysts rised to 623 K, the conversion efficiency increased by another four times. The processes in electron-beam plasma that provide the implementation of the main mechanisms of methane conversion are also discussed in the paper.