Conversion of Methane in Plasma of Pulsed Nanosecond Discharges

Abstract

Investigations of methane conversion in mixtures CH4–CO2 and CH4–O2 of various composition, pressure, and temperature processed by pulsed nanosecond discharges of various types and durations were carried out. The main products of carbon dioxide conversion (dry reforming) of methane were carbon oxide (CO), hydrogen (H2), ethane (C2H6), and carbon (C). Gas mixture treatment by discharges with pulse duration 1, 5, and 15 ns demonstrated that the energy efficiency of carbon dioxide conversion of methane depends on the power of the discharge pulse. Dependencies of CH4 conversion on gas mixture pressure for spark, diffuse, and corona discharge showed that the most efficient dry reforming of methane occurred in spark discharge with pulse duration of 15 ns at a pressure of 1 atm. with energy cost of conversion of one CH4 molecule being 15 electron-volts per molecule. The main products of oxidative conversion of methane were ethane and ethylene C2H4. It was shown that the catalyst NaOH/CaO was considerably more effective than nickel catalyst, and the use of it allowed to increase methane oxidative conversion degree by more than an order of magnitude. It was found that CH4 oxidative conversion and C2H6 yield were growing up with an increase in temperature, whereas C2H4 yield began to decrease at a temperature more than 420 K. The most efficient oxidative conversion of methane was realized in spark discharge in the presence of NaOH/CaO catalyst with energy cost of conversion of one CH4 molecule being 50 electron-volts per molecule.