The present investigation concentrated on the oxidative conversion of methane in an atmospheric pressure, nonthermal plasma formed by negative dc corona discharge. The corona creates negatively charged oxygen species, which react with methane and form methyl radicals. The products contain C2 hydrocarbones (acetylene, ethylene and ethane) and other carbonaceous species including carbon deposits, CO2, H2O and
syngas (H2+ CO). The conversion. and
selectivity of desired C2 products depend on the residence time (total feed flowrate) and the methane to oxygen ratio in the feed. All the experiments are conducted at room temperature and only with dc negative corona discharge (i.e, no oven or other heat source is used), and the temperature increases slightly (100-200 0 C) due to the
exothermic reactions and the discharge itself. According to the results: Methane conversion increases significantly with decreasing flowrate or increasing residence time, but C2 hydrocarbon selectivity
decreases slightly and therefore, the yield of
C2 hydrocarbons increases significantly. Moreover, increasing the methane to oxygen ratio at a constant flowrate leads to an increase in C2 selectivity. Also, the methane
conversion and C2 yield go through a maximum at a methane to oxygen ratio of 5. The largest C2 yield is 23.1 % with 35%
methane conversion and 66% C2 selectivity at a flowrate of 5.5cm3/min (CH4/O2=5, without any diluent), when the dc negative
Corona with 4mA input power was used. The results suggest that dc gas discharge technique is a promising method for direct conversion of methane into more valuable hydrocarbons.
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