A molecular beam mass spectrometric investigation of plasma assisted oxidation and pyrolysis of methane

A new experimental setup coupled a dielectric barrier discharge flow reactor with a molecular beam mass spectrometer (MBMS) was developed for detailed species diagnostics on plasma assisted oxidation and pyrolysis system. The mixture of methane and oxygen diluted by argon was selected as the feed gas. The MBMS technique with photoionization or electron ionization provided access to not only stable molecules but also highly reactive species involved in the methane plasma, including ions, excited species and radicals. The qualitative identification of various components is achievable based on the information of exact mass and ionization energy. The corresponding quantitative information can be obtained by integrated ion signal and ionization cross-sections. The experimental results showed that oxidation and pyrolysis of methane were triggered by plasma at room temperature. For the pyrolysis case, hydrocarbons ranging from C2 up to C5 were detected. While for the oxidation case, the formation of acetaldehyde and ketene together with formaldehyde and methanol was observed. The parameters of applied voltage and oxygen concentration in the feed gas were found to have effective control on the reactivity and selectivity of the plasma respectively. The degree of methane consumption is the largest when the oxygen concentration in the feed gas is less than half of that at stoichiometric conditions and a higher voltage is applied. (C) 2018 The Combustion Institute. Published by Elsevier Inc. All rights reserved.