The Decomposition of Methane in Glow Discharge at Liquid-Air Temperature

Abstract

The decomposition of methane in the glow discharge at liquid‐air temperature has been investigated under different experimental conditions. Contrary to the earlier conclusion of Brewer and Kueck that the reaction products are only hydrogen and ethylene, they are invariably found to be hydrogen, a polymer of composition (CH₂)_n, and ethane, ethylene, and acetylene, the last three resulting presumably from the mutual interaction of the primary active species CH₄⁺, CH₃⁺, CH₂⁺, CH⁺ formed from methane. In the absence of hydrogen, ethane predominates; in its presence, ethylene and acetylene proportions increase due, it is suggested, to the dehydrogenating action of atomic hydrogen. In the negative glow, the rate of methane decomposition is directly proportional to the current, and the electronic efficiency, i.e., the number of methane molecules decomposed per electronic charge, is ∼10 both for alternating and direct current. In the positive column, the rate is directly proportional to current only if pressure and field strength are constant; with constant current, the rate increases with pressure and field strength but in a manner which does not lend itself at present to a quantitative expression; the electronic efficiency is ∼0.2 for alternating and ∼0.6 for direct current. The results lead to the conclusion that a 60‐cycle alternating current discharge approximates closely to that with direct current. These may be explained by considerations of the electrical energies involved. No marked difference in reaction rate or products is observed by substituting iron for aluminum electrodes, or by variation in current density. A certain chemical activity might be attributed to the Faraday dark space.