Conversion of methane to higher hydrocarbons using nonthermal plasma

This study examines the conversion of methane to methanol and other higher hydrocarbons using nonthermal plasma generated by pulsed discharge. A coaxial-type plasma reactor with a glass dielectric interposed between the wire and the cylinder electrodes was used. A sharp-rising square wave pulsed voltage was used with a rise time of 50 ns and peak voltage of about 20 kV. Methane, oxygen and argon were mixed and fed to the reactor. The experimental results indicated that ethylene (C₂H₄), ethane (C₂H₆), methanol (CH₃OH), formaldehyde (HCHO), hydrogen (H₂), carbon monoxide (CO) and carbon dioxide (CO₂) were the major products of the plasma chemical reactions. Effect of the parameters gas residence time, input power, and partial pressure of argon were studied experimentally. The production efficiency and the selectivity of products (ratio of number of molecules converted from methane to products) were greatly dependent on these parameters. Particularly, it was found that the methanol and formaldehyde production have an optimum specific input power. The highest methanol and formaldehyde production efficiency and selectivity were achieved for a methane and oxygen ratio of 85/15, partial pressure of argon of 50 kPa and input energy of 12 kJ/L. This maximum production efficiency, of about 3.0 μL/J, and selectivity of 52% were obtained at the optimum conditions