Experimental investigation of alumina and quartz as dielectrics for a cylindrical double dielectric barrier discharge reactor in argon diluted methane plasma

► Regime of the DBD in a methane/argon mixture is sub-filamentary. ► Rate of conversion of methane in argon is higher than in pure methane. ► Methane conversion in argon in the DBD does not produce soot. ► Greater dielectric permittivity increases discharge power and rate of conversion of methane. Non-oxidative conversion of methane into higher hydrocarbons was studied under argon, at atmospheric pressure, in the non-equilibrium environment of the dielectric barrier discharge (DBD). In this study, two concentric dielectric barriers, a short plasma zone with a wide discharge gap have been used to investigate methane conversion in reactors employing alumina and quartz as dielectrics. As energy transfer to the plasma in a DBD system is determined by the capacitive properties of the dielectrics, discharge energy varies between quartz and alumina reactors at the same applied voltage and the conversion of methane and yield of hydrogen therefore also varies between quartz and alumina reactors. Although the dielectric strength of alumina is lower than that of quartz, this disadvantage is offset by increased dielectric permittivity resulting in greater dielectric capacity, in turn leading to increased gap voltage and associated higher conversion rates. Methane conversion was performed in a majority argon carrier. The addition of methane in low concentrations results in a modified argon discharge, one operating in the transition region between homogeneous glow and filamentary discharge regimes. Under these conditions, methane conversion rates were observed to vary with methane concentration, applied voltage and residence time. Experimental results are presented and interpreted in terms of ionization phenomena, metastable species activity and discharge power.