Plasma reforming of toluene as a model tar compound from biomass gasification: effect of CO2 and steam

In this study, plasma reforming of toluene as a tar model compound from biomass gasification has been carried out using an AC gliding arc discharge reactor. The influence of steam and CO2 addition on the reforming of toluene has been evaluated. The results show that the highest toluene conversion (59.9%) was achieved when adding 3 vol% CO2 at a toluene concentration of 16.1 g/Nm3 and a specific energy input of 0.25 kWh/m3. Further increasing CO2 concentration to 12 vol% decreased the conversion of toluene. The presence of steam in the plasma CO2 reforming of toluene creates oxidative OH radicals which contribute to the enhanced conversion of toluene and energy efficiency of the plasma reforming process through stepwise oxidation of toluene and reaction intermediates. Hydrogen and C2H2 were identified as the major gas products in the plasma reforming of toluene without CO2 or steam, with a yield of 9.7% and 14.5%, respectively, while syngas was the primary products with a maximum yield of 58.3% (27.5% for H2 and 30.8% for CO) in the plasma reforming with the addition of 12 vol% CO2. The plausible reaction pathways and mechanism in the plasma reforming of toluene have been proposed through the combination of the analysis of gas and condensed products and spectroscopic diagnostics.