Steam reforming of toluene as biomass tar model compound in a gliding arc discharge reactor

Non-thermal plasma is considered a promising and attractive approach for the removal of tars from biomass gasification to deliver a clean and high quality syngas (a mixture of H2 and CO). In this study, an AC gliding arc discharge (GAD) reactor has been developed for the conversion of toluene as a tar model compound using nitrogen as a carrier gas. The presence of steam in the plasma reaction produces OH radicals which open a new reaction route for the conversion of toluene through a stepwise oxidation of toluene and intermediates, resulting in a significant enhancement in both the conversion of toluene and the energy efficiency of the plasma process. The effects of steam-to-carbon (S/C) molar ratio, toluene feed rate and specific energy input (SEI) on the performance of the plasma steam reforming of toluene have been investigated. The optimal S/C molar ratio was found to be between 2 and 3 for high toluene conversion and energy efficiency. The maximum toluene conversion of 51.8% was achieved at an optimal S/C molar ratio of 2, a toluene feed flow rate of 4.8 ml/h and a SEI of 0.3 kWh/m3, while the energy efficiency of the plasma process reached a maximum (∼46.3 g/kWh) at a toluene feed flow rate of 9.6 ml/h and a SEI of 0.19 kWh/m3. H2, CO and C2H2 were identified as the major gas products with a maximum syngas yield of 73.9% (34.9% for H2 and 39% for CO). Optical emission spectroscopy (OES) has been used to understand the role of steam on the formation of reactive species in the plasma conversion of toluene. The possible reaction pathways in the plasma conversion of toluene have also been proposed by combined means of the analysis of gas and liquid samples and OES diagnostics

Plasma activation of CO₂ in a dielectric barrier discharge: A chemical kinetic model from the microdischarge to the reactor scales

The conversion of CO2 into value-added chemicals or fuels has attracted much attention over the past years. Plasma technology represents a highly promising alternative due to its non-equilibrium nature, deemed crucial for CO2 dissociation reactions. Gaining a deep understanding of the reaction mechanisms involved under plasma conditions is essential to improve the performance of such processes. Among other theoretical calculations, plasma chemical kinetic modelling constitutes a very suitable approach to address this challenge. In this work, a zero-dimensional model of a dielectric barrier discharge (DBD) reactor is applied to CO2 splitting, providing a novel approach for including experimental parameters as discharge power and flow rate based on the analysis of the different scales involved. The model choices is extensively discussed as regards experimental parameters, cross-sectional data and the chemical reactions considered. The predictions of the model are in good agreement with existing experimental data and therefore the model is considered valid to analyse the CO2 splitting reaction mechanism based on its results. It is concluded that the electron impact dissociation is the dominant process towards CO2 conversion, which could explain the low energy efficiency achieved since only ∼10% of the electron energy is consumed by mechanism. The remaining energy would be lost towards vibrational excitation not leading to CO2 dissociation in DBD reactors

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

AbstractIn 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.</jats:p