Removal of Toluene as a Biomass Tar Surrogate in a Catalytic Nonthermal Plasma Process

In this study, a packed-bed dielectric barrier discharge (DBD) reactor was developed to investigate the removal of biomass tar in a fuel gas atmosphere. Toluene was used as the tar surrogate, and the catalyst used was a Nickel-based catalyst (Ni/gamma-Al2O3) because of its high activity and low cost. In addition, another two kinds of packing materials (glass pellets and gamma-Al2O3 pellets) were employed to make a comparison with the Ni/gamma-Al2O3 catalyst. The research has focused on the removal efficiency of toluene and the effects of carrier gas, reaction temperature, Ni loading, and concentration of toluene. The results indicated that two supplementary packing materials could not realize an effective removal of toluene. On the contrary, Ni/gamma-Al2O3 combined with plasma showed a significant synergetic effect and hence a great toluene removal potential. On one hand, the removal efficiency initially decreased within the temperature range of 200-300 degrees C and then significantly increased within the temperature of 300-400 degrees C during plasma-catalytic process. At the optimal temperature of 400 degrees C, the toluene removal efficiency could reach the maximum values of 80.2%, 91.7%, and 100.0% when the Ni loading was 3, 5, and 10 wt %, respectively. On the other hand, an increase in the inlet toluene concentration slightly reduced removal-efficiency but increased the energy efficiency, reaching the highest value of 16.8 g/kWh. The introduction of plasma enhanced the methanation reaction of the fuel gas occurring in the catalytic process, which was favorable at high temperatures. Based on these findings, the mechanisms and pathways of toluene destruction in the plasma-catalytic process were proposed and elucidated.