Study of steam reforming of toluene used as model compound of tar produced by biomass gasification

Catalytic elimination of tars contained in the produced gas is crucial to improve the process of biomass gasification in circulating fluidized bed gasifier—permitting gas cleanup and increasing syngas (CO + H2) yield. Natural olivine, often used as primary catalyst, was previously improved by Ni addition. The catalyst Ni/olivine developed and tested in pilot scale showed very good performances in tar reduction and increasing H2 content in the produced gas. To understand the tar decrease, a model study in laboratory scale fixed bed reactor of toluene steam reforming is presented here. The toluene conversion obtained with Ni/olivine at 560 °C is the same as with olivine at 850 °C. Moreover, with Ni/olivine only CO, CO2 and H2 are produced but with olivine 20% of benzene, polyaromatics and methane are formed additionally to the previous gases. Carbon deposit characterised by TEM and TPO is negligible at 800 °C due to the specific Ni–olivine interactions. A kinetic model established, taking into consideration a zero order for water and first order for toluene gives the kinetic parameters (Ea = 196 kJ mol−1 and A(k′) = 3.14 × 1013 m3 (kgcat h)−1) comparable to those reported for steam reforming of benzene or tars on commercial nickel catalysts.