Catalytic Steam Reforming of Biomass-Derived Tar over the Coal/Biomass Blended Char: Effect of Devolatilization Temperature and Biomass Type

Catalytic tar steam reforming over char was conducted in a two-stage fixed-bed reactor. This reactor was divided into two zones: the devolatilization zone, where the biomass tar is released, and the tar reforming zone, where the tar and char are contacted and reformed into products. The temperature of the tar reforming zone was maintained at 800 degrees C for all experiments. The effects of devolatilization temperature (600, 700, and 800 degrees C) and biomass type (rice straw, RS, and Leucaena leucocephala wood, LN) on the catalytic performance of char during tar steam reforming were investigated. Biomass chars and coal/biomass blended chars (C/RS and C/LN) were prepared as the catalyst for tar steam reforming. Results revealed that compared with biomass chars, C/RS and C/LN performed a better catalytic activity in tar steam reforming, resulting in a higher carbon conversion into gas and a lower carbon conversion into tar. The main catalytic roles of the coal/biomass blended char can be explained by the improvement of the Brunauer-Emmett-Teller (BET) surface area during co-pyrolysis and the existence of alkali and alkaline earth metallic species (AAEMs), particularly K, as the stable silicate form. Considering the effect of devolatilization temperature, the tar released at 700 degrees C can be mostly converted among all types of char. Tars containing the mixture of phenolic compounds (i.e., phenol and methyl phenol) and aromatic compounds (i.e., naphthalene and methyl naphthalene) were favorable to reform over the char surface to achieve the relatively high tar conversion. In addition, LN tar was easier to convert than the RS tar in both cases of with and without char because of the lower proportion of a stable aromatic compound. The outcome of this study can be beneficial for the design and operation of the tar removal process during biomass gasification using the low-cost carbon-based catalyst.