Changes of biochar physiochemical structures during tar H₂O and CO₂ heterogeneous reforming with biochar

In order to investigate the detail changes of biochar physiochemical structures during the tar heterogeneous reforming with biochar under H₂O and CO₂ atmosphere, the experiment was carried out by a two-stage fluidized bed/fixed bed reactor. The physiochemical structures of biochar samples were analyzed by the SEM-EDX, XPS, FTIR and Raman. The results show that during the heterogeneous reforming of biomass tar with biochar, H₂O/CO₂ not only has a direct effect on the cracking of tar, but also indirectly affects tar H₂O/CO₂ reforming by changing biochar structures. The tar heterogeneous reforming in H₂O atmosphere takes place from the interior of biochar particles to the surface, while it only occurs on biochar surface under CO₂ atmosphere. H₂O increases the concentration of metal catalysts (mainly K and Ca) on the surface of biochar, while CO₂ have little effect on it. Tar is thermally decomposed and reformed on biochar under H₂O or CO₂ atmosphere, resulting in the increase of hydrocarbon C[sbnd]H. With the concentration of reforming agent increasing, the effect of H₂O on the surface oxygen-containing functional groups plays a more dominant role than that of CO₂. The increase of H₂O/CO₂ concentration greatly promotes the transformation of small aromatic ring system to large aromatic ring structure in biochar during tar reforming.