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 CH. 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.