Catalytic Cracking Of Biomass Using Char-based Catalyst In A Two-stage Fixed-bed Reactor

For the purpose of inhibiting the tar formation and improving hydrogen production, a two-stage fixed-bed reactor was used to investigate the secondary cracking of the primary volatiles derived from pyrolysis of pine wood. The study includes three parts as follows.First, the catalytic effect of wood char and other chars on the pyrolysis volatiles was studied. It was found that the wood char (charcoal) was catalytically active for the tar cracking at 500-600℃, which were mainly oxygenated compounds; while at 650-700℃, the thermal effect became a dominant mode of the tar cracking. And above 600℃, the autogenerated steam gasified the charcoal, resulting in a marked increase in the yield of gaseous product and a significant change in the gas composition. It was found that an anthracite char, a bituminous coal char, a lignite char and graphite also behaved with catalytic activities towards the tar cracking, but only L-char showed more significant catalytic effect.Second, the K2CO3-loaded charcoals were used as catalyst. Whether the catalysts were added in an impregnation way or in a dry mixing way, they all had great effects on pyrolysis bio-oil derived from pine wood, especially the impregnation way, and the loading of catalyst had great influence on the catalytic capability. It was observed that potassium carbonate promoted the decomposition of phenols and naphthalenes even at a lower temperature below 725℃. At a higher loading of K2CO3, the charcoal was gasified by the autogenated steam to a higher degree.Third, the Ni or biometallic Ni/Ca-loaded charcoals were used as catalyst. It was found that the Ni-loaded charcoal had a high catalytic activity for tar cracking, especially for naphthalenes decomposition and charcoal gasification. We also studied the charcoal/Ni/Ca composite catalysts, it was observed that the catalytic effect was less than the charcoal/Ni catalyst. SEM analysis shows that Ni was dispersed finely on the char surface for the Ni-loaded charcoal, but metal particles showed poorer dispersion in the charcoal/Ni/Ca composite catalyst.