Catalytic performance of activated lignite chars on biomass tar cracking

The tar problems are the major obstacle to developing the biomass pyrolysis technology. The coal chars derived from in situ pyrolysis and/or partially gasification are a promising alternative tar cracking catalyst with great industrial application potential because of its cheap and easily available characteristics. This work investigated the application of lignite chars as catalysts for biomass tar decomposition. Raw lignite char was further gasified with CO2 for 5 min (GC5) and 15 min (GC15) and used as tar cracking catalysts. Effects of pyrolysis temperature, char/biomass mass ratio, and pore structure of char on the pyrolysis tar removal were studied. The results showed that increasing pyrolysis temperature and char/biomass mass ratio would promote tar decomposition. When using GC15 as catalyst, tar yield was as low as 0.10 wt% at the temperature of 850 degrees C and the mass ratio of 2. Gasification treatment increased the specific surface area of raw char from 284.1 to 342.7 m(2)/g (GC5) and 435.6 m(2)/g (GC15). Comparing the catalytic activity of lignite chars with commercial activated carbon demonstrated that mesopores were more influential than micropores in tar removal. In addition, water produced during biomass pyrolysis could in situ contribute to tar reforming and char gasification reactions. The results obtained in this study suggested that a cheaper coal char-based catalyst with excellent performance for biomass tar cracking could be achieved by combining with a coal gasification process and optimizing gasification conditions.

Automated summary

Tar problems are a significant barrier to the development of biomass pyrolysis technology. The use of coal chars derived from in situ pyrolysis and/or partial gasification as catalysts for tar cracking shows promise due to their low cost and easy availability. This study investigates the application of lignite chars as catalysts for biomass tar decomposition, and the results demonstrate that increasing pyrolysis temperature and char/biomass mass ratio promote tar decomposition, while water produced during biomass pyrolysis contributes to tar reforming and char gasification reactions.