Abstract

CO2 can be used to activate biomass for production of activated carbon at high temperatures (usually above 700 °C). At typical pyrolysis temperatures, CO2 might also involve in biomass pyrolysis, which was investigated via pyrolysis of lignin at temperatures from 400 to 700 °C in N2 and CO2 atomsphere, respectively. The results suggested that CO2 interfered with the pyrolysis process, facilitating formation of bio-oil and biochar but not gases via suppressing further gasification of volatiles. This reserved more mono-ring phenolics in bio-oil and also formed more heavier phenolics through secondary condensation routes. As for biochar, CO2 enhanced the aromatization process, generating the carbon-rich biochar of higher heating value. The in-situ characterization of the functionalities of biochar during pyrolysis suggested that CO2 accelerated removal of the aliphatics like -OH, -C-H, CO, and C-O-C. This rendered the biochar of hydrophobic surface but less fragmentized structures than that obtained in N2.

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