Impacts of CO2 atmosphere on property of the biochar from pyrolysis of lignin.

CO 2 can be used to activate biomass for production of activated carbon at high temperatures (usually above 700 °C). At typical pyrolysis temperatures, CO 2 might also involve in biomass pyrolysis, which was investigated via pyrolysis of lignin at temperatures from 400 to 700 °C in N 2 and CO 2 atomsphere, respectively. The results suggested that CO 2 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, CO 2 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 CO 2 accelerated removal of the aliphatics like -OH, -C-H, C O, and C-O-C. This rendered the biochar of hydrophobic surface but less fragmentized structures than that obtained in N 2. [Display omitted] ● CO 2 interferes with formation of volatiles and biochar in lignin pyrolysis. ● CO 2 enhances the formation of biochar and bio-oil at the expense of gases. ● CO 2 suppress cracking of volatiles into gas but promotes secondary condensation. ● CO 2 aids removal of aliphatic structures, making biochar of hydrophobic. ● CO 2 promotes aromatization, producing carbon-rich biochar of higher energy yield. [ABSTRACT FROM AUTHOR]