Nitrogen-doped porous biocarbon materials originated from heavy bio-oil and their CO₂ adsorption characteristics

To realize the high -value utilization of biocoke derived from heavy bio-oil, N -doped porous biocarbon materials were prepared through co -pyrolysis of biocoke with urea and KOH activation, and their physiochemical structures and CO2 adsorption capacity were analyzed. Compared with direct heat treatment of biocoke at 550 degrees C, Ndoping at the same temperature would reduce the biocarbon yield and block its pores, but the pore structure could be recovered through further heating to 800 degrees C. KOH activation at 800 degrees C could produce highly porous biocarbon materials with BET surface areas of 1710.20-3361.45 m(2)/g in the expense of yield reduction. The mass ratio of KOH to biocarbon material significantly affect its pore formation and distribution. Moderate activation (ratio of 2, 550NBC-800-2) could generate more micropores, over activation (ratio of 3 and 4, 550NBC-800-3/4) could further increased its total surface area, but resulted in the damage/merging of micropores to mesopores. KOH activation was found to increase the O-containing groups and decrease the large ring systems in the biocarbon as well, but the etching of KOH would lead to the releasing of N previously existed/doped in the biocarbon. The CO2 adsorption performance of the biocarbon material was closely related to its pore structure and surface N -doping. At a high CO2 pressure (1 bar), the CO2 adsorption capacity of biocarbon materials was more dependent on its micropore areas. But at a low CO2 pressure (0.15 bar), N -doping, especially to form more N-5 in biocarbon, was observed to be more important than its micropores.