Influence of CO2 atmosphere on property of biochar from pyrolysis of cellulose

CO2 is a reactive gas frequently used for converting biomass or biochar into carbon materials with developed structures at high temperatures. However, at the temperatures (400-700 degrees C) typically employed for pyrolysis, CO2 might also involve in pyrolysis and impact properties of the biochar formed, which was investigated in this study with cellulose as feedstock and N-2 or CO2 as the carrier gas. The results indicated that CO2 promoted the formation of biochar below 600 degrees C by suppressing cracking of biochar and enhancing secondary condensation of the volatiles. This reduced the size and abundance of the organics with pi-conjugated structures in the bio-oil. CO2 as an atmosphere produced the biochar with a carbon content higher than that produced in N-2 by 9.96%, and correspondingly the oxygen content was lowered by 36.68% in the biochar, as CO2 facilitated deoxygenation and dehydrogenation reactions during the pyrolysis. The presence of CO2 in the pyrolysis also made the biochar more aromatic and thermally more stable, which enhanced both energy yield and energy density of the process. As the heating temperature increases, CO2 as an atmosphere will significantly affect the evolution of the oxygen-containing function of the biochar surface.