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

CO 2 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 °C) typically employed for pyrolysis, CO 2 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 CO 2 as the carrier gas. The results indicated that CO 2 promoted the formation of biochar below 600 °C by suppressing cracking of biochar and enhancing secondary condensation of the volatiles. This reduced the size and abundance of the organics with π-conjugated structures in the bio-oil. CO 2 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 CO 2 facilitated deoxygenation and dehydrogenation reactions during the pyrolysis. The presence of CO 2 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, CO 2 as an atmosphere will significantly affect the evolution of the oxygen-containing function of the biochar surface. [Display omitted] • Impact of CO 2 on properties of biochar in pyrolysis of cellulose was studied. • CO 2 enhances formation of biochar but not the π-conjugated organics in bio-oil. • CO 2 suppresses cracking while enhances secondary condensation of volatiles. • CO 2 facilitates deoxygenation/dehydrogenation to produce carbon-rich biochar. • Evolution of functional groups of biochar is affected by N 2 /CO 2 atmospheres. [ABSTRACT FROM AUTHOR]