Exchange of organics with homogenous volatiles shapes nature of biochar of varied aspects

During pyrolysis of biomass, contact between volatiles and nascent biochar is inevitable, and the volatile-char interactions are highly dependent on not only composition of volatiles but also surface property of biochar. Herein, the potential interactions of the biochar produced at varied temperatures (500, 600 or 700(degrees)C) with the volatiles generated at 500(degrees)C from pyrolysis of poplar sawdust were investigated, aiming to probe the exchange of organics on the varied biochar from the interactions. The results showed that biochar-600 or biochar-700 catalyzed cracking of phenols, sugars and sugar-derivatives to generate more gases. Biochar-500, in comparison, catalyzed aromatization of volatiles to form more phenols of single or multiple rings and enhanced tar content in bio-oil, relating to catalytic effects of its abundant oxygen-containing species. During the catalysis, some organics on surface of the biochar were removed while some carbonaceous deposit from the volatiles deposited, resulting in relative increase of ash content, reduced thermal stability, filling of micropores and formation of fragmented morphology of the spent biochar. The in-situ IR characterization showed that biochar500 could maintain higher abundance of the intermediates bearing oxygen-containing species, facilitating their subsequent condensation, while biochar-700 catalyzed rapid cracking of these oxygen-containing organics.