Investigation of Property of Biochar in Staged Pyrolysis of Cellulose

Pyrolysis involves heating of a feedstock from room temperature in an oxygen-deficient atmosphere, during which the heating at low temperature could potentially change the structure of feedstock and impacted the subsequent pyrolysis. In this study, the initial torrefaction of cellulose at 170, 260 and 350 degrees C and the subsequent pyrolysis at 600 degrees C was conducted, aiming to probe effect of the low-temperature pretreatment on evolution of the pyrolysis products, especially biochar. The results showed that the cellulose crystals could be partially destroyed at 260 degrees C and completely removed at 350 degrees C, and meanwhile aromatization reactions took place. This favored the formation of gases through further aromatization in the pyrolysis at 600 degrees C, but generated less light organics, especially for the pretreatment at 350 degrees C. The pretreatment at 260 degrees C, however, facilitated formation of anhydrate sugars and organics with pi-conjugated structures. In addition, the torrefaction also enhanced the graphitization degree of biochar obtained at 600 degrees C through promoting the deoxygenation reactions, generating the biochar with higher C/O ratio, higher heating value, higher thermal stability and hydrophobicity. Besides, the torrefaction also significantly reduced formation of the reaction intermediates with aliphatic structures and the oxygen-containing functionalities such as-OH, C--O and C-O-C in/on the biochar.