Volatile-char interactions during biomass pyrolysis: Effect of char preparation temperature

In this study, the effect of char preparation temperature on the interactions between cellulose volatiles and acid-washed sawdust char was investigated experimentally on a fixed-bed pyrolysis system. The results indicated that significant volatile-char interactions did exist at the pyrolysis temperature of 500 °C as evidenced by the great changes in the composition and distribution of pyrolysis products. The oxygen-containing functional groups as well as the aromatic ring systems in the char both acted as active sites during the volatile-char interactions. The changes in chemical structure of biochar caused by the different preparation temperatures would notably affect the final products of cellulose pyrolysis. Meanwhile, the acid-washed sawdust char was still found to participate in the reaction process, lower temperature chars would have higher reactivities, and an obvious weight loss of char was also observed after interactions. In addition, volatile-char interactions significantly increased the yields of non-condensable gases, especially those of CO and CO2, while decreased the yield of condensable vapors. The introduction of biochar into cellulose pyrolysis could promote the ring scission of pyranoses as well as the decarbonylation/decarboxylation and dehydration reactions, thus caused the yields of anhydrosugars and monoaromatic compounds decreased and the yields of light ketones and acids increased.