Changes in Biochar Functional Groups and Its Reactivity after Volatile–Char Interactions during Biomass Pyrolysis

In this study, biochars prepared under 500–900 °C interacted with cellulose volatiles at 500 °C, and the effects of volatile–char interactions on the changes of biochar functional groups and its reactivity were investigated. The Fourier transform infrared (FTIR) spectrum deconvolution method was introduced to semiquantitatively evaluate the changes in the functional groups, and the reactivity of biochar was characterized with thermogravimetry as well. The results indicated that the surface functional groups varied significantly for the biochars prepared under different temperatures, and the changing trend in biochar functional groups during volatile–char interactions also differed. The active surface functional groups of the lower-temperature biochar including the carboxyl and aliphatic C–H groups were largely consumed, while the surface of the higher-temperature biochar might absorb/deposit the infrared-active coke precursors. The reactivity of biochar decreased after volatile–char interactions due to the consumption of active functional groups and the dehydrogenation condensation of biochar during the interactions. The combustion reactivity of biochar was in positive correlation to the biochar activity during volatile–char interactions. The lower-temperature biochar with higher combustion reactivity was found to be more active during the volatile–char interactions as well.