In-depth comparison of the physicochemical characteristics of bio-char derived from biomass pseudo components: Hemicellulose, cellulose, and lignin

Abstract

Bio-char is a porous, recalcitrant, and highly aromatic carbon-rich material which can be widely used in energy, agriculture, environment, and material industry. In this study, a systematic comparison of the physicochemical characteristics of bio-char derived from three pseudo components of biomass (cellulose char (CC), hemicellulose char (HC), lignin char (LC)) was carried out at different pyrolysis temperatures (250, 350, 450, 550, 650, 750, and 850 °C). The results indicated wide variation in the physicochemical properties and quality of bio-char depending on different pyrolysis temperatures and biomass feedstock composition. Mass and energy yields of CC, HC, and LC decreased with the increase in the pyrolysis temperature, however, LC exhibited higher mass and energy yield than CC and HC because of its better thermal stability. With the increase in the pyrolysis temperature, the carbon content in CC, HC, and LC increased, while the contents of hydrogen and oxygen decreased, because the oxygen and hydrogen containing groups were easily fallen off at higher pyrolysis temperature based on the FTIR analysis. XRD analysis showed that the crystalline structure (Iα-triclinic and Iβ-monoclinic) of cellulose in CC and HC disappeared with the increase in the pyrolysis temperature above 350 °C. However, the graphite structure (002) and (101) in CC, HC, and LC increased. 13C NMR analysis indicated that the carbon structure of alkyl-C, O-alkyl-C, and carboxylic-C gradually decreased in CC, HC and LC as the pyrolysis temperature increased, while the aryl-C increased, indicating the formation of a more polyaromatic graphite-like structure at higher pyrolysis temperature. SEM results revealed that the volume of CC and LC reduced because of the significant particle agglomeration during pyrolysis process. However, the volume of HC sharply increased because of the transformation of hemicellulose into foam-like material at higher temperature. The lower values of mean absolute error strongly suggests that it is feasible to predict the properties (the contents of C, H, O, mass and energy yield) of real biomass derived bio-char based on the properties of three pseudo components derived bio-char.