Reactivity of cellulose during hydrothermal carbonization of lignocellulosic biomass

Hydrothermal carbonization (HTC) of pure cellulose (CE) and birchwood (BW) samples was carried out at temperatures between 160 and 280 degrees C, 0.5 h residence time and biomass-to-water ratio 1:5, to investigate the reactivity of cellulose in lignocellulosic biomass. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) showed that the CE samples remained unaltered at temperatures up to 220 degrees C, but were significantly decomposed at 230 degrees C producing a thermal recalcitrant aromatic and high energy-dense material. FTIR showed that dehydration and aromatization reactions occurred at temperature equal or higher than 230 degrees C for the CE samples while a similar increase in aromatization for the BW hydrochars was evident only at temperatures equal or higher than 260 degrees C. Acid hydrolysis, TGA and FTIR suggested that a higher thermal resistance of naturally occurring cellulose in BW (when compared to CE sample) could be related to a `protecting shield' offered by interlinked lignin in the plant matrix.