Abstract:Corn stover is a major agricultural waste, it is abundantly available across China, and its annual production was about 200 million tons in recent years. However, there were limited reports on hydrothermal carbonization of corn stover in the past few years. Thus, corn stover was chosen as the precursor for hydrothermal conversation of the present work. To explore the hydrothermal carbonization process of corn stover and chemical, energetic properties of hydrochar, corn stover was hydrothermally treated at different reaction temperatures from 180℃ to 290℃ for 8h. The results showed that with the increase of reaction temperature, the hydrochar yield was reduced from 71% at 180℃ to 36% at 290℃, and the carbon content of hydrochars was increased from 44.86% of feedstock to 72.36% at 290℃. Simultaneously, when the reaction temperature was increased, the oxygen content of hydrochars was obviously decreased, which was reduced from 44.2% of feedstock to 15.36% at 290℃, thus energy density of hydrochars was clearly increased. When the reaction temperature was up to 290℃, the hydrochar exhibited coal-like oxygen/carbon and hydrogen/carbon atomic ratios, and the higher heating value reached 29.79MJ/kg. Compared with the feedstock, functional group of hydrochars was decreased when the reaction temperature was enhanced. However, the characteristic peaks of C=C, C=O and aromatic functional group in Fourier transform infrared (FTIR) spectra were strengthened. The thermal stability of hydrochars was also increased in thermogravimetry (TG) analysis. Elemental components and FTIR analyses suggested that corn stover during hydrothermal carbonization mainly underwent dehydration and decarboxylation reactions when the operating temperature was below 230℃, however, the process was governed primarily by condensation polymerization and aromatization when the temperature was above 230℃.
