Upgrading the characteristics of biochar from cellulose, lignin, and xylan for solid biofuel production from biomass by hydrothermal carbonization

In this study, hydrothermal carbonization of the main lignocellulosic components was investigated as a method of renewable solid biofuel production from biomass. Hydrothermal carbonization of cellulose, xylan, and lignin was experimentally conducted between 150 °C and 280 °C, and the chemical and fuel properties of the resulting biochars were investigated. The properties of each of the three biomass components were greatly improved by hydrothermal carbonization and were similar to coal-like fuel substances; an increase in fixed carbon and carbon contents was also observed. Furthermore, by assessing carbon recovery and energetic retention efficiency, we could establish the optimum condition for hydrothermal carbonization of biomass to produce energy. The C/O and C/H ratios of all of the obtained biochars were decreased and found to be similar to those of lignite and sub-bituminous coal. The calorific values of the biochars were between 23–26 MJ/kg at a reaction temperature of 220 °C. The results of this study indicate that hydrothermal carbonization can be used as an effective method to generate highly energy-efficient renewable fuel resources from biomass.