Optimized synthesis of granular fuel and granular activated carbon from sawdust hydrochar without binder

In this study, a facile and eco-friendly method for synthesis of granular fuel and granular activated carbon was developed. The approach needs not to add a harmful binder due to inherent characteristics of sawdust hydrochar and has not been previously reported. Granular fuel was prepared from densification of sawdust hydrochar acquired from hydrothermal carbonization. Sawdust hydrochar was also pelletized and activated with FeCl3 and ZnCl2 to obtain granular activated carbon. The effects of the temperature used for the hydrothermal carbonization process on the characteristics of granular fuel and granular activated carbon were investigated. The results showed that at the optimal temperature of 230 °C, the high heat value, energy density, and equilibrium moisture content of granular fuel were 23.53 MJ/kg, 35.87 GJ/m3, and 0.73%. Equilibrium moisture content was improved about 7 times compared to sawdust. In addition, the hydrothermal carbonization temperature was negatively correlated with the Brunauer-Emmett-Teller surface area and the iodine adsorption value of granular activated carbon. The compression strength of granular activated carbon was excellent (up to 8.8 MPa), which was high enough to use in adsorption bed. For optimal granular fuel and granular activated carbon properties, the best temperature was found to be 230 °C, and the Brunauer-Emmett-Teller surface area and the iodine adsorption value of granular activated carbon were 641 m2/g and 626 mg/g. As the environmental problems acquire increasingly attentions, the granular fuel and granular activated carbon could be promising and eco-friendly materials for future applications.