A Study on the Physicochemical Properties of Hydrochar by Hydrothermal Carbonization With Cooling-Reheating Process

Hydrothermal carbonization (HTC) has gained attention as a sustainable method for converting biomass into energydense materials. This process occurs at relatively low temperature ranges (180–260°C) in high-pressure sealed environments. However, a well-known limitation of HTC is the reduced yield of hydrochar, leading to ongoing efforts to explore alternative solutions. Current approaches focus on modifying operational parameters and incorporating catalysts to address this challenge. Therefore, this study aims to investigate the integration of the cooling-reheating (CRH) process as a complementary method to the HTC process. The CRH process is well-documented for its ability to redistribute carbides and form fine spherical structures in alloys. Preliminary studies suggest that applying CRH to biomass may enhance its energy yield. This study examines how integrating the CRH method into the HTC process affects the physicochemical properties of hydrochar derived from wood waste. The analyses conduced included ultimate analysis, calorific value assessment, and specific surface area measurement. The results indicated that integrating the CRH process improved both solid yield and calorific value compared to the standalone HTC process. Additionally, the fixed carbon content increased slightly, while ash content decreased by up to 17.6%. Specific surface area measurements demonstrated consistent enhancements, with the most significant improvement—a 1.52-fold increase—observed at 260°C.