Hydrothermal Carbonization of Sugarcane Leaves and Bagasse for Solid Fuels: Process Optimization Using Response Surface Methodology

High Resolution Image Download MS PowerPoint Slide The cultivation and processing of sugarcane for sugar production generate significant agricultural and agro-industrial residues. The valorization of this generated residue for energy production offers a promising path to reduce net carbon emissions while addressing biomass waste management challenges. Hydrothermal carbonization (HTC) is an effective method for converting waste biomass, without drying, into energy-dense coal-like solid fuels. In this study, the HTC of sugarcane leaves (SCL) from farming and sugarcane bagasse (SCB) from the processing sugar industry was systematically investigated and optimized using a Box–Behnken response surface methodology (RSM). The effects of reaction temperature (160–220 °C), reaction time (4–12 h), and biomass-to-water ratio (1–2.5 g/30 mL) on hydrochar yield were evaluated, enabling the development of statistically significant predictive models. The maximum hydrochar yields of 78.30% for SCL and 82.00% for SCB were achieved at 160 °C, 12 h, and biomass loadings of 1.75 and 1.69 g, respectively. In addition to the optimization of hydrochar yield, the influence of HTC parameters on the fuel properties of hydrochar was widely assessed using proximate and ultimate analyses, calorific value estimation, thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, and Brunauer–Emmett–Teller (BET) surface area measurements. The optimized hydrochars exhibited moderate increases in higher heating values to 15.88 MJ/kg (SCL) and 17.40 MJ/kg (SCB) as compared to 14.74 and 15.61 MJ/kg for raw SCL and SCB, respectively, indicating energy densification compared to the raw biomass. Notably, improvements in fuel characteristics, including enhanced carbon content and fuel ratio, indicate better combustion behavior and carbonization. A Van Krevelen plot highlighted the improved coal-like characteristics, showing the effectiveness of HTC in upgrading sugarcane residues into solid fuels. This work provides a comparative assessment of sugarcane leaves and bagasse valorization, supporting the potential option of HTC as a sustainable route for producing clean solid fuels from agro-industrial waste without the drying steps.