Hydrothermal carbonization of sugarcane industry by-products and process water reuse: structural, morphological, and fuel properties of hydrochars

Abstract

Hydrothermal carbonization (HTC) has emerged as a promising technology for sustainable use and waste valorization. One major challenge of HTC technology is the process water (PW) disposal or reuse, which is rich in dissolved organic carbon. This study evaluated the (i) potential of HTC to transform sugarcane industry by-products (sugarcane bagasse and vinasse) into useful materials for energy purposes, after, (ii) carry out the PW reuse in a novel HTC process with sugarcane bagasse. Relationships among composition, structure and morphology with fuel properties of hydrochars were evaluated. All hydrochars had lower volatile matter and higher fixed carbon content compared to the raw biomass. In addition, the decrease of H/C and O/C atomic ratios indicated an enhancement of the dehydration and deoxygenation reactions. Furthermore, the higher heating values (HHV) of hydrochars were in the range of 21.10–23.78 MJ kg-1, compared to 15.43 MJ kg-1 of the sugarcane bagasse. This result added to those from the van Krevelen diagram showed that the hydrochars presented fuel properties similar to conventional non-renewable energy sources, such as bituminous coal. Overall, the PW reuse did not promote great differences in the hydrochar properties and, consequently, no big changes on their fuel properties. Further, the hydrochar produced with sugarcane bagasse, vinasse, and sulfuric acid showed the highest heating value, and it was the most hydrophobic hydrochar among the others investigated. Therefore, the present study showed HTC and PW reuse as promising methods to treat the sugarcane industry by-products for solid fuel production.