Hydrochar production from defective coffee beans by hydrothermal carbonization

[Display omitted] •Defective coffee beans upgrading into solid biofuels was evaluated.•Energy and fuel properties of precursor biomass have been altered by HTC.•High quality solid biofuels were obtained from residues that impair coffee quality. This study aimed to produce and characterize hydrochars from defective coffee beans and its application as a solid fuel. Defective coffee beans were used as precursor residue for hydrochar synthesis. Reactions were run in a high-pressure reactor at temperatures of 150, 200 and 250 °C, under autogenesis pressure, for 40 min. Solid phase was recovered by filtration and characterized by CHNO-S analyzer, thermogravimetric analysis and differential scanning calorimetry. Hydrothermal carbonization temperature was key to change energy values and fuel properties. These results suggest hydrothermal carbonization is an effective and simple strategy for converting coffee waste into functional, high-quality, and energy-dense solid biofuels.