Influence of the biomass particle size during the hydrothermal carbonization of Jatropha curcas fruit residue to unlock its potential in bioenergy production

Numerous studies have focused on producing renewable energy using different technologies, such as energy crops as feedstock. However, the effect of the side products has not been deeply studied so far because of their heterogeneity, particle size, and low energy value. In this study, it is evaluated two side products (fruit husk – FHK, seed shells – SSH) derived from Jatropha curcas L. cultivation, processed with five different particle size ranges (PSRs) under hydrothermal carbonization (HTC), were evaluated with a focus on the hydrochar's (HC) potential as a renewable solid fuel. The HTC process significantly influences certain physicochemical properties of the HC, depending on the feedstock and PSR. Compounds prone to hydrolysis migrate predominantly to the liquid phase during HTC, while inorganic components remain concentrated in the solid phase. HCs derived from SSH exhibit high energy yield (68.7–71.7) and energy density (1.22–1.26), making them suitable for energetic applications. Furthermore, the HTC process effectively reduced the ash factor (c.a. 25 %), enhancing combustion efficiency of SHH's HC. FTIR analysis showed similar spectra for the raw materials and their respective hydrochars, indicating consistent retention of certain functional groups under applied processing conditions. ICP-OES analysis highlighted that calcium (Ca) was the dominant inorganic compound in SSH, while potassium (K) is predominant in FHK. Therefore, the analysis of the HCs revealed that the initial lignocellulose content and ash content were more critical determinants of HC composition than the initial PSR. • HTC process effectively reduces the ash factor (c.a. 25 %). • SSH-derived HCs have higher energy yield (90.54–94.56) and density (1.61–1.67). • Fiber composition and ash content are key HC composition determinants. • SSH HCs have high calcium and FHK HCs have high potassium. • Particle density of SSH HCs is higher than FHK HCs.