Characterization and thermal analysis of mixed shrub and coffee husk bio-pellets at various molding conditions

Recent advancements in renewable energy sources have highlighted the development of bio-pellets derived from lignocellulosic materials owing to the renewable nature of the biomass utilized. Beyond the parameters established by the Indonesian National Standard, it is crucial to understand the changes in mass and thermal properties. This understanding is essential for analyzing the thermal stability and degradation of bio-pellets. The bio-pellets were synthesized from various compositions of Gamal ( Gliricidia sepium ), Lamtoro ( Leucaena leucocephala ), and Coffee ( Coffea canephora ) husk in ratios (Gamal/G: Lamtoro/L: Coffee husk/C) of 0:1:1, 1:0:1, 1:1:0, 1:1:2, 2:1:1, and 1:2:1 at temperatures of 180 °C and 225 °C, with processing durations of 3 and 5 min. These diverse bio-pellet compositions were evaluated for their proximate values, mineral contents, and calorific values, according to the Indonesian National Standard (SNI 8675-2018). The composition with the highest calorific value (1:1:2) was subjected to thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the bio-pellets met the SNI 8675-2018 requirements for density (0.90–1.12 g/cm ³ ), moisture content (4.24–7.51%), volatile matter (68.13–76.81%), fixed carbon content (20.50–25.85%), calorific value (17.8–20.8 MJ/kg), Na ₂ O content (0.014–0.046%), and K ₂ O content (0.96–2.52%). However, the ash content (2.54–6.13%) and sulfur content (0.05–0.13%) did not meet the standards in some samples, while none of the samples met the requirements for Cl content (0.33–0.54%). TGA and DSC analyses revealed variations in mass and thermal properties owing to differences in temperature and processing time, which affected the thermal stability of the bio-pellets. These findings provide insights into the temperature and decomposition rate of bio-pellets, which can inform the future development of lignocellulose-based bio-pellets as renewable energy sources.