Valorization of palm kernel shell waste into briquettes: Assessing physicochemical properties and combustion characteristics

The palm oil industry plays a key socio-economic role in tropical countries but generates waste with untapped economic potential. This work aims to advance sustainable solutions through valorization of plantation waste, specifically palm kernel shells, as biochar briquettes. In particular, this study assesses the potential of these briquettes for practical use by examining the physicochemical properties and combustion characteristics. The briquettes exhibit low moisture (5.3 wt%), moderate ash (9.54 wt%), volatile matter (39.72 wt%), fixed carbon (45.45 wt%), and a calorific value of 5477.18 Cal/g. Physicochemical evaluations via proximate and ultimate analyses, and FTIR spectroscopy allow comparison against mainstream products, with FTIR indicating increased carbonization and hydrophobicity. The assessment indicates that the briquette developed in the current study has favorable characteristics and is therefore industrially promising. Combustion kinetics and thermodynamic parameters are investigated using thermogravimetric analysis, which reveals ignition and burnout temperatures of 270–281 °C and 523–549 °C, respectively. The maximum burning rate reaches 8.92 %/min at 20 °C/min. Four isoconversional methods (Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall, Starink, and Tang) are applied. Results indicate comparable average activation energies (126–138 kJ/mol), validating method consistency and supporting robust kinetic interpretation. Thermodynamic analysis confirms endothermic devolatilization, positive ΔG (127–139 kJ/mol), and negative ΔS (-0.138 to -0.142 kJ/mol.K), suggesting formation of ordered transition complexes. These findings highlight the industrial potential of biochar briquettes as a sustainable biomass fuel, supporting a circular economy.