Characterisation and thermal analysis of Raphia palm kernel for bioenergy and bioremediation applications

This study investigates the characterisation and thermal analysis of Raphia palm kernel- an underutilised biomass. Unlike previous research that focused on oil extraction from the biomass and subsequent transesterification of the extracted oil, this study evaluates the pyrolytic performance of the biomass for bioenergy production and bioremediation applications. The biomass proximate analysis revealed low moisture (6.12 wt%), high volatile matter (73.67 wt%), moderate ash (10.68 wt%), and fixed carbon (9.53 wt%). The ultimate analysis showed an HHV of 18.5 MJ/kg, with significantly high carbon (48.0 wt%), hydrogen (5.8 wt%), and oxygen (45.3 wt%) and low nitrogen (0.8 wt%) and sulphur (0.1 wt%). The biomass's high volatile and carbon contents confirm its suitability for thermochemical conversion into bio-oil and syngas, while the low nitrogen and sulphur contents indicate a potential for reduced pollutant emissions. Crystallographic analysis confirmed the biomass's amorphous nature, while the functional group analysis identified cellulose, hemicellulose, and lignin groups. The thermal analysis revealed three distinct degradation stages, with the highest weight loss occurring at 180–480 °C. The average activation energies were 143.462, 144.900, 142.575, 146.908, and 149.600 kJ/mol for the Coats–Redfern, Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), Friedman, and Distributed Activation Energy Model (DAEM) methods, respectively, indicating moderate thermal stability. The positive enthalpy values obtained from the thermodynamic analysis confirm that the thermal degradation process is endothermic. The values of Gibbs free energy remained positive across the conversion range investigated, indicating that the degradation process requires external energy input. The entropy change values showing a transition from negative to positive as conversion increases reflect increased disorder during decomposition. The study suggests Raphia palm kernel as a viable biomass resource suitable for bioenergy and bioremediation.