Non-oxidative thermal decomposition of oil palm empty fruit bunch pellets: fuel characterisation, thermogravimetric, kinetic, and thermodynamic analyses

Abstract

The pre-treatment and pelletisation of oil palm empty fruit bunches (OPEFB) can potentially improve its biofuel properties for efficient thermal energy recovery. Therefore, this paper examines the physicochemical, thermal, kinetic, and thermodynamic properties of OPEFB pellets as a potential feedstock for pyrolysis. Physicochemical analysis revealed high proportions of carbon, volatiles, and fixed carbon compared to nitrogen and sulphur. Morphological analysis showed that the pellet microstructure is comprised of a dense network of polymeric fibres, whereas its ash has consistently shaped agglomerated particles with fine-textured surfaces. Thermogravimetric analysis (TGA) revealed the OPEFB pellets experienced significant mass loss (ML = 72.8–80.4%) and residual mass (RM = 19.6–27.2%) during thermal decomposition from 30 to 800 °C. The DTG plots revealed thermal decomposition occurred in three stages: I (30–150 °C), II (150–600 °C), and III (600–800 °C) due to drying, devolatilization, and char degradation, respectively. Kinetic analysis showed the activation energy, Ea, ranged from 76.87 to 195.78 kJ/mol, while frequency factor, A, was from 4.77 × 1001 to 1.22 × 1018 min−1 for the Flynn-Wall Ozawa and Kissinger-Akahira Sunose models. The highest kinetic parameters were observed at α = 0.40, indicating the rate-determining step for OPEFB pellets decomposition under pyrolysis condition occurs at 40% conversion. Thermodynamic analysis showed that thermal decomposition of OPEFB pellets was characterised by the formation of an activated complex, high reactive multiphase first-order reactions, and short reaction times. In conclusion, the results indicate that OPEFB pellets is a potentially suitable feedstock for pyrolysis owing to its excellent fuel properties and environmentally friendly nature.