Physicochemical characterisation and kinetic modelling of wet torrefied oil palm trunk in pyrolysis condition

Over 218 million tonnes of oil palm trunks (OPT) waste is produced annually by Malaysian oil palm industry, which can be converted to biofuels via wet torrefaction. This study assessed the fuel characteristics of wet torrefied OPT (WT-OPT) using proximate analysis, higher heating value (HHV) analysis, Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy–energy dispersive X–ray spectroscopy (SEM–EDX). Increasing wet torrefaction temperature and residence time increased the fixed carbon content and HHV of OPT. SEM–EDX revealed the presence of microspheres of 5-hydroxymethylfurfural (5-HMF) in OPT wet torrefied at 180 and 220°C for 72 h, an intermediate compound that can contribute to the HHV enhancement in WT-OPT. FTIR and EDX results revealed that higher temperature and residence time concentrate the carbon content of OPT. Wet torrefaction at 180°C for 72 h decreased the activation energy and pre-exponential factor of OPT from 301.88 to 171.70 kJ mol⁻¹ and from 4.43 × 10²⁸ to 3.25 × 10¹² s⁻¹, respectively, during pyrolysis. The estimated thermodynamic parameters, particularly the change in entropy which generally decreased by more than 140 J mol⁻¹ K⁻¹, indicated increase in stability of certain WT-OPT.