Pyrolysis kinetic study of the thermal degradation of pre-treated empty fruit bunches

Abstract

Empty fruit bunch (EFB) wastes are a significant source of biomass waste in Malaysia and have the potential to be a high-quality source of energy. This study aims to evaluate the kinetic of EFB biochar degradation and its characteristics under three conditions of washing pre-treatments. Prior to biochar production via slow pyrolysis process, stirring and soaking techniques were utilised as part of the pre-treatment for the washing process, with varying solid-to-liquid (S:L) ratios of 1:50, and 1:50 to 1:70, respectively. The study analysed the higher heating value (HHV), pyrolysis yield and kinetic activation energy of the biochar. The morphology and elemental composition of the biochar samples were determined using ultra-high resolution scanning electron microscopy (UHR-SEM) and energy dispersive X-Ray detector (EDX). The Coats-Redfern model was used to estimate the activation energies of the EFB biochar from thermogravimetric (TGA) data in a temperature range of 30 °C to 800 °C and a constant heating rate of 10 °C/min under a nitrogen atmosphere. The results showed that washing pre-treatment significantly changed the morphology and elemental compositions of the EFB biochar samples. The higher S:L ratio of 1:70 has a more significant impact on the breakdown of the lignocellulosic structure of EFB. The soaked samples had slightly lower biochar and bio-oil yields (22.73 mf wt. % to 24.86 mf wt. % and 27.97 mf wt. % to 39.39 mf wt. %, respectively) than the stirred samples (25.22 mf wt. % and 49.59 mf wt. %). The pre-treatment process improved the carbon content while reducing potassium by 60.7 to 81.39%. The HHVs of EFB-4 (28.24 MJ/kg) and EFB-3 (26.57 MJ/kg) were higher than those of EFB-2 (26.2 MJ/kg) and EFB-1 (23.14 MJ/kg), indicating an improvement in their fuel properties. The higher kinetic activation energies of EFB-4 (43.27 to 48.30 MJ/mol) indicate better thermal stability than the others. Therefore, concerning improved fuel properties, the recommended pre-treatment of EFB for the pyrolysis process is soaking at 90 °C with an S:L ratio of 1:70. The kinetic analysis revealed that the pyrolysis of pre-treated EFBs follows a multi-step reaction mechanism, with different activation energies for each stage. The obtained kinetic parameters can be used to optimize the pyrolysis process and design efficient pyrolysis reactors for the valorization of EFBs. Overall, this study provides valuable insights into the thermal behavior of pre-treated EFBs and their potential for bioenergy production.