Thermal degradation of jackfruit peel in nitrogen atmosphere: A comparative study of kinetic models

Abstract

This study presents a comparative analysis of kinetic models to evaluate the thermal degradation of jackfruit peel in a nitrogen atmosphere. Thermogravimetric analysis was performed to examine the decomposition behavior of JFP, revealing three distinct stages: moisture evaporation (30–105 °C), active pyrolysis (105–380 °C) involving hemicellulose and cellulose degradation, and lignin decomposition with char formation (380–900 °C). The thermal behavior was further analyzed using multiple kinetic models, including Kissinger–Akahira–Sunose, Flynn–Wall–Ozawa, Friedman, Starink, and Tang methods, to determine activation energy (E_a) at different conversion levels. The comparative kinetic analysis demonstrated variations in E_a, with average values of 166.25 kJ/mol Kissinger–Akahira–Sunose, 167.60 kJ/mol Flynn–Wall–Ozawa, 167.82 kJ/mol Friedman, 155.98 kJ/mol Starink, and 166.53 kJ/mol Tang. The highest E_a of 313.65 kJ/mol was observed at a conversion fraction (α) of 0.7, indicating the breakdown of stable lignin structures, whereas a significant decline in E_a at α = 0.9 suggests the completion of decomposition and possible secondary reactions. A statistical analysis was performed to evaluate the reliability of the kinetic parameters. Activation energies, slopes, standard errors, pre-exponential factors, and confidence intervals were examined for each model and conversion level. At lower conversions (α = 0.2–0.6), the activation energies were stable with low uncertainty. As conversion increased (α ≥ 0.7), uncertainty increased due to reduced mass loss, char formation, and experimental noise. The Friedman method captured greater variation at higher conversions but exhibited higher uncertainty. Negative activation energy values at α = 0.9 reflect statistical uncertainty rather than intrinsic reaction behavior. The results confirm the multi-step nature of Jackfruit peel, with different kinetic models capturing variations in reaction pathways. The study highlights the influence of heating rate on thermal decomposition, with higher heating rates shifting degradation peaks to elevated temperatures. Importantly, the choice of kinetic model significantly affects the estimation of activation energy and, consequently, the prediction of optimal pyrolysis conditions, which is crucial for maximizing bioenergy yield and designing efficient thermochemical conversion systems. With a volatile matter content of 74.90%, fixed carbon of 12.98%, and a higher heating value of 16.98 MJ/kg, JFP is a promising feedstock for thermochemical conversion.