Comprehensive thermal properties, kinetic, and thermodynamic analyses of biomass wastes pyrolysis via TGA and Coats-Redfern methodologies

Abstract

• Conducted comprehensive pyrolysis analysis on five different biomass waste materials. • Estimated key kinetic parameters using the Coats-Redfern method. • Macadamia nutshell showed the highest pyrolysis stability index. • Evaluated enthalpy, Gibbs free energy, and entropy for all biomass samples. • Observed variations in pyrolysis behavior, peak temperatures, and decomposition rates. This study comprehensively analyzes the thermal decomposition characteristics as well as the kinetic and thermodynamic parameters of five biomass wastes, including coffee husk, groundnut shell, macadamia nutshell, rice husk, and tea waste, using Thermogravimetric Analysis (TGA) and the Coats-Redfern method. The TGA experiments were conducted on a PerkinElmer STA 6000 instrument under an inert N 2 atmosphere with a heating rate of 20 °C/min, spanning a temperature range from 25 °C to 950 °C. The results identified three distinct pyrolysis stages: drying, devolatilization, and char formation, with macadamia nutshell demonstrating the highest thermal reactivity and efficient devolatilization characteristics, reflected by its lowest initial devolatilization temperature (175 °C) and highest peak temperature (380 °C). Kinetic analysis revealed that coffee husk had the highest overall activation energy ( E a ) of 60.59 kJ/mol, indicating complex thermal degradation behavior. The thermodynamic evaluation showed that coffee husk also exhibited the highest enthalpy change (ΔH=55.46 kJ/mol) but the lowest Gibbs free energy change (ΔG=148.34 kJ/mol), suggesting high energy requirements for decomposition but relatively more spontaneous reactions compared to other biomass types. Macadamia nutshell demonstrated high ΔG (163.24 kJ/mol) and moderate ΔH (32.44 kJ/mol), reflecting greater resistance to spontaneous decomposition. The comprehensive pyrolysis index ( CPI ) and devolatilization index ( D dev ) confirmed macadamia nutshell as the most reactive biomass, while rice husk exhibited the lowest reactivity. The findings highlight the importance of multi-step kinetic analysis for accurately understanding pyrolysis processes, providing critical insights for optimizing biomass conversion for energy production. Future research should explore co-pyrolysis with varied biomass mixtures and advanced kinetic modeling to enhance energy yields.