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

Abstract

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 N2 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 devo- latilization temperature (175 ◦C) and highest peak temperature (380 ◦C). Kinetic analysis revealed that coffee husk had the highest overall activation energy (Ea) 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 (Ddev) confirmed macadamia nutshell as the most reactive biomass, while rice husk exhibited the lowest reac- tivity. The findings highlight the importance of multi-step kinetic analysis for accurately understanding pyrolysis proces