Impact of Demineralization on Various Types of Biomass Pyrolysis: Behavior, Kinetics, and Thermodynamics

This study systematically investigates the effects of demineralization on the pyrolysis characteristics, kinetics, and thermodynamics of three biomass types (eucalyptus, straw, and miscanthus) using thermogravimetric analysis (TGA) combined with multiple kinetic approaches. The Coats–Redfern integral model was employed to determine the reaction mechanisms. The results indicate that the primary weight-loss temperature ranges for eucalyptus, straw, and miscanthus were 222.02~500.23 °C, 205.43~500.13 °C, and 202.30~490.52 °C, respectively. Demineralization increased the initial pyrolysis temperature and significantly enhanced the reaction rates. Kinetics analysis revealed that the ash content significantly influences the activation energy of the pyrolysis reaction. The average activation energies follow the trend eucalyptus (193.48 kJ/mol) < miscanthus (245.66 kJ/mol) < straw (290.13 kJ/mol). After demineralization, the activation energies of both straw and miscanthus pyrolysis decreased, with the largest reduction observed in straw, which dropped by 77.53 kJ/mol. However, the activation energy for eucalyptus pyrolysis increased by 12.52 kJ/mol after demineralization. The Coats–Redfern model and thermodynamic analysis demonstrated that each type of biomass followed distinct reaction mechanisms at different stages, which were altered after demineralization. Additionally, demineralization leads to higher ΔH and Gibbs free energy ΔG for eucalyptus, but lower values for straw and miscanthus, which indicate that the ash content has a significant impact on the biomass pyrolysis reaction. These findings provide fundamental insights into the role of ash in biomass pyrolysis kinetics and offer theoretical support for the design of pyrolysis reactors.