Exploring kinetic and thermodynamic mechanisms of switchgrass pyrolysis using iterative linear integral isoconversional method and master plots approach

Abstract

This study aimed to explore the kinetic mechanism of switchgrass pyrolysis through isoconversional kinetic analysis and master plots approach. The pyrolysis kinetics of switchgrass was experimentally studied by thermogravimetric analysis at 5, 10, 20, and 40 K min−1. The experimental kinetic data of switchgrass pyrolysis was processed by the iterative linear integral isoconversional method and the obtained effective activation energies varied significantly with conversion: from 190.3 to 216.7, 217.3 ± 0.9 and 219.4 to 301.4 kJ·mol−1 in the conversion range of 0.05 – 0.45, 0.45 – 0.75 and 0.75 – 0.95, respectively. The significant conversion dependence of activation energies indicated switchgrass pyrolysis was a kinetically complex process, which was caused by the overlapping decomposition reactions of lignocellulosic components contained in switchgrass. Based on the master plots approach and the general empirical reaction model, the pyrolysis kinetic process of switchgrass pyrolysis followed the reaction model: f(α) = α-0.307·(1–1.020α)2.276. The frequency factor of switchgrass pyrolysis varied from 4.2 × 1012 to 3.9 × 1018 s−1 in the conversion range of 0.05 – 0.95, and a kinetic compensation effect between the frequency factor and activation energy was discovered. Based on the kinetic results, the changes in Gibbs free energy, enthalpy and entropy for switchgrass pyrolysis were calculated. It is expected that this study can provide a methodological guideline for the kinetics and thermodynamics of lignocellulosic biomass pyrolysis.