Temperature-programmed pyrolysis of sunflower seed husks: application of reaction models for the kinetic and thermodynamic calculation

Abstract

This work aims to investigate the slow pyrolysis of sunflower seed residues using thermogravimetric tests carried out at five heating rates: 5, 10, 15, 20, and 25 K min−1. The kinetic triplet for global reaction, represented by activation energy (Ea), Arrhenius pre-exponential factor (A), and reaction mechanism (f(α)), and the kinetic parameters for pseudo-components were determined. Thermodynamic activation parameters as enthalpy, Gibbs free energy, and entropy were calculated by using the transition state theory. The Ea values determined by isoconversional methods varied between 79.11 and 162.57 kJ mol−1, and the master plots methodology indicated the reaction mechanism of sunflower seed residues as the three-dimensional Jader equation, resulting in global parameters of 102.51 kJ mol−1 and 8.96 × 105 s−1 for Ea and A, respectively. The presence of three pseudo-components (hemicelluloses, cellulose, and lignin) was considered for the modeling of independent parallel reactions, which resulted in Ea values ranging from 72.4 to 170.2 kJ mol−1 and the A values ranging from 1.31×104 mol−2 s−1 to 1.21×1013 mol−1 s−1, with reaction orders varying between 1 and 3. The values of thermodynamic parameters indicated that the pyrolysis of sunflower residues tends to remain continuous once the necessary energy is supplied and that the activated state presented a higher degree of organization than the reactants. This present work is the first one to investigate the kinetic triplet and the independent parallel reaction model for sunflower residue pyrolysis. The results were useful for biomass management, indicating the kinetic and thermodynamic values for pyrolysis optimization.