Pyrolysis of Humins Obtained from Acid-catalyzed Depolymerization of Rice Husk Cellulose: Model-free Approach to Non-isothermal Kinetics

Abstract

Humins (HUs) are one of the main by-products during levulinic acid production. In this work, HUs obtained from rice husk biorefining were investigated. The pyrolysis process in non-isothermal conditions (from 15°C to 900°C) using thermal analyses (TGA) was investigated. The HUs decomposition/pyrolysis process revealed a mass-loss between 65 and 93% depending on the variation of the heating rate. The loss of mass was attributed to the vaporization of water, followed by two main stages such as active (in two peaks) and passive pyrolysis. The Kissinger model-free method was applied to calculate kinetic parameters, estimating E_a of 97.8 kJ·mol^-1 (for active pyrolysis – peak 1) and 260.2 kJ·mol^-1 (for active pyrolysis – peak 2), respectively. The thermodynamic parameters (?H, ?S, and ?G) were calculated for active pyrolysis region. The values of ?H were positives, indicating that the reaction is endothermic. Evaluating spontaneity of the reaction, positive ?G and negative ?S values characterize a non-spontaneous process. Therefore, these encouraging results lead to the HUs valorization in new concepts of biorefinery.