Study on thermal degradation characteristics, kinetics, thermodynamic, and reaction mechanism analysis of Arachis hypogaea shell pyrolysis for its bioenergy potential

Abstract

The present research aims towards the study of thermal degradation kinetics and thermodynamics of Arachis hypogaea shells (AHS) to evaluate its potential for bioenergy production. Physicochemical characterization, i.e., proximate, ultimate, compositional analysis, and higher heating value (HHV) were carried out in addition to thermogravimetric (TG) analysis. Physicochemical characterization revealed high volatile matter (75.2 wt.%) with considerably lower moisture, ash contents, and significantly higher HHV (17 MJ/kg). TG analysis of AHS was conducted from ambient to 800 °C at multiple heating rates (10, 15, and 25 °C/min) using nitrogen as carrier gas. TG and derivative thermogravimetric (DTG) analysis disclosed that the maximum degradation occurs in the temperature ranging from 150 to 450 °C (~64%). The iso-conversional methods that were employed to determine kinetic and thermodynamic parameters are Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Starink, and Friedman. Average values of activation energies as calculated by these models were 175.05, 173.65, 171.83, 175.95 kJ/mol respectively. The values of pre-exponential factor (A0) lie in the magnitude of 109–1020 s−1. The calculated average values of Gibbs free energy (ΔG) by FWO, KAS, Starink, and Friedman were 154.61, 154.66, 154.70, 154.63 kJ/mol, respectively. The average change in enthalpy (ΔH) and change in entropy (ΔS) for the degradation process were in between 166.54–170.65 kJ/mol and 19.99–27.05 J/mol.K, respectively. Reaction mechanism estimation was done using the Z-plot method associated with the Criado method which confirmed that thermal degradation of AHS follows multiple reaction mechanisms. The results suggest that AHS has the potential to be effectively used for the generation of bioenergy. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.