Pyrolysis of Onion Peel Waste: Investigation of Comprehensive Pyrolysis Index, Reaction Mechanism, Kinetic, and Thermodynamic Properties Using TGA Analysis

Abstract

The rising demand for onion production results in significant waste, harming the environment. Onion waste is unsuitable for animal feed and difficult to dispose of due to its strong odor and potential for phytopathogen growth. Pyrolysis is a promising method for repurposing food waste, requiring minimal infrastructure and offering rapid processing and environmental benefits. The main goal of this study was to examine the potential of onion peel as a viable and sustainable pyrolysis feedstock by utilizing kinetic and thermodynamic studies. This study utilized a thermal analyzer to investigate the thermal decomposition of onion peel waste in a nitrogen atmosphere at heating rates of 15, 20, and 25°C/min, from room temperature to 800°C. The study applied four model-free isoconversional kinetic techniques—Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), Starink (STK), and Friedman (FR)—to analyze the relationship between activation energy (Eα) and the degree of conversion (α). The average activation energies from KAS, FWO, STK, and FR were 81.22 kJ/mole, 89.06 kJ/mole, 83.64 kJ/mole, and 68.14 kJ/mole, respectively. The reaction mechanism of thermally degraded onion peel follows one-dimensional diffusion, three-dimensional diffusion, power law, exponent power first-order, exponent power second-order, first- and third-order reactions, and Avrami–Erofeev reaction mechanism models. Thus, onion peel is a promising feedstock for bioenergy generation due to its low energy barrier and activation energy.