Kinetics study and Py-GC-MS analysis of pyrolysis in chicken bone waste for sustainable utilisation in thermal conversion

Abstract

Chicken bone waste is generated by the food service industry and individual households. The main issues in bone waste management are related to illegal discharge or high disposal costs. However, their valorisation raises great prospects towards the achievement of environmental sustainability and circular bioeconomy. In this study, chicken bone waste feedstocks were sourced from the fried chicken process (CBF) and purchased from one of the world's largest fast-food restaurant chains as well as from household waste (CBO). The feedstocks were enzymatically pretreated, in preparation to be subjected to further processes, and then sonicated, dried, and milled. The elemental analysis revealed that both CBF and CBO had similar carbon, hydrogen, and nitrogen contents (c.a. 28% C, 4.5% H and 5% N). Mineral analysis showed calcium and phosphorus as key components, with phosphorus increasing and calcium decreasing after pyrolysis due to thermal degradation of calcium carbonate. The pyrolysis results demonstrated significant differences in kinetic parameters and reactivity. CBF, derived from pressure frying, displayed a lower temperature for the initial decomposition peak and a higher rate of volatile release compared to CBO. The activation energy profiles showed that while both samples had similar average activation energies (approximately 201-202 kJ/mol), CBF exhibited higher reactivity and a faster release of volatiles (total reactivity index RM_tot 0.0305), and higher CPI indices for all elementary steps, and higher pyrolysis stability indexes R_w. Pyrolysis of CBF and CBO was modelled by applying the isoconversional Friedman method with fit quality R² > 0.999. Pyrolysis (Py-Gc-MS) of chicken bone at 500 °C and 700 °C indicated a dominance of hydrocarbons and nitrogen-containing compounds, with CBF having higher fatty acid content due to frying oil residues. These findings highlight the influence of cooking methods on the pyrolytic behaviour of chicken bone waste, providing valuable insights for optimizing biochar production and other applications involving organic waste pyrolysis.