Pyrolysis Behavior, Kinetic Analysis, and Biochar Production from Waste Flowers

Abstract

Waste flowers constitute a significant portion of organic waste, offering the potential for sustainable waste management through pyrolysis. This study explores the pyrolysis behavior, kinetic parameters, and biochar production from waste flowers. Thermogravimetric analysis (TGA) was employed to examine thermal degradation characteristics under varying heating rates (10, 20, and 50 °C min^–1). Kinetic analysis was performed using model-free methods such as the Friedman method (FM), Ozawa–Flynn–Wall (OFW), Starink method (STM), Kissinger–Akahira–Sunose (KAS), and Criado model to determine the pyrolysis kinetic parameters. Further, the biochar was produced in a semibatch reactor at 450 °C with a 10 °C min^–1 heating rate and 100 mL min^–1 nitrogen flow rate. The characterization of the biochar included proximate and elemental analysis, calorific value, bulk density, Brunauer–Emmett–Teller (BET) surface area, pH, Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) analysis, and water-holding capacity. The decomposition results were confirmed in three stages: moisture removal, active pyrolysis, and residue formation. Kinetic results revealed a multistep reaction mechanism, with average activation energies of 236.35, 232.29, 234.74, and 221.50 kJ mol^–1 derived from KAS, OFW, STM, and FM, respectively. Pyrolysis of marigold flowers (MG) yielded 36.64 wt % biochar at 450 and 10 °C min^–1 heating rate. Further, the biochar exhibited a 57.10% carbon content, 33.57 MJ kg^–1 higher heating value (HHV), 9.96 m² g^–1 BET surface area, and 29.14 mV zeta potential, demonstrating its potential for soil amendment, carbon sequestration, and pollutant adsorption. This study emphasizes the value of MG as a feedstock for biochar production, contributing to circular economy initiatives.