Elucidating the bioenergy potential of raw, hydrothermally carbonized and torrefied waste Arundo donax biomass in terms of physicochemical characterization, kinetic and thermodynamic parameters

The present investigation aimed to understand the pyrolysis kinetic behavior of raw Arundo donax (Raw-AD), hydrothermally carbonized Arundo donax (HTC-AD), and torrefied Arundo donax (TOR-AD) in a thermogravimetric analyzer at dynamic heating rates. The physicochemical characterization analysis revealed that fuel properties have been enhanced after hydrothermal carbonization and torrefaction. The characterization techniques such as FE-SEM, EDX, FTIR, and XRD have been used to investigate the biomass surface morphology, inorganic elements, functional groups, and crystallinity. The kinetic parameters were calculated using the model-free methods of Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), and Vyazovkin (VZK), whereas Criado's z(α) master plot was used to elucidate the reaction mechanism. The average activation energy was obtained to be 259.11, 262.53, and 250.13 kJ/mol for Raw-AD, 115.31, 110.39, and 107.26 kJ/mol for HTC-AD, and 243.46, 242.68, and 233.79 kJ/mol for TOR-AD using OFW, KAS, and VZK method respectively. The thermodynamic analysis divulged that pyrolysis proceeded through various reaction mechanisms.