Thermal Degradation and Pyrolysis Kinetics of Alkaline-Pretreated Pinewood under Non-Isothermal Conditions

Pinewood (PW) residues are abundant lignocellulosic wastes, but their elevated volatile and oxygenated fractions can complicate pyrolysis by promoting complex devolatilization behavior. This challenge motivates the use of NaOH pretreatment of PW to enhance thermal conversion efficiency. This study investigates the catalytic effect of sodium hydroxide (NaOH) on the pyrolysis kinetics of PW under non-isothermal conditions. Thermogravimetric analysis (TGA) was conducted on untreated PW and samples pretreated with varying concentrations of NaOH (0.2, 0.5, 1, and 2 wt %) at four different heating rates (2.5, 5, 10, and 20 K/min). The results demonstrated that NaOH addition facilitates biomass decomposition by reducing peak pyrolysis temperatures. This catalytic effect was intensified with increasing NaOH concentration. To interpret the observed trends, kinetic modeling was performed using three iso-conversional methods: Friedman, Flynn-Ozawa-Wall (FWO), and Kissinger–Akahira–Sunose (KAS). Thermodynamic parameters of activation were also calculated to complement the kinetic analysis and aid in identifying the most effective NaOH treatment. The modeling results revealed notable reductions in activation energy (Eα) for samples pretreated with 0.2 and 0.5 wt % NaOH, confirming the catalytic role of NaOH in enhancing thermal degradation at lower temperatures potentially by promoting glycosidic bond cleavage.