Alkali/acid treatment of willow tree leaves to improve gasification performance for syngas production

It is important to examine thermal degradation behavior and analyze the characteristics of gasification products. This study investigates the catalytic effects of alkali (NaOH) and acid (H₂SO₄) treatments on the CO₂-assisted gasification of willow tree leaves (WTL) to enhance syngas production. Experiments were conducted using both a thermogravimetric analyzer (TGA) at multiple heating rates (5, 20, and 35 °C/min) and a horizontal tube reactor (HTR) at 20 °C/min, with kinetic analysis performed via a four-step reaction model. The results demonstrate that chemical treatments significantly alter thermal degradation behavior, reaction kinetics, and product distribution. Notably, thermogravimetric analysis revealed that the acid-treated sample (WTLH₂SO₄) showed the highest degradation temperatures, while the alkali-treated sample (WTLNaOH) exhibited the highest degradation rates, demonstrating their distinct catalytic roles. Also, process performance indicators increased with increasing heating rates, with WTLNaOH showing the highest value due to enhanced maximum degradation rate (15.52 wt%/min at 35 °C/min). Further, kinetic analysis revealed that the activation energy values were highly dependent on both heating rate and catalyst type, with alkali treatment stabilizing high-energy decomposition pathways. Meanwhile, alkali treatment (WTLNaOH) yielded the highest CO concentration (11.04 vol%) and a gas yield of 49.89 wt%, attributed to enhanced Boudouard reaction, while acid treatment (WTLH₂SO₄) achieved the highest overall gas yields (62.00 wt%). In addition, solid residue analysis confirmed modified mineral phases dominated by calcium. This work confirms that ion-exchange treatments can effectively tune the gasification performance of biomass, with enhanced syngas and solid residue characteristics.