Selective oxidative pretreatment enhances biomass torrefaction: Effects of low-concentration H2O2 and thermal severity

Growing demand for renewable and carbon-neutral solid fuels has intensified interest in upgrading biomass through efficient thermochemical pathways. This study investigates the combined effects of low-concentration hydrogen peroxide (H 2 O 2 , 0–6.04%) pretreatment and torrefaction on the physicochemical evolution and fuel quality of lignocellulosic biomass. Mild oxidative pretreatment selectively modified early-stage composition, with 2.5% H 2 O 2 promoting partial dehydration and carbon densification while temporarily reducing the heating value. Higher concentrations stabilized compositional changes without causing extensive degradation. Torrefaction temperature emerged as the dominant factor governing mass yield, elemental composition, devolatilisation behaviour, and carbonization severity, whereas the influence of H 2 O 2 was secondary but strongly temperature dependent. Oxidation enhanced delignification and oxygen removal at ≤210 °C, approached kinetic balance at 250 °C, and promoted rapid deoxygenation and aromatic condensation at ≥290 °C. Energy-related indicators revealed that H 2 O 2 pretreatment can either suppress or enhance fuel performance depending on process severity. Response surface methodology demonstrated strong predictive capability (R 2 = 0.9620–0.9920) and identified 288.5 °C and 6.04% H 2 O 2 as optimal operating conditions. Overall, peroxide-assisted torrefaction provides a controllable and scalable strategy for upgrading solid biofuels, with promising potential for industrial integration.