Multiscale mechanistic insight into torrefaction as an efficient pretreatment strategy for upgrading gasification of waste paper

• Torrefied samples' properties and torrefaction kinetics/mechanisms was analyzed. • Structural changes and reaction pathways in torrefaction was multiscale revealed. • 5 % O 2 boosted deoxygenation effiency by 1.19 times in waste paper torrefaction. • Pre-removal of volatiles during torrefaction reduces gasification tar formation. • Effect on gasification reactivity and CO yield boost mechanism was revealed. To elucidate the multiscale mechanistic effects of torrefaction on the pyrolysis and gasification behavior of waste paper, changes in the macroscopic physicochemical properties, reaction kinetics, and microscopic mechanisms during torrefaction of waste paper were first systematically examined using advanced multiscale characterization techniques, including thermogravimetric analysis coupled with mass spectrometry (TG-MS), Fourier transform infrared spectroscopy (FTIR), and 13 C nuclear magnetic resonance (¹³C NMR). The impact of torrefaction on tar formation, gasification reactivity, and syngas production from waste paper was then evaluated. Results indicate that torrefaction involves depolymerization, decomposition, and debranching of waste paper, followed by aromatization and cyclization of aliphatic compounds, culminating in condensation into polycyclic aromatic hydrocarbons (PAHs) under severe torrefaction conditions. This process is accompanied by oxygen removal and carbon enrichment. As torrefaction intensity increases, re-condensation and graphitization of waste paper intensify, slightly reducing gasification reactivity. However, carbon enrichment and increased concentrations of alkali and alkaline earth metals (AAEMs) significantly enhance CO yield, while the pre-removal of volatile matter reduces tar formation. These findings provide valuable insights for optimizing torrefaction-coupled pyrolysis and gasification processes for waste paper valorization.