Study of thermal dissolution characteristics of oxygenated structures in biomass

To achieve high-value utilization of biomass resources, this study elucidates the selective extraction characteristics of oxygenated compounds by investigating the influence of reaction temperature (240–360 °C) and time (0–120 min). Thermal dissolution (TD) experiments were conducted on three representative agricultural/forestry and marine biomass materials—Pine sawdust (Ps), corncob (Cb), and Enteromorpha prolifera (Ep), using solvents with distinct properties: ethanol (ET) and tetrahydrofuran (THF). The results showed that ET consistently outperformed THF in soluble yield across all biomass types. The highest yield (82.35%) was achieved from Ps at 300 °C for 90 min using ET. GC/MS analysis revealed that the soluble products were primarily composed of oxygenated compounds, including phenols, alcohols, esters, etc. Saccharides were detected in Ep extracts (10.39%) under the conditions of 300 °C and 90 min. ET exhibited selectivity towards ethers and esters, while THF demonstrated selectivity towards phenols, alcohols, esters, and furans. Temperature and reaction time significantly influenced the component distribution of soluble products, with similar trends observed for three biomasses. Analysis (ultimate analysis, XPS, and FTIR) showed TD decreased biomass oxygen content, transferring oxygenated structures to the soluble products. The remaining residues, rich in carbon (30.04–67.24%), are suitable for further application. This research clarifies that TD is a dual-purpose sustainable energy technology: it valorizes biomass into high-value biofuel precursors and carbon-dense solid fuels, providing a viable pathway to integrate biomass into the global sustainable energy chain and reduce fossil reliance.