Recyclable solvent vapor fractionation of lignocellulosic biomass via supercritical CO₂ synergy: Achieving green processing and ultra-low solvent consumption

The complete utilization of lignocellulosic biomass requires efficient and sustainable pretreatment methods, such as organic solvent pretreatment, which produces high-quality lignin and highly digestible carbohydrates. However, conventional organic solvent pretreatment faces challenges, including complex process flow, high solvent consumption, and reliance on strong acid-base catalysts. To address these limitations, this study developed a novel supercritical carbon dioxide (SCCO₂)-assisted solvent vapor pretreatment method. SCCO₂-assisted ethanol/water solvent vapor disrupted the biomass structure and dissolved specific components, while intermittent cooling induced solvent vapor-liquid phase transition for component separation and enrichment. Results demonstrated 92.26 % cellulose retention and 89.01 % lignin removal with good structural homogeneity of the separated lignin under solvents with only 25 % ethanol loading. The vapor-phase pretreatment design enabled solvent reuse, and biomass treated with twice-reused solvents still exhibited excellent component separation. Solvent consumption was significantly reduced, lowering the total solvent-to-biomass ratio of the pretreatment to 3.3: 1. Life cycle assessment (LCA) results indicated that reducing organic solvent usage could significantly minimize environmental impacts. This technique provides an environmentally efficient strategy for pretreating lignocellulosic biomass.