Time-Dependent Mechanisms in Sustainable Corn Stalk Holocellulose Liquefaction: Unraveling Phase Evolution under H3PO4 Catalysis with a Binary Solvent System

To enable green valorization of agricultural waste-derived biomacromolecules, this study developed a diethylene glycol/glycerol (DEG/GI) binary solvent system under H3PO4 catalysis, investigating its synergistic liquefaction mechanisms and directional regulation potential for bio-oil production from corn stalk holocellulose (CSHC). Time-resolved analysis of solid, liquid, and gaseous phases elucidated depolymerization-polymerization mechanisms and product evolution. A unique DEG/GI synergy afforded 95.90% bio-oil in a yield of 95.90% within 40 min. During the depolymerization stage (0–40 min), CSHC depolymerization dominated, accompanied by high CO/CO2 release and a transient rise and eventual disappearance of crystallinity (CrI). While initial H+ consumption by GI esterification suppressed hemicellulose hydrolysis, the ensuing liquefaction products promoted cellulose conversion. Beyond 40 min, the bio-oil yield decreased and solid residue increased, indicating a shift toward condensation and repolymerization. This work unveils glycerol’s role in pathway regulation under mild conditions, offering a sustainable strategy for targeted conversion of holocellulose into bio-oil, with implications for producing functional biobased materials.