Hydrothermal valorization of cellulose tuned by non-corrosive Lewis acids and bases

Cellulose, the most abundant component of biomass, is an essential renewable and carbon–neutral resource that can be converted into valuable products through hydrothermal treatment. However, the industrial application of hydrothermal technology for cellulose valorization is hindered by the formation of complex products which are challenging to separate. This study introduces a novel strategy for regulating product formation in cellulose hydrothermal conversion using non-corrosive Lewis acids and bases, integrating density functional theory calculations with experimental investigations. Frontier molecular orbital analysis reveals that peroxodisulfate, with strong electrophilicity, acts as a Lewis acid, directing the reaction toward the formation of levulinic acid. Conversely, peroxymonosulfate and thiourea, as nucleophilic Lewis bases, promote the accumulation of hydroxymethylfurfural by preventing its further degradation to levulinic acid and polymerization to carbon microspheres. Thiosulfate, with excessively strong nucleophilicity, inhibits the conversion of cellulose into sugars, thereby altering the whole hydrothermal decomposition pathways. Focusing on thiourea as a model additive, the study identified optimal conditions for hydroxymethylfurfural accumulation: a thiourea-to-cellulose ratio of 0.05:1, a reaction temperature of 220 °C, and a reaction time of 2 h. Additionally, increasing the initial reaction pressure from 0.1 MPa to 1.5 MPa resulted in a 92 % increase in hydroxymethylfurfural yield. This study provides a theoretical foundation for regulating cellulose hydrothermal processing via Lewis acids and bases, offering new insights into selective product formation and advancing biomass valorization technologies.