Stepwise pretreatment involving dilute acid and amine for corn stover fractionation toward full lignocellulose-oriented valorization†

Lignocellulose valorization is interwoven with fractionation and by tuning the pretreatment setup and conditions, the characteristics of both polysaccharides and lignin could be tailored to match upgrading demands. Here, a stepwise pretreatment approach involving dilute acid and amine was developed for corn stover fractionation. Under the optimized prehydrolysis conditions (3% H₂SO₄, 120 °C and 2 h), up to ∼97.8% of original xylan was released in the form of xylose, along with a negligible amount of furfural. The signal patterns of confocal laser scanning microscopy revealed that the removal of hemicellulose caused lignin redistribution within the cell wall. At high biomass loading (58%, w/w), amine pretreatment extracted up to ∼82% of lignin with abundant β-O-4 linkages (37–41/100Ar) and strong fluorescence (turquoise and light blue). Enzymatic hydrolysis of mechanochemically pretreated cellulose (MCC) and thermochemically pretreated cellulose (TCC) resulted in glucan conversion of 96.1 and 92.8%, respectively, at 30 mg Cellic® CTec3 HS/g for 72 h. Furthermore, mass balance demonstrated that the combined dilute acid–amine pretreatment could potentially be an efficient fractionation method for lignocellulose. Moreover, a mechanistic understanding of the interactions between lignocellulose components and pretreatment solvents is described. Overall, this pretreatment approach offers the right balance between fractionation of all lignocellulose constituents and preservation of their structural integrity, while simultaneously opening a window for lignin functionalization and depolymerization.