Lignin-stabilizing fractionation enables production of uncondensed lignin and digestible carbohydrates

Abstract

The efficient and economical fractionation of lignocellulosic biomass (LCB) is pivotal for the sustainability of integrated biorefining. However, irreversible lignin condensation remains a major hurdle during fractionation and subsequent valorization. In this study, alkali fractionation strategies incorporating lignin stabilization were designed to effectively deconstruct LCB, yielding highly digestible carbohydrates and uncondensed lignin. The results demonstrate that alkali fractionation effectively disrupts the LCB structure, increasing the surface area and pore volume. Using Cellic CTec3 (14 FPU per g) and xylanase (7.7 FPU per g) at a 3% substrate loading, glucan and xylan conversions reached 97% and 75%, respectively. Crucially, the introduction of stabilization agents effectively tailored the lignin's chemical structure and functional properties. Specifically, 2-naphthol serves as a potent nucleophilic trapping agent, capturing highly reactive carbocation intermediates to suppress condensation. This stabilization yielded light-colored, low-molecular-weight lignin (M_w ∼ 2400 Da) with a remarkably high content of non-condensed phenolic hydroxyl groups (97%). Overall, this stabilization-assisted alkali fractionation offers a synergistic approach to maximize the valorization of both carbohydrates and lignin, which could improve the economic feasibility of biorefining.