Simultaneous transformation of lignocellulosic components using acidic deep eutectic solvents: From action mechanism to scale extraction

Achieving the balanced valorization of lignocellulosic components is essential for improving atom economy and sustainability in biorefinery, yet remains challenging. Herein, a green and scalable strategy was developed for the synergistic conversion of lignocellulosic biomass to polyphenoliclignin and lignocellulosic nanofibers (LCNFs) using customized acidic deep eutectic solvents (DESs). The acidity and hydrogen-bonding capability of the designed DESs were regulated by altering the hydrogen bond donors, including formic, acetic, lactic, and oxalic acids. Kamlet-Taft solvatochromic analysis and DFT calculations showed that the oxalic acid‑based DES (OD) had the strongest hydrogen‑bonding ability ( = 3.340) and acidity ( = 1.882). This efficiently disrupted the hydrogen-bonding network and selectively cleaved lignin ether bonds and glycosidic bonds in amorphous cellulose. Consequently, LCNFs with a high crystallinity index (CrI) of 83% and an average diameter of 7.64 nm were obtained. Simultaneously, high-quality lignin (ODL) was produced with a yield of 63.3%, phenolic hydroxyl content of 11%, nearly 100% purity, and a low molecular weight of 2038 Da. Structural characterization revealed that ODL exhibited substantially reduced and linkages, with guaiacyl (G) and syringyl (S) units accounting for 54.5% and 44.3%, respectively, demonstrating the selective cleavage and structural regulation of lignin by acidic DESs. Furthermore, the DES system was successfully scaled up to a processing capacity of 100 kg lignocellulose per day. This work provides a scalable and mechanistically informed platform for the integrated production of high-purity lignin and LCNFs from lignocellulosic biomass.