Facilitating superior delignification, enhanced enzymatic hydrolysis, and robust ethanol fermentation of poplar sawdust through lysine-based ternary deep eutectic solvent pretreatment

Amino acid-based deep eutectic solvents (DES) have emerged as a quintessential class of alkaline DES, known for exceptional delignification in lignocellulose pretreatment under mild conditions, thereby enhanced the economic feasibility of biorefinery. This study introduces an innovative ternary DES comprised of cetyltrimethylammonium bromide (CTAB), ethanolamine (EA), and lysine (Lys), engineered for efficient pretreatment of poplar sawdust (PS). Results show that increased Lys concentration progressively reduces pH, conductivity, and polarity, while significantly enhancing hydrogen bond donor and acceptor capacities. The amino and carboxyl groups in Lys synergistically establish a robust three-dimensional hydrogen-bonded network. Specifically, DES pretreatment dramatically improves PS fractionation: compared with the Lys-free control, Lys introduction elevates lignin removal from 42.2% to 87.2%, and xylan removal from 78.5% to 99.9%, respectively. Meanwhile, cellulose digestibility increases from 65.5% to 96.0%, and ethanol yield rises from 56.3% to 89.9%. Structural characterization unveiled that Lys remarkably promoted selective cleavage of lignin linkages, thereby dismantling the lignin framework. This reorganization reduces lignin’s specific surface area, enhances cellulose exposure, and boosts enzymatic hydrolysis. Notably, the DES exhibits excellent recyclability. These findings highlight the great potential of alkaline DES for sustainable biorefining and valorization of forestry biomass residues.