Evaluating the effectiveness of alkylammonium halide-based deep eutectic solvent pretreatments in heightening carbohydrates and lignin separation from poplar sawdust

The molecular architecture of hydrogen bond acceptors (HBA) within deep eutectic solvents (DES) emerges as a key factor in bioconversion of lignocellulose. This work constructed a series of DES systems by employing diverse alkylammonium halide as HBAs, enabling an investigation into the synergistic interplay between alkyl chain length and halide anion identity on the deconstruction of poplar sawdust (PS). Notably, the cetyltrimethylammonium bromide (CTAB)-based DES displayed a reduced surface potential, weakened hydrogen bonding energy, and diminished polarity, outperforming counterparts based on short-chain alkylamines or alternative halide-containing HBA. When applied in the pretreatment of PS, this DES has achieved a removal of 68.4 % lignin and 94.0 % xylan, while elevating the cellulose digestibility to 76.5 %. Structural analysis unveiled that the CTAB-based DES profoundly disrupted the pivotal β-O-4 ether bonds and aromatic structure within lignin, and thus enhancing substrate digestibility. The long-chain hydrophobic alkyl chains and highly-polar bromide ions empowered the DES with superior penetration and deconstruction capabilities toward lignocellulose, highlighting the paramount significance of HBA’s molecular structure in refining DES pretreatment paradigms for efficient biomass transformation.