Valorization of rapeseed straw through the enhancement of cellulose accessibility, lignin removal and xylan elimination using an n-alkyltrimethylammonium bromide-based deep eutectic solvent.

n-Alkyltrimethylammonium bromide (CTAB)-based deep eutectic solvent (DESs) has potential in the efficient delignification and utilization of carbohydrates in biomass. In this research, DESs containing Brønsted acid and Lewis acid were prepared with CTAB (alkyl-chain length 12-18), organic acids and metal chlorides, and the optimal treatment conditions were acquired by pretreatment optimization. Through the pretreatment with TTAB/LCA/Fe (1:4:0.0111, mol:mol:mol) (162.5 °C, 61.7 min), lignin (89.2 %) and xylan (77.9 %) were effectively eliminated, and the hydrophobicity of rapeseed straw substantially declined from 4.62 to 2.09 m/g, acquiring the highest enzymatic saccharification efficiency of 92.5 %. The relationship of DES properties and enzymatic saccharification efficiency was explored. Additionally, hemicellulose in rapeseed straws could be efficiently transformed into furfural (3.75 g/L) and xylo-oligosaccharides (3.64 g/L). To clarify the structural and property changes brought by pretreatment, rapeseed straws were testified by FT-IR, SEM and CLSM and deeply discussed. The interaction between lignocellulose and TTAB/LCA/Fe was elucidated by molecular dynamics simulations and quantum chemical calculations, explaining the effectual treatment performance and hemicellulose upgrading at the molecular level. Eventually, a potential pretreatment mechanism of TTAB/LCA/Fe was proposed. This established TTAB/LCA/Fe treatment holds great promise for valorization of biomass into biofuels and biobased chemicals.