Implementing efficient and sustainable pretreatment of Sorghum stalks for delignification and xylan separation with a ternary deep eutectic solvent under mild conditions.

Acidic deep eutectic solvent (DES) has garnered significant attention in biomass pretreatment due to its effectiveness. Octadecyl trimethyl ammonium chloride (OTAC) is a highly efficient surfactant, which is expected to create new DES with additional pretreatment functions. Accordingly, a new ternary deep eutectic solvent (TDES) was synthesized from OTAC, propionic acid (PA), and p-toluene sulfonic acid (p-TsOH) for pretreating sorghum stalk under the relatively mild condition to enhance enzymatic saccharification of sorghum stalks. Through the treatment with OTAC:PA:p-TsOH (1:2:0.1, mol:mol:mol) at 80 °C for 30 min, the enzymolysis efficiency of sorghum stalks was increased to 69.3 %. The accessibility of sorghum stalk to cellulose was increased to 414.3 mg dye/g cellulose while the surface area of lignin decreased to 517 m/g. Along with the altered cellulose crystal structure and surface properties, the pretreatment mechanism for improving enzymatic hydrolysis capacity was proposed. Overall, this research implemented an efficient pretreatment using TDES OTAC:PA:p-TsOH for the valorization of sorghum stalk, providing a novel approach for the depolymerization and value-added utilization of lignocellulosic biomass in biorefining technology.