Development of Acacia dealbata biorefinery: Cascade processing based on autohydrolysis and deep eutectic solvents

Acacia dealbata wood (ADW), a biomass of increasing interest as an alternative lignocellulosic feedstock, was valorized through a two-step fractionation strategy. First, a hydrothermal pretreatment was applied to recover the hemicellulosic fraction as oligosaccharides, mainly xylooligosaccharides (XOS). At a severity factor of 3.82, 70% of hemicelluloses were solubilized, yielding a liquor containing 21.77 g/L of XOS. The resulting solid was subsequently subjected to a delignification process using deep eutectic solvents (DES) based on choline chloride (ChCl) and organic acids, lactic acid (LA), formic acid (FA), and acetic acid (AA), to identify the most suitable system for lignin extraction and to obtain a cellulose-rich solid fraction. In addition, DES delignification was compared with organosolv systems (ethanol- and ethyl lactate-based formulations, with and without catalysts). Among all systems evaluated, ChCl:LA (1:4) showed the best overall performance under the tested conditions, achieving a 9% greater delignification than the ethanol–ethyl lactate system catalyzed with sulfuric acid. Overall, ChCl:LA (1:4) enabled the extraction of 59% of lignin with a purity of 90%, while retaining 81% of glucan in the solid fraction and achieving 61% enzymatic digestibility. The recovered lignin was characterized by FTIR, TGA-DTG, 2D-HSQC, and SEM, revealing the formation of high-purity lignin nanoparticles with antioxidant properties. This proposed acacia wood fractionation scheme represents a promising approach for the development of a multiproduct biorefinery using pretreatments of growing interest for biomass valorization.