Comparative study of alkaline, acidic, and deep eutectic solvent pretreatments on lignocellulosic biomass for enhanced enzymatic hydrolysis

Unlocking the potential of lignocellulosic biomass for sustainable biofuel production remains a significant challenge. This study investigated the efficacy of the novel solvent superphosphoric acid (P₂O₅), along with three newly synthesized Deep Eutectic Solvents (DESs): choline chloride (ChCl) combined with oxalic acid (ChCl-O), adipic acid (ChCl-A), and citric acid (ChCl-C) in the pretreatment of biomass. These novel solvents were evaluated against conventional solvents NaOH and H₂SO₄ in the pretreatment of corn stover (CS), rice straw (RS), and sugarcane bagasse (SB). The primary objective of pretreatment was to selectively remove lignin and hemicellulose and maximize cellulose accessibility for enzymatic hydrolysis. Remarkably, the ChCl-O DES outperformed conventional solvents, achieving a cellulose content of 56.54% in CS. Moreover, SB exhibited exceptional glucose yields after pretreatment, with 10% P₂O₅ yielding 79.52% and ChCl-O DES yielding 61.28%. FTIR and XRD analyses confirmed substantial delignification and hemicellulose removal by P₂O₅ and DES. SEM micrographs visually depicted the disruptive effects of P₂O₅ and DES on the lignin–hemicellulose matrix, creating a highly porous, cellulose-rich surface. These novel solvents (P₂O₅ and DES) enhanced biomass fractionation and improved cellulose accessibility, thereby facilitating efficient enzymatic hydrolysis.