Sustainable Valorization of Lignocellulosic Biomass: Recent Advances in Physicochemical Pretreatment Methods and the Potential of Deep Eutectic Solvents

Transitioning to a sustainable framework that emphasizes bioenergy is essential to reduce the dependence on fossil fuel resources that continue to dominate the world’s energy sector. With an estimated 182 billion tons global annual production, lignocellulosic biomass (LCB) has emerged as a renewable and abundant alternative that holds promise for the production of biofuels and biomaterials. The direct biorefinery of LCB is hindered owing to the inherent recalcitrance of its interconnected components primary cellulose, hemicellulose and lignin. Thus, achieving an effective delignification necessitates the application of a specific and powerful pretreatment. This process disrupts the linkages between the components, thereby improving the accessibility of fermentable sugars by increasing surface area, and facilitating lignin extraction or removal. Recently, extensive efforts have been made to develop and improve several pretreatments enabling a potent yet sustainable conversion of LCB. This review highlights recent advances and reported outcomes in the physicochemical pretreatment of lignocellulosic biomass, emphasizing the optimal operating conditions that enable improved overall efficiency. In particular, deep eutectic solvent (DES)-based systems have emerged as green and versatile media, allowing effective fractionation of lignocellulosic components into cellulose and lignin fractions suitable for subsequent valorization. Owing to their degradability, tunability, and compatibility with diverse feedstocks, DESs represent a promising route toward sustainable biorefinery. Furthermore, the integration of microwave assistance is discussed as a synergistic enhancement that can further improve process performance and economic feasibility, offering a balanced pathway for efficient and sustainable biomass conversion.