Challenging Pretreatment Technologies of Lignocellulosic Biomass

Lignocellulosic biomass, derived from agricultural and forestry waste, is a promising renewable resource for biofuels and biochemicals. However, its recalcitrant structure, which is comprised of intertwined cellulose, hemicellulose, and lignin, hinders efficient conversion, necessitating pretreatment as a crucial step to disrupt this matrix and enhance enzymatic hydrolysis. Pretreatment methods are categorized based on their target components: hemicellulose depolymerization strategies such as acid pretreatment (e.g., inorganic, organic, and solid acids) and physicochemical methods like steam explosion improve sugar release but face challenges like inhibitor formation and high energy costs; lignin removal strategies, including alkaline, oxidative, and biological pretreatments, effectively degrade lignin yet struggle with reagent recovery and low working efficiency; and selective fractionation strategies, such as organosolv, ionic liquids, and deep eutectic solvents, aim for high-value utilization but encounter issues with solvent sustainability and costs. Emerging technologies like dry acid pretreatment with biodetoxification (DryPB), ammonia-based methods, and densifying lignocellulosic biomass with chemicals (DLC) offer improved efficiency, reduced waste, and high product yields, highlighting the need for future optimization in cost-effectiveness, selectivity, and integration for scalable biorefineries.