The role of task-specific ionic liquids in lignocellulosic biomass pretreatment and catalytic valorization

The transition to a circular bioeconomy necessitates innovative technologies capable of valorizing lignocellulosic biomass, a structurally complex and highly recalcitrant feedstock. This review critically examines the application of task-specific ionic liquids (TSILs) in the pretreatment and catalytic conversion of biomass into high-value chemicals and fuels. Through deliberate molecular design, TSILs can transform a recalcitrant waste stream into a versatile chemical resource by selectively deconstructing cellulose hydrogen-bonding networks and lignin-carbohydrate complexes. Their pivotal role is examined across three key areas: (i) Advanced fractionation, where TSILs demonstrate high technical efficiency in cellulose dissolution and lignin isolation, often at the expense of increased separation complexity. (ii) Integrated catalytic conversion, where dual solvent–catalyst systems achieve high yields of biomass-derived platform chemicals, with up to ~ 90% furfural, ~ 91% 5-HMF, and ~ 18 wt% levulinic acid, depending on TSIL class and feedstock. (iii) System sustainability, where IL-recycling efficiencies exceeding 95% over multiple cycles are attained by novel recycling protocols, including membrane-assisted and electrochemical methods, with operating costs being reduced as a result. By linking structure–function relationships to process performance, this review highlights how TSILs overcome biomass recalcitrance while also addressing the techno-economic barriers to industrial-scale implementation. Further, dedicated consideration is also given to computer-aided IL design (CAILD), double-salt task-specific ILs (DS-TSILs), and integrated molecular-process design frameworks as promising frontiers for rational TSIL engineering. We conclude that continued advances in solvent recyclability, energy efficiency, and scale-up will be decisive in translating TSIL-based biorefineries from laboratory innovation to industrial implementation in a sustainable circular economy.