Deep eutectic solvents as promising pretreatment agents for sustainable lignocellulosic biorefineries: A review

[Display omitted] •Deep eutectic solvents possess excellent potential for fractionation of biomass.•DESs effectively accelerate lignin removal and cellulose valorisation from LCB.•Process efficacy is enhanced by combinatorial DES based assistive pretreatment.•Different biofuels and value-added products can be derived from LCB using DESs. Increasing reliance on non-renewable fuels has shifted research attention to environmentally friendly and sustainable energy sources.The inherently recalcitrant nature of lignocellulosic biomass (LCB) makes downstream processing of the bioprocess challenging. Deep eutectic solvents (DESs) are popular and inexpensive green liquids found effective for LCB valorisation. DESs have negligible vapor-pressure and are non-flammable, recyclable, cost-economic, and thermochemically stable. This review provides a detailed overview on the DESs types, properties and their role in effective delignification and enzymatic digestibility of polysaccharides for cost-effective conversion of LCB into biofuels and bioproducts. The conglomeration of DESs with assistive pretreatment techniques can augment the process of biomass deconstruction. The current challenges in upscaling the DESs-based pretreatment technology up to commercial scale is summarized, with possible solutions and future directions. These insights would fill the knowledge-gaps to towards development of lignocellulosic biorefineries and to address the global energy crisis and environment issues.