Deep eutectic solvents in the pretreatment of feedstock for efficient fractionation of polysaccharides: current status and future prospects

The effective and efficient valorization of polysaccharide-rich feedstocks is undisputedly a key factor in the quest for a more sustainable planet and a biobased economy. Several covalent and non-covalent interactions within the biomacromolecules define the complex, intricate, and rigid structure of lignocellulose and related biomasses. However, none of the current methods to disrupt the complex interactions of feedstocks and enhance their hydrolysis for subsequent valorization are highly selective and efficient enough, hence the need for new methodologies in this respect. Deep eutectic solvents (DES) are special types of ionic liquids, which are cheaper, less toxic, and more biocompatible than other ionic liquids. They have been identified as important green solvents and functional fluids with immense potential for catalytic transformation of polysaccharide-rich biomass into a diverse range of products. The unique properties of DES enable them to effectively dissolve and convert biomass into valuable end products. This review paper sheds light on the application of DES in the deconstruction and fractionation of different feedstocks, particularly in the pretreatment step. In this regard, it covers the recent advancements in the applications of various DES in the valorization of biomass and its major components (i.e., cellulose, xylan, chitin, starch, pectin) with special emphasis on the relationship between the inherent properties of DES and their dissolution potential. Focus is also placed on the toxicity, biocompatibility, and reusability of DES. Finally, this article addresses the current and potential issues in the industrial application of DES, with a special focus on future opportunities.