Application of deep eutectic solvents in biomass valorization

High reliance on crude oil for energy consumption results in an urgent need to explore and develop alternative renewable sources. One of the most promising routes is the transformation of biomass into biofuels and valueadded chemicals. The introduction of deep eutectic solvents (DESs) in 2004 has received considerable amount of attention across different research fields particularly in biomass processing. The effectiveness of DESs in breaking down the recalcitrant structure of lignin in biomass highlights its impact on transformation of biomass into various value-added products. In comparison with some common solvents used in biomass valorization, DESs are able to produce highly concentrated solutions of carbohydrates, sometimes liquid at approximately room temperature. Besides, DESs are widely regarded as a promising green solvent due to its low cost, low toxicity and biodegradable properties. In this paper, firstly some background information on lignocellulosic biomass and DESs were given. Then, the mechanism and role of DES in pretreating biomass were discussed such as the impacts of DESs on the selectivity of chemical processes and dissolution of biomass by DESs. This review also highlighted the advantages and limitations of DESs associated with its usage on biomass pretreatment.