Deep eutectic solvent with bifunctional Bronsted-Lewis acids for highly efficient lignocellulose fractionation

Green and low cost deep eutectic solvents (DESs) are promising to replace the solid acids and ionic liquids in biomass fractionation process. To enhance the lignocellulose pretreatment efficiency, an acidic DES that composed of Bronsted acid (ZnCl2) as hydrogen bond acceptor and Lewis acid (lactic acid) as hydrogen bond donator was designed. This bifunctional DES was used for the extraction of lignin from poplar sawdust. Under the optimal pretreatment condition, the ZnCl2-lactic acid DES could recover 95.2 wt% of lignin with a purity of 92.1%. The recovered lignin demonstrated a low polydispersity of 1.67 and small amount of beta-aryl-ethers. Moreover, the acidic DES had a good recyclability and reusability. Such performance was attributed to the presence of bifunctional acid sites, which help selectively cleave lignin-carbohydrate complex linkages. The acidity and polarity of Bronsted acid can be modulated by the Lewis acid, thus synergistically promote the lignin extraction and production.

Automated summary

Green and low cost deep eutectic solvents (DESs) have the potential to replace solid acids and ionic liquids in biomass fractionation. In this study, an acidic DES composed of Bronsted acid and Lewis acid was designed for lignin extraction from poplar sawdust. The bifunctional DES showed high lignin recovery, low polydispersity, and good recyclability.