As an effective substitute for ionic liquids (ILs), deep eutectic solvents (DESs) are known as a new generation of green solvents. In addition, DESs are considered to be the best solvents to replace traditional organic solvents and ILs due to their advantages of economy, simple preparation and biodegradability, which can be used to further break through the technical bottleneck in the field of biomass pretreatment. This study synthesized a series of choline chloride-based (ChCl-based) DESs and used them to pretreat microcrystalline cellulose (MCC) without dissolution, in order to achieve the purpose of improving the saccharification effect. DES-9 (ChCl/hydroquinone), DES-12 (ChCl/acetamide) and DES-16 (ChCl/acetic acid) were better pretreatment solvents. The optimum conditions for the pretreatment of MCC by DES-9 and DES-12 were both at 110 °C for 4 h, and the optimum condition of DES-16 was at 90 °C for 4 h. Compared with untreated MCC (26.66%), the saccharification yield of pretreated MCC with DES-16 increased by 20.5%. Finally, the structure and morphology changes of MCC before and after pretreatment were investigated in detail through the degree of polymerization (DP), SEM and enzyme adsorption. The results showed that DESs pretreatment made the surface of MCC become rough, which enhanced the accessibility of cellulose and enzymes, improving the saccharification effect.

Graphical abstract